Babies born in winter are bigger, brighter & more successful

Around the ‘Net, you’ll find headlines like:

Your birth month influences your risk for diseases
https://blogs.discovermagazine.com/d-brief/2015/06/09/birth-month-risk-diseases/

Here's how your birth month affects the rest of your life
http://www.businessinsider.com.au/how-birth-month-matters-2012-7?op=1#january-people-born-this-month-are-statistically-more-likely-to-have-alzheimers-crohns-disease-and-epilepsy-1

Can we see any causal link(s)? One possibility is in-utero exposure to vitamin D, at critical times in embryonic development. When exposed to sunlight, the skin produces vitamin D. Peak vitamin production appears in summer. In this case, the correlation would be with the season, rather than the month — & the same effects in different months in the northern & southern hemispheres:

Babies born in winter are bigger, brighter & more successful
http://www.independent.co.uk/news/science/babies-born-in-winter-are-bigger-brighter-and-more-successful-523070.html

Season of birth & childhood intelligence: findings from the Aberdeen children of the 1950s cohort study
http://www.ncbi.nlm.nih.gov/pubmed/16953958 / astrology astrologers time of year baby born plots course extensive research seven-year period babies born in winter big bright successful adults summer study scientists Harvard University monitored development boys girls worldwide large seasonal variations weight length height head size mental ability researchers effects pregnant mother growing foetus seasonal variations diet hormones temperature exposure to sunlight viruses infections influence baby's baby American Australian psychiatrists anthropologists Harvard Queensland universities measured children mental motor tests birth eight months four seven years compared summer births born winter significantly longer at birth heavier taller larger head circumference age seven higher scores intelligence exercises IQ intelligence quotient seven winter spring born children heavier taller head circumferences significantly larger summer autumn born children results babies born winter longest winter spring borns birth weighed the most age seven tallest tall taller tallest heavy heavier heaviest researchers work medical journal Schizophrenia Research conclude winter spring babies bigger anthropometric variables smarter neurocognitive variables new study series projects worldwide evaluating effect seasons human health longevity physical intellectual development scientists Germany Germany's Max Planck Institute for Demographic Research people born autumn live longer born in spring ill in old age census data Denmark Austria Australia seasonal link to life expectancy older than 50 Austria adults born between October December lived seven months longer those born between April and June dietary changes seasonal infections phenomenon mother giving birth in spring spends the last phase of her pregnancy winter eat fewer vitamins Gabriele Doblhammer scientists research stops breast-feeding starts giving her baby normal solid food solids hot weeks of summer babies prone to infections digestive system season of birth optimist pessimist summer's babies brighter outlook winter-born grumblers American Australian researchers offer explanations differences early years of life theory foetal exposure changing seasonal factors temperature rainfall ultraviolet radiation /