Examining overweight and obesity as risk factors for common mental disorders using fat mass and obesity-associated (FTO) genotype-instrumented analysis: The Whitehall II Study, 1985-2004

Investigation of the interaction between Genetic Risk Score (GRS) and fatty acid quality indices on mental health among overweight and obese women

BACKGROUND & AIMS

Mental disorders are associated with dietary fatty acids and genome-wide association studies have found multiple risk loci robustly related to depression, anxiety, and stress. The aim of this study is to investigate the interaction of genetic risk score (GRS) and dietary fat quality indices on mental health.

METHODS

This cross-sectional study included 279 overweight and obese women for N6/N3 ratio and 378 overweight and obese women for CSI aged 18-68 years. Using reliable and verified standard protocols, body composition, anthropometric indices, blood pressure, physical activity, and dietary fat quality were measured. Serum samples were used to determine biochemical tests. A genetic risk score (GRS) was calculated using the risk alleles of the three SNPs. A generalized linear model (GLM) was applied to assess the interactions between GRS and fat quality indices. Mental health was evaluated using Depression Anxiety Stress Scales (DASS-21).

RESULTS

The mean (± SD) age and BMI of our participants were 36.48 (8.45) and 30.73 (3.72) kg/m2 respectively. There was a marginally significant mean difference among tertiles of the CSI in terms of stress (P = 0.051), DASS-21 (P = 0.078) in the crude model. After adjusting for age, energy intake, physical activity and BMI in model 1, there was a positive interaction between GRS and T3 of N6/N3 ratio on anxiety (β = 0.91, CI = 0.08,1.75, P = 0.031), depression (β = 1.05, CI = 0.06,2.04, P = 0.037), DASS-21 (β = 2.22, CI= -0.31,4.75, P = 0.086).

CONCLUSION

Our findings indicate that higher ratio of N-6 to N-3 considering genetics were predictive of mental disorder in our population.

Obesity as a causal risk factor for depression: Systematic review and meta-analysis of Mendelian Randomization studies and implications for population mental health

BACKGROUND/OBJECTIVES

Obesity has been associated with elevated risk of depression. If this association is causal, the increasing obesity prevalence might lead to worsening population mental health, but the strength of the causal effect has not been systematically evaluated.

SUBJECTS/METHODS

The current study provides a systematic review and meta-analysis of studies examining associations between body mass index and depression using Mendelian randomization with multiple genetic variants as instruments for body mass index. We used this estimate to calculate the expected changes in prevalence of population psychological distress from the 1990s-2010s, which were compared with the empirically observed trends in psychological distress in the Health Survey for England (HSE) and U.S. National Health Interview Surveys (NHIS).

RESULTS

Meta-analysis of 8 Mendelian randomization studies indicated an OR = 1.33 higher depression risk associated with obesity (95% confidence interval 1.19, 1.48). Between 15% and 20% of the participants of HSE and NHIS reported at least moderate psychological distress. The increase of obesity prevalence from the 1990s-2010s in HSE and NHIS would have led to a 0.6 percentage-point increase in population psychological distress.

CONCLUSIONS

Mendelian randomization studies suggest that obesity is a causal risk factor for elevated risk of depression. The increasing obesity rates may have modestly increased the prevalence of depressive symptoms in the general population. Mendelian randomization relies on methodological assumptions that may not always hold, so other quasi-experimental methods are needed to confirm the current conclusions.

Mendelian randomisation study of body composition and depression in people of East Asian ancestry highlights potential setting-specific causality

BACKGROUND

Extensive evidence links higher body mass index (BMI) to higher odds of depression in people of European ancestry. However, our understanding of the relationship across different settings and ancestries is limited. Here, we test the relationship between body composition and depression in people of East Asian ancestry.

METHODS

Multiple Mendelian randomisation (MR) methods were used to test the relationship between (a) BMI and (b) waist-hip ratio (WHR) with depression. Firstly, we performed two-sample MR using genetic summary statistics from a recent genome-wide association study (GWAS) of depression (with 15,771 cases and 178,777 controls) in people of East Asian ancestry. We selected 838 single nucleotide polymorphisms (SNPs) correlated with BMI and 263 SNPs correlated with WHR as genetic instrumental variables to estimate the causal effect of BMI and WHR on depression using the inverse-variance weighted (IVW) method. We repeated these analyses stratifying by home location status: China versus UK or USA. Secondly, we performed one-sample MR in the China Kadoorie Biobank (CKB) in 100,377 participants. This allowed us to test the relationship separately in (a) males and females and (b) urban and rural dwellers. We also examined (c) the linearity of the BMI-depression relationship.

RESULTS

Both MR analyses provided evidence that higher BMI was associated with lower odds of depression. For example, a genetically-instrumented 1-SD higher BMI in the CKB was associated with lower odds of depressive symptoms [OR: 0.77, 95% CI: 0.63, 0.95]. There was evidence of differences according to place of residence. Using the IVW method, higher BMI was associated with lower odds of depression in people of East Asian ancestry living in China but there was no evidence for an association in people of East Asian ancestry living in the USA or UK. Furthermore, higher genetic BMI was associated with differential effects in urban and rural dwellers within China.

CONCLUSIONS

This study provides the first MR evidence for an inverse relationship between BMI and depression in people of East Asian ancestry. This contrasts with previous findings in European populations and therefore the public health response to obesity and depression is likely to need to differ based on sociocultural factors for example, ancestry and place of residence. This highlights the importance of setting-specific causality when using genetic causal inference approaches and data from diverse populations to test hypotheses. This is especially important when the relationship tested is not purely biological and may involve sociocultural factors.

Mental and Body Health: The Association between Psychological Factors, Overweight, and Blood Pressure in Young Adults

Comorbidity between cardiometabolic risk factors and major mental health disorders is a public health concern. The close interconnection between the mental and physical aspects of health precludes considering each condition separately. Accordingly, this study sought to explore the interrelationships between psychological factors, overweight, and blood pressure in young adults. One hundred and forty-five young adults participated in the study and were classified according to two independent characteristics: weight condition (normal weight, overweight) and blood pressure (low blood pressure, high blood pressure). Anxiety, depression, and emotional dysregulation were assessed. The results confirmed certain associations, highlighting how cardiometabolic risk factors, such as blood pressure and body mass index, were associated in different ways with mental health, although an interaction between the variables was not reported. In particular, a relationship between body mass index and depression and between anxiety and blood pressure was detected.

Mendelian Randomization: A Review of Methods for the Prevention, Assessment, and Discussion of Pleiotropy in Studies Using the Fat Mass and Obesity-Associated Gene as an Instrument for Adiposity

Pleiotropy assessment is critical for the validity of Mendelian randomization (MR) analyses, and its management remains a challenging task for researchers. This review examines how the authors of MR studies address bias due to pleiotropy in practice. We reviewed Pubmed, Medline, Embase and Web of Science for MR studies published before 21 May 2020 that used at least one single-nucleotide polymorphism (SNP) in the fat mass and obesity-associated (FTO) gene as instrumental variable (IV) for body mass index, irrespective of the outcome. We reviewed: 1) the approaches used to prevent pleiotropy, 2) the methods cited to detect or control the independence or the exclusion restriction assumption highlighting whether pleiotropy assessment was explicitly stated to justify the use of these methods, and 3) the discussion of findings related to pleiotropy. We included 128 studies, of which thirty-three reported one approach to prevent pleiotropy, such as the use of multiple (independent) SNPs combined in a genetic risk score as IVs. One hundred and twenty studies cited at least one method to detect or account for pleiotropy, including robust and other IV estimation methods (n = 70), methods for detection of heterogeneity between estimated causal effects across IVs (n = 72), methods to detect or account associations between IV and outcome outside thought the exposure (n = 85), and other methods (n = 5). Twenty-one studies suspected IV invalidity, of which 16 explicitly referred to pleiotropy, and six incriminating FTO SNPs. Most reviewed MR studies have cited methods to prevent or to detect or control bias due to pleiotropy. These methods are heterogeneous, their triangulation should increase the reliability of causal inference.

