Birth season and vitamin D concentration in adulthood.

BACKGROUND: Recent evidences suggest that the season of birth may influence human development and vulnerability to develop certain diseases. METHODS: A retrospective analysis was hence carried out in the laboratory information system of the University Hospital of Parma (North-West Italy), to retrieve values of total serum vitamin D (25-hydroxyvitamin D) measured in a the whole cohort of unselected outpatients age 18 years and older referred for routine health check-up during January to December 2014. Vitamin D was then stratified according to birth season. RESULTS: The study population consisted in 11,150 unselected Italian residents (median age 62 years; 8,592 women and 2,558 men). Serum vitamin D values were found to be significantly lower in subjects born in winter than in those born in spring and summer. More specifically, winter season birth was associated with 11% increased risk of developing vitamin D deficiency later in life compared to spring birth. Daily sunlight hours at birth independently predicted vitamin D concentration in adulthood. CONCLUSIONS: The results of this large, cross-sectional retrospective investigation attest that subjects born in winter have a total vitamin D concentration in adulthood that is significantly lower than those born in seasons with longer daylight periods.