MONTH OF BIRTH, SOCIOECONOMIC BACKGROUND AND DEVELOPMENT IN SWEDISH MEN

Month of birth and height. A case study in rural Spain

INTRODUCTION

Season of birth correlates to a wide range of health conditions throughout life measured by anthropometrics. This study explores whether the month of birth and weather during gestation influence male adult height, based on Spain's rural population before the end of the modernization process.

METHODS

The database of heights (N = 16.266) is composed of conscripts who reached the age of 21 between 1908 and 1985 (birth cohorts 1886-1965). The population sample has been taken from a municipality in inner Spain: Hellín, in the region of Castilla-La Mancha, mainly an agrarian area, with poor resources and low income until the 1970 s/1980 s. Two different methodologies have been implemented: a harmonic regression using sinusoidal covariables and a random forest model.

RESULTS

we find that being born at the end of the summer and during the autumn was favorable to height. The birth month with the highest statures is September, with heights 0.5 cm above the annual average and 0.9 cm above February, the birth month with the lowest average height. Furthermore, we can observe that rainfall and temperature during gestation had little additional influence due to a substitution effect with the birth month variable.

CONCLUSIONS

Our results suggest that the seasonal effects on height can be significant and that it can be partially affected by environmental factors during early life. Our findings could be of interest for low-income populations and developing rural societies.

Season of birth has no effect on symptoms of depression and anxiety in older adults

There remains a lack of conclusive evidence as to the merit of season of birth as a predictor of mental illness across contexts. We studied 72,370 individuals (55% women; mean age 66) from the Survey on Health, Ageing and Retirement in Europe. Depressive symptoms were assessed with EURO-D scale and symptoms of anxiety with modified Beck Anxiety Inventory. Multilevel modeling was used to assess the association of season of birth as well as month of birth with symptoms of depression and anxiety, by sex and region. Adjusting for sex and age, month of birth explained only 0.01% to 0.07% of anxiety and depressive symptoms with non-significant improvement in the overall models; using season of birth instead of month of birth added 0.00% to 0.04% of explained variance. When stratified by sex and European region, age explained 0.23% to 5.19% of anxiety and depressive symptoms; the addition of month of birth or season of birth improved the models by negligible amount. Season of birth and month of birth are not reliable predictors of anxiety and depression across the life course.

Birth month, birth season, and overall and cardiovascular disease mortality in US women: prospective cohort study

OBJECTIVES

To evaluate the associations between birth month, birth season, and overall and cardiovascular disease mortality, and to examine the role of familial and socioeconomic factors in these associations.

DESIGN

Prospective cohort study.

SETTING

Nurses' Health Study, established in 1976, an ongoing prospective cohort study in the United States.

PARTICIPANTS

Female registered nurses who reported information on date of birth at study enrolment (n=116 911, 1976-2014, followed for 38 years).

EXPOSURE

Birth month and astronomical birth season (based on solstices and equinoxes as boundaries of the season categories).

MAIN OUTCOME MEASURES

Age and various multivariable adjusted hazard ratios and 95% confidence intervals for the association between birth months (using November as the reference), astronomical birth season (using autumn as the reference), and overall and cardiovascular disease specific mortality were assessed using Cox proportional hazards models.

RESULTS

Among study participants, 43 248 overall deaths were documented during 4 136 364 person years of follow-up since enrolment, including 8360 cardiovascular disease related deaths. In fully adjusted multivariable analyses, no significant association was observed between birth month, birth season, and overall mortality. Compared with women born in November, increased cardiovascular disease mortality was observed among those born from March to July (hazard ratio for March, 1.09, 95% confidence interval 0.98 to 1.21; April, 1.12, 1.00 to 1.24; May, 1.08, 0.98 to 1.20; June, 1.07, 0.96 to 1.19; and July 1.08, 0.98 to 1.20). Those born in April had the highest cardiovascular disease mortality, and those born in December had the lowest (December, 0.95, 0.85 to 1.06). The relative difference between the lowest and highest risk month was 17.89%. Women born in spring (1.10, 1.04 to 1.17) and summer (1.09, 1.03 to 1.16) had a higher cardiovascular disease mortality than women born in the autumn. Adjustment for familial and socioeconomic factors did not change these results. The relative difference between the lowest and highest risk season was 10.00%.

