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

Am J Hum Biol. 2011 Mar;23(2):190-200. doi: 10.1002/ajhb.21101. Epub 2010 Nov 30.
Krenz-Niedba?a M, Puch EA, Ko?ci?ski K.
Department of Human Evolutionary Biology, Adam Mickiewicz University, Umultowska 89, Pozna?, 61-614, Poland. martak at amu.edu.pl.

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. Am. J. Hum. Biol., 2010. © 2010 Wiley-Liss, Inc.
Copyright © 2010 Wiley-Liss, Inc. PMID: 21319248
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See also VitaminDWiki

• Vitamin D: Before, During, and After Pregnancy Overview
• Pre-Birth Vitamin D Levels Determine Your Health for Life
• Is the variation in winter babies due to vitamin D – 2009 Wall Street Journal - nice graphs
• 7X more likely to have babies with low birth weight when mother very low on vitamin D – March 2010
• Pregnancy vitamin D and bone mass at age 9 - Jan 2006 file
• Less child bone if mother lacked vitamin D – Dec 2010
• 2X more allergies if 11th womb week was in Spring – Vitamin D or pollen? Oct 2010