Does prenatal exposure to vitamin D-fortified margarine and milk alter birth weight? A societal experiment - CORRIGENDUM.

In our recent paper ‘Does prenatal exposure to vitamin D-fortified margarine and milk alter birth weight? A societal experiment’ published in British Journal of Nutrition we explored the association between a national vitamin D fortification programmes of margarine and milk and birth weight. Based on available official documents from the Nordic Council of Ministers the initiation of vitamin D fortification of margarine was introduced in 1961. However, we have recently uncovered evidence from old law texts that questions this onset date. This information source suggests that mandatory fortification apparently started even before World War II for vitamin D and for vitamin A. While this new evidence makes the onset date of the vitamin D fortification of margarine uncertain all sources of information that we have come across confirms that the date of termination of the fortification programme was indeed in 1985. For the voluntary vitamin D fortification of milk insecurity has arisen about the termination date in 1976. A similar Ministerial order that cancelled the permission to fortify milk in 1976 appears to have been issued in 1974 as well. Which of the two Ministerial orders that in reality cancelled the milk fortification is unclear. The voluntary vitamin D fortification of milk was, however, confirmed to commence in 1972 by all law texts. During the study period margarine was also fortified with vitamin A, and the new evidence reveals that the vitamin A dose was increased by 25% (from 20 to 25 IU/g) in 1962. There were also minor increases in 1971 from 25 to 26 IU/g and in 1985 from 26 to 28 IU/g. Therefore, we request the editor and readers to disregard the estimates based on analyses in 1961 and 1976, and to keep in mind that changes in vitamin A fortification also took place (Fig. 1). In the original paper we investigated potential effects of prenatal exposure to vitamin D fortification on mean birth weight and risk of low and high birth weight. We found no difference in risk of low and high birth weight between exposed and non-exposed children. Contrary to our expectations, we found inconsistent effects of the vitamin D fortification on mean birth weight; the mean birth weight was lower among exposed than non-exposed in all analyses except in the analyses based on margarine fortification in 1961 (Fig. 2). However, the mean difference in birth weight did not exceed 60 grams, and we questioned the clinical relevance.