CONCLUSION

Participants born in the spring and summer (especially those born in March-July) had a slight but significant increase in cardiovascular disease specific mortality. However, no seasonal birth month effect was observed among women for overall mortality. Familial and socioeconomic factors did not appear to alter these associations. Further studies are required to confirm these findings and reveal mechanisms of these seasonal birth month effects in cardiovascular disease mortality.

Association between body height and month of birth among women of European origin in northern and southern hemispheres

OBJECTIVES

The purpose of this study was to examine the potential association between month of birth and body height among women in northern and southern hemispheres.

METHODS

Body heights of adult women of European origin born between 1935 and 1981 who lived in Poland (N = 3,933) and in Australia (N = 1,118) were examined in relation to month of birth by analysis of variance.

RESULTS

No association between month of birth and body height was observed in either Polish or Australian women. For Polish women, a clear, statistically significant secular trend in body height was confirmed for the analyzed period (P < .0001). No such trend occurred among the Australian women.

CONCLUSIONS

Results do not confirm a significant association between month of birth and adult body height in women. It is, however, important to see a difference in secular trends, which was large in Polish women and nonexistent in Australian females.

Understanding the links between month of birth, body height, and longevity: why some studies reveal that shorter people live longer – further evidence of seasonal programming from the Polish population

There is a lack of agreement in the literature as to whether adult height depends on month of birth and whether height affects lifespan. Additionally, the relationship between stature and longevity involves conflicting findings and the results remain mixed due to several confounders, such as: year of birth, somatotype, relative body weight, genetic inheritance, diet, diseases, etc. Here, we hypothesize that the season of birth effect can also be involved in shaping the mysterious link between body height and longevity. To assess the links between month of birth, adult height, and longevity in the Polish population, data on 848,860 individuals, of whom 483,512 were men (57%) and 365,348 were women (43%), born in the years 1896-1988 and died in the years 2004-2008, were collected from the ‘PESEL’ database and signalments in the censuses obtained from identity card offices throughout Poland. ANOVA and the LSD test were performed. A significant relationship between month of birth and lifespan was found. Individuals born in autumn and winter months lived significantly longer than those who were born in the middle of the year (May). The amplitudes of lifespan were 16 months in men and 14 months in women. As expected, subjects of both sexes born in autumn and winter months were significantly shorter than their peers born around the middle of the year. In conclusion, the results of the study not only corroborate the theory of seasonal programming of longevity and support the idea that some undetermined factors from early stages of ontogeny and associated with season of birth have long-term effects on phenotype in later life in terms of adult height and longevity, but also bear out the hypothesis that month of birth can be another important confounding factor with respect to the relationship between adult height and longevity.

The influence of birth season on height: Evidence from Indonesia

OBJECTIVES

Literature on the effect of birth month on height has generally considered regions in temperate climates. However, because many climatic conditions there change with seasons, it is difficult to isolate potential causes. This study estimated the effect of birth month and season on terminal height by analyzing the population of a country with only a few factors driving its climate.

MATERIALS AND METHODS

The sample was derived from nationally representative data of the Indonesian population. We considered 9,262 men and 10,314 women 20-50 years of age. We applied cosinor analysis to a time series of height by birth month. We then applied a more flexible approach by regressing height on a series of dummy variables for birth month (and, subsequently, season) and birth year fixed effects by sex.

RESULTS

There was no statistically significant difference in height by birth month. However, although weakly significant, men born in the dry season (June-September) were 2.3 mm shorter than those born in the wet season (the remaining months). The corresponding figure for women was 2.6 mm, a statistically significant difference.

DISCUSSION

We eliminated some potential factors previously suggested in the literature, including insolation, the position of our planet with respect to the sun, food availability, and maternal workload. We speculate that babies born in the dry season were affected in the third trimester by the high disease burden that characterizes the wet season.

