Vitamin D: what supplements do for bones, and what large trials found they do not do

Vitamin D has the widest gap in nutrition between what observational studies promised and what randomised trials delivered. The bone role is settled. Almost everything else vitamin D was expected to prevent has not held up when it was properly tested.

What it does in the body

• Vitamin D lets the gut absorb calcium and keeps blood calcium and phosphate high enough for bones to mineralise normally. Evidence E source
• Few foods naturally contain vitamin D. Fatty fish such as trout, salmon, tuna and mackerel, and fish liver oils, are among the best sources. Evidence E source
• Fortified foods provide most of the vitamin D in American diets, and almost all US milk is fortified with about 3 mcg (120 IU) per cup. — US population Evidence E source

How much you need

• The RDA for vitamin D is 15 mcg (600 IU) a day for adults up to 70 and 20 mcg (800 IU) from 71. — adults Evidence E source
• The Tolerable Upper Intake Level for vitamin D is 100 mcg (4,000 IU) a day for adults. — adults 19+ Evidence E source
• A blood 25(OH)D level of at least 50 nmol/L (20 ng/mL) is generally considered adequate. Below 30 nmol/L (12 ng/mL) indicates deficiency. — healthy individuals Evidence E source
• Reanalysed person by person rather than trial by trial, the intake needed to put 97.5 per cent of people above 50 nmol/L in winter is 92 micrograms a day, six times the recommended amount. — children and adults aged 2 to 89 years in 11 randomised trials, with winter serum 25(OH)D as the outcome Evidence A source
• The recommended amount was worked out largely on white populations: dark-skinned people living far from the equator need two to four times as much to reach the same blood level. — people of Black or South Asian descent aged 5 to 86 years, wintertime serum 25(OH)D as the outcome Evidence A source
• Putting vitamin D into everyday foods works, and it lifts blood levels by about 21 nmol/L at an average dose of 16 mcg a day. The form matters: D3 beat D2. — 2 398 adults and 1 532 children across 34 publications, all free of illness affecting vitamin D absorption Evidence A source

How well your body absorbs it

• Five salmon dinners a week, 750 g in all, still left blood vitamin D falling through the autumn. The fall was smaller than in the people eating cod or no fish, but it was a fall. — 63 healthy adults with overweight or obesity in South-Western Norway, randomised to salmon, to cod, or to their usual food without fish Evidence B source
• Two salmon products carrying the same 5 mcg of vitamin D a day did not work the same way: the fattier salmon sausage slowed the autumn decline, the 25 g of smoked salmon did nothing measurable. — 120 non-obese women aged 20 to 25 in Poland, randomised to 25 g of smoked salmon a day, 100 g of salmon sausage a day, or no change Evidence B source
• Vitamin D made in mushrooms by ultraviolet light does not all survive the pan, and the same trial found the comparison capsules held more vitamin D than their labels claimed. — 43 prediabetic, vitamin D deficient adults with 25(OH)D at or below 20 ng/ml and BMI above 25, each eating a daily chef-prepared entrée with 100 g of fresh sliced cooked mushrooms Evidence B source
• The researchers who saw vitamin D disappear from cooked mushrooms named cooking loss first among the reasons the mushrooms underperformed, ahead of anything about the people eating them. — prediabetic adults with overweight or obesity, compared against earlier findings in younger healthy subjects Evidence B source
• How much vitamin D a mushroom ends up holding is set in the factory, not in the field: the dose of ultraviolet light, the wavelength and even whether the mushroom was sliced all move the answer. — edible mushrooms, chiefly Agaricus bisporus, in postharvest food technology experiments rather than in people Evidence D source
• Taking vitamin D with a meal that contains fat helps, but the common advice that it will not be absorbed without fat is stronger than the evidence behind it. — adults in the clinical arm, plus cell and mouse work, across 46 studies selected from 2 069 identified Evidence B source
• Whether the kind of fat eaten alongside vitamin D changes how much gets in is still unsettled, and the trial that raised the question said so about its own explanation. — young women in the trial itself, with the cited comparisons drawn from trials in adults of various ages Evidence B source

What too little does

• In children, vitamin D deficiency causes rickets, in which bone fails to mineralise properly and becomes soft and deformed. — children Evidence E source
• In adults, vitamin D deficiency leads to osteomalacia, in which existing bone is incompletely mineralised and weak. — adults and adolescents Evidence E source

