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Vitamin D

In Australia and New Zealand most vitamin D comes from sunlight rather than food, so low status is most common in people who get little sun, such as housebound or institutionalised older adults and people with dark skin. In randomised trials, vitamin D on its own did not reduce fractures or falls or meaningfully change bone density in adults not selected for deficiency, while vitamin D combined with calcium was linked to a small reduction in fractures in older adults. Trials also found a small overall reduction in acute respiratory infections. Vitamin D3 raised blood levels more than D2 in trials, mainly at large infrequent doses, and people on plant-based diets tend to have lower vitamin D intake and status.

Evidence retrieved up to

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6 research claims

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What the research shows

In Australia and New Zealand, sunlight rather than food is the main source of vitamin D for adults, and low vitamin D status is most common among housebound or institutionalised older adults, people with dark skin, and others who regularly avoid the sun or work indoors.

Take care: see the safety noteRisk

Who this is about

adults living in Australia and New Zealand

Safety note

Sun exposure that makes vitamin D also raises skin-cancer risk, and Australasia has a high incidence of skin cancer. The position statement says sun protection should still be used for prolonged exposure at UV index 3 or above, even by people with low vitamin D, and that people at high skin-cancer risk should discuss supplements with their doctor instead of relying on sun.

Details and sources

Practical note

Graded moderate: a consensus position statement summarising consistent observational prevalence data; no pooled analysis was fetched. The statement defines adequate status as a serum 25-OHD of at least 50 nmol/L at the end of winter.

Sources

In randomised trials of adults not selected for vitamin D deficiency, vitamin D supplements on their own did not reduce fractures or falls and did not meaningfully change bone mineral density.

No known concerns at usual amountsNo clear effect

Who this is about

adults not selected for vitamin D deficiency, mostly older community-dwelling adults

Details and sources

Practical note

Graded high: three meta-analyses of randomised trials agree (Bolland 2018, 81 trials; Cochrane 2014, high-quality evidence for vitamin D alone; Reid 2014, 23 trials on bone density). Results were similar for doses above 800 IU a day and for high versus low doses. Few trial participants had very low baseline levels, so the finding does not address correcting deficiency.

Safety note

In the Cochrane review, mild hypercalcaemia was more common with vitamin D or analogues than with placebo. The position statement reports that a single annual 500 000 IU dose in older women increased falls and fractures.

Sources

In older adults, vitamin D taken together with calcium, as part of a healthy lifestyle, may help reduce the risk of hip and other fractures; the absolute effect was small in people living in the community and larger in people living in institutions.

Take care: see the safety noteBenefit

Who this is about

post-menopausal women and older men

Safety note

The Cochrane review found a small but significant increase in gastrointestinal symptoms and kidney disease with vitamin D plus calcium, and more mild hypercalcaemia with vitamin D; it found no increase in deaths.

Details and sources

Practical note

Graded moderate rather than the review's high: allocation concealment was unclear in over half of trials, and the benefit comes from vitamin D combined with calcium, so the calcium contribution cannot be separated. Cochrane estimated about one fewer hip fracture per 1000 community-dwelling older adults a year and nine fewer per 1000 in institutions. The 2012 position statement cited 800 IU (20 micrograms) a day as the reference intake for adults over 70.

Sources

Across randomised trials, vitamin D supplementation, as part of a healthy lifestyle, may help reduce the risk of acute respiratory infections, though the overall reduction was small.

No known concerns at usual amountsBenefit

Who this is about

children and adults in randomised trials of vitamin D supplementation

Details and sources

Practical note

Graded moderate: double-blind trials mostly at low risk of bias, downgraded one level for heterogeneity and an effect close to no difference (OR 0.92, 95% CI 0.86 to 0.99). Protection was seen in subgroups given daily doses of 400-1000 IU for up to 12 months and in children aged 1 to 15, but tests for interaction were not significant. Relevance to COVID-19 was not established.

Safety note

The meta-analysis found no difference in serious adverse events between vitamin D and placebo.

Sources

In randomised trials in adults, vitamin D3 raised blood 25-hydroxyvitamin D more than vitamin D2, with the clearest difference for large infrequent doses and no significant difference with daily dosing.

No known concerns at usual amountsBenefit

Who this is about

adults in trials comparing vitamin D2 and D3 supplements

Details and sources

Practical note

Graded moderate: a meta-analysis of randomised trials with a direct comparison, downgraded one level for inconsistency, since the advantage of D3 held for bolus doses but was lost with daily supplementation. VeganHealth summarises the bolus doses as 50,000 IU or more.

Vegan note

Vitamin D2 is made by exposing yeast or mushrooms to UV light; most D3 comes from sheep's wool or fish oil, although some D3 products are verified as vegan. With daily dosing the D2 versus D3 difference was not significant.

Sources

Adults following vegetarian or vegan diets generally have lower vitamin D intake and blood levels than meat-eaters, although inadequate vitamin D intake is also common among meat-eaters.

No known concerns at usual amountsRisk

Who this is about

adults following vegetarian or vegan diets

Details and sources

Practical note

Graded low: observational comparisons from a systematic review of 141 studies without pooling; the review authors are employees of a company that markets fortified foods and supplements. Status also varies strongly by season and sun exposure.

Vegan note

In the EPIC-Oxford cohort, as summarised by VeganHealth, vegans had the lowest average vitamin D levels of any diet group, though on average still in the range the US Institute of Medicine considers healthy. Fortified plant milks and UV-treated mushrooms are among the few plant-based food sources.

Sources