Foods fortified with vitamin D₃ improve vitamin D status, but not bone health or muscle strength Original paper

Low vitamin D status, a problem especially prevalent during the winter months in immigrants with darker skin living in northern countries, has been associated with poor bone health and decreased muscle strength. A potential solution to this problem is the consumption of foods fortified with vitamin D₃.

This 12-week, double-blind, randomized controlled trial took place in the winter. It included 143 women of Danish and Pakistani origin (aged 18–50) living in Denmark. They were randomized into four groups: (i) Danish women receiving fortified foods, (ii) Pakistani women receiving fortified foods, (iii) Danish women receiving nonfortified foods, or (iv) Pakistani women receiving nonfortified foods. The fortified foods provided 30 μg (1,200 IU) of D₃ per day.

The primary outcome was changes in serum levels of 25(OH)D (aka 25-hydroxyvitamin D₃). The secondary outcomes were muscle strength and bone turnover markers.

D₃-fortified foods raised serum 25(OH)D from 53.3 to 77.8 nmol/L in Danish women, and from 44.5 to 54.7 nmol/L in Pakistani women. However, there were no improvements in muscle strength or bone health markers.

The baseline 25(OH)D levels of the participants were only borderline insufficient. It is possible that secondary outcomes would have shown an improvement if the participants had started from a state of vitamin D deficiency (i.e., <30 nmol/L).