Who is most likely to fall short

• People with a BMI of 30 or more, and people who have had gastric bypass surgery, tend to have lower vitamin D levels. — adults with obesity or bypass surgery Evidence E source
• Most people meet at least some of their vitamin D need through sunlight, but limiting UV exposure is prudent because UV radiation is a carcinogen and the most preventable cause of skin cancer. Evidence E source

What the evidence does and does not show

• In trials, vitamin D supplements did not lower the risk of total, hip or non-vertebral fractures compared with placebo. — 25,871 generally healthy adults in the VITAL trial Evidence B source
• The US Preventive Services Task Force concluded with moderate certainty that vitamin D supplements do not reduce falls or the injuries that come from them. — community-dwelling adults aged 65 and over Evidence A source
• Clinical trials have generally not shown that vitamin D supplements reduce the incidence of cancer. — adults in clinical trials Evidence B source
• The VITAL trial found vitamin D supplements did not significantly reduce heart attacks, strokes, revascularisation or cardiovascular deaths. — adults in the VITAL randomised trial Evidence B source
• In the VITAL trial, 2,000 IU a day of vitamin D3 for a median of 5.3 years did not lower the risk of fracture in 25,871 US adults who were not selected for vitamin D deficiency. — men 50+ and women 55+ in the United States, not recruited on the basis of vitamin D deficiency, low bone mass or osteoporosis Evidence B source
• A meta-analysis of 81 randomised trials in 53,537 people found vitamin D supplements had no effect on total fractures, hip fractures or falls, and no clinically relevant effect on bone density at any site. — adults over 18, all settings; trials of hydroxylated analogues excluded Evidence A source
• The Cochrane review of 53 trials in 91,791 people rates as high quality the evidence that vitamin D on its own does not prevent hip fracture or any new fracture. — post-menopausal women and older men in community, nursing home and hospital settings Evidence A source
• The same Cochrane review found that vitamin D taken with calcium gives a small reduction in hip fracture, worth about one fracture prevented per 1,000 people a year in the community and about nine per 1,000 a year in care homes. — post-menopausal women and older men; community residents versus institution residents Evidence A source
• The best-known benefit of vitamin D outside bone, fewer coughs and colds, did not survive the addition of one large trial: the 2025 update no longer finds a statistically significant effect. — participants of all ages in trials of vitamin D against placebo or lower-dose control, with acute respiratory infection incidence collected prospectively as a pre-specified efficacy outcome Evidence A source
• In children under five, vitamin D shaved a sliver off the share who ever saw a doctor for a respiratory infection, but did not change how many visits each child made. — children up to five years of age, supplemented from early pregnancy through to age five; trials in children with chronic respiratory or systemic conditions excluded Evidence A source
• In older adults from the general population, 2,000 IU of vitamin D a day for five years did not prevent type 2 diabetes. — US adults with a mean age of 67 and no diabetes at enrolment, 51 per cent women, mean body mass index 27.5; previous trials had been confined to people with prediabetes Evidence B source
• In people who have just had a first episode suggesting multiple sclerosis, a very high pulse dose of vitamin D cut disease activity over two years by about a third. — untreated patients aged 18 to 55 with a clinically isolated syndrome of under 90 days, serum vitamin D below 100 nmol/L and MRI meeting dissemination criteria; median age 34, 70 per cent women Evidence B source
• High-dose vitamin D in pregnancy likely cuts childhood wheeze by about a fifth, but the same trials could not show it prevents asthma. — pregnant or breastfeeding women and their children, in 4 studies comparing a high dose with a low or standard dose Evidence A source
• In the group most often told they are at risk of deficiency because of skin pigmentation, vitamin D supplements did not lower the number of acute respiratory infections. — ethnic groups other than white, with or without a white comparator; three randomised trials contributed to the pooled estimate Evidence A source
• Calcifediol, the half-processed form, raises blood 25(OH)D more than ordinary vitamin D3 does at the same job, though three of seventeen studies found the opposite. — 1 575 participants across 17 studies, searched to November 2023, English and French only Evidence A source