Depression and Metabolic Syndrome: A Narrative Review

We reviewed the literature to investigate the relationship between depression and metabolic syndrome. Major depressive disorder is characterized by a low mood or a loss of interest for longer than two weeks. Metabolic syndrome describes multiple metabolic risk factors including obesity, insulin resistance, dyslipidemia, and hypertension. We divided our findings into environmental, genetic, epigenetic, and biological pathway links between depression and the different aspects of metabolic syndrome. We found various sources linking obesity and metabolic syndrome genetically, environmentally, biological pathway-wise, and, while not fully explored, epigenetically. Diabetes and depression were also found to be linked environmentally with both conditions increasing the risk of the other. Depression was also shown to be linked to cardiovascular complications as it increased the risk of occurrence of such complications in healthy people. These findings have led us to believe that there is a link between depression and metabolic syndrome on various levels, especially obesity.

Higher adiposity and mental health: causal inference using Mendelian randomization

Higher adiposity is an established risk factor for psychiatric diseases including depression and anxiety. The associations between adiposity and depression may be explained by the metabolic consequences and/or by the psychosocial impact of higher adiposity. We performed one- and two- sample Mendelian randomization (MR) in up to 145 668 European participants from the UK Biobank to test for a causal effect of higher adiposity on 10 well-validated mental health and well-being outcomes derived using the Mental Health Questionnaire (MHQ). We used three sets of adiposity genetic instruments: (a) a set of 72 BMI genetic variants, (b) a set of 36 favourable adiposity variants and (c) a set of 38 unfavourable adiposity variants. We additionally tested causal relationships (1) in men and women separately, (2) in a subset of individuals not taking antidepressants and (3) in non-linear MR models. Two-sample MR provided evidence that a genetically determined one standard deviation (1-SD) higher BMI (4.6 kg/m2) was associated with higher odds of current depression [OR: 1.50, 95%CI: 1.15, 1.95] and lower well-being [ß: -0.15, 95%CI: -0.26, -0.04]. Findings were similar when using the metabolically favourable and unfavourable adiposity variants, with higher adiposity associated with higher odds of depression and lower well-being scores. Our study provides further evidence that higher BMI causes higher odds of depression and lowers well-being. Using genetics to separate out metabolic and psychosocial effects, our study suggests that in the absence of adverse metabolic effects higher adiposity remains causal to depression and lowers well-being.

Symptoms of depression, anxiety, and post-traumatic stress disorder and their relationship to health-related behaviors in over 12,000 US military personnel: Bi-directional associations

Background Military personnel are at greater risk of psychological disorders and related symptoms than civilians. Limited participation in health-promoting behaviors may increase presence of these disorders. Alternatively, these symptoms may limit engagement in health-promoting behaviors. Methods Self-reported data from the 2015 Department of Defense Health Related Behaviors Survey were used to assess bi-directional relationships between health-related behaviors (obesity, physical activity [PA], alcohol, smoking, sleep) and self-reported psychological disorders (generalized anxiety disorder [GAD], depression, post-traumatic disorder [PTSD]) in U.S. military personnel. Outcomes Among 12 708 respondents (14.7% female; 28.2% 17-24 y; 13.7% obese), self-reported depression was reported by 9.2%, GAD by 13.9%, and PTSD by 8.2%. Obesity and short sleep were associated with self-reported depression, GAD, and PTSD; current smoking was associated with higher odds of GAD; higher levels of vigorous PA were associated with lower odds of GAD; higher levels of moderate PA associated with lower odds of PTSD; and higher alcohol intake associated with higher odds of depression and PTSD. Self-reported depression, GAD, and PTSD were associated with higher odds of short sleep, obesity, and low levels of PA. Interpretation Obesity, short sleep, and limited engagement in health-promoting behaviors are associated with higher likelihood of self-reported psychological disorders, and vice-versa. Encouraging and improving health-promoting behaviors may contribute to positive mental health in military personnel.

Does vitamin D affect the association between FTO rs9939609 polymorphism and depression?

Background & objectives: Depression is a highly prevalent and multifactorial psychological disorder. Fat Mass and Obesity-Associated (FTO) gene and the serum vitamin D level are proposed to be involved in pathophysiology of depression. This study aimed to investigate the interactions between one FTO gene single nucleotide polymorphism, depression, and serum vitamin D level in overweight adults.Methods: One hundred and ninety-seven overweight adults were recruited in this cross-sectional study. FTO genotyping was performed by amplification refractory mutation system polymerase chain reaction (ARMS-PCR). Depression severity was assessed using Beck's depression inventory (BDI-II). Serum vitamin D levels were measured using a direct competitive enzyme-linked immunosorbent assay (ELISA) method.Results: A-allele carriers had higher Beck's depression score (P = 0.03). Multivariate regression models showed a positive association between the A-allele of FTO rs9939609 polymorphism and depression. Serum vitamin D level had no effect on the association between FTO genotype and depression.Conclusion: A-allele of FTO rs9939609 polymorphism might be associated with depression independent of serum vitamin D level. Further longitudinal studies are needed to confirm these results.

Breakfast skipping alone and in interaction with inflammatory based quality of diet increases the risk of higher scores of psychological problems profile in a large sample of Iranian adults

The authors investigate the association of breakfast skipping and its interaction with a dietary inflammatory index (DII) with the severity of psychological disorders. A total of 2876 Iranian general adults were enrolled in this cross-sectional study. Psychological problems profile score was calculated using the regression method in the framework of factor analysis based on depression, anxiety and psychological distress. The higher scores indicate more severity of mental problem. The frequency of breakfast eating in a week was assessed. Dietary intakes were assessed using a food-frequency questionnaire and twenty-seven items were included in the calculation of DII. In the crude model, individuals who ate breakfast seldom had the highest odds for having worse psychological problems profile (OR 3⋅59; 95 % CI 2⋅52, 5⋅11). Adjustment for various confounders did not change the associations (OR 3⋅35; 95 % CI 2⋅11, 5⋅32). In the adjusted multinomial logistic regression model, participants with high DII (>median) who skipped breakfast had highest risk of being in the higher tertiles of psychological problems profile compared with those who had low DII (<median) and ate breakfast (OR 6⋅67; 95 % CI 3⋅45, 12⋅90). Similar results were observed in women and men regarding the impact of breakfast skipping alone and interaction with DII on scores of psychological problems profile. Breakfast skipping is associated with higher risk of psychological problems. Similar findings were obtained in the stratified analysis by sex. Our findings confirmed that the DII and breakfast skipping are associated with mental health, interactionally. Further longitudinal studies are needed to confirm the true link between breakfast skipping and psychological problems.

Physical working conditions and subsequent disability retirement due to any cause, mental disorders and musculoskeletal diseases: does the risk vary by common mental disorders?

PURPOSE

Physical work exposures and common mental disorders (CMD) have been linked to increased risk of work disability, but their joint associations with disability retirement due to any cause, mental disorders or musculoskeletal diseases have not been examined.

METHODS

The data for exposures and covariates were from the Finnish Helsinki Health Study occupational cohort surveys in 2000-2002, 2007 and 2012. We used 12,458 observations from 6159 employees, who were 40-60 years old at baseline. CMD were measured by the General Health Questionnaire (GHQ-12, cut-off point 3+). Four self-reported work exposures (hazardous exposures, physical workload, computer and shift work) were combined with CMD and categorized as "neither", "work exposure only", "CMD only", and "both". Associations with register-based disability retirement were assessed with Cox proportional hazards models for sample survey data adjusting for confounders over 5-year follow-up. Additionally, synergy indices were calculated for the combined effects.

RESULTS

Those reporting CMD and high physical workload had a greater risk of disability retirement due to any cause (HR 4.26, 95% CI 3.60-5.03), mental disorders (HR 5.41, 95% CI 3.87-7.56), and musculoskeletal diseases (HR 4.46, 95% CI 3.49-5.71) when compared to those with neither. Synergy indices indicated that these associations were synergistic. Similar associations were observed for CMD and hazardous exposures, but not for combined exposures to CMD and computer or shift work.

