An analysis of risk factors for spontaneously occurring type 2 diabetes mellitus in rhesus macaques (Macaca mulatta)

BACKGROUND

Type 2 Diabetes Mellitus (T2D) is a chronic disease with a high prevalence worldwide. Human literature suggests factors beyond well-known risk factors (e.g., age, body mass index) for T2D: cytomegalovirus serostatus, season of birth, maternal age, birth weight, and depression. Nothing is known, however, about whether these variables are influential in primate models of T2D.

METHODS

Using a retrospective methodology, we identified 22 cases of spontaneously occurring T2D among rhesus monkeys at our facility. A control sample of n = 1199 was identified.

RESULTS

Animals born to mothers that were ≤5.5 years of age, and animals that showed heightened Activity and Emotionality in response to brief separation in infancy, had a greater risk for development of T2D in adulthood.

CONCLUSIONS

Knowledge of additional risk factors for T2D could help colony managers better identify at-risk animals and enable diabetes researchers to select animals that might be more responsive to their manipulations.

Is there an association between family members' season of birth that could influence birth seasonality? Evidence from Spain and France

The number of births varies by season. Research on birth seasonality has shown that women's season of birth somehow influences that of their children, but factors underlying the intergenerational transmission of birth seasonality remain unknown. With data from Spain and France, we analysed the possibility of transmission of birth season between generations, testing whether relatives tended to be born in the same season. Results indicated that there was an association-a similarity-between parents' and children's birth seasons, partially explaining the stability of seasonal patterns over time. This association also existed between parents' birth seasons. While parents' association is directly explained by an excess of marriages with spouses born in the same month, the overall association may be explained by two facts: different socio-demographic groups show differentiated birth patterns, and relatives share socio-demographic features. Birth season seems to be related to family characteristics, which should be controlled for when assessing birth-month effects on subsequent social/health outcomes.

Season of Birth in Patients with Schizophrenia in Thailand

Objective

An excess of schizophrenia births in the winter or spring is a well-known finding in Western studies; however, few studies from equatorial regions have been done. Our purpose is to investigate the seasonality of schizophrenia births in Thailand.

Methods

This was a retrospective study in which patients with schizophrenia were identified from computerized records at Thammasat University Hospital. The Edwards test was used to detect any birth seasonality patterns among the patients with schizophrenia. Subsequently, the data were compared against the general population birth month data to examine potential seasonal effects using the Walter-Elwood seasonality test.

Results

There are 949 patients with schizophrenia, with a mean age of 39.3 years. The results demonstrate no evidence of distinctive seasonality in birth patterns among patients with schizophrenia (P = .329). The overall monthly distribution of births did not differ between the general population and patients with schizophrenia (P = .365).

Conclusion

In Thailand, a tropical country, there does not appear to be an effect of season of birth and the later development of schizophrenia.

Season of Birth and Cardiovascular Mortality in Atrial Fibrillation: A Population-Based Cohort Study

Background: The fetal origins hypothesis have associated early life exposures with the development of adverse health outcomes in adulthood. Season of birth has been shown to be associated with overall and cardiovascular mortality. Methods: We performed a retrospective database study to explore the association between season of birth and mortality in patients with atrial fibrillation. Results: A total of 8962 patients with AF were identified in the database with 1253 deaths recorded. AF patients born in spring and summer had a higher mortality rate when compared to those born in autumn and winter (hazard ratio (HR) 1.13, 95% confidence interval (CI) 1.01–1.26, p = 0.03). This effect was consistent in the male subgroup (HR 1.25, 95% CI 1.03–1.51, p = 0.02 for males born in spring; HR 1.24, 95% CI 1.03–1.51, p = 0.03 for males born in summer when compared to winter as the reference) but not in females (HR 1.02, 95% CI 0.79–1.31, p = 0.88 for females born in spring; HR 1.11, 95% CI 0.87–1.42, p = 0.39 for females born in summer when compared to winter as the reference). Results persisted after adjustment for baseline characteristics and clinical risk profile. A similar pattern was observed with cardiovascular mortality. Conclusion: Birth in spring or summer is associated with a higher risk of cardiovascular mortality in male AF patients, but not in females. This could be related to the underlying differences in rates of major adverse clinical events between genders. Further studies should aim at clarifying the mechanisms behind this association, which may help us understand the higher level of risk in female patients with AF.

Association Between Season of Birth and Cognitive Aging in Older Adults: Pan-European Population-Based Study on 70,000 Individuals

BACKGROUND

Several early-life factors have been associated with higher risk of developing dementia. It is unclear whether season of birth (SOB) can affect cognitive aging in older adults or not.

OBJECTIVE

We aimed to study the association of SOB with the level of cognitive performance as well as with the rate of cognitive decline.

METHODS

We studied 70,203 individuals who participated in the Survey of Health, Aging and Retirement in Europe. Cognition was measured with tests on verbal fluency and immediate and delayed recall. We assessed the association of SOB with the level of cognitive performance using multiple linear regression and with the rate of cognitive decline using linear mixed-effects models.

RESULTS

When compared to individuals born in winter and adjusted for sociodemographic and health-related characteristics, being born in summer was associated with a higher level of delayed recall (B 0.05; 95%CI 0.01 to 0.09) and verbal fluency (B 0.15; 95%CI 0.00 to 0.29) and being born in fall with a higher level of immediate recall (B 0.04; 95%CI 0.01 to 0.08) and verbal fluency (B 0.15; 95%CI 0.01 to 0.29). Individuals born in summer had a higher yearly decline in delayed recall (B -0.005; 95%CI -0.009 to 0.000), while the scores in delayed recall in participants born in spring showed an inverse trend (B 0.005; 95%CI 0.000 to 0.010).

CONCLUSION

Individuals born in winter seem to carry a life-long disadvantage in a lower level of cognitive performance; however, being born in winter does not seem to affect the rate of cognitive decline.

