Vitamin D deficiency is common among otherwise healthy pregnant women and may have consequences for them as well as the early development and long-term health of their children. However, the importance of maternal vitamin D status has not been widely studied.

D-tect includes an in-depth examination of the influence of exposure to vitamin D early in life and during critical periods of growth for development of type 1 diabetes, obesity and fractures of the wrist, arm and clavicle during child- and adulthood.

In 1985 mandatory fortification of margarine with vitamin D was cancelled, and hence all individuals born in Denmark after this day were not any more exposed to fortified margarine prior to conception or during gestation. Apart from determining the influences of exposure prior to conception and during pre- and postnatal life, the project will examine the importance of vitamin D exposure during specific seasons and trimesters, by comparing disease incidence among individuals born before and after fortification termination.

Additionally, a validated method will be used to determine neonatal vitamin D status using stored dried blood spots from individuals who develop the before mentioned disease. The study will help determine the effects of vitamin D exposure during critical periods in life.

The results will change our current understanding of the significance of vitamin D, for a long-term health and the occurrence of diseases, as well as greatly qualify the current debate in Denmark on whether to resume the vitamin D fortification.