CONCLUSIONS

Identification of mental health problems among employees in physically demanding jobs is important to support work ability and reduce the risk of premature exit from work due to disability.

Resistant dextrin reduces obesity and attenuates adipose tissue inflammation in high-fat diet-fed mice

Resistant dextrin (RD), a short chain glucose polymer, has been shown to improve type 2 diabetes mellitus (T2DM) in clinical studies. However, the improvement of adipose tissue inflammation and specific mechanisms of RD supplementation in obesity have not been fully investigated. Therefore, we examined whether RD attenuates obesity and adipose tissue inflammation in high-fat diet (HFD)-fed mice. Male C57BL/6 mice were fed a chow diet, a HFD or a HFD with RD supplementation for 12 weeks. Body weight (BW), fasting blood glucose (FBG), epididymal fat accumulation, serum total triglyceride (TG), free fatty acid (FFA) and inflammatory cytokine levels (TNF-α, IL-1β, IL-6, IL-10) were measured. Inflammation markers and macrophage infiltration in epididymal adipose tissue were observed. After 12 weeks of intervention, the body weight gain of mice in RD supplementation group was less than that in HFD group. FBG, epididymal fat accumulation, serum TG and FFA levels were reduced in RD supplementation group compared with HFD group. Moreover, serum and mRNA levels of IL-6 were significantly reduced in the RD supplementation group. In addition, RD supplementation reduced macrophage infiltration, regulated polarization of macrophage and inhibited NF-κB signaling in epididymal adipose tissue. In conclusion, RD reduces obesity and attenuates adipose tissue inflammation in HFD-fed mice, and the inhibition of NF-κB signaling may be a presumed mechanism for its effects.

Body-weight and psychological well-being in the UK general population

Background

While the consequences of body weight for physical health are well explored, the evidence for psychological well-being is less straightforward. An instrumental variable approach is used to address the endogenous relationship between body weight and well-being in the UK general population.

Methods

Data from the Health Survey for England (2003, 2004 and 2006) are used to fit linear and ordered probit instrument variable models for a sample of 13 862 individuals, with frequent white meat consumption instrumenting for body-weight. Non-linearities in the relationship, robustness to weak instruments and relaxation of strict exogeneity assumption are further examined.

Results

Accounting for endogeneity and conditional on health a protective effect on well-being is observed. A unit increase in body mass index (BMI) improves General Health Questionnaire (GHQ) by 0.17 (95% CI: 0.02-0.31) points and reduces the probability of reporting very low GHQ by 2.5% (95% CI: 0.01-0.05). Empirical testing showed that the instrument performs well, with increased meat consumption adding 0.58 points (95% CI: 0.42-0.74) to ones' BMI.

Conclusions

We present support for the jolly-fat hypothesis, however, caution is recommended in drawing inferences. Further research needs to resolve the mixed findings in the literature.

Weight change increases the odds of psychological distress in middle age: bidirectional analyses from the Whitehall II Study

BACKGROUND

Mood disorders and adiposity are major public health challenges. Few studies have investigated the bidirectional association of weight and waist circumference (WC) change with psychological distress in middle age, while taking into account the potential U-shape of the association. The aim of this study was to examine the bidirectional association between psychological distress and categorical change in objectively measured weight and WC.

METHODS

We analysed repeated measures (up to 17 522 person-observations in adjusted analyses) of psychological distress, weight and WC from the Whitehall II cohort. Participants were recruited at age 35-55 and 67% male. Psychological distress was assessed using the General Health Questionnaire. We used random-effects regressions to model the association between weight and WC changes and psychological distress, with and without a 5-year lag period.

RESULTS

Psychological distress was associated with weight and WC gain over the subsequent 5 years but not the second 5-year period. Weight gain and loss were associated with increased odds for incident psychological distress in models with and without time-lag [odds ratio (OR) for incident psychological distress after 5-year time-lag: loss 1.20, 95% confidence interval (CI) 1.00-1.43; gain>5% 1.20, 95% CI 1.02-1.40]. WC changes were only associated with psychological distress in models without time-lag (OR for incident psychological distress: loss 1.29, 95% CI 1.02-1.64; gain>5% 1.33, 95% CI 1.11-1.58).

CONCLUSIONS

Weight gain and loss increase the odds for psychological distress compared with stable weight over subsequent 10 years. In contrast, the association between psychological distress and subsequent weight and WC changes was limited to the first 5 years of follow-up.

Using genetics to understand the causal influence of higher BMI on depression

BACKGROUND

Depression is more common in obese than non-obese individuals, especially in women, but the causal relationship between obesity and depression is complex and uncertain. Previous studies have used genetic variants associated with BMI to provide evidence that higher body mass index (BMI) causes depression, but have not tested whether this relationship is driven by the metabolic consequences of BMI nor for differences between men and women.

METHODS

We performed a Mendelian randomization study using 48 791 individuals with depression and 291 995 controls in the UK Biobank, to test for causal effects of higher BMI on depression (defined using self-report and Hospital Episode data). We used two genetic instruments, both representing higher BMI, but one with and one without its adverse metabolic consequences, in an attempt to 'uncouple' the psychological component of obesity from the metabolic consequences. We further tested causal relationships in men and women separately, and using subsets of BMI variants from known physiological pathways.

RESULTS

Higher BMI was strongly associated with higher odds of depression, especially in women. Mendelian randomization provided evidence that higher BMI partly causes depression. Using a 73-variant BMI genetic risk score, a genetically determined one standard deviation (1 SD) higher BMI (4.9 kg/m2) was associated with higher odds of depression in all individuals [odds ratio (OR): 1.18, 95% confidence interval (CI): 1.09, 1.28, P = 0.00007) and women only (OR: 1.24, 95% CI: 1.11, 1.39, P = 0.0001). Meta-analysis with 45 591 depression cases and 97 647 controls from the Psychiatric Genomics Consortium (PGC) strengthened the statistical confidence of the findings in all individuals. Similar effect size estimates were obtained using different Mendelian randomization methods, although not all reached P < 0.05. Using a metabolically favourable adiposity genetic risk score, and meta-analysing data from the UK biobank and PGC, a genetically determined 1 SD higher BMI (4.9 kg/m2) was associated with higher odds of depression in all individuals (OR: 1.26, 95% CI: 1.06, 1.50], P = 0.010), but with weaker statistical confidence.

CONCLUSIONS

Higher BMI, with and without its adverse metabolic consequences, is likely to have a causal role in determining the likelihood of an individual developing depression.

Searching for the causal effects of body mass index in over 300 000 participants in UK Biobank, using Mendelian randomization

Mendelian randomization (MR) has been used to estimate the causal effect of body mass index (BMI) on particular traits thought to be affected by BMI. However, BMI may also be a modifiable, causal risk factor for outcomes where there is no prior reason to suggest that a causal effect exists. We performed a MR phenome-wide association study (MR-pheWAS) to search for the causal effects of BMI in UK Biobank (n = 334 968), using the PHESANT open-source phenome scan tool. A subset of identified associations were followed up with a formal two-stage instrumental variable analysis in UK Biobank, to estimate the causal effect of BMI on these phenotypes. Of the 22 922 tests performed, our MR-pheWAS identified 587 associations below a stringent P value threshold corresponding to a 5% estimated false discovery rate. These included many previously identified causal effects, for instance, an adverse effect of higher BMI on risk of diabetes and hypertension. We also identified several novel effects, including protective effects of higher BMI on a set of psychosocial traits, identified initially in our preliminary MR-pheWAS in circa 115,000 UK Biobank participants and replicated in a different subset of circa 223,000 UK Biobank participants. Our comprehensive MR-pheWAS identified potential causal effects of BMI on a large and diverse set of phenotypes. This included both previously identified causal effects, and novel effects such as a protective effect of higher BMI on feelings of nervousness.