Being Born in Winter-Spring and at Around the Time of an Influenza Pandemic Are Risk Factors for the Development of Schizophrenia: The Apna Study in Navarre, Spain

Background: We analyzed the relationship between the prevalence of schizophrenia and the season of birth and gestation during a period of an influenza pandemic. Methods: Cross-sectional analysis of a prospective population-based cohort of 470,942 adults. We fitted multivariant logistic regression models to determine whether the season of birth and birth in an influenza-pandemic year (1957, 1968, 1977) was associated with schizophrenia. Results: 2077 subjects had been diagnosed with schizophrenia. Logistic regression identified a significantly greater prevalence of schizophrenia in men than in women (OR = 1.516, CI 95% = 1.388–1.665); in those born in the winter or spring than in those born in the summer or autumn (OR = 1.112, CI 95% = 1.020–1.212); and in those born in a period of an influenza pandemic (OR = 1.335, CI 95% = 1.199–1.486). The increase in risk was also significant when each influenza pandemic year was analyzed separately. However, neither month of birth nor season of birth, when each of the four were studied individually, were associated with a statistically significant increase in that risk. Conclusions: The winter–spring period and the influenza pandemics are independent risk factors for developing schizophrenia. This study contradicts many previous studies and thus revitalizes a locked debate in understanding the neurodevelopmental hypothesis of this disorder.

Handedness and Relative Age in International Elite Interactive Individual Sports Revisited

Relative age effects (RAE) describe the unintended side effect of annual age grouping such that athletes born close to a specific cutoff date are more likely to be associated with attaining higher performance status than athletes born later. One factor suggested to override the RAE is handedness. Given the left-handers' rarity and their proposed performance advantage in interactive sports, left-handedness may be associated with a lower likelihood of suffering from selection inequalities like RAE in those sports compared with right-handedness. Here, in a two-study approach, we tested that hypothesis by examining male and female athletes from various interactive individual sports sampled over a 10-year period from 2007 to 2016. Study 1 investigated distributions of birth and handedness of senior athletes listed in the top 200 of year-end world rankings in table tennis, tennis, squash, and fencing (épée, foil, and saber). Study 2 followed a similar design but focused on junior athletes in the fencing disciplines and tennis. Unlike the above prediction, in both studies, birth distribution was not found to be reliably associated with handedness in any of the sports or disciplines considered. Left-handers were consistently overrepresented in épée, foil, and table tennis, occasionally in saber and tennis, and not at all in squash. Birth frequencies decreased from quartile Q1 (January to March) to Q4 in almost any sporting domain at the junior level, whereas such trend was rarely found at the senior level. In conclusion, while providing novel insight on the role handedness may play at the junior level, our findings do not support the hypothesis that left-handedness helps override birth-related inequalities in high sporting achievement in elite interactive individual sports.

Relative Age Effect in Elite German Soccer: Influence of Gender and Competition Level

The relative age effect (RAE) is associated with (dis)advantages in competitive sports. While the RAE in elite male soccer reveals a skewed birthdate distribution in relation to a certain cut-off date, research of RAE in elite female soccer is affected by small number of samples and conflicting results. The purpose of this study was to investigate the RAE in elite adult German soccer regarding gender and competition level. The sample comprised 680 female and 1,083 male players of the two top German leagues during the 2019/20 season and German national teams (A-Team to Under 19). Differences between the observed and expected birthdate distributions were analyzed using chi-square statistics and effect sizes followed by calculating odds ratios. Results showed a statistically significant RAE with small effect size across all players included for both genders (female players: P < 0.001, W = 0.16, male players: P < 0.001, W = 0.23). The identified RAE was based on an over-representation of players born at the beginning of the year. According to gender and competition level, RAEs were more pronounced in German male soccer. While significant RAEs were found among males in the first two leagues (first league: P < 0.001, W = 0.19, second league: P < 0.001, W = 0.26), the RAE of females was more pronounced in the second league (first league: P = 0.080, W = 0.16, second league: P = 0.002, W = 0.20). The analysis of RAE regarding the national teams revealed a statistically significant RAE with large effect size for only the youngest investigated age group of male players (Under 19: P = 0.022, W = 0.52). Our data show an RAE in female and male German adult soccer, which could be accompanied by a loss of valuable elite players during the youth phase of the career. Consequently, the pool of talented players at the adult level would be limited.

Season of Birth Impacts the Neonatal Nasopharyngeal Microbiota

Objective: Pathogenic airway bacteria colonizing the neonatal airway increase the risk of childhood asthma, but little is known about the determinants of the establishment and dynamics of the airway microbiota in early life. We studied associations between perinatal risk factors and bacterial richness of the commensal milieu in the neonatal respiratory tract. Methods: Three hundred and twenty-eight children from the Copenhagen Prospective Studies on Asthma in the Childhood2000 (COPSAC2000) at-risk birth cohort were included in this study. The bacterial richness in each of the nasopharynxes of the 1-month old, asymptomatic neonates was analyzed by use of a culture-independent technique (T-RFLP). Information on perinatal risk factors included predisposition to asthma, allergy and eczema; social status of family; maternal exposures during pregnancy; mode of delivery; and postnatal exposures. The risk factor analysis was done by conventional statistics and partial least square discriminant analysis (PLSDA). Results: The nasopharyngeal bacterial community at 1-month displayed an average of 35 (IQR: 14-55, range 1-161) phylogenetically different bacteria groups. Season of birth was associated with nasopharyngeal bacterial richness at 1-month of age with a higher bacterial richness (p = 0.003) and more abundant specific bacterial profiles representing Gram-negative alpha-proteobacteria and Gram-positive Bacilli in the nasopharynx of summer-born children. Conclusion: Early postnatal bacterial colonization of the upper airways is significantly affected by birth season, emphasizing a future focus on the seasonality aspect in modelling the impact of early dynamic changes in airway bacterial communities in relation to later disease development.

Exposure to the Danish Mandatory Vitamin D Fortification Policy in Prenatal Life and the Risk of Developing Coeliac Disease-The Importance of Season: A Semi Ecological Study

Few studies have examined the role of maternal diet in relation to development of coeliac disease (CD). In Denmark, cancellation of mandatory vitamin D fortification of margarine in June 1985 provided this opportunity. This study examined if season of birth or prenatal exposure to extra vitamin D from food fortification were associated with developing CD later in life. A strength of this study is the distinctly longer follow-up of patients (30 years). This register-based study has a semi-ecological design. Logistic regression analysis was used to estimate odds ratios and to calculate 95% confidence intervals. The odds ratio for developing CD was 0.81 (95% CI 0.66; 1.00 p = 0.054), comparing those with fetal exposure to mandatory vitamin D fortification policy of margarine to those without after adjusting for gender and season of birth. There was a statistically significant season effect particularly for children born in autumn (OR 1.6 95% CI 1.16; 2.21) and born in summer (OR 1.5 95% CI 1.1; 2.1) when compared to children born in winter. Although this study did not find evidence to support the premise that prenatal exposure to small extra amounts of vitamin D from a mandatory food fortification policy lowered risk of developing CD, the small number of CD cases and observed association between season of birth and CD suggest that environmental exposure ought to be further explored.

