Mendelian randomization analysis does not support causal associations of birth weight with hypertension risk and blood pressure in adulthood

Methodological approaches, challenges, and opportunities in the application of Mendelian randomisation to lifecourse epidemiology: A systematic literature review

Diseases diagnosed in adulthood may have antecedents throughout (including prenatal) life. Gaining a better understanding of how exposures at different stages in the lifecourse influence health outcomes is key to elucidating the potential benefits of disease prevention strategies. Mendelian randomisation (MR) is increasingly used to estimate causal effects of exposures across the lifecourse on later life outcomes. This systematic literature review explores MR methods used to perform lifecourse investigations and reviews previous work that has utilised MR to elucidate the effects of factors acting at different stages of the lifecourse. We conducted searches in PubMed, Embase, Medline and MedRXiv databases. Thirteen methodological studies were identified. Four studies focused on the impact of time-varying exposures in the interpretation of "standard" MR techniques, five presented methods for repeat measures of the same exposure, and four described methodological approaches to handling multigenerational exposures. A further 127 studies presented the results of an applied research question. Over half of these estimated effects in a single generation and were largely confined to the exploration of questions regarding body composition. The remaining mostly estimated maternal effects. There is a growing body of research focused on the development and application of MR methods to address lifecourse research questions. The underlying assumptions require careful consideration and the interpretation of results rely on select conditions. Whilst we do not advocate for a particular strategy, we encourage practitioners to make informed decisions on how to approach a research question in this field with a solid understanding of the limitations present and how these may be affected by the research question, modelling approach, instrument selection, and data availability.

Joint association and interaction of birth weight and lifestyle with hypertension: A cohort study in UK Biobank

Low birth weight and unhealthy lifestyle are both associated with an increased risk of hypertension. The authors aimed to assess the joint association and interaction of birth weight and lifestyle with incident hypertension. The authors included 205 522 participants free of hypertension at baseline from UK Biobank. A healthy lifestyle score was constructed using information on body mass index, physical activity, diet, smoking status and alcohol intake. Cox proportional hazard models were used to investigate the impact of birth weight, healthy lifestyle score and their joint effect on hypertension. The authors documented 13 548 (6.59%) incident hypertension cases during a median of 8.6 years of follow-up. The multivariate adjusted hazard ratios and 95% confidence intervals were 1.12 (1.09, 1.15) per kg lower birth weight and 0.76 (0.75, 0.77) per score increment in healthy lifestyle score. Healthy lifestyle reduced the risk of hypertension in any category of different birth weight groups. The preventive effect of healthy lifestyle on hypertension was the most pronounced at lower birth weight with <2500 g and 2500-2999 g, respectively. Addictive interaction between birth weight and healthy lifestyle score was observed with the relative excess risk due to interaction of 0.04 (0.03, 0.05). Our findings emphasized the importance of healthy lifestyle for hypertension prevention, especially among the high-risk population with lower birth weight.

Newborn body composition and child cardiovascular risk markers: a prospective multi-ethnic Asian cohort study

BACKGROUND

Early epidemiological studies have associated low birthweight with increased cardiovascular risk. We aimed to examine whether the fat and fat-free components of birthweight have differing relationships with childhood cardiovascular risk markers.

METHODS

In the Growing Up in Singapore Towards healthy Outcomes (GUSTO) cohort, air displacement plethysmography was conducted within 24 h after delivery in 290 naturally conceived singletons. We investigated associations of newborn cohort-specific standardized z-score of fat mass, fat-free mass, body fat percentage and birthweight on child (at 6 years of age) carotid intima-media thickness, pulse wave velocity, blood pressure, prehypertension/hypertension (>110/70 mmHg) and standardized systolic and diastolic blood pressure (SBP and DBP) trajectories (at 3-6 years of age), taking account of maternal education, height, tobacco exposure, parity, ethnicity, child's sex, gestational age, age at follow-up, and other maternal factors.

RESULTS

Clear inverse associations were seen for blood pressure with z-score of fat mass [SBP, β (95% CI): -1.31 mmHg (-2.57, -0.06); DBP: -0.79 mmHg (-1.74, 0.15)] and body fat percentage [SBP: -1.46 mmHg (-2.73, -0.19); DBP: -0.80 mmHg (-1.75, 0.16)], but not with fat-free mass [SBP: 0.27 mmHg (-1.29, 1.83)]; DBP: -0.14 mmHg (-1.30, 1.03)]. Being in the lowest tertile of fat mass or body fat percentage was associated with higher blood pressure trajectories and prehypertension/hypertension risk [OR (95% CI), fat mass: 4.23 (1.41, 12.68); body fat percentage: 3.22 (1.09, 9.53)] without concomitantly higher overweight/obesity risk.

CONCLUSIONS

At birth, low adiposity was associated with increased childhood blood pressure. Low newborn adiposity might serve as a marker of poor fetal growth or suboptimal intrauterine conditions associated with hypertension risk later in life.