Nature as a Trialist?: Deconstructing the Analogy Between Mendelian Randomization and Randomized Trials

Mendelian randomization (MR) studies are often described as naturally occurring randomized trials in which genetic factors are randomly assigned by nature. Conceptualizing MR studies as randomized trials has profound implications for their design, conduct, reporting, and interpretation. For example, analytic practices that are discouraged in randomized trials should also be discouraged in MR studies. Here, we deconstruct the oft-made analogy between MR and randomized trials. We describe four key threats to the analogy between MR studies and randomized trials: (1) exchangeability is not guaranteed; (2) time zero (and therefore the time for setting eligibility criteria) is unclear; (3) the treatment assignment is often measured with error; and (4) adherence is poorly defined. By precisely defining the causal effects being estimated, we underscore that MR estimates are often vaguely analogous to per-protocol effects in randomized trials, and that current MR methods for estimating analogues of per-protocol effects could be biased in practice. We conclude that the analogy between randomized trials and MR studies provides further perspective on both the strengths and the limitations of MR studies as currently implemented, as well as future directions for MR methodology development and application. In particular, the analogy highlights potential future directions for some MR studies to produce more interpretable and informative numerical estimates.

Causal associations between body mass index and mental health: a Mendelian randomisation study

Background

Body mass index (BMI) is correlated negatively with subjective well-being and positively with depressive symptoms. Whether these associations reflect causal effects is unclear.

Methods

We examined bidirectional, causal effects between BMI and mental health with Mendelian randomisation using summary-level data from published genome-wide association studies (BMI: n=339 224; subjective well-being: n=204 966; depressive symptoms: n=161 460). Genetic variants robustly related to the exposure variable acted as instrumental variable to estimate causal effects. We combined estimates of individual genetic variants with inverse-variance weighted meta-analysis, weighted median regression and MR-Egger regression.

Results

There was evidence for a causal, increasing effect of BMI on depressive symptoms and suggestive evidence for a decreasing effect of BMI on subjective well-being. We found no evidence for causality in the other direction.

Conclusion

This study provides support for a higher BMI causing poorer mental health. Further research should corroborate these findings and explore mechanisms underlying this potential causality.

Fat mass and obesity-associated (FTO) rs9939609 polymorphism modifies the relationship between body mass index and affective symptoms through the life course: a prospective birth cohort study

Although bi-directional relationships between high body mass index (BMI) and affective symptoms have been found, no study has investigated the relationships across the life course. There has also been little exploration of whether the fat mass and obesity-associated (FTO) rs9939609 single-nucleotide polymorphism (SNP) is associated with affective symptoms and/or modifies the relationship between BMI and affective symptoms. In the MRC National Survey of Health and Development (NSHD), 4556 participants had at least one measure of BMI and affective symptoms between ages 11 and 60-64 years. A structural equation modelling framework was used with the BMI trajectory fitted as latent variables representing BMI at 11, and adolescent (11-20 years), early adulthood (20-36 years) and midlife (36-53 years) change in BMI. Higher levels of adolescent emotional problems were associated with greater increases in adult BMI and greater increases in early adulthood BMI were associated with higher subsequent levels of affective symptoms in women. The rs9939609 risk variant (A allele) from 2469 participants with DNA genotyping at age 53 years showed mostly protective effect modification of these relationship. Increases in adolescent and early adulthood BMI were generally not associated with, or were associated with lower levels, of affective symptoms in the FTO risk homozygote (AA) group, but positive associations were seen in the TT group. These results suggest bi-directional relationships between higher BMI and affective symptoms across the life course in women, and that the relationship could be ameliorated by rs9939609 risk variant.

Causal inference in obesity research

Obesity is a risk factor for a plethora of severe morbidities and premature death. Most supporting evidence comes from observational studies that are prone to chance, bias and confounding. Even data on the protective effects of weight loss from randomized controlled trials will be susceptible to confounding and bias if treatment assignment cannot be masked, which is usually the case with lifestyle and surgical interventions. Thus, whilst obesity is widely considered the major modifiable risk factor for many chronic diseases, its causes and consequences are often difficult to determine. Addressing this is important, as the prevention and treatment of any disease requires that interventions focus on causal risk factors. Disease prediction, although not dependent on knowing the causes, is nevertheless enhanced by such knowledge. Here, we provide an overview of some of the barriers to causal inference in obesity research and discuss analytical approaches, such as Mendelian randomization, that can help to overcome these obstacles. In a systematic review of the literature in this field, we found: (i) probable causal relationships between adiposity and bone health/disease, cancers (colorectal, lung and kidney cancers), cardiometabolic traits (blood pressure, fasting insulin, inflammatory markers and lipids), uric acid concentrations, coronary heart disease and venous thrombosis (in the presence of pulmonary embolism), (ii) possible causal relationships between adiposity and gray matter volume, depression and common mental disorders, oesophageal cancer, macroalbuminuria, end-stage renal disease, diabetic kidney disease, nuclear cataract and gall stone disease, and (iii) no evidence for causal relationships between adiposity and Alzheimer's disease, pancreatic cancer, venous thrombosis (in the absence of pulmonary embolism), liver function and periodontitis.

Body mass index and psychiatric disorders: a Mendelian randomization study

Obesity is a highly prevalent risk factor for cardiometabolic diseases. Observational studies suggest that obesity is associated with psychiatric traits, but causal inference from such studies has several limitations. We used two-sample Mendelian randomization methods (inverse variance weighting, weighted median and MR-Egger regression) to evaluate the association of body mass index (BMI) with three psychiatric traits using data from the Genetic Investigation of Anthropometric Traits and Psychiatric Genomics consortia. Causal odds ratio estimates per 1-standard deviation increment in BMI ranged from 0.88 (95% CI: 0.62; 1.25) to 1.23 (95% CI: 0.65; 2.31) for bipolar disorder; 0.93 (0.78; 1.11) to 1.41 (0.87; 2.27) for schizophrenia; and 1.15 (95% CI: 0.92; 1.44) to 1.40 (95% CI: 1.03; 1.90) for major depressive disorder. Analyses removing potentially influential SNPs suggested that the effect estimates for depression might be underestimated. Our findings do not support the notion that higher BMI increases risk of bipolar disorder and schizophrenia. Although the point estimates for depression were consistent in all sensitivity analyses, the overall statistical evidence was weak. However, the fact that SNP-depression associations were estimated in relatively small samples reduced power to detect causal effects. This should be re-addressed when SNP-depression associations from larger studies become available.

Depressive symptoms and obesity: instrumental variable analysis using mother-offspring pairs in the 1970 British Cohort Study

BACKGROUND

The extent to which depression and obesity are causally related remains to be determined. We used intergenerational data on mother-offspring pairs in an instrumental variable analysis to examine the longitudinal association between adolescent depressive symptoms and body mass index (BMI) in adulthood.

METHODS

A total of 4733 mother-offspring pairs were identified from the 1970 British Cohort Study. Mothers completed the Malaise Inventory to assess depressive symptoms on three occasions across their offsprings' childhood/adolescence (aged 5, 10 and 16 years). Height and weight were recorded in mother and offspring (aged 16 years). Measures of height, weight and the Malaise Inventory were repeated in the participant at the age of 42 years.

RESULTS

Maternal malaise score was associated with offspring malaise score, thus confirming the validity of the chosen instrumental variable. A higher mother's malaise score was associated with higher offspring BMI at follow-up (B=0.043; 95% confidence interval (CI): 0.013, 0.072). There was a higher risk of adulthood offspring obesity in mothers with two or three episodes of depression compared with one or none (odds ratio, 1.42; 95% CI: 1.14, 1.76). The maternal malaise-offspring BMI association remained (P=0.003) after adjustment for offspring malaise score, suggesting that maternal mental health influences offspring obesity through mechanisms other than depression. Results from standard and instrumental variable analyses did not support a causal pathway in a direction from BMI to depression.

CONCLUSIONS

Our data support a causal pathway linking adolescent depressive symptoms to adiposity in adulthood over 26 years follow-up. The reverse direction, that is, adiposity to depression, was not supported.