What too much does

• Vitamin D toxicity causes marked hypercalcemia and, in extreme cases, kidney failure, soft-tissue calcification, arrhythmia and death. — people with excessive intake Evidence E source
• Signs of vitamin D toxicity are unlikely below 250 mcg (10,000 IU) a day. — adults Evidence E source
• Over three years, 4,000 IU and 10,000 IU of vitamin D3 a day left bone density at the wrist lower than 400 IU a day did, in healthy adults who were not deficient to begin with. — 311 community-dwelling healthy adults aged 55 to 70 in Calgary, Canada, with baseline 25(OH)D of 30 to 125 nmol/L Evidence B source
• Vitamin D with calcium carries a small increase in kidney disease and in mild high blood calcium, and does not affect death rates. — post-menopausal women and older men in trials of vitamin D with or without calcium Evidence A source
• The European upper limit is not one number for everybody. Adults and teenagers may go to 100 mcg a day, but for children aged one to ten the ceiling is half that. — European Union population by age group Evidence E source

Medicines it interacts with

• The weight-loss drug orlistat lowers absorption of vitamin D from both food and supplements, and blood levels fall with it. — people taking orlistat with a reduced-fat diet Evidence E source
• Statins cut cholesterol production, and since the body builds vitamin D from cholesterol, they may reduce how much it makes. — people taking statins Evidence E source

What to do with this

This is the one nutrient on the site where eating better will not solve the problem, so the practical question is different from the others.

If you eat oily fish twice a week, you are doing what food can do. Tinned salmon, sardines and mackerel count, keep in a cupboard and cost little. Beyond that, fortified milk and similar products carry small amounts that add up quietly.

If you do not eat fish, the next step is a blood test rather than a better shopping list. It is worth asking for one outright in a few situations: a BMI of 30 or more, gastric bypass surgery, skin that stays covered, or a condition that interferes with absorbing fat. A supplement is then insurance against being deficient, at a dose someone has actually looked at rather than the largest capsule on the shelf.

One number from the intake section is worth carrying away. The recommended 15 micrograms was worked out to cover a population, and when the same data were reanalysed person by person, the intake needed to put 97.5 per cent of people above 50 nmol/L in winter came out at 92 micrograms a day. That is no kind of dose to go and take. It is a reason to test rather than to calculate.

It matters most if you have darker skin and live far from the equator. The recommendation was worked out largely on white populations, and that group needs two to four times as much vitamin D to reach the same blood level.

Where to get it from food

The bottom line

Vitamin D matters for bone mineralisation, and deficiency causes real disease. The large trials that tested supplements for fractures, falls, cancer and heart disease still came back negative. The last benefit outside bone that people still quoted has now gone the same way. Adding one large trial to the 2025 update on coughs and colds left no statistically significant effect, and in the group most often warned about deficiency because of skin pigmentation, supplements did not lower the number of acute respiratory infections either. Five years of 2,000 IU a day did not prevent type 2 diabetes. Two signals did survive and neither is settled. After a first episode suggesting multiple sclerosis, a very high pulse dose cut disease activity over two years by about a third, and in pregnancy high-dose vitamin D likely cuts childhood wheeze by about a fifth while showing nothing on asthma. Both of those belong to particular patients under particular care. All of it is a reason to treat a supplement as insurance against running low, rather than as protection against chronic illness. Very few foods contain much of it, which is why clinicians check a blood level instead of asking what you eat, and why the food table below is so short. The newest evidence sharpens what food can and cannot do. Five salmon dinners a week, 750 g in all, still left blood vitamin D falling through a Norwegian autumn, and two salmon products carrying the same 5 micrograms a day behaved differently from each other. Vitamin D made in mushrooms by ultraviolet light does not all survive the pan. Fortification is the part that works: pooled across 34 publications, an average of 16 micrograms a day from fortified food raised blood levels by 21 nmol/L, more in people who started low, and D3 did more than D2. The advice to take vitamin D with fat is only half supported, since absorption also happened without fat, and which kind of fat matters is still unsettled. Calcifediol, the half-processed form a doctor may prescribe, raised blood levels more than D3 in 12 of 17 studies, with three going the other way. One correction on safety: the European upper limit is 100 micrograms a day for adults and teenagers and half that for children aged one to ten, so the ceiling on this page is an adult ceiling.

