To study the association between extra vitamin D from a mandatory margarine fortification program and chance of live birth among infertile women.
Nationwide cohort study.
The study population consisted of 16,212 women diagnosed with infertility from June 1, 1980, to August 31, 1991.
We took advantage of the mandatory vitamin D fortification program of margarine in Denmark that was abruptly stopped on May 31, 1985. The termination of the vitamin D fortification served as a cutoff point to separate the study population into various exposure groups.
Odds ratios and 95% confidence intervals for the association between vitamin D exposure status and chance of a live birth within 12, 15, and 18 months after first infertility diagnosis.
Women who were diagnosed with infertility during the vitamin D–exposed period had an increased chance of a live birth compared with women diagnosed with infertility during the nonexposed period. For women diagnosed with infertility during the wash-out period, the chance of a live birth was also increased, but somewhat lower. Similar estimates were obtained with longer follow-up, in women with anovulatory infertility, and little seasonal variation was observed when calendar period of conception was applied.
Our findings suggest that infertile women exposed to extra vitamin D from a margarine fortification program had an increased chance of live birth compared with women not exposed to extra vitamin D from fortification.