Birth seasonality of childhood central nervous system tumors: Analysis of primary data from 16 Southern-Eastern European population-based registries

Season of birth, a surrogate of seasonal variation of environmental exposures, has been associated with increased risk of several cancers. In the context of a Southern-Eastern Europe (SEE) consortium, we explored the potential association of birth seasonality with childhood (0-14 years) central nervous system (CNS) tumors. Primary CNS tumor cases (n = 6,014) were retrieved from 16 population-based SEE registries (1983-2015). Poisson regression and meta-analyses on birth season were performed in nine countries with available live birth data (n = 4,987). Subanalyses by birth month, age, gender and principal histology were also conducted. Children born during winter were at a slightly increased risk of developing a CNS tumor overall [incidence rate ratio (IRR): 1.06, 95% confidence intervals (CI): 0.99-1.14], and of embryonal histology specifically (IRR: 1.13, 95% CI: 1.01-1.27). The winter peak of embryonal tumors was higher among boys (IRR: 1.24, 95% CI: 1.05-1.46), especially during the first 4 years of life (IRR: 1.33, 95% CI: 1.03-1.71). In contrast, boys <5 years born during summer seemed to be at a lower risk of embryonal tumors (IRR: 0.73, 95% CI: 0.54-0.99). A clustering of astrocytomas was also found among girls (0-14 years) born during spring (IRR: 1.23, 95% CI: 1.03-1.46). Although the present exploratory results are by no means definitive, they provide some indications for age-, gender- and histology-related seasonal variations of CNS tumors. Expansion of registration and linkage with cytogenetic reports could refine if birth seasonality is causally associated with CNS tumors and shed light into the complex pathophysiology of this lethal disease.

Season of birth, stillbirths, and neonatal mortality in Sweden: the Sami and non-Sami population, 1800-1899

Seasonal patterns of neonatal mortality and stillbirths have been found around the world. However, little is known about the association between season of birth and infant mortality of pre-industrial societies in a subarctic environment. In this study, we compared how season of birth affected the neonatal and stillbirth risk among the Sami and non-Sami in Swedish Sápmi during the nineteenth century. Using digitised parish records from the Demographic Data Base at Umeå University, we applied logistic regression models for estimating the association of season of birth with stillbirths and neonatal mortality, respectively. Higher neonatal mortality was found among the winter- and autumn-born Sami, compared to summer-born infants. Stillbirth risk was higher during autumn compared to summer among the Sami, whereas we found no seasonal differences in mortality among the non-Sami population. We relate the higher neonatal mortality risk among winter-born Sami to differences in seasonality of living conditions associated with reindeer herding.

Polygenic risk for schizophrenia and season of birth within the UK Biobank cohort

BACKGROUND

There is strong evidence that people born in winter and in spring have a small increased risk of schizophrenia. As this 'season of birth' effect underpins some of the most influential hypotheses concerning potentially modifiable risk exposures, it is important to exclude other possible explanations for the phenomenon.

METHODS

Here we sought to determine whether the season of birth effect reflects gene-environment confounding rather than a pathogenic process indexing environmental exposure. We directly measured, in 136 538 participants from the UK Biobank (UKBB), the burdens of common schizophrenia risk alleles and of copy number variants known to increase the risk for the disorder, and tested whether these were correlated with a season of birth.

RESULTS

Neither genetic measure was associated with season or month of birth within the UKBB sample.

CONCLUSIONS

As our study was highly powered to detect small effects, we conclude that the season of birth effect in schizophrenia reflects a true pathogenic effect of environmental exposure.

Longitudinal change of sleep timing: association between chronotype and longevity in older adults

Evening-oriented sleep timing preferences have been associated with risk of diabetes, cardiovascular diseases, obesity, psychiatric disorders, and increased mortality. This research aims to explore the relationship between diurnal preferences (chronotype), daily habits, metabolic health, and mortality, using longitudinal data from The University of Manchester Longitudinal Study of Cognition in Normal Healthy Old Age (6375 participants at inception, recruited in the North of England) with a long follow-up period (up to 35.5 years). Mixed models were used to investigate the influence of aging, socio-demographic, and seasonal factors on sleep timing. Results show that sleep timing shifted towards earlier time with aging. Test seasons influence chronotype of older adults but working schedules challenge seasonality of sleep timing. Moreover, the season of birth may set chronotype in adulthood. Individual chronotype trajectories were clustered using latent class analysis and analyzed against metabolic health and mortality. We observed a higher risk of hypertension in the evening-type cluster compared to morning-type individuals (Odds ratio = 1.88, 95%CI = 1.02/3.47, p = .04). Evening-type cluster was also associated with traits related to lower health such as reduced sport participation, increased risk of depression and psychoticism personality, late eating, and increased smoking and alcohol usage. Finally, Cox regression of proportional hazards was used to study the effects of chronotype on longevity after adjusting for sleep duration, age, gender, smoking, alcohol usage, general health, and social class. The survival analysis (82.6% censored by death) revealed that evening-type chronotype increased the likelihood of mortality (Hazard ratio = 1.15, 95%CI = 1.04/1.26, p = .005). Taken together, chronotype is influenced by aging and seasonal effects. Evening-type preference may have detrimental outcomes for human well-being and longevity.