Sources

1. vitd-01 · Position of an expert body · expert body statement
   Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal bone mineralization and to prevent hypocalcemic tetany.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · extracted
2. vitd-14 · Position of an expert body · expert body statement
   Few foods naturally contain vitamin D. The flesh of fatty fish (such as trout, salmon, tuna, and mackerel) and fish liver oils are among the best sources.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
3. vitd-16 · Position of an expert body · expert body statement
   Fortified foods provide most of the vitamin D in American diets. For example, almost all of the U.S. milk supply is voluntarily fortified with about 3 mcg/cup (120 IU), usually in the form of vitamin D3.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
4. vitd-02 · Position of an expert body · expert body recommendation
   Adults 19-50 years: 15 mcg (600 IU); Adults >70 years: 20 mcg (800 IU) (value from the source's table, not a sentence)
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
5. vitd-03 · Position of an expert body · expert body recommendation
   Tolerable Upper Intake Level (adults 19-70 and >70): 100 mcg (4,000 IU) (value from the source's table, not a sentence)
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
6. vitd-04 · Position of an expert body · expert body statement
   ≥50 nmol/L or ≥20 ng/mL are generally considered adequate for bone and overall health in healthy individuals (value from the source's table, not a sentence)
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · extracted
7. vitd-r1-1 · Meta-analysis or systematic review · individual participant data meta-analysis of randomised trials
   Our IPD-derived estimates of vitamin D intakes required to maintain 97.5% of winter 25(OH)D concentrations ≥ 25 and ≥ 30 nmol/L are 6 and 12 µg/day, respectively (unadjusted model). The intake estimates to maintain 90%, 95% and 97.5% of concentrations ≥ 50 nmol/L are 33.4, 57.5 and 92.3 µg/day, respectively (unadjusted) and 17.0, 28.1 and 43.6 µg/day, respectively (adjusted for mean values for baseline serum 25(OH)D, age and BMI).
   Cashman et al., European Journal of Nutrition, 2021 · checked 2026-09-17 · independently re-checked
8. vitd-r1-2 · Meta-analysis or systematic review · individual participant data meta-analysis of randomised trials
   To maintain serum 25(OH)D concentrations ≥ 25 and 30 nmol/L in 97.5% of individuals, 23.9 and 27.3 µg/day of vitamin D, respectively, were required among South Asian and 24.1 and 33.2 µg/day, respectively, among Black participants...The vitamin D intake required by dark-skinned individuals to maintain 97.5% of winter 25(OH)D concentrations ≥ 50 nmol/L was 66.8 µg/day.
   Cashman et al., European Journal of Nutrition, 2022 · checked 2026-09-17 · independently re-checked
9. vitd-e2-06 · Meta-analysis or systematic review · meta-analysis of randomised controlled trials
   Random-effects meta-analysis of all studies combined (mean dose 16.2 μg/d) indicated a pooled treatment effect of 21.2 nmol/L (95% CI: 16.2, 26.2), with a greater effect for studies using cholecalciferol than ergocalciferol.
   Dunlop et al., The Journal of Nutrition, 2021 · checked 2026-09-18 · independently re-checked
10. vitd-e2-01 · Randomised controlled trial(s) · randomised controlled trial
    The findings suggest that 750 g/week of salmon was not sufficient to prevent a decrease in serum 25-hydroxyvitamin D3 in autumn in South-Western Norway in adults with overweight/obesity.
    Helland et al., British Journal of Nutrition, 2020 · checked 2026-09-18 · independently re-checked
11. vitd-e2-02 · Randomised controlled trial(s) · randomised controlled trial
    Nevertheless, differences between the groups were observed concerning the changes in 25(OH)D serum concentration (p < 0.05) with the biggest decrease in the control group and the smallest decrease in the salmon sausage intervention group.
    Nutrients, 2024 (VISA 2) · checked 2026-09-18 · independently re-checked
12. vitd-e2-03 · Randomised controlled trial(s) · randomised controlled trial
    After 16 weeks, both D2-UVB-mushroom entrée doses, which were significantly lower after cooking, produced modest or no increases in 25OHD2 or total 25OHD relative to the positive control subjects who actually consumed about 1242 and 7320 IU per day of D3 (higher than stated on the label).