Body mass index: Has epidemiology started to break down causal contributions to health and disease?

OBJECTIVES

To review progress in understanding the methods and results concerning the causal contribution of body mass index (BMI) to health and disease.

METHODS

In the context of conventional evidence focused on the relationship between BMI and health, this review considers current literature on the common, population-based, genetic contribution to BMI and how this has fed into the developing field of applied epidemiology.

RESULTS

Technological and analytical developments have driven considerable success in identifying genetic variants relevant to BMI. This has enabled the implementation of Mendelian randomization to address questions of causality. The product of this work has been the implication of BMI as a causal agent in a host of health outcomes. Further breakdown of causal pathways by integration with other "omics" technologies promises to deliver additional benefit.

CONCLUSIONS

Gaps remain in our understanding of BMI as a risk factor for health and disease, and while promising, applied genetic epidemiology should be considered alongside alternative methods for assessing the impact of BMI on health. Potential limitations, relating to inappropriate or nonspecific measures of obesity and the improper use of genetic instruments, will need to be explored and incorporated into future research aiming to dissect BMI as a risk factor.

Alternative Pathway Analyses Indicate Bidirectional Relations between Depressive Symptoms, Diet Quality, and Central Adiposity in a Sample of Urban US Adults

BACKGROUND

Temporality between socioeconomic status (SES), depressive symptoms (DS), dietary quality (DQ), and central adiposity (CA) is underexplored.

OBJECTIVES

Alternative pathways linking SES to DQ, DS, and CA were tested and models compared, stratified by race and sex.

METHODS

With the use of data from the Healthy Aging in Neighborhoods of Diversity across the Life Span (baseline age: 30-64 y; 2 visits; mean follow-up: 4.9 y), 12 structural equation models (SM) were conducted and compared. Time-dependent factors included the Center for Epidemiologic Studies-Depression [CES-D total score, baseline or visit 1 (v1), follow-up or visit 2 (v2), mean across visits (m), and annual rate of change (Δ)], 2010 Healthy Eating Index (HEI) (same notation), and central adiposity principal components' analysis score of waist circumference and trunk fat (kg) (Adipcent) (same notation). Sample sizes were white women (WW, n = 236), white men (WM, n = 159), African American women (AAW, n = 395), and African American men (AAM, n = 274), and a multigroup analysis within the SM framework was also conducted.

RESULTS

In the best-fitting model, overall, ∼31% of the total effect of SES→Adipcent(v2) (α ± SE: -0.10 ± 0.03, P < 0.05) was mediated through a combination of CES-D(v1) and ΔHEI. Two dominant pathways contributed to the indirect effect: SES→(-)CES-D(v1)→(+)Adipcent(v2) (-0.015) and SES→(+) ΔHEI→(-)Adipcent(v2) (-0.017), with a total indirect effect of -0.031 (P < 0.05). In a second best-fitting model, SES independently predicted Adipcent(v1, -0.069), ΔHEI(+0.037) and CES-D(v2, -2.70) (P < 0.05), with Adipcent(v1) marginally predicting ΔHEI(-0.014) and CES-D(v2, +0.67) (P < 0.10). These findings were indicative of DS's and CA's marginally significant bidirectional association (P < 0.10). Although best-fit-selected models were consistent across race × sex categories, path coefficients differed significantly between groups. Specifically, SES→Adipcent[v1(+0.11), v2(+0.14)] was positive among AAM (P < 0.05), and the overall positive association of Adipcent(v1)→CES-D(v2) was specific to AAW (+0.97, P < 0.10).

CONCLUSIONS

Despite consistent model fit, pathways linking SES to DQ, DS, and CA differed markedly among the race × sex groups. Our findings can inform the potential effectiveness of various mental health and dietary interventions.

Body Mass Index and Depressive Symptoms: Testing for Adverse and Protective Associations in Two Twin Cohort Studies

Studies have suggested both adverse and protective associations of obesity with depressive symptoms. We examined the contribution of environmental and heritable factors in this association. Participants were same-sex twin pairs from two population-based twin cohort studies, the Older Finnish Twin Cohort (n = 8,215; mean age = 44.1) and the US Midlife Development in the United States (MIDUS; n = 1,105; mean age = 45.1). Body mass index (BMI) was calculated from self-reported height and weight. Depressive symptoms were assessed using Beck's Depression Inventory (BDI; Finnish Twin Cohort), and by negative and positive affect scales (MIDUS). In the Finnish Twin Cohort, higher BMI was associated with higher depressive symptoms in monozygotic (MZ) twins (B = 2.01, 95% CI = 1.0, 3.0) and dizygotic (DZ) twins (B = 1.17, 0.5, 1.9) with BMI >22. This association was observed in within-pair analysis in DZ twins (B = 1.47, CI = 0.4, 2.6) but not in within-pair analysis of MZ twins (B = 0.03, CI = -1.9, 2.0). Consistent with the latter result, a bivariate genetic model indicated that the association between higher BMI and higher depressive symptoms was largely mediated by genetic factors. The results of twin-pair analysis and bivariate genetic model were replicated in the MIDUS sample. These findings suggest an association between obesity and higher depressive symptoms, which is largely explained by shared heritable biological mechanisms.

Food insecurity, mental health and quality of life among people living with HIV commencing antiretroviral treatment in Ethiopia: a cross-sectional study

BACKGROUND

Studies from high-income settings show that both food insecurity and common mental disorders (CMDs) are associated with lower quality of life among people living with HIV (PLHIV). However, there is limited research among PLHIV in sub-Saharan Africa. In this study we tested the hypothesis that food insecurity and CMDs would be associated with poorer quality of life of PLHIV in Ethiopia.

METHODS

A cross-sectional study was carried out with 348 PLHIV who were initiating antiretroviral therapy recruited from two primary care centers and a tertiary Hospital in southwest Ethiopia. Food insecurity, CMD, and quality of life were measured using instruments adapted and validated in Ethiopia (Household Food Insecurity Access Scale, Kessler-6, and WHOQOL-HIV-BREF-ETH, respectively). Multiple linear regression analysis was used to identify factors associated with quality of life after adjusting for confounders.

RESULTS

The prevalence of severe household food insecurity among PLHIV was 38.7 %. After adjusting for confounders, severe food insecurity (β = -3.24, 95 % CI: -6.19; -0.29) and higher levels of CMD symptoms (β = -1.72 for each 1 point increase, 95 % CI: -1.94; -1.49) were associated with lower quality of life. Other factors associated with lower quality of life were advanced HIV disease (β = -3.80, 95 % CI: -6.18; -1.42), and being underweight (BMI = 17.0 - 18.5 kg/m(2)) (β = -3.45, 95 % CI: -6.18; -0.71). Owning more household assets was associated with higher quality of life (β = 0.99 for owning one more asset, 95 % CI: 0.09; 1.89).

CONCLUSION

Poor mental health and food insecurity are associated with lower quality of life in PLHIV. There is a need for longitudinal studies to elucidate the pathways linking CMD, food insecurity and quality of life.

Association of Body Mass Index with Depression, Anxiety and Suicide-An Instrumental Variable Analysis of the HUNT Study

Objective

While high body mass index is associated with an increased risk of depression and anxiety, cumulative evidence indicates that it is a protective factor for suicide. The associations from conventional observational studies of body mass index with mental health outcomes are likely to be influenced by reverse causality or confounding by ill-health. In the present study, we investigated the associations between offspring body mass index and parental anxiety, depression and suicide in order to avoid problems with reverse causality and confounding by ill-health.

Methods

We used data from 32,457 mother-offspring and 27,753 father-offspring pairs from the Norwegian HUNT-study. Anxiety and depression were assessed using the Hospital Anxiety and Depression Scale and suicide death from national registers. Associations between offspring and own body mass index and symptoms of anxiety and depression and suicide mortality were estimated using logistic and Cox regression. Causal effect estimates were estimated with a two sample instrument variable approach using offspring body mass index as an instrument for parental body mass index.

