Vitamin D levels, supplements and fortification worldwide
What it found
Vitamin D levels vary widely around the world, and the authors say screening everyone is not justified.
They recommend modest daily doses of around 800 to 1000 IU for healthy people who take supplements.
What they found
Studies in people
Worldwide vitamin D levels
In Latin America, Oceania and North America, the share of people with 25-hydroxyvitamin D below 25 nmol/L ranged from 5 to 18 percent. In Europe, Asia and Africa, the share ranged from 24 to 49 percent.
Darker skin and deficiency
In Finland, 25-hydroxyvitamin D below 30 nmol/L was found in 4.5 percent of Russian speaking migrants, compared with 28.0 percent of Kurdish and 50.4 percent of Somalian migrants.
Calcium intake matters
In many African countries, habitual dietary calcium intake is extremely low, which increases the risk of skeletal problems even when vitamin D levels look adequate.
Daily versus bolus dosing
In 60 healthy young adults, the same total dose of vitamin D3 given daily or monthly led to similar 25-hydroxyvitamin D levels by day 25. The monthly dose caused a faster rise over the first two weeks.
Bolus doses and falls
In recent trials of bolus doses of vitamin D, the intervention appeared to increase the risk of falls and fractures. The authors say bolus dosing is not generally recommended.
Fortification raises levels
A review of 34 publications found that food fortification raised 25-hydroxyvitamin D by 21.2 nmol/L on average. In Finland, mean levels rose from 47.6 to 65.4 nmol/L over the decade from 2000 to 2011, alongside an increase in supplement use from 11 to 41 percent.
Other findings
Testing problems
The value from a single 25-hydroxyvitamin D sample can vary substantially depending on the test and laboratory used. This has made it hard to compare levels between populations and over time.
Screening not justified
The authors say screening the general population for vitamin D deficiency seems poorly justified. An Australian study estimated almost 3.5 million unnecessary vitamin D tests in 2020, costing more than AUD87 million.
What the authors conclude
“Overall, active screening for vitamin D deficiency at the population level, in the absence of a clinical presentation, does not appear to be justified.”
Also in their conclusions
- They conclude that active screening for vitamin D deficiency at the population level, in the absence of a clinical presentation, does not appear to be justified.
- They recommend that approaches to increasing vitamin D levels in the population may focus on food fortification, and/or supplemental approaches, either through managed programmes or encouragement for self-administration.
- They advise that where supplementation is used in healthy community dwelling individuals, daily oral doses of around 800 to 1000 IU cholecalciferol are recommended.
How it was done
Vitamin D is important for muscle and bone health, but levels of 25-hydroxyvitamin D vary markedly around the world. The authors wanted to look at how to keep the whole population at a level that minimises the risk of poor health outcomes.
The authors reviewed global data on vitamin D levels, measurement methods, supplementation and food fortification. They also looked at guidelines and screening programmes from around the world.
What it can’t tell you
- The paper is a review of existing research, not a new trial, so it cannot prove cause and effect.
- The studies on bolus dosing had far too few participants to inform safety outcomes.
- The efficacy of vitamin D supplementation in a vitamin D-deficient population remains uncertain.
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 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error