Long-term changes of socioeconomic differences in height among young adult men in Southern Sweden, 1818-1968

The study explores the long-term trends in socioeconomic differences in height among young adult men. We linked information from conscript inspections to a longitudinal demographic database of five parishes in Southern Sweden. Detailed information on the occupation and landholding was used to investigate the differences in height. Even if there is indication of a reduction in the magnitude of the differences in height over time the reduction is neither dramatic nor uniform. The most systematic and consistent difference is that sons of fathers with white collar occupations were taller than others. They were 4cm taller than the sons of low-skilled manual workers in the first half of the 19th century, and almost 2cm taller in the mid-20th century. This difference is much smaller than those found between elite and destitute groups historically, in for example Britain, but comparable to that found in other studies on 19th century populations using information on family background. Most of the reduction in the socioeconomic differences in height was a result of reduced height penalty and premium for small disadvantaged and privileged groups. Changes in the distribution of income and the economic structure are plausible explanations for the changes in socioeconomic differences in height.

The height gap in 19th-century America: net-nutritional advantage of the elite increased at the onset of modern economic growth

We present evidence on the 19th-century trend in the height of male US passport applicants. These men represent a much wealthier segment of contemporary society than found in most stature samples previously analyzed. The height trend among the wealthy is much more robust in comparison to the average population that experienced a decline in stature. The resulting increase in the 'height gap'--by roughly 1 in. between cohorts born around 1820 and 1860--is in congruence with evidence on rising wealth inequality and the notion of dietary change in antebellum America.

Month of birth and mortality in Sweden: a nation-wide population-based cohort study

Background

Month of birth – an indicator for a variety of prenatal and early postnatal exposures – has been associated with life expectancy in adulthood. On the northern hemisphere, people born in the autumn live longer than those born during the spring. Only one study has followed a population longitudinally and no study has investigated the relation between month of birth and mortality risk below 50 years.

Methods and results

In this nation-wide Swedish study, we included 6,194,745 subjects, using data from population-based health and administrative registries. The relation between month of birth (January – December) and mortality risk was assessed by fitting Cox proportional hazard regression models using attained age as the underlying time scale. Analyses were made for ages >30, >30 to 50, >50 to 80 and >80 years. Month of birth was a significant predictor of mortality in the age-spans >30, >50 to 80, and >80 years. In models adjusted for gender and education for ages >30 and >50 to 80 years, the lowest mortality was seen for people born in November and the highest mortality in those born in the spring/summer, peaking in May for mortality >30 years (25‰ excess hazard ratio compared to November, [95% confidence interval = 16–34 ]) and in April for mortality >50 to 80 years (42‰ excess hazard ratio compared to November, [95% confidence interval = 30–55]). In the ages >80 years the pattern was similar but the differences in mortality between birth months were smaller. For mortality within the age-span >30 to 50 years, results were inconclusive.

Conclusion

Month of birth is associated to risk of mortality in ages above 50 years in Sweden. Further studies should aim at clarifying the mechanisms behind this association.

Season of birth and exceptional longevity: comparative study of american centenarians, their siblings, and spouses

This study explores the effects of month of birth (a proxy for early-life environmental influences) on the chances of survival to age 100. Months of birth for 1,574 validated centenarians born in the United States in 1880-1895 were compared to the same information obtained for centenarians' 10,885 shorter-lived siblings and 1,083 spouses. Comparison was conducted using a within-family analysis by the method of conditional logistic regression, which allows researchers to control for unobserved shared childhood or adulthood environment and common genetic background. It was found that months of birth have significant long-lasting effect on survival to age 100: siblings born in September-November have higher odds to become centenarians compared to siblings born in March. A similar month-of-birth pattern was found for centenarian spouses. These results support the idea of early-life programming of human aging and longevity.

Month of birth, socioeconomic background and height in rural Chinese men

This study examines the effects of birth month and socioeconomic factors on height in rural Chinese men. The analysis of sample data of 833 adult men, 18-52 years of age, collected from 600 families in rural Hebei in 2005, shows that adult men born in winter months (November to January) are, on average, 1.04 cm shorter (p<0.01) than those born during the rest of the year. In addition to the conventional OLS regression models, the household fixed and random effects models also indicate that the month-of-birth effect exists when socioeconomic variables are controlled for. The birth-month effect on height is, however, smaller than effects of socioeconomic variables, including the household registration status, household economy and father's class status.