Birth weight influences differently on systolic and diastolic blood pressure in children and adolescents aged 8-15

AIM

Globally, hypertension is one of the main threats to public health and a significant risk factor predisposing individuals to various cardiovascular conditions. Hypertension in the young is particularly complex and challenging. Accumulating evidence has implicated that low birth weight is vital for elevated blood pressure, and birth weight was negatively correlated with blood pressure. However, fewer studies with conflicting results have addressed the associations between birth weight and blood pressure in children and adolescents, and there is no relevant research conducted in the NHANES population. The principal objective of this project was to investigate the relationship between birth weight and blood pressure in children and adolescents in NHANES.

METHODS

A total of 7600 subjects aged 8 to15 were enrolled in the present study from the National Health and Nutrition Examination Survey (NHANES) 2007-2018. Outcome variables were systolic blood pressure(SBP) and diastolic blood pressure(DBP). Birth weight was regarded as an independent variable. EmpowerStats software and R (version 3.4.3) were performed to examine the association between birth weight and SBP or DBP.

RESULTS

Birth weight was negatively correlated with SBP in the fully-adjusted model(β = -0.02, 95%CI: -0.04 to -0.04, p = 0.0013), especially in non-Hispanic White (β = -0.03, 95%CI: -0.06 to -0.00,p = 0.0446), aged between 13 to 15(β = -0.03, 95%CI: -0.04 to -0.01, p = 0.0027), and male individuals(β = -0.03, 95%CI: -0.05 to -0.01, p = 0.0027). However, there was no unidirectional association between birth weight and DBP in the fully adjusted model(β = -0.01, 95%CI: -0.03 to 0.02, p = 0.5668) and in sub-analysis. An inverted U-shaped and J-shaped relationship was uncovered between birth weight and DBP in those aged 13 or above and Mexican Americans, respectively. The inflection point calculated by a recursive algorithm of birth weight in these groups was all 105 oz.

CONCLUSIONS

The current study identified that birth weight was negatively related to SBP but not significantly related to DBP in children and adolescents aged 8 to 15, highlighting different potential mechanisms behind high SBP and high DBP in the young. However, an inverted U-shaped and J-shaped relationship between birth weight and DBP was observed, suggesting that targeted intervention measures should be taken for different groups of people rather than generalizations.

Elevated Blood Pressure (≥120/80 mmHg) Is Associated with Elevated Serum Plasminogen Activator Inhibitor-1, Low Birth Weight, and Family History of Diabetes in Young Normal Weight Japanese Women

Objective: We examined whether elevated blood pressure (BP) (≥120/80 mmHg) was associated with several anthropometric, metabolic, and clinical variables, including the family history of type 2 diabetes (FHD) and low birth weight, in young normal weight Japanese women. Methods: BP, body composition, and fasting glucose, insulin, lipids, lipoproteins, apolipoproteins, and adipokines were measured in 332 young Japanese women. They received a questionnaire on birth weight and FHD. Results: The prevalence of low birth weight was 2.4% and that of positive FHD was 22.9%. Homeostasis model assessment-insulin resistance averaged <1.5 and did not differ cross-sectionally between 32 women with elevated BP and 300 women with normal BP although mean body mass index was higher in the former than in the latter (21.7 ± 2.9 kg/m² vs. 20.8 ± 2.2 kg/m², P = 0.02). Women with elevated BP had higher fat mass index (P = 0.02) and trunk fat percentage (P = 0.04). They had lower high-density lipoprotein (HDL) cholesterol and apolipoprotein A1 (both P = 0.01) while fasting triglycerides and apolipoprotein B did not differ. In addition, they had higher plasminogen activator inhibitor-1 (PAI-1) (P = 0.001). Furthermore, the prevalence of low birth weight (9.4% vs. 1.7%, P = 0.03) and positive FHD (40.6% vs. 20.0%, P = 0.01) was higher in women with elevated BP. Multivariable logistic regression analyses revealed that elevated BP was independently associated with PAI-1 [odds ratio (OR); 1.05, 95% confidence interval (CI): 1.02-1.08, P = 0.001], low birth weight (OR: 12.3, 95% CI: 2.3-67.3, P = 0.04), and FHD (OR: 3.0, 95% CI: 1.3-7.9, P = 0.01). Conclusion: Elevated BP was associated with positive FHD, low birth weight, and elevated serum PAI-1 in young normal weight Japanese women.

Impact of early life exposures on respiratory disease

The antecedents of asthma and chronic obstructive pulmonary disease (COPD) lie before school age. Adverse effects are transgenerational, antenatal and in the preschool years. Antenatal adverse effects impair spirometry by causing low birth weight, altered lung structure and immune function, and sensitizing the foetus to later insults. The key stages of normal lung health are lung function at birth, lung growth to a plateau age 20-25 years, and the phase of decline thereafter; contrary to perceived wisdom, accelerated decline is not related to smoking. There are different trajectories of lung function. Lung function usually tracks from preschool to late middle age. Asthma is driven by antenatal and early life influences. The airflow obstruction, emphysema and multi-morbidity of COPD all start early. Failure to reach a normal plateau and accelerated decline in lung function are risk factors for COPD. Airway disease cannot be prevented in adult life; prevention must start early.