Results

Both own and offspring body mass index were positively associated with depression, while the results did not indicate any substantial association between body mass index and anxiety. Although precision was low, suicide mortality was inversely associated with own body mass index and the results from the analysis using offspring body mass index supported these results. Adjusted odds ratios per standard deviation body mass index from the instrumental variable analysis were 1.22 (95% CI: 1.05, 1.43) for depression, 1.10 (95% CI: 0.95, 1.27) for anxiety, and the instrumental variable estimated hazard ratios for suicide was 0.69 (95% CI: 0.30, 1.63).

Conclusion

The present study’s results indicate that suicide mortality is inversely associated with body mass index. We also found support for a positive association between body mass index and depression, but not for anxiety.

Sarcopenic obesity and risk of new onset depressive symptoms in older adults: English Longitudinal Study of Ageing

Background:

We examined the role of sarcopenic obesity as a risk factor for new-onset depressive symptoms over 6-year follow-up in a large sample of older adults.

Methods:

The sample comprised 3862 community dwelling participants (1779 men, 2083 women; mean age 64.6±8.3 years) without depressive symptoms at baseline, recruited from the English Longitudinal Study of Ageing. At baseline and 4-year follow-up, handgrip strength (kg) of the dominant hand was assessed using a hand-held dynamometer, as a measure of sarcopenia. The outcome was new onset depressive symptoms at 6-year follow-up, defined as a score of ⩾4 on the 8-item Centre of Epidemiological Studies Depression scale. Sarcopenic obesity was defined as obese individuals (body mass index ⩾30 kg m⁻²) in the lowest tertile of sex-specific grip strength (<35.3 kg men; <19.6 kg women).

Results:

Using a multivariable logistic regression model, the risk of depressive symptoms was greatest in obese adults in the lowest tertile of handgrip strength (odds ratio (OR), 1.79, 95% confidence interval (CI), 1.10, 2.89) compared with non-obese individuals with high handgrip strength. Participants who were obese at baseline and had a decrease of more than 1 s.d. in grip strength over 4-year follow-up were at greatest risk of depressive symptoms (OR=1.97, 95% CI, 1.22, 3.17) compared with non-obese with stable grip strength.

Conclusions:

A reduction in grip strength was associated with higher risk of depressive symptoms in obese participants only, suggesting that sarcopenic obesity is a risk factor for depressive symptoms.

Mendelian randomization studies: a review of the approaches used and the quality of reporting

BACKGROUND

Mendelian randomization (MR) studies investigate the effect of genetic variation in levels of an exposure on an outcome, thereby using genetic variation as an instrumental variable (IV). We provide a meta-epidemiological overview of the methodological approaches used in MR studies, and evaluate the discussion of MR assumptions and reporting of statistical methods.

METHODS

We searched PubMed, Medline, Embase and Web of Science for MR studies up to December 2013. We assessed (i) the MR approach used; (ii) whether the plausibility of MR assumptions was discussed; and (iii) whether the statistical methods used were reported adequately.

RESULTS

Of 99 studies using data from one study population, 32 used genetic information as a proxy for the exposure without further estimation, 44 performed a formal IV analysis, 7 compared the observed with the expected genotype-outcome association, and 1 used both the latter two approaches. The 80 studies using data from multiple study populations used many different approaches to combine the data; 52 of these studies used some form of IV analysis; 44% of studies discussed the plausibility of all three MR assumptions in their study. Statistical methods used for IV analysis were insufficiently described in 14% of studies.

CONCLUSIONS

Most MR studies either use the genotype as a proxy for exposure without further estimation or perform an IV analysis. The discussion of underlying assumptions and reporting of statistical methods for IV analysis are frequently insufficient. Studies using data from multiple study populations are further complicated by the combination of data or estimates. We provide a checklist for the reporting of MR studies.

Revisiting Mendelian randomization studies of the effect of body mass index on depression

Mendelian Randomization studies, which use genetic instrumental variables (IVs) as quasi-experiments to estimate causal effects, report inconsistent findings regarding effects of body mass index (BMI) on mental health. We used genetic IV to estimate effects of BMI on depression and evaluated validity of a commonly used IV. Female Nurse's Health Study participants (n=6989, average age 56.4, [Standard Deviation 6.91] years at first depression assessment) self-reported BMI, which was averaged across eight reports prior to depression assessment (mean=24.96, SD 4.50). Genetic instruments included fat mass and obesity-associated protein (FTO) alleles, melanocortin receptor 4 (MC4R) alleles, and polygenic risk scores based on 32 established polymorphisms for BMI. Depression was assessed using multiple symptom measures, scaled to the Geriatric Depression Scale 15, averaged across up to 7 biennial waves. We used over-identification tests to assess the validity of genetic IVs. In conventional estimates, each additional BMI point predicted 0.024 (95% Confidence Interval (CI): 0.020-0.029) higher average depression scores. Genetic IV estimates were not significant when based on FTO (beta: 0.064, CI: -0.014, 0.142), MC4R (beta: 0.005, CI: -0.146, 0.156), polygenic score excluding FTO (beta=-0.003, 95%-CI -0.051, 0.045), or mechanism-specific scores. The over-identification test comparing IV estimates based on FTO to estimates based on the polygenic score excluding FTO rejected equality of estimated effects (P=0.014). Results provide no evidence against a null effect of BMI on depression and call into question validity of FTO as an instrument for BMI in Mendelian Randomization studies.

Potential anti-obesogenic properties of non-digestible carbohydrates: specific focus on resistant dextrin

Alterations in the composition and metabolic activity of the gut microbiota appear to contribute to the development of obesity and associated metabolic diseases. However, the extent of this relationship remains unknown. Modulating the gut microbiota with non-digestible carbohydrates (NDC) may exert anti-obesogenic effects through various metabolic pathways including changes to appetite regulation, glucose and lipid metabolism and inflammation. The NDC vary in physicochemical structure and this may govern their physical properties and fermentation by specific gut bacterial populations. Much research in this area has focused on established prebiotics, especially fructans (i.e. inulin and fructo-oligosaccharides); however, there is increasing interest in the metabolic effects of other NDC, such as resistant dextrin. Data presented in this review provide evidence from mechanistic and intervention studies that certain fermentable NDC, including resistant dextrin, are able to modulate the gut microbiota and may alter metabolic process associated with obesity, including appetite regulation, energy and lipid metabolism and inflammation. To confirm these effects and elucidate the responsible mechanisms, further well-controlled human intervention studies are required to investigate the impact of NDC on the composition and function of the gut microbiota and at the same time determine concomitant effects on host metabolism and physiology.

FTO genotype and aging: pleiotropic longitudinal effects on adiposity, brain function, impulsivity and diet

Although overweight and obesity are associated with poor health outcomes in the elderly, the biological bases of obesity-related behaviors during aging are poorly understood. Common variants in the FTO gene are associated with adiposity in children and younger adults as well as with adverse mental health in older individuals. However, it is unclear whether FTO influences longitudinal trajectories of adiposity and other intermediate phenotypes relevant to mental health during aging. We examined whether a commonly carried obesity-risk variant in the FTO gene (rs1421085 single-nucleotide polymorphism) influences adiposity and is associated with changes in brain function in participants within the Baltimore Longitudinal Study of Aging, one of the longest-running longitudinal aging studies in the United States. Our results show that obesity-related risk allele carriers of FTO gene show dose-dependent increments in body mass index during aging. Moreover, the obesity-related risk allele is associated with reduced medial prefrontal cortical function during aging. Consistent with reduced brain function in regions intrinsic to impulse control and taste responsiveness, risk allele carriers of FTO exhibit dose-dependent increments in both impulsivity and intake of fatty foods. We propose that a common neural mechanism may underlie obesity-associated impulsivity and increased consumption of high-calorie foods during aging.

Do genetic risk scores for body mass index predict risk of phobic anxiety? Evidence for a shared genetic risk factor

BACKGROUND

Obesity and anxiety are often linked but the direction of effects is not clear.