Heart rate variability related to season of birth: A replication study

Low heart rate variability (HRV) has strongly been associated with an increased risk for cardiovascular disease. With cardiovascular disease being the number one cause of global deaths, factors that influence its development are relevant to understand. Season of birth has been suggested as one of the factors influencing the development of HRV. The current study was set up to replicate the finding that men born in winter have higher HRV later in life compared to those born in other seasons. To this end, we studied a sample of 1,871 healthy participants from the Brain Resource International Database during rest and during task. Furthermore, sex and age differences and associations with personality traits and psychiatric symptoms were explored. We replicated the earlier finding that men born in winter have a lower ratio of low frequency (LF) power to high frequency (HF) power during rest compared to summer and fall, and, although less pronounced, higher HF compared to summer. A difference between summer and winter for LF/HF in men was internally replicated using data recorded during task. Additionally, for both sexes, LF/HF ratio increased with age, and LF and HF both decreased. In general, LF/HF was lower in women, but heart rate was higher. In men, low HRV was associated with depression and the personality trait openness. In conclusion, results from a large multicenter data set covering the entire lifespan demonstrate that HRV changes with age in both sexes and confirm that season of birth influences HRV later in life in men.

This is a replication study, showing heart rate variability (HRV) to vary with season of birth (SoB). Since both HRV and SoB have been related to cardiovascular disease, the relationship is relevant to understand. We used an almost five times larger sample than the original sample, covering wider geographic areas and the full lifespan. Additionally, age and sex differences in HRV were found. Replicating earlier findings provides solid evidence for a relationship between SoB and HRV later in life, thereby providing insights on how HRV develops and ultimately how increased risk for cardiovascular disease can be reduced.

Interaction Between Season of Birth and COMT Val158Met (rs4680) in ADHD in a Large Sample of Chinese Han Participants

OBJECTIVE

To investigate the interaction between catechol-O-methyltransferase gene (COMT) Val108/158Met (rs4680) and season of birth (SOB) on ADHD and its symptoms.

METHOD

We conducted transmission disequilibrium tests (TDTs) in 976 trios, then further performed the above analyses in subgroups according to SOB. Quantitative analyses were performed for ADHD symptoms evaluated by ADHD Rating Scale-IV in 1,530 ADHD cases.

RESULTS

Overall, there was no association between COMT and ADHD. After stratification, we found an increased transmission of the Val allele in the trios born in spring, while a decreased transmission was observed in the autumn months. We also observed a significant interaction between Val108/158Met and SOB on ADHD symptoms. Among those born in spring, Met carriers had milder ADHD symptoms compared with Val homozygotes, whereas opposite association was found in those born in autumn.

CONCLUSION

Our study provided evidence for the modifying effect of SOB on the association between COMT and ADHD along with its symptoms.

[Effect of cytokine genes and season of birth on personality]

AIM

To evaluate the interaction effects of season of birth and immune system genes on the personality traits 'Novelty seeking' (NS) and 'Self-directedness' (SD). Based on results on an influence of the immune system on the brain processes, the authors hypothesized that the interaction of immune system genes and season of birth, which is relevant for immune phenotype, can contribute to the development of personality traits.

MATERIAL AND METHODS

NS and SD were measured in 336 healthy volunteers, aged from 16 to 67 years, using the Temperament and Character Inventory (TCI-125). IL1B C3954T, IL4 C-589T, IL13 C1112T and TNFA G-308A polymorphisms were genotyped.

RESULTS

An interaction effect of IL4 C-589T and season of birth on the personality traits was found (F2,322=6.03, pcorr=0.011, η2=0.04). Carriers of the minor allele T, who were born in winter, had lower NS and higher SD. There was a nominal main effect of genotype on SD (F=5.44, p=0.020) as well, with higher SD scores in carriers of the allele T compared to the CC genotype.

CONCLUSION

The results suggest that the etiology of personality and immune characteristics can share common genetic elements including IL-4.

The Use of Electronic Medical Record Data to Analyze the Association Between Atrial Fibrillation and Birth Month

OBJECTIVES

Cardiovascular disease is a condition of enormous public health concern. Recently, a population study newly revealed associations between cardiovascular diseases and birth month. Here, we investigated the association between atrial fibrillation in cardiovascular disease and birth month.

METHODS

We retrospectively extracted birth date data from 6,016 patients with atrial fibrillation (3,876 males; 2,140 females) from our electronic medical records. The number of live births in Japan fluctuates seasonally. Therefore, we corrected the number of patients for each birth month based on a Japanese population survey report. Then, a test of the significance of the association between atrial fibrillation and birth month was performed using a chi-square test. In addition, we compared the results of an analysis of patient data with that of simulated data that showed no association with birth month.

RESULTS

The deviations of birth month were not significant (overall: p = 0.631, males: p = 0.842, females: p = 0.333). The number of female patients born in the first quarter of the year was slightly higher than those born in the other quarters of the year (p = 0.030). However, by comparing the magnitudes of dispersion in the simulated data, it seems that this finding was mere coincidence.

CONCLUSION

An association between atrial fibrillation and birth month could not be confirmed in our Japanese study. However, this might be due to differences in ethnicity. Further epidemiologic studies on this topic may result in reduction of disease risk in the general population and contribute to public health.

Indigenous Infant Mortality by Age and Season of Birth, 1800-1899: Did Season of Birth Affect Children's Chances for Survival?

This paper focuses on the influence of season of birth on infant mortality among the Sami and non-Sami populations in northern Sweden during the nineteenth century. The source material is a set of data files from the Demographic Data Base at Umeå University, making it possible to combine age at death (in days), month of death, and month of birth over the course of the entire century. Cox regression models reveal that for the first week of life, season of birth had no influence on the risk of mortality. For the Sami, the results showed that being born during winter was related to a higher risk of neonatal mortality, and being born during summer was related to a higher risk of mortality after six months of age. Furthermore, for the Sami, the neonatal mortality showed a U-shaped pattern with a minimum in June–August, whereas the corresponding pattern among the non-Sami was flatter. The findings shed light on vulnerability in two populations sharing the same environment, but diverging in terms of social, economic, and cultural factors.

