Overview
- A review of 37 clinical trials reported that vitamin D supplements are unlikely to prevent acute respiratory infections.
- Studies link low vitamin D to immune function, blood pressure, cardiovascular risk, mental health and pregnancy outcomes, yet trial results on supplementation benefits are inconsistent.
- There is longstanding consensus that infants should receive vitamin D supplements at least through their first year to prevent rickets.
- The NHS and UK government advise seasonal supplementation, as most vitamin D comes from sunlight and dietary sources are limited to oily fish, egg yolks, mushrooms and fortified foods.
- A nutritionist quoted in UK reporting said roughly 30–40% of people may be deficient in winter, a figure presented as an expert estimate rather than official data.