Season of birth and subsequent body size: the potential role of prenatal vitamin D

OBJECTIVES

The relationship between season of birth and various physical and psychological outcomes was reported in many studies, although the underlying mechanism still remains unrecognized. The aim of this study was to explore the season-of-birth effect on body size in the sample of 1,148 eight-year-old Polish urban children and propose the mechanism responsible for this effect.

METHODS

The children were examined three times at their birthdays and at two cross-sectional surveys. Effects of the season of birth were checked by fitting the cosine function to empirical values and by comparison between two groups born in different periods of the year.

RESULTS

Data gathered at three examinations led to the same results: season-of-birth effect occurred only in boys and only in those relatively shortly breastfed and/or descended from the families of low-socioeconomic status. Specifically, the individuals born in October-April were taller (by 2-3 cm), heavier (by 2-3 kg), and fatter than those born in May-September.

CONCLUSIONS

The following explanatory mechanism has been formulated: insolation in Poland is minimal in November-February (winter period), and so ultraviolet absorption and vitamin D production is then the lowest. Vitamin D regulates embryo's cellular differentiation, and its deficiency triggers permanent developmental changes. Therefore, individuals conceived in autumn (i) are at the greatest risk of early vitamin D deficiency, (ii) are born in summer, and (iii) are relatively small in their further lives. The contribution of low-socioeconomic status, short breastfeeding, and being a male to the occurrence of the season-of-birth effect is also discussed.

Month of birth and offspring count of women: data from the Southern hemisphere

BACKGROUND

Several studies indicate that the month of birth affects later reproductive output of women in the Northern hemisphere.

METHODS

To investigate whether a comparable but time-shifted effect is also present in the Southern hemisphere where the seasonal variation of the environment is reversed, we analysed the association between birth month and offspring count in post-reproductive New Zealand women. We further examined whether this association differed with the hemisphere of birth as well as the socio-economic background.

RESULTS

We find that the association between birth month and offspring count of New Zealand women born in the Southern, albeit not Northern, hemisphere is a mirror image of the pattern reported from Austrian women: on average, women born during the Southern hemisphere summer months have fewer children than women born in winter. This association is highly significant within the lowest family income category but insignificant within higher family income categories.

CONCLUSIONS

This study provides evidence for a causal link between the seasonality of the environment during the pre- and perinatal period and offspring count of women. It further indicates that the main contribution of the birth month effect found in the present study comes from the lowest family income category.

Early life determinants of physical activity in 11 to 12 year olds: cohort study

OBJECTIVE

To examine factors in early life (up to age 5 years) that are associated with objectively measured physical activity in 11-12 year olds.

DESIGN

Prospective cohort study.

SETTING

Avon longitudinal study of parents and children, United Kingdom.

PARTICIPANTS

Children aged 11-12 years from the Avon longitudinal study of parents and children.

MAIN OUTCOME MEASURE

Physical activity levels in counts per minute (cpm) and minutes of moderate to vigorous physical activity for seven days measured with a uniaxial actigraph accelerometer.

RESULTS

Valid actigraph data, defined as at least three days of physical activity for at least 10 hours a day, were collected from 5451 children. Several factors were associated with physical activity at ages 11-12 years. Regression coefficients are compared with the baseline of "none" for categorical variables: maternal brisk walking during pregnancy (regression coefficient 5.0, 95% confidence interval -8.5 to 18.5; cpm for <1 h/wk and > or =2 h/wk of physical activity 17.7, 5.3 to 30.1), maternal swimming during pregnancy (21.5, 10.9 to 32.1 and cpm for <1 h/wk and > or =2 h/wk of physical activity 24.2, 7.8 to 40.7), parents' physical activity when the child was aged 21 months (28.5, 15.2 to 41.8 and cpm of physical activity for either parent active and both parents active 33.5, 17.8 to 49.3), and parity assessed during pregnancy (2.9, -7.6 to 13.4 and cpm of physical activity for 1 and > or =2 parity 21.2, 7.1 to 35.3).

CONCLUSIONS

Few factors in early life predicted later physical activity in 11-12 year olds. Parents' physical activity during pregnancy and early in the child's life showed a modest association with physical activity of the child at age 11-12 years, suggesting that active parents tend to raise active children. Helping parents to increase their physical activity therefore may promote children's activity.