Association of neovascular age-related macular degeneration with month and season of birth in Italy

In order to investigate the influence of season and month of birth on the risk of neovascular age-related macular degeneration (n-AMD) in Italy, we evaluated the month birth and sex of all patients, recorded in the anti-vascular endothelial growth factor (VEGF) monitoring registry of the Italian Medicines Agency, born between 1925–1944, who received intravitreal anti-VEGF injections for n-AMD between January 1, 2013 and July 29, 2015. The numbers of all births in Italy in the same years, extracted from the Italian National Institute of Statistics, were used to calculate the expected number of n-AMD cases. Overall, 45,845 patients (19,207 men, 26,638 women) received intravitreal anti-VEGF for n-AMD; in the same years, 20,140,426 people (10,334,262 male, 9,806,164 female) were born in Italy. Comparing the observed number of n-AMD cases with the expected number of n- AMD cases in each season, we found that the season-specific risk for n-AMD was 2.5% higher for those born in summer (OR=1.03, Bonferroni-corrected P=0.008) and 3% lower for those born in winter (OR=0.96, Bonferroni-corrected P=0.0004). When considering the month of birth, the risk of n-AMD was 5.9% lower for people born in January (OR=0.93, Bonferroni-corrected P=0.0012). The factors causing such differences should be determined.

Prevalence of atopic dermatitis in infants by domestic water hardness and season of birth: Cohort study

BACKGROUND

Atopic dermatitis (AD) appears to be more common in regions with hard domestic water and in children with a fall/winter birth. However, it is unknown whether a synergistic effect exists.

OBJECTIVE

We sought to evaluate the association between domestic water hardness and season of birth, respectively, with onset of AD within the first 18 months of life in a large Danish birth cohort.

METHODS

Of children from the Danish National Birth Cohort, 52,950 were included. History of physician-diagnosed AD and population characteristics were obtained from interviews. Birth data were obtained from the Civil Registration System, and domestic water hardness data were obtained from the Geological Survey of Denmark and Greenland. The relative prevalence (RP) of AD was calculated by using log-linear binomial regression.

RESULTS

The prevalence of AD was 15.0% (7,942/52,950). The RP of AD was 5% (RP_trend, 1.05; 95% CI, 1.03-1.07) higher for each 5° increase in domestic water hardness (range, 6.60-35.90 German degrees of hardness [118-641 mg/L]). Although the RP of AD was higher in children with a fall (RP, 1.24; 95% CI, 1.17-1.31) or winter (RP, 1.18; 95% CI, 1.11-1.25) birth, no significant interaction was observed with domestic water hardness. The population attributable risk of hard domestic water on AD was 2%.

CONCLUSION

We observed that early exposure to hard domestic water and a fall/winter birth was associated with an increase in the relative prevalence of AD within the first 18 months of life. Although the 2 exposures did not interact synergistically, a dose-response relationship was observed between domestic water hardness and AD.

Association of season of birth with DNA methylation and allergic disease

BACKGROUND

Season of birth influences allergy risk; however, the biological mechanisms underlying this observation are unclear. The environment affects DNA methylation, with potentially long-lasting effects on gene expression and disease. This study examined whether DNA methylation could underlie the association between season of birth and allergy.

METHODS

In a subset of 18-year-old participants from the Isle of Wight (IoW) birth cohort (n = 367), the risks of birth season on allergic outcomes were estimated. Whole blood epigenome-wide DNA methylation was measured, and season-associated CpGs detected using a training-and-testing-based technique. Validation method examined the 8-year-old Prevention and Incidence of Asthma and Mite Allergy (PIAMA) cohort. The relationships between DNA methylation, season of birth and allergy were examined. CpGs were analysed in IoW third-generation cohort newborns.

RESULTS

Autumn birth increased risk of eczema, relative to spring birth. Methylation at 92 CpGs showed association with season of birth in the epigenome-wide association study. In validation, significantly more CpGs had the same directionality than expected by chance, and four were statistically significant. Season-associated methylation was enriched among networks relating to development, the cell cycle and apoptosis. Twenty CpGs were nominally associated with allergic outcomes. Two CpGs were marginally on the causal pathway to allergy. Season-associated methylation was largely absent in newborns, suggesting it arises post-natally.

CONCLUSIONS

This study demonstrates that DNA methylation in adulthood is associated with season of birth, supporting the hypothesis that DNA methylation could mechanistically underlie the effect of season of birth on allergy, although other mechanisms are also likely to be involved.

Season of Birth Predicts Emotional and Behavioral Regulation in 18-Month-Old Infants: Hamamatsu Birth Cohort for Mothers and Children (HBC Study)

Background

Previous research has demonstrated that the season of birth may predict development of emotional and behavioral regulation during childhood or adolescence. This study examined whether the season of birth predicts effortful control (i.e., the ability to voluntarily choose course of actions during conflict and to plan for the future) and aggression (i.e., the use of physical force and expression of anger toward others) in 18-month-old infants.

Methods

Participants included 885 infants who were enrolled in the Hamamatsu Birth Cohort for Mothers and Children in Hamamatsu, Japan. Seasons of birth were categorized into winter (December, January, and February), spring (March, April, and May), summer (June, July, and August), and autumn (September, October, and November). At 18 months of age, effortful control was assessed using the Early Childhood Behavior Questionnaire, and aggression was measured using the Cardiff Infant Contentiousness Scale. Structural equation modeling analysis with measurement and structural equations was conducted to test our prediction.

Results

Effortful control was higher in infants born in spring [B = 0.095, 95% CI (0.014 to 0.175), p = 0.021, β = 0.146] and summer [B = 0.078, 95% CI (0.001 to 0.156), p = 0.049, β = 0.118] than in those born in winter. In addition, aggression was lower in those born in spring [B = −0.286, 95% CI (−0.551 to −0.021), p = 0.035, β = −0.135] than those born in winter, even after controlling for seven covariates.

Conclusion

The findings suggest that season of birth may determine development of emotional and behavioral regulation skills during early infancy. Future research should pay more attention to the underlying mechanisms of the effects of birth season on development of emotional and behavioral regulation during infancy.

The Reduction in Circulating Melatonin Level May Contribute to the Pathogenesis of Ovarian Cancer: A Retrospective Study

Ovarian cancer is the third most common gynaecological malignancy. Changes in circadian rhythms such as bright light exposure may affect female reproductive physiology. Night shift work is associated with higher risks of developing gynaecological cancers. In addition, the season of birth is also suggested as an important environmental risk factor for developing gynaecological cancers. Melatonin may play an important role in this association as a marker of circadian rhythms. Serum from 96 women with ovarian cancer and 40 healthy women were collected and the level of melatonin was measured. In addition 277 women with ovarian cancer and 1076 controls were retrospectively collected for season of birth analysis over seven years. The serum levels of melatonin were significantly lower in women with ovarian cancer compared with healthy women (p<0.05). However there was no difference in melatonin levels in perimenopausal and postmenopausal patients. In addition, there is no statistically significant difference in seasonal distribution of birth between ovarian cancer patients and the control group. The melatonin levels in ovarian cancer patients and controls were not associated with the season of birth. Our results demonstrate the lower serum levels of melatonin in ovarian cancer patients which may contribute to the pathogenesis of ovarian cancer. The incidence of ovarian cancer was not associated with the season of birth. The serum levels of melatonin do not appear to be associated with season of birth in ovarian cancer patients.