    Calvo et al., European Journal of Clinical Nutrition, 2014 · checked 2026-09-18 · independently re-checked
13. vitd-e2-04 · Randomised controlled trial(s) · randomised controlled trial, authors' interpretation
    Unanticipated D2 cooking loss from fresh UVB mushrooms and probable low absorption and/or hydroxylation may explain the smaller increase in 25OHD2 in our prediabetic overweight/obese cohort compared with past findings in younger, healthy subjects.
    Calvo et al., European Journal of Clinical Nutrition, 2014 · checked 2026-09-18 · independently re-checked
14. vitd-e2-05 · Mechanistic or laboratory data · meta-analysis of food technology experiments
    For sliced Agaricus bisporus, an optimum was identified at 16,664 J/m2 and 3.2 W/m2, yielding 16.27 μg/g vitamin D₂ (95% CI: 13.69-18.85).
    Food Research International, 2026 · checked 2026-09-18 · independently re-checked
15. vitd-e2-07 · Randomised controlled trial(s) · systematic review
    Vitamin D was better absorbed when it was consumed with fat-containing meals, but absorption also occurred without fat or oily vehicles.
    Maurya & Aggarwal, Nutrition Reviews, 2018 · checked 2026-09-18 · independently re-checked
16. vitd-e2-10 · Randomised controlled trial(s) · randomised controlled trial, discussion of mechanism
    Hence, it seems that to date it still is an unsolved problem whether or not the different fatty acids influence vitamin D absorption.
    Nutrients, 2024 (VISA 2) · checked 2026-09-18 · independently re-checked
17. vitd-05 · Position of an expert body · expert body statement
    In children, vitamin D deficiency is manifested as rickets, a disease characterized by a failure of bone tissue to become properly mineralized, resulting in soft bones and skeletal deformities.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · extracted
18. vitd-06 · Position of an expert body · expert body statement
    In adults and adolescents, vitamin D deficiency can lead to osteomalacia, in which existing bone is incompletely or defectively mineralized during the remodeling process, resulting in weak bones.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · extracted
19. vitd-13 · Position of an expert body · expert body statement
    Individuals with a body mass index (BMI) of 30 or more have lower serum 25(OH)D levels
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · extracted
20. vitd-15 · Position of an expert body · expert body statement
    However, despite the importance of the sun for vitamin D synthesis, limiting skin exposure to sunlight and UV radiation from tanning beds is prudent. UV radiation is a carcinogen, and UV exposure is the most preventable cause of skin cancer.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
21. vitd-07 · Randomised controlled trial(s) · randomised trials cited by expert body
    Vitamin D supplementation did not lower the risk of total fractures, hip fractures, or nonvertebral fractures as compared with placebo.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
22. vitd-08 · Meta-analysis or systematic review · systematic review by expert body
    The USPSTF...concluded with moderate certainty that vitamin D supplementation does not reduce the numbers of falls or injuries, such as fractures, resulting from falls.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
23. vitd-09 · Randomised controlled trial(s) · clinical trials cited by expert body
    The results of clinical trials have generally failed to show that vitamin D supplementation with or without calcium supplementation reduces the incidence of cancer.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
24. vitd-10 · Randomised controlled trial(s) · randomised controlled trial
    The VITAL clinical trial...found that vitamin D supplements did not significantly decrease rates of heart attacks, strokes, coronary revascularization, or deaths from cardiovascular causes.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
25. vitd-b01 · Randomised controlled trial(s) · randomised controlled trial
    Supplemental vitamin D₃, as compared with placebo, did not have a significant effect on total fractures (which occurred in 769 of 12,927 participants in the vitamin D group and in 782 of 12,944 participants in the placebo group; hazard ratio, 0.98; 95% confidence interval [CI], 0.89 to 1.08; P = 0.70), nonvertebral fractures (hazard ratio, 0.97; 95% CI, 0.87 to 1.07; P = 0.50), or hip fractures (hazard ratio, 1.01; 95% CI, 0.70 to 1.47; P = 0.96).
