The aims of this study were to get an overall view of 25-hydroxyvitamin D (25[OH]D) concentrations in healthy Finnish children, to find the major factors influencing the levels, and to find if there are differences in 25(OH) concentrations already at birth or later in childhood between children who develop islet autoimmunity (IA) or type 1 diabetes (T1D) and autoantibody negative children.

The study population comprised of children born in 1994-2004 participating in Type 1 Diabetes Prediction and Prevention study (DIPP) clinics in Turku, Oulu and Tampere University Hospitals, Finland.

In this study we showed there was a marked increase in the 25(OH)D concentrations in healthy children, who were over the age of two years, in year 2003. Seasonal variation was significant, and it remained the same after year 2003. A largescale program for vitamin D fortification of dairy products and other foodstuffs was begun in Finland in 2003.

The median 25(OH)D concentrations were lowest at birth and highest at the age of six months, and they were not associated with the development of IA or T1D during childhood in follow-up lasting up to 14 years. The concentrations were associated with geographical location, sampling year and month, age of the child and for the samples taken at birth also with maternal age and maternal intake of vitamin D during pregnancy.

D-vitamiini ja tyypin 1 diabetes. Seerumin 25-hydroksi-D-vitamiinipitoisuus ja tyypin 1 diabeteksen riski lapsilla.