The relationship between the season of birth and early-onset food allergies in children

BACKGROUND

This study examined the relationship between the season of birth (SoB) and other factors with the development of FA.

METHODS

A multicenter, cross-sectional pilot study recruited 1197 patients with FA. The main study recruited 440 incident cases (FA group) definitively diagnosed as FA at 0-1 year of age. In both studies, the frequency of autumn-winter births (AWBs) in FA patients was compared to the regional control population. In the main study, we analyzed the differences in the SoB and other factors between patients in the FA group and those in the non-FA group (n = 332) in allergy clinics.

RESULTS

The pilot study showed that the frequency of AWB (57.6%) in the FA patients was significantly higher than that of the regional control population (50.4%, OR, 1.34; p < 0.001). The main study also showed the dominance of AWB (62.7%) in the FA group in comparison with that in the regional control population (50.2%, OR, 1.70; p < 0.001). Preterm birth (OR, 0.43; p = 0.027) and the presence of two or more elder siblings (OR, 0.27; p = 0.012) were significantly associated with a lower frequency of FA than those of non-FA. AWB (RR, 1.21; p = 0.020) and preterm birth (RR, 0.55; p = 0.017) were significantly associated with a number of trigger foods. The SoB effect was observed in FA patients irrespective of the presence of infantile eczema.

CONCLUSIONS

AWB was predominant in the patients with newly diagnosed food allergies.

Sun exposure inversely related to food sensitization during infancy

BACKGROUND

Autumn and winter birth (AWB) has been reported to be a risk factor for the development of food allergies. However, the association between seasonal factors and allergic sensitization during early infancy remains unclear.

METHODS

We collected data from 732 patients regarding the total and specific immunoglobulin E (tIgE, sIgE) levels in infants younger than 6 months old from November 2001 to October 2012 from the institutional clinical database system. We then analyzed the relationship between the birth month and the value of each parameter. Furthermore, we identified any correlations between the number of sensitized patients and the monthly climatological parameters.

RESULTS

The number of tIgE samples obtained from AWB patients (n = 482) was 2.1 times higher than that from patients born in the spring and summer (SSB, n = 225). The number of sIgE samples to egg white, cow's milk, and wheat, the sensitized ratio and the median sIgE titer were also all higher in AWB. The number of sensitized AWB patients to these allergens was 2.75, 3.05, and 3.97 times higher, respectively. A periodic change in the number of sensitized patients was observed annually (highest in October-November and lowest in May). Among the climatological parameters examined, the average solar radiation during the 3-month period after birth showed the strongest negative correlation with the number of sensitized patients (egg white: r = -0.976, cow's milk: r = -0.969, wheat: r = -0.975).

CONCLUSIONS

The amount of solar radiation immediately after birth had a strong negative correlation with allergen sensitization before 6 months of age.

Season of birth is different in Inuit suicide victims born into Traditional than into Modern Lifestyle: a register study from Greenland

BACKGROUND

There is growing evidence that living conditions at birth play a role in medical conditions later in life. Population-based studies from the Northern Hemisphere have shown that persons born in the spring or summer are at greater risk of committing suicide. A statistical correlation with light availability at birth has been observed in past research, but the cause remains unknown. Greenland is one of the most extreme of natural human habitats with regard to seasonal changes in light. The combination of rapid social changes and reliable population statistics offers a unique opportunity to make comparisons between persons born into a Traditional Lifestyle and those born into a Modern Lifestyle. The aim of this work was to assess whether season of birth differed between suicide victims born into an old or into a modern lifestyle.

METHODS

Official population and mortality registers were used. Suicide victims born (1903-1950) into the Traditional Lifestyle were compared with those born into the Modern Lifestyle (1961-1980). Rayleigh's test for circular distributions was used to assess the season of birth in suicide victims. Data regarding season of birth in the general population were collected.

RESULTS

Persons born in March-June in the Traditional Lifestyle were much less likely to commit suicide than those born during other periods of the year. This is contrary to the findings of other studies. The seasonal differences had disappeared for those born into the Modern Lifestyle. The suicide rate increased from very low rates to about 140 suicides/100 000 person-years in the 1980s.

CONCLUSIONS

The reason behind a variation in season of birth in suicide victims born into the old lifestyle is unknown. It is also unknown why the seasonal difference had disappeared with modern lifestyle. Possible influence of artificial light, nutrition, microbiota and seasonal infections are discussed. The underlying causes behind suicides may be different in traditional and modern Greenland.

Season of birth, sex and sleep timing preferences

Objective: To evaluate whether the season of birth and sex are associated with preferences for bedtime among Chinese adults. Methods: A national population-based study on sleep preferences was conducted among Chinese in 2008. A questionnaire was used to collect information on the sleep time of Chinese adults. Analysis of covariance was used to examine the relationship between season of birth and preferences for bedtime. Two sets of potential confounders were used in the adjusted models. Model 1 adjusted for age. Model 2 additionally adjusted for area, occupation, education level, smoking, and drinking. Participants and Measurements: The questionnaire was administered to a sample of 3959 Chinese adults. Results: Men had a higher delayed mean sleep onset and offset time (22:38 and 6:32) than women (22:18 and 6:25). Men also slept for a shorter duration compared to women (7 h 54 min vs. 8 h 7 min). Women born in fall had the latest sleep onset time sleep offset time (22:23/6:30), compared to their counterparts born in winter. These associations were attenuated by additional adjustments of more confounders. Conclusions: There were significant differences in sleep timing preferences between men and women. Season of birth was not associated with sleep timing in Chinese adults.

Lack of pattern of birth in patients with bulimia nervosa

OBJECTIVE

An excess of bulimia nervosa (BN) births during the fall has been recently reported, but this finding has not been yet adequately replicated. The purpose of our study was to evaluate the presence of a seasonal birth pattern in a representative clinical sample of women with BN.