    LeBoff et al., New England Journal of Medicine, 2022 · checked 2026-09-16 · independently re-checked
26. vitd-b04 · Meta-analysis or systematic review · meta-analysis of randomised trials
    In pooled analyses, vitamin D had no effect on total fracture (36 trials; n=44 790, relative risk 1·00, 95% CI 0·93-1·07), hip fracture (20 trials; n=36 655, 1·11, 0·97-1·26), or falls (37 trials; n=34 144, 0·97, 0·93-1·02). Results were similar in randomised controlled trials of high-dose versus low-dose vitamin D and in subgroup analyses of randomised controlled trials using doses greater than 800 IU per day. In pooled analyses, there were no clinically relevant between-group differences in bone mineral density at any site (range -0·16% to 0·76% over 1-5 years).
    Bolland, Grey and Avenell, The Lancet Diabetes & Endocrinology, 2018 · checked 2026-09-16 · independently re-checked
27. vitd-b05 · Meta-analysis or systematic review · Cochrane systematic review
    There is high quality evidence that vitamin D alone, in the formats and doses tested, is unlikely to be effective in preventing hip fracture (11 trials, 27,693 participants; risk ratio (RR) 1.12, 95% confidence intervals (CI) 0.98 to 1.29) or any new fracture (15 trials, 28,271 participants; RR 1.03, 95% CI 0.96 to 1.11).
    Avenell et al., Cochrane Database of Systematic Reviews, 2014 · checked 2026-09-16 · independently re-checked
28. vitd-b06 · Meta-analysis or systematic review · Cochrane systematic review
    There is high quality evidence that vitamin D plus calcium results in a small reduction in hip fracture risk (nine trials, 49,853 participants; RR 0.84, 95% confidence interval (CI) 0.74 to 0.96; P value 0.01). In low-risk populations (residents in the community: with an estimated eight hip fractures per 1000 per year), this equates to one fewer hip fracture per 1000 older adults per year (95% CI 0 to 2). In high risk populations (residents in institutions: with an estimated 54 hip fractures per 1000 per year), this equates to nine fewer hip fractures per 1000 older adults per year (95% CI 2 to 14).
    Avenell et al., Cochrane Database of Systematic Reviews, 2014 · checked 2026-09-16 · independently re-checked
29. vitd-r2-1 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised trials
    For the primary comparison of any vitamin D versus placebo, the intervention did not statistically significantly affect overall ARI risk (OR 0·94 [95% CI 0·88-1·00], p=0·057; 40 studies; 61 589 participants; I2=26·4%). Pre-specified subgroup analysis did not reveal evidence of effect modification by age, baseline vitamin D status, dosing frequency, or dose size.
    Jolliffe et al., The Lancet Diabetes & Endocrinology, 2025 · checked 2026-09-17 · independently re-checked
30. vitd-r2-2 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis
    Vitamin D supplementation may result in a slight reduction in the proportion of children who make ARI-related healthcare visits compared to placebo (risk ratio (RR) 0.95, 95% confidence interval (CI) 0.91 to 1.00; P = 0.03; 10 studies, 2447 participants; low-certainty evidence), but probably does not reduce the mean number of ARI-related healthcare visits per child (mean difference (MD) 0.07, 95% CI -0.06 to 0.20; P = 0.32; 3 studies, 561 participants; moderate-certainty evidence).
    van Arragon et al., Cochrane Database of Systematic Reviews, 2026 · checked 2026-09-17 · independently re-checked
31. vitd-r2-3 · Randomised controlled trial(s) · randomised controlled trial with meta-analysis
    T2D incidence (cases/1000py) at median follow-up of 5.3 y was 3.98 for vitamin D and 4.37 for placebo (hazard ratio [HR] = 0.91; 95% confidence interval [CI] = 0.76, 1.09). Results did not differ by age, sex, BMI, or baseline 25-hydroxyvitamin D, and vitamin D had no effect on glycemic traits at 2 years. Meta-analysis of 4 trials (n = 5205; 936 T2D cases) obtained HR = 0.89 (CI = 0.80, 0.99).
    Tobias et al., Nature Communications, 2025 · checked 2026-09-17 · independently re-checked
32. vitd-r2-4 · Randomised controlled trial(s) · randomised controlled trial
    Disease activity was observed in 94 patients (60.3%) in the vitamin D group and 109 patients (74.1%) in the placebo group (hazard ratio [HR], 0.66 [95% CI, 0.50-0.87]; P = .004), and median time to disease activity was longer in the vitamin D group (432 vs 224 days; log-rank P = .003).
