BACKGROUND/OBJECTIVES: Prenatal vitamin-D deficiency may be associated with increased risk of obesity later in life. Using two national vitamin-D fortification programs as the setting for a societal experiment, we investigated whether exposure to vitamin-D from fortified margarine and low-fat milk during foetal life was associated with body size at 7 years of age.

SUBJECTS/METHODS: Vitamin-D fortification of margarine was mandatory in Denmark from 1961 to 1985, and voluntary fortification of low-fat milk was permitted from 1972 to 1976. Using information on body mass index (BMI) Z-score at the age of 7 years of 54 270 children, who were measured during the mandatory Copenhagen School Health examination, we compared children according to whether the mothers were pregnant during the fortification programs or not. The comparisons were performed for children born just before and after initiation or termination of margarine and milk fortification periods, respectively. In total four sets of analyses were performed.

RESULTS: We observed no difference in mean BMI Z-score between children exposed to vitamin-D fortification in utero and non-exposed children. Similar results were observed for overweight and obesity.

CONCLUSIONS: Prenatal exposure to vitamin-D from fortification of margarine and low-fat milk showed no association with body size at 7 years.