METHOD

Using genetic instrumental variable (IV) analyses in 5911 female participants from the Nurses' Health Study (NHS, initiated 1976) and 3697 male participants from the Health Professional Follow-up Study (HPFS, initiated 1986), we aimed to determine whether obesity increases symptoms of phobic anxiety. As instrumental variables we used the fat mass and obesity-associated (FTO) gene, the melanocortin 4 receptor (MC4R) gene and a genetic risk score (GRS) based on 32 single nucleotide polymorphisms (SNPs) that significantly predict body mass index (BMI). 'Functional' GRSs corresponding with specific biological pathways that shape BMI (adipogenesis, appetite and cardiopulmonary) were considered. The main outcome was phobic anxiety measured by the Crown Crisp Index (CCI) in 2004 in the NHS and in 2000 in the HPFS.

RESULTS

In observational analysis, a 1-unit higher BMI was associated with higher phobic anxiety symptoms [women: β = 0.05, 95% confidence interval (CI) 0.030-0.068; men: β = 0.04, 95% CI 0.016-0.071). IV analyses showed that BMI was associated with higher phobic anxiety symptoms in the FTO-instrumented analysis (p = 0.005) but not in the GRS-instrumented analysis (p = 0.256). Functional GRSs showed heterogeneous, non-significant effects of BMI on phobic anxiety symptoms.

CONCLUSIONS

Our findings do not provide conclusive evidence in favor of the hypothesis that higher BMI leads to higher levels of phobic anxiety, but rather suggest that genes that influence obesity, in particular FTO, may have direct effects on phobic anxiety, and hence that obesity and phobic anxiety may share common genetic determinants.

Inverse association between obesity predisposing FTO genotype and completed suicide

The A allele of rs9939609 in the FTO gene predisposes to increased body mass index (BMI) and obesity. Recently we showed an inverse association between the obesity related A allele of rs9939609 and alcohol dependence which was replicated by others. Since this finding raises a possibility that FTO may be associated with other psychiatric phenotypes, we aimed to examine association of rs9939609 with completed suicide. We genotyped rs9939609 in 912 suicide victims and 733 controls using TaqMan approach. We observed an inverse association between suicide and the rs9939609 A allele (OR = 0.80, P = 0.002, P_cor = 0.006) with genotype distribution suggesting a co-dominant effect. Given the link between alcoholism and suicide under influence of alcohol reported in Polish population, confounding by alcohol addiction was unlikely due to apparently similar effect size among cases who were under influence of ethanol at the time of death (OR = 0.76, P = 0.003, N = 361) and those who were not (OR = 0.80, P = 0.007, N = 469). The search for genotype-phenotype correlations did not show significant results. In conclusion, our study proves that there is an inverse association between rs9939609 polymorphism in FTO gene and completed suicide which is independent from association between FTO and alcohol addiction.

Depressive symptoms and body mass index: co-morbidity and direction of association in a British birth cohort followed over 50 years

BACKGROUND

An unhealthy body mass index (BMI) has been associated with depression but the direction of association is uncertain. Our aim was to estimate the co-morbidity and direction of association between BMI and depressive symptoms at several ages, from childhood to mid-adulthood.

METHOD

The data were from 18,558 individuals born in 1 week in March 1958, in England, Scotland and Wales, with follow-up at ages 7, 11, 16, 23, 33, 42, 45 and 50 years. Depression (scores>or=90th percentile) was identified from child/adolescent (teacher questionnaires) and adult (self-complete questionnaires and clinical interview) measures. BMI (kg/m2) measured in child/adolescence and adulthood was classified as underweight, normal, overweight or obese.

RESULTS

In cross-sectional analyses, obesity and underweight (not overweight) from 11 to 45 years were associated respectively with 1.3-2.1 and 1.5-2.3 times the risk of depression compared with normal weight. Using the time-lagged generalized estimating equation (GEE) approach, we tested (a) whether underweight or obesity at prior ages (7 to 45 years) predicted subsequent risk of depression (11 to 50 years), adjusting for baseline depression; and (b) whether depression at prior ages (7 to 42 years) predicted subsequent risk of underweight or obesity (11 to 45 years), adjusting for baseline BMI. In longitudinal analyses, underweight predicted subsequent depression in both sexes [odds ratio (OR) 1.25, 95% confidence interval (CI) 1.11-1.40] and depression predicted subsequent underweight in males only (OR 1.84, 95% CI 1.52-2.23). Obesity predicted subsequent depressive symptoms in females only (OR 1.34, 95% CI 1.14-1.56), but depression did not predict obesity.

CONCLUSIONS

Clinicians should consider screening routinely for depression patients with unhealthy BMI, namely underweight and obesity, and vice versa.

Association of metabolically healthy obesity with depressive symptoms: pooled analysis of eight studies

The hypothesis of metabolically healthy obesity posits that adverse health effects of obesity are largely avoided when obesity is accompanied by a favorable metabolic profile. We tested this hypothesis with depressive symptoms as the outcome using cross-sectional data on obesity, metabolic health and depressive symptoms. Data were extracted from eight studies and pooled for individual-participant meta-analysis with 30,337 men and women aged 15-105 years (mean age=46.1). Clinic measures included height, weight and metabolic risk factors (high blood pressure, high triglycerides, low high-density lipoprotein cholesterol, high C-reactive protein and high glycated hemoglobin). Depressive symptoms were assessed using clinical interview or standardized rating scales. The pooled sample comprised 7673 (25%) obese participants (body mass index ⩾30 kg m(-2)). Compared to all non-obese individuals, the OR for depressive symptoms was higher in metabolically unhealthy obese individuals with two or more metabolic risk factors (1.45; 95% confidence interval (CI)=1.30, 1.61) and for metabolically healthy obese with ⩽1 metabolic risk factor (1.19; 95% CI=1.03, 1.37), adjusted for sex, age and race/ethnicity. Metabolically unhealthy obesity was associated with higher depression risk (OR=1.23; 95% CI=1.05, 1.45) compared with metabolically healthy obesity. These associations were consistent across studies with no evidence for heterogeneity in estimates (all I(2)-values<4%). In conclusion, obese persons with a favorable metabolic profile have a slightly increased risk of depressive symptoms compared with non-obese, but the risk is greater when obesity is combined with an adverse metabolic profile. These findings suggest that metabolically healthy obesity is not a completely benign condition in relation to depression risk.

Relationship between obesity and the risk of clinically significant depression: Mendelian randomisation study

BACKGROUND

Obesity has been shown to be associated with depression and it has been suggested that higher body mass index (BMI) increases the risk of depression and other common mental disorders. However, the causal relationship remains unclear and Mendelian randomisation, a form of instrumental variable analysis, has recently been employed to attempt to resolve this issue.

AIMS

To investigate whether higher BMI increases the risk of major depression.

METHOD

Two instrumental variable analyses were conducted to test the causal relationship between obesity and major depression in RADIANT, a large case-control study of major depression. We used a single nucleotide polymorphism (SNP) in FTO and a genetic risk score (GRS) based on 32 SNPs with well-established associations with BMI.

RESULTS

Linear regression analysis, as expected, showed that individuals carrying more risk alleles of FTO or having higher score of GRS had a higher BMI. Probit regression suggested that higher BMI is associated with increased risk of major depression. However, our two instrumental variable analyses did not support a causal relationship between higher BMI and major depression (FTO genotype: coefficient -0.03, 95% CI -0.18 to 0.13, P = 0.73; GRS: coefficient -0.02, 95% CI -0.11 to 0.07, P = 0.62).

CONCLUSIONS

Our instrumental variable analyses did not support a causal relationship between higher BMI and major depression. The positive associations of higher BMI with major depression in probit regression analyses might be explained by reverse causality and/or residual confounding.