    Thouvenot et al., JAMA, 2025 · checked 2026-09-17 · independently re-checked
33. vitd-r2-5 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis
    Compared to low/standard dose, high-dose vitamin D given to pregnant or breastfeeding women likely reduces the risk of childhood wheeze (RR 0.79, 95% CI 0.64 to 0.98; 3 studies, 1439 participants; moderate-certainty evidence), but likely results in little to no difference in childhood asthma, although the direction and magnitude of effect is similar to that for wheeze (RR 0.81, 95% CI 0.63 to 1.04; 2 studies, 1355 participants; moderate-certainty evidence).
    Patchen et al., Cochrane Database of Systematic Reviews, 2025 · checked 2026-09-17 · independently re-checked
34. vitd-c06 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised controlled trials
    There was no significant effect of vitamin D supplementation on differences in ARTI incidence in ethnic minority groups (OR, 1·40; 95 % CI: 0·70, 2·79; P = 0·34), nor African American (OR, 1·77; 95 % CI: 0·51, 6·19; P = 0·37) or Asian/Pacific (OR, 1·08; 95 % CI: 0·77, 2·68; P = 0·66) subgroups.
    Bournot et al., Public Health Nutrition, 2024 · checked 2026-09-17 · independently re-checked
35. vitd-e2-08 · Meta-analysis or systematic review · meta-analysis of randomised and non-randomised trials
    This meta-analysis suggests that calcifediol is more effective in increasing serum 25(OH)D concentrations compared to cholecalciferol.
    European Journal of Clinical Nutrition, 2025 · checked 2026-09-18 · independently re-checked
36. vitd-11 · Position of an expert body · expert body statement
    Excess amounts of vitamin D are toxic. Because vitamin D increases calcium absorption in the gastrointestinal tract, vitamin D toxicity results in marked hypercalcemia (total calcium greater than 11.1 mg/dL), hypercalciuria, and high serum 25(OH)D levels (typically >375 nmol/l [150 ng/mL]).
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · extracted
37. vitd-12 · Position of an expert body · expert body statement
    Signs and symptoms of toxicity are unlikely at daily intakes below 250 mcg (10,000 IU)
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin D · checked 2026-09-15 · independently re-checked
38. vitd-b10 · Randomised controlled trial(s) · randomised controlled trial
    At trial end, radial volumetric BMD was lower for the 4000 IU group (-3.9 mg HA/cm3 [95% CI, -6.5 to -1.3]) and 10 000 IU group (-7.5 mg HA/cm3 [95% CI, -10.1 to -5.0]) compared with the 400 IU group with mean percent change in volumetric BMD of -1.2% (400 IU group), -2.4% (4000 IU group), and -3.5% (10 000 IU group).
    Burt et al., JAMA, 2019 · checked 2026-09-16 · independently re-checked
39. vitd-b07 · Meta-analysis or systematic review · Cochrane systematic review
    Hypercalcaemia, which was usually mild (2.6 to 2.8 mmol/L), was more common in people receiving vitamin D or an analogue, with or without calcium (21 trials, 17,124 participants, RR 2.28, 95% CI 1.57 to 3.31)... There was also a small increased risk of gastrointestinal symptoms (15 trials, 47,761 participants, RR 1.04, 95% CI 1.00 to 1.08)... and a significant increase in renal disease (11 trials, 46,548 participants, RR 1.16, 95% CI 1.02 to 1.33).
    Avenell et al., Cochrane Database of Systematic Reviews, 2014 · checked 2026-09-16 · independently re-checked
40. vitd-e2-09 · Position of an expert body · expert body statement
    the UL for children aged 1-10 has been increased from 25µg a day to 50µg a day
    Upper intake levels reviewed for vitamin D and calcium, European Food Safety Authority, 2012 · checked 2026-09-18 · independently re-checked
41. vitd-17 · Position of an expert body · expert body statement
    The weight-loss drug orlistat (Xenical and alli), together with a reduced-fat diet, can reduce the absorption of vitamin D from food and supplements, leading to lower 25(OH)D levels.
    NIH Office of Dietary Supplements, Vitamin D - Health Professional Fact Sheet · checked 2026-09-16 · independently re-checked
42. vitd-18 · Position of an expert body · expert body statement
    Statin medications reduce cholesterol synthesis. Because endogenous vitamin D is derived from cholesterol, statins may also reduce vitamin D synthesis.
    NIH Office of Dietary Supplements, Vitamin D - Health Professional Fact Sheet · checked 2026-09-16 · independently re-checked