Body height differentiation by season of birth: Girls from Cracow, Poland

Published studies world wide demonstrate that measures of human development and health status vary depending on the month of birth but these patterns are not always consistent and sometimes even conflict. Direct factors related to the birth season that may significantly differentiate morphological and functional traits and mechanisms causing these relations have not been found so far. On the basis of cross-sectional material, gathered in the years 1983 and 2000 by the Department of Anthropology of the Academy of Physical Education in Cracow, two main hypotheses have been verified: (1) average body height differences by month of birth are statistically insignificant, (2) the magnitude of these differences does not change with time. Metric data of 4672 girls aged 5-18 years, born in 1965-1978 and 1982-1995, were used. The total sample was also subdivided into prepubertal (5-9 years) and adolescent (10-18 years) groups. The age of the individuals was calculated to the nearest day and the procedure of standardization on the interpolated values of regional norms was applied. A highly significant relationship between the birth month and average values of height was revealed in preadolescent girls. The results obtained for the entire material proved insignificant. The patterns of the month-of-birth effect on body height for girls born in 60./70. and 80./90. show high similarity, though the effect seems weaker in the latter sample. Winter proved to be the most favorable birth season for later body height.

Season of birth, natural light, and myopia

PURPOSE

To investigate the possible roles of season of birth and perinatal duration of daylight hours (photoperiod) in the development of myopia.

DESIGN

Retrospective, population-based, epidemiological study.

PARTICIPANTS

A total of 276 911 adolescents (157 663 male, 119 248 female) 16 to 22 years old. All were Israeli-born conscripts to the Israeli Defense Forces who were examined during the 5-year period 2000 through 2004.

METHODS

Noncycloplegic refraction was determined by autorefractometer and validated by qualified optometrists. Myopia, defined on the basis of right eye spherical equivalence, was classified as mild (-0.75 to -2.99 diopters [D]), moderate (-3.0 to -5.99 D), or severe (-6.0 D or worse). The photoperiod was recorded from astronomical tables and classified into 4 categories. Using multivariate logistic regression models, we calculated odds ratios (ORs) for several risk factors of myopia including season of birth.

MAIN OUTCOME MEASURE

The OR for photoperiod categories as risk factors for myopia.

RESULTS

Overall prevalences of mild, moderate, and severe myopia were 18.8%, 8.7%, and 2.4%, respectively. There were seasonal variations in moderate and severe myopia according to birth month, with prevalence highest for June/July births and lowest for December/January. On multivariate logistic regression, the ORs of photoperiod categories for moderate and severe myopia were highly significant and demonstrated a dose-response pattern. Odds ratios for severe myopia were highest for the shortest versus the longest photoperiods (1.24; 95% confidence interval, 1.15-1.33; P<0.001). Mild myopia was not associated with season of birth or perinatal light exposure. Other risk factors were gender (1.14 for female), education level (1.32 for age above 12), and father's origin (1.31 for Eastern vs. Israeli origin).

CONCLUSION

Myopia in this population is associated with birth during summer months. The exact associating mechanism is not known but might be related to exposure to natural light during the early perinatal period.

Correlation of month and season of birth with height, weight and degree of obesity of rural Japanese children

Month and season of birth are thought to influence height, weight and degree of obesity in schoolchildren. A cross-sectional study was designed to measure the height and weight of all children aged 6-15 years attending primary and junior high schools in Tokushima Prefecture, Japan. Data were standardized (z-scores) and analysed separately by gender and age. The mean z-score for height and weight were the highest in subjects born during the months of spring and the lowest in those born during the months of winter (p < 0.0001), whereas the means were significantly higher in children born during the months of summer than in those born during the months of autumn (p < 0.0001). A gradually decreasing trend of height and weight was observed in children of both genders born between May and Mar (from spring to winter). There was no significant difference in degree of obesity among the four seasons of birth for boys and girls. The highest prevalence of obese boys have born during spring (among 6-year-old boys) and summer (among 7-year-old boys), whereas the highest prevalence of obese girls have born during spring (among 6-year-old girls) and winter (among 10-year-old girls). Our findings suggest that month and season of birth influence height and weight of schoolchildren in Tokushima but not their degree of obesity.