Vitamin D: who really needs supplements?
Nutrition
Key points
- VITAL (about 26,000 U.S. adults): 2,000 IU a day did not lower cancer or cardiovascular events.
- Meta-analysis of 81 trials: supplements did not prevent fractures or falls.
- Supplements are needed for deficiency and in high-risk groups.
- Too much vitamin D can be harmful.
High hopes, modest results
Low vitamin D levels are linked in observational studies to many diseases, which led to widespread supplement use. But being linked is not the same as being caused, and randomized trials tell a different story.
What the research shows
VITAL. In this U.S. trial, about 25,900 adults aged 50 and older (and women 55 and older) took 2,000 IU of vitamin D a day or a placebo for a median of 5.3 years. Vitamin D did not lower the incidence of invasive cancer or major cardiovascular events (Manson et al., 2019).
Bones. A meta-analysis of 81 randomized trials found that vitamin D supplements did not prevent fractures or falls and did not meaningfully improve bone density in adults (Bolland et al., 2018).
Who may need supplements
- people with confirmed deficiency;
- older adults who are housebound or in nursing homes;
- people with conditions that affect absorption;
- breastfed infants (the American Academy of Pediatrics recommends 400 IU a day);
- people with very little sun exposure or darker skin who live at northern latitudes, after discussing with a doctor.
What to do
- Get vitamin D from food (fatty fish, eggs, fortified milk and cereals) and moderate sun exposure.
- Physical activity and strength training do more for bones than supplements (Bull et al., 2020).
- Discuss testing and doses with your doctor rather than taking megadoses on your own.
Frequently asked questions
How much vitamin D do adults need?
The RDA is 600 IU a day for adults up to 70 and 800 IU for those over 70. The upper limit for adults is 4,000 IU a day.
Should everyone get a vitamin D blood test?
The USPSTF found insufficient evidence to recommend routine screening in adults without symptoms. Testing makes sense when there are risk factors.
Sources
- Manson et al. (2019). Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. New England Journal of Medicine 380(1):33-44. doi:10.1056/NEJMoa1809944
- Bolland et al. (2018). Effects of vitamin D supplementation on musculoskeletal health: a systematic review, meta-analysis, and trial sequential analysis. The Lancet Diabetes & Endocrinology 6(11):847-858. doi:10.1016/S2213-8587(18)30265-1
- Bull et al. (2020). World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine 54(24):1451-1462. doi:10.1136/bjsports-2020-102955
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