METHOD

We registered the month of birth of 216 female patients who fulfilled all the criteria for BN according to DSM-IV on admission to a specialized eating disorders service in Spain.

RESULTS

Our analyses showed no significant variation in the season of birth of our BN sample when compared to a general population.

DISCUSSION

Our data do not support the hypothesis of a season of birth bias in BN.

Birth seasonality in schizophrenia: effects of gender and income status

AIMS

The aim of this study was to examine the correlations of birth seasonality in schizophrenia, considering influences of gender and income status.

METHODS

The sample consisted of 1 000 000 people in the general population randomly selected from the Taiwan National Health Insurance Research Database. Data for the birth-year period 1950-1989 were extracted for analysis (n = 631 911; 306 194 male, 325 717 female). Subjects with schizophrenia (2796 male, 2251 female) were compared with the general population. Subgroups divided by birth-year periods (10-year interval), gender, and income status (low, medium, high) were analyzed using both the Walter and Elwood seasonality and chi-squared tests.

RESULTS

The winter/spring birth excess in schizophrenia was 5.3% when compared with the general population. There was a statistically significant excess in winter/spring births than summer/autumn births inschizophrenia patients (relative risk [RR], 1.12; 95% confidence interval [CI]: 1.06-1.18). This winter/spring birth excess in schizophrenia was observed only in female subjects (RR, 1.20; 95%CI: 1.10-1.30), not in male subjects (RR, 1.03; 95%CI: 0.98-1.14), in all subgroups of income status, but was most pronounced in the low income subgroup (RR, 1.20, 1.09, 1.13; 95% CI: 1.05-1.37, 1.01-1.17, 1.02-1.25 for low, medium, and high income status, respectively).

CONCLUSION

A gender difference with female predominance of the effect of birth seasonality in schizophrenia, and a more pronounced effect in low income status were noted.

Prenatal vitamin D deficiency induces an early and more severe experimental autoimmune encephalomyelitis in the second generation

In a previous study, we demonstrated that mouse adult F(1) offspring, exposed to a vitamin D deficiency during pregnancy, developed a less severe and delayed Experimental Autoimmune Encephalomyelitis (EAE), when compared with control offspring. We then wondered whether a similar response was observed in the subsequent generation. To answer this question, we assessed F(2) females whose F(1) parents (males or females) were vitamin D-deprived when developing in the uterus of F(0) females. Unexpectedly, we observed that the vitamin D deficiency affecting the F(0) pregnant mice induced a precocious and more severe EAE in the F(2) generation. This paradoxical finding led us to assess its implications for the epidemiology of Multiple Sclerosis (MS) in humans. Using the REFGENSEP database for MS trios (the patient and his/her parents), we collected the parents' dates of birth and assessed a potential season of birth effect that could potentially be indicative of the vitamin D status of the pregnant grandmothers. A trend for a reduced number of births in the Fall for the parents of MS patients was observed but statistical significance was not reached. Further well powered studies are warranted to validate the latter finding.

Challenging the hypothesized link to season of birth in patients with schizophrenia

The cause of schizophrenia is unknown; however, one hypothesis is that seasonality of birth contributes to its development, with an excess of winter-spring births observed in those with schizophrenia. There are over 200 studies exploring this issue at the writing of this article with most of the studies revealing a decrease in late summer births and an increase number of winter-spring births of those individuals with the disease.The primary objective of this study was to evaluate the seasonality of birth for 376 institutionalized patients with schizophrenia receiving clozapine treatment in a New York State psychiatric hospital. This was a retrospective review of a clozapine database accessed between January 1, 2001 to January 1, 2011, which included date of birth for the national clozapine registry, confirming the accuracy of the information. The psychiatric diagnoses for the patients included in this study were documented to ensure that this research included individuals with schizophrenia. The author hypothesized that due to the long-term institutionalization often required for refractory schizophrenia, the New York state hospitalized patients were assumed to be of Northern Hemispheric birth origin. The study sample included 376 patients, 16 of which did not have a definitive diagnosis of schizophrenia. The author chose to evaluate all 376 patients in the sample due to the introduction of clozapine therapy, which would substantiate the presence of a refractory psychotic disorder, such as schizophrenia. The author found that the seasonality distribution did not reflect any difference in percentage from that which would be expected in the general population, challenging the hypothesis that seasonality of birth contributes to the development of schizophrenia. The author provides a review of literature and discusses some of the theories surrounding the season of birth hypothesis. A larger patient sample should be studied to confirm the findings of this smaller population sample.

Infant mortality, season of birth and the health of older Puerto Rican adults

The increasing prevalence of heart disease and diabetes among aging populations in low and middle income countries leads to questions regarding the degree to which endogenous early life exposures (exposures in utero) are important determinants of these health conditions. We devised a test using infant mortality (IMR) to verify if season of birth is a good indicator of early life (in utero) conditions that precipitate adult onset of disease. We linked annual IMR at the municipality (municipio) level from the late 1920s to early 1940s with individual birth year and place using a representative sample of older Puerto Rican adults (n = 1447) from the Puerto Rican Elderly: Health Conditions (PREHCO) study. We estimated the effects of season of birth on adult heart disease and diabetes for all respondents and then for respondents according to whether they were born when IMR was lower or higher, controlling for age, gender, obesity, respondent's educational level, adult behavior (smoking and exercise) and other early life exposures (childhood health, knee height and childhood socioeconomic status (SES)). The pattern of effects suggests that season of birth reflects endogenous causes: (1) odds of heart disease and diabetes were strong and significant for those born during the lean season in years when IMR was lower; (2) effects remained consistent even after controlling for other childhood conditions and adult behavior; but (3) no seasonality effects on adult health for adults born when IMR was higher. We conclude that in this population of older Puerto Rican adults there is continued support that the timing of adverse endogenous (in utero) conditions such as poor nutrition and infectious diseases is associated with adult heart disease and diabetes. It will be important to test the validity of these findings in other similar populations in the developing world.

