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Research · Supplements

Vitamin D

In trials of people not selected for deficiency, vitamin D did not lower fractures, falls, cancer, cardiovascular events, depression or all-cause death. A 2025 update found no significant drop in respiratory infections. In prediabetes, diabetes onset fell by 15%. Hypercalcemia was more common on vitamin D, and very high doses were linked to more falls and lower bone density.

Add to Bio HackChecked 2026-11-12
Status
Dietary supplement in the US. Prescription high-dose forms also exist.
Also called
vitamin D3, cholecalciferol, vitamin D2, ergocalciferol, 25-hydroxyvitamin D, calcifediol, sunshine vitamin
Taken for
bone health, fractures, falls, immunity, colds and respiratory infections, muscle strength, heart health, cancer prevention, longevity, mood, depression, type 2 diabetes, blood sugar, pregnancy, testosterone, dementia, autoimmune disease, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, Crohn's disease, ulcerative colitis, psoriasis, lupus, teeth, cavities, gum disease, fibroids, period pain, PMS, PCOS, endometriosis pain

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help12

Reported risks3

What people take it for, and what was found

Shown to help12

Strong

Rheumatoid arthritis disease activity

Shown to lower disease activity modestly in adults with rheumatoid arthritis. Reviews disagree on CRP, ESR and pain.

The numbers and sources
Effect
Across 6 studies (438 patients), vitamin D lowered DAS28 (WMD -0.41, 95% CI -0.59 to -0.23), ESR (WMD -3.40) and tender joint count (WMD -1.44) against control [6]. Across 11 RCTs, it lowered pain scores (WMD -1.30) and DAS28-CRP (WMD -0.58, 95% CI -0.86 to -0.31), while CRP, ESR and HAQ did not change [7]. A third meta-analysis of 11 studies found lower DAS28 (WMD -0.83, 95% CI -1.38 to -0.28), CRP and ESR, with no change in HAQ or pain scores [8].
Population
Adults with rheumatoid arthritis in RCTs [6][7][8].
Sources
[6], [7], [8]
Caveats
The reviews disagree on CRP, ESR and pain, and heterogeneity was high [7].
Moderate

Depressive symptoms in people with depression

Shown to lower depressive symptom scores in adults with depression, in small trials with high heterogeneity.

The numbers and sources
Effect
Across 15 RCTs (962 participants diagnosed with depression), vitamin D lowered depressive symptom scores against placebo (SMD -0.98, 95% CI -1.28 to -0.68, I² 79%). The largest reductions were at daily doses up to 5,000 IU [26]. A Bayesian review of 7 studies found an SMD of -0.88 (95% credible interval -1.38 to -0.35) for vitamin D-containing supplements, with prediction intervals that crossed no effect [27].
Population
Adults with depressive disorders or clinically relevant depressive symptoms in randomized trials [26][27].
Sources
[26], [27]
Caveats
Heterogeneity was high in both reviews [26][27]. The Bayesian review also counted regimens that added other nutrients, so the two reviews do not answer exactly the same question [27]. The trials were small.
Moderate

Type 2 diabetes prevention

Shown to lower new type 2 diabetes about 15% in adults with prediabetes. In older adults not selected for prediabetes, VITAL found no significant difference.

The numbers and sources
Effect
In 3 trials of adults with prediabetes, vitamin D lowered new-onset diabetes by 15% (HR 0.85, 95% CI 0.75 to 0.96), a 3-year absolute risk reduction of 3.3%. Return to normal glucose regulation rose (rate ratio 1.30, 95% CI 1.16 to 1.46) [28]. In VITAL, among 22,220 older US adults not selected for prediabetes, type 2 diabetes incidence was 3.98 per 1,000 person-years on 2,000 IU a day and 4.37 on placebo (HR 0.91, 95% CI 0.76 to 1.09). Pooled with 3 earlier trials, the HR was 0.89 (95% CI 0.80 to 0.99) [29].
Population
Adults with prediabetes in trials of 20,000 IU a week, 4,000 IU a day or eldecalcitol [28]; US adults with mean age 67.2 over a median 5.3 years [29].
Sources
[28], [29]
Caveats
The two pooled analyses share most of their prediabetes trials. Results in prediabetes do not apply to the general population [28], where VITAL found no significant difference [29].
Moderate

Cavities in children

Shown to lower new cavities about half in children in older trials, rated low certainty. Vitamin D in pregnancy did not change cavities in one trial.

The numbers and sources
Effect
Across 24 controlled clinical trials (2,827 children), vitamin D given as D2, D3 or ultraviolet light lowered the rate of new cavities (relative rate 0.53, 95% CI 0.43 to 0.65), with no robust difference between the forms [43]. A 2024 Cochrane review found one trial of high-dose against low-dose vitamin D in pregnancy, with no clear difference in cavities in the children's baby teeth (RR 0.99, 95% CI 0.70 to 1.41, 496 children, very low certainty) [44]. In that trial, 2,400 IU a day from week 24 of pregnancy, on top of 400 IU standard care, was not associated with cavities at age 6 [45].
Population
Children in controlled trials, 22 of the 24 predating modern trial design [43]. Children of women in the COPSAC2010 pregnancy trial in Copenhagen [44][45].
Sources
[43], [44], [45]
Caveats
The older trials showed significant heterogeneity and publication bias, and the author rates the conclusion low certainty [43]. The newer finding comes from one pregnancy trial [44][45].
ModerateStudied in women

Fibroid size in women with fibroids

Shown to shrink fibroids slightly or slow their growth against placebo over 2 to 3 months in women with fibroids, most with low vitamin D, in small trials.

Compared with placebo [56][58][59]; controls the source abstract does not describe [57]

The numbers and sources
Effect
Across 5 randomized trials (511 participants), vitamin D lowered fibroid size against placebo (SMD -0.48, 95% CI -0.66 to -0.31), more in trials lasting over 8 weeks (SMD -0.62, 95% CI -0.88 to -0.37), and raised serum vitamin D (SMD 3.1, 95% CI 0.66 to 5.55) [56]. A second review of 3 trials (328 participants) found the percentage change in fibroid diameter or volume differed from controls by -5.7 over 2 to 6 months (95% CI -10.63 to -0.76, I² 99%). The trials gave 50,000 IU weekly for 8 or 12 weeks, or every 2 weeks for 10 weeks [57]. In one 12-week trial, fibroid volume did not fall significantly on vitamin D (MD -0.71, P 0.085) and rose on placebo (MD 2.53, P 0.001) [58]. After hysteroscopic removal of fibroids, 1,000 IU a day for 12 months halved recurrence against placebo, a difference that was not significant (P 0.17), and recurrent fibroids were 7.7 mm smaller (P < 0.001) [59].
Population
511 women with fibroids in 5 randomized trials [56]; 328 premenopausal women with fibroids and vitamin D insufficiency in 3 trials [57]; women with fibroids in a 12-week trial [58]; 109 women, mean age 37.9, after hysteroscopic myomectomy [59].
Sources
[56], [57], [58], [59]
Caveats
The trials were small and short, and heterogeneity