Vitamin D levels, supplements and food fortification in global populations
What it found
Vitamin D blood levels vary widely around the world and are shaped by sun, skin colour, clothing and diet.
Daily supplements of 800 to 1000 IU or fortified foods can raise these levels in people.
What they found
Studies in people
Global vitamin D levels
Blood levels of vitamin D differ greatly between regions. In Latin America, Oceania and North America, 5% to 18% of people had very low levels. In Europe, Asia and Africa, that figure was 24% to 49%.
D2 versus D3 forms
Animal-derived vitamin D3 raises blood levels more than plant-derived vitamin D2 in people. Vitamin D3 also stays in the body longer, so it is usually the preferred form for supplements.
Daily versus large doses
In a study of 60 healthy young adults, a single large monthly dose raised blood vitamin D much faster in the first two days than a smaller daily dose. However, large single doses have been linked to more falls and fractures in other trials in people.
Food fortification results
Adding vitamin D to foods like milk and cereal raised average blood levels by 21.2 nmol/L across 34 publications in people. In Finland, average levels rose from 47.6 to 65.4 nmol/L over ten years after fortification began, though supplement use also increased.
Testing the general population
Widespread blood testing for vitamin D in healthy people is not well supported by current evidence. An Australian review estimated almost 3.5 million unnecessary tests in 2020, costing over AUD87 million.
What the authors conclude
- They advise that keeping vitamin D levels up across populations is best done through diet, lifestyle changes or fortified foods rather than mass blood testing.
- They recommend daily doses of 800 to 1000 IU of vitamin D3 for healthy people who need a supplement, and they advise against using large single doses because of links to falls and fractures in trials.
- They suggest that targeted screening or supplementation may still be appropriate for groups at very high risk of severe deficiency, such as older people in care homes or those with darker skin living far from the equator.
How it was done
The authors wanted to look at vitamin D from a whole population view rather than just for individual patients with bone disease. They aimed to find ways to keep average vitamin D levels high enough to lower health risks across entire countries.
The authors gathered and examined published research on vitamin D levels, testing methods, supplements and fortified foods in populations worldwide. They did not run new trials but summarised existing studies and guidelines on behalf of an international working group.
What it can’t tell you
- This is a summary of existing research, so it cannot prove cause and effect on its own.
- The observational surveys it draws on can show links between vitamin D levels and health outcomes, but they cannot show that one causes the other.
- Large trials mentioned found no benefit of vitamin D pills for many diseases, but mostly tested people who already had adequate levels.
Who paid
- Funding
- Funded by Medical Research Council (from the PubMed record).
- Authors work at
- University of Southampton, UK; University of Southampton and University Hospital Southampton NHS Foundation Trust, UK; University of Siena, Italy
The paper
- Title
- Optimisation of vitamin D status in global populations
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Harvey NC, Ward KA, Agnusdei D, et al (2024). Optimisation of vitamin D status in global populations. Osteoporosis international. doi:10.1007/s00198-024-07127-zFree full textPubMed 38836946DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error