A 2020 meta-analysis published in Diabetes Care found that vitamin D supplementation significantly reduced the risk of type 2 diabetes in people with pre-diabetes. The analysis showed that 21.2% of participants in the vitamin D group reverted to normoglycaemia compared to 14.1% in the control group. However, the benefit was observed only in non-obese participants, not in obese participants.
Professor Tim Spector, an epidemiologist and founder of Zoe, said that while early studies suggested vitamin D helped with osteoporosis, large studies on fractures found no difference. He noted that vitamin D is not useful for the vast majority of people in preventing fractures. The Royal Osteoporosis Society states that vitamin D helps the body absorb and use calcium, keeping bones and muscles strong. Spector added that taking vitamin D during a viral infection may reduce its duration by a few hours, and it is probably useful for those at risk of multiple sclerosis.
Spector acknowledged that the effects of vitamin D supplements are not fully understood. Uncertainties remain about the optimal dosage for reducing type 2 diabetes risk and why the benefit differs by weight. The mechanism by which vitamin D may reduce diabetes risk is also unclear.