The environment and susceptibility to schizophrenia

In the present article the putative role of environmental factors in schizophrenia is reviewed and synthesized. Accumulating evidence from recent studies suggests that environmental exposures may play a more significant role in the etiopathogenesis of this disorder than previously thought. This expanding knowledge base is largely a consequence of refinements in the methodology of epidemiologic studies, including birth cohort investigations, and in preclinical research that has been inspired by the evolving literature on animal models of environmental exposures. This paper is divided into four sections. In the first, the descriptive epidemiology of schizophrenia is reviewed. This includes general studies on incidence, prevalence, and differences in these measures by urban-rural, neighborhood, migrant, and season of birth status, as well as time trends. In the second section, we discuss the contribution of environmental risk factors acting during fetal and perinatal life; these include infections [e.g. rubella, influenza, Toxoplasma gondii (T. gondii), herpes simplex virus type 2 (HSV-2)], nutritional deficiencies (e.g., famine, folic acid, iron, vitamin D), paternal age, fetal/neonatal hypoxic and other obstetric insults and complications, maternal stress and other exposures [e.g. lead, rhesus (Rh) incompatibility, maternal stress]. Other putative neurodevelopmental determinants, including cannabis, socioeconomic status, trauma, and infections during childhood and adolescence are also covered. In the third section, these findings are synthesized and their implications for prevention and uncovering biological mechanisms, including oxidative stress, apoptosis, and inflammation, are discussed. Animal models, including maternal immune activation, have yielded evidence suggesting that these exposures cause brain and behavioral phenotypes that are analogous to findings observed in patients with schizophrenia. In the final section, future studies including new, larger, and more rigorous epidemiologic investigations, and research on translational and clinical neuroscience, gene-environment interactions, epigenetics, developmental trajectories and windows of vulnerability, are elaborated upon. These studies are aimed at confirming observed risk factors, identifying new environmental exposures, elucidating developmental mechanisms, and shedding further light on genes and exposures that may not be identified in the absence of these integrated approaches. The study of environmental factors in schizophrenia may have important implications for the identification of causes and prevention of this disorder, and offers the potential to complement, and refine, existing efforts on explanatory neurodevelopmental models.

Is season of birth related to disordered eating and personality in women with eating disorders?

We assessed the relation between season of birth and eating disorder symptoms and personality characteristics in a sample of 880 women with eating disorders and 580 controls from two Price Foundation Studies. Eating disorder symptoms were assessed using the Structured Interview of Anorexic and Bulimic Disorders and the Structured Clinical Interview for DSM-IV. Personality traits were assessed using the Temperament and Character Inventory and the Frost Multidimensional Perfectionism Scale. Date of birth was obtained from a sociodemographic questionnaire. No significant differences were observed 1) in season of birth across eating disorder subtypes and controls; nor 2) for any clinical or personality variables and season of birth. We found no evidence of season of birth variation in eating disorders symptoms or personality traits. Contributing to previous conflicting findings, the present results do not support a season of birth hypothesis for eating disorders.

A season-of-birth/DRD4 interaction predicts maximal body mass index in women with bulimia nervosa

We have earlier reported that season of birth interacts with the hypofunctional 7-repeat (7R) allele of the dopamine-4 receptor gene (DRD4) to promote weight gain and obesity in women with seasonal affective disorder (SAD). This study examined whether this gene-environment interaction influences body weight regulation in women with bulimia nervosa (BN). In 188 female probands with BN, we performed an analysis of covariance predicting maximum lifetime body mass index (BMI) using season-of-birth, DRD4 genotype (7R present/absent), and past history of anorexia nervosa (yes/no) as independent variables, and age at maximum weight as the co-variate. Consistent with our SAD study, the birth-season x DRD4 interaction was a significant predictor of maximal BMI. Although in SAD, the spring-birth/7R+ group had markedly elevated maximal BMIs and high rates of obesity, in this BN sample, the fall-birth/7R+ group exhibited the highest BMI values (N=17: mean maximal BMI=28.2 kg/m(2) (SE 0.9) vs 25.2 kg/ m(2) (SE 0.3) for all other probands combined (N=171); p=0.002). The lifetime rate of obesity (BMI>30) was also higher in the fall-birth/7R+ vs 'other' group (29.9 vs 8.8%, respectively, p=0.008). These data offer further evidence that season of birth interacts with the 7R allele of DRD4 to influence body weight regulation in female overeating populations.

Epidemiologic evidence supporting the role of maternal vitamin D deficiency as a risk factor for the development of infantile autism

This study examines whether maternal vitamin D deficiency is a risk factor for infantile autism disease (IAD). We used epidemiologic data seasonal variation of birth rates and prevalence of IAD for cohorts born before 1985. For seven studies reporting spring-to-summer excess birth rates for IAD, the season progressed from broad near 30 degrees N latitude, spring/summer in midlatitudes, to winter at the highest latitude. Also, using data from 10 studies, we found a strong effective latitudinal (related to wintertime solar ultraviolet B radiation) increase in IAD prevalence. These findings are consistent with maternal vitamin D deficiency's being a risk factor for IAD, possibly by affecting fetal brain development as well as possibly by affecting maternal immune system status during pregnancy. Further investigation of this hypothesis is warranted.

Season of birth, gender, and social-cultural effects on sleep timing preferences in humans

STUDY OBJECTIVE

The present study aimed to analyze season of birth effects on preferred sleep-wake cycle timing as assessed by Morningness-Eveningness Questionnaire (MEQ).

PARTICIPANTS AND MEASUREMENTS

The MEQ was administered to a sample of 5,720 university students (3,851 Italians and 1,869 Spaniards; 3,877 female and 1,843 male; mean age 22.23 +/- 2.98 years).

RESULTS

Females preferred to go to bed significantly earlier and sleep longer than males, regardless of season of birth and nationality. Subjects born in spring and summer went to bed and reached midpoint of sleep later than subjects born in fall and winter. Nationality significantly affected all the sleep parameters considered except duration.

CONCLUSION

Overall, the effect of the season of birth on sleep preference timing was significant but quantitatively small. We suggest an evolutionary context for the different contributions of genetic and environmental factors in modulating sleep-wake cycles in humans.

Birth distribution of schizophrenic patients in Japan (Tochigi)

The monthly birth distribution of schizophrenic inpatients was examined in the Tochigi prefecture, Japan. A significant excess (26%) above the expected birth counts was found for patients born in the winter months (December-February). These data are consistent with the previous reports from European and North American countries.