Instrumental variable methods for causal inference

A goal of many health studies is to determine the causal effect of a treatment or intervention on health outcomes. Often, it is not ethically or practically possible to conduct a perfectly randomized experiment, and instead, an observational study must be used. A major challenge to the validity of observational studies is the possibility of unmeasured confounding (i.e., unmeasured ways in which the treatment and control groups differ before treatment administration, which also affect the outcome). Instrumental variables analysis is a method for controlling for unmeasured confounding. This type of analysis requires the measurement of a valid instrumental variable, which is a variable that (i) is independent of the unmeasured confounding; (ii) affects the treatment; and (iii) affects the outcome only indirectly through its effect on the treatment. This tutorial discusses the types of causal effects that can be estimated by instrumental variables analysis; the assumptions needed for instrumental variables analysis to provide valid estimates of causal effects and sensitivity analysis for those assumptions; methods of estimation of causal effects using instrumental variables; and sources of instrumental variables in health studies.

Genome-wide association studies of obesity and metabolic syndrome

Until just a few years ago, the genetic determinants of obesity and metabolic syndrome were largely unknown, with the exception of a few forms of monogenic extreme obesity. Since genome-wide association studies (GWAS) became available, large advances have been made. The first single nucleotide polymorphism robustly associated with increased body mass index (BMI) was in 2007 mapped to a gene with for the time unknown function. This gene, now known as fat mass and obesity associated (FTO) has been repeatedly replicated in several ethnicities and is affecting obesity by regulating appetite. Since the first report from a GWAS of obesity, an increasing number of markers have been shown to be associated with BMI, other measures of obesity or fat distribution and metabolic syndrome. This systematic review of obesity GWAS will summarize genome-wide significant findings for obesity and metabolic syndrome and briefly give a few suggestions of what is to be expected in the next few years.

The future is now: early life events preset adult behaviour

To consider the evidence that human and animal behaviours are epigenetically programmed by lifetime experiences. Extensive PubMed searches were carried out to gain a broad view of the topic, in particular from the perspective of human psychopathologies such as mood and anxiety disorders. The selected literature cited is complemented by previously unpublished data from the authors' laboratories. Evidence that physiological and behavioural functions are particularly sensitive to the programming effects of environmental factors such as stress and nutrition during early life, and perhaps at later stages of life, is reviewed and extended. Definition of stimulus- and function-specific critical periods of programmability together with deeper understanding of the molecular basis of epigenetic regulation will deliver greater appreciation of the full potential of the brain's plasticity while providing evidence-based social, psychological and pharmacological interventions to promote lifetime well-being.

Plasma C-reactive protein, genetic risk score, and risk of common cancers in the Atherosclerosis Risk in Communities study

PURPOSE

Many studies, including the Atherosclerosis Risk in Communities (ARIC) cohort, reported a positive association between plasma C-reactive protein (CRP)-a biomarker of low-grade chronic inflammation-and colorectal cancer risk, although it is unclear whether the association is causal. Our aims were to assess the associations of a CRP genetic risk score (CRP-GRS) created from single-nucleotide polymorphisms (SNPs) with colorectal cancer risk, as well as examine plasma CRP and CRP-GRS in relation to common cancers in the ARIC cohort.

METHODS

Cox proportional hazards models were used to prospectively estimate hazard ratios (HRs) and 95 % confidence interval (95 % CI) of total, colorectal, lung, prostate, and breast cancers in relation to: (1) CRP-GRS among 8,657 Whites followed in 1987-2006 and (2) log-transformed plasma CRP among 7,603 Whites followed in 1996-2006. A weighted CRP-GRS was comprised of 20 CRP-related SNPs located in/near CRP, APOC1, HNF1A, LEPR, and 16 other genes that were identified in genome-wide association studies.

RESULTS

After multivariable adjustment, one standard deviation increment of the CRP-GRS was associated with colorectal cancer risk (HR 1.19; 95 % CI 1.03-1.37), but not with any other cancer. One unit of log-transformed plasma CRP was associated with the risk of total, colorectal, lung, and breast cancers: HRs (95 % CIs) were 1.08 (1.01-1.15), 1.24 (1.01-1.51), 1.29 (1.08-1.54), and 1.27 (1.07-1.51), respectively. HRs remained elevated, although lost statistical significance for all but breast cancer, after excluding subjects with <2 years of follow-up.

CONCLUSIONS

The study corroborates a causative role of chronic low-grade inflammation in colorectal carcinogenesis.

Comparing Adult Males and Females in the United States to Examine the Association between Body Mass Index and Frequent Mental Distress: An Analysis of Data from BRFSS 2011

Background. There is conflicting evidence regarding the association of body mass index (BMI) with mental distress. Studies have focused on different dimensions of mental health and used different definitions and many of them have not controlled for confounding factors. The aim of this study was to examine the relationship between frequent mental distress (FMD) and BMI among adults in the United States, with special emphasis on gender differences. Methods. Data from the Behavioral Risk Factor Surveillance System (BRFSS) for the year 2011 were used in logistic regression models to predict FMD, defined as having 14 or more days of poor mental health in the previous month. Sociodemographic factors, tobacco and alcohol use, diet and physical activity, and number of chronic diseases were controlled for. Results. 11.95% (n = 53,715) of the participants with valid responses (n = 496,702) had FMD. The adjusted ORs of having FMD among underweight, overweight, and obese females were 1.13 (95% CI: 1.10, 1.60), 1.10 (95% CI: 1.03, 1.19), and 1.21 (95% CI: 1.13, 1.31), respectively, but they were not statistically significant for males. Conclusions. These findings suggest a relationship between BMI and FMD, independent of other variables. It may be useful to explore longitudinal trend in this association.

Prevalência de transtornos mentais comuns em jovens brasileiros recém-incorporados ao Serviço Militar Obrigatório e fatores associados

A saúde mental de militares das Forças Armadas é uma área de investigação ainda pouco explorada no Brasil. O presente estudo teve por objetivo estimar a prevalência de transtornos mentais comuns (TMC) e identificar os fatores a estes associados em jovens brasileiros recém-incorporados ao serviço militar obrigatório: os recrutas. A população de estudo foi composta de 78 jovens adultos do sexo masculino. A ocorrência de TMC (variável dependente) foi avaliada por meio do General Health Questionnaire, versão 12 itens (GHQ-12). Para estimar as associações entre TMC e as variáveis independentes foram utilizados o teste χ²(Qui-quadrado)e a regressão logística. Os resultados mostraram uma prevalência de TMC de 43,6% (IC 95% 33,14 - 54,64). As razões de prevalência de TMC mostraram-se entre 4 e 5 vezes maiores entre os que apresentavam distúrbios do sono, sendo que estes se mostraram como único fator associado a TMC. Estes resultados parecem indicar que as situações vivenciadas pelos recrutas em seu ambiente de trabalho podem estar associadas com TMC de forma causal. Outros estudos, com desenho longitudinal, são necessários para que tal efeito seja confirmado.

FTO at rs9939609, food responsiveness, emotional control and symptoms of ADHD in preschool children

The FTO minor allele at rs9939609 has been associated with body mass index (BMI: weight (kg)/height (m)²) in children from 5 years onwards, food intake, and eating behaviour. The high expression of FTO in the brain suggests that this gene may also be associated with behavioural phenotypes, such as impulsivity and control. We examined the effect of the FTO minor allele (A) at rs9939609 on eating behaviour, impulsivity and control in young children, thus before the BMI effect becomes apparent. This study was embedded in the Generation R Study, a population-based cohort from fetal life onwards. 1,718 children of European descent were genotyped for FTO at rs9939609. With logistic regression assuming an additive genetic model, we examined the association between the FTO minor allele and eating behaviour, impulsivity and control in preschool children. There was no relation between FTO at rs9939609 and child BMI at this age. The A allele at rs9939609 was associated with increased food responsiveness (OR 1.21, p = 0.03). Also, children with the A allele were less likely to have symptoms of ADHD (OR 0.74, p = 0.01) and showed more emotional control (OR 0.64, p = 0.01) compared to children without the A allele. Our findings suggest that before the association between FTO and BMI becomes apparent, the FTO minor allele at rs9939609 leads to increased food responsiveness, a decreased risk for symptoms of ADHD and better emotional control. Future studies are needed to investigate whether these findings represent one single mechanism or reflect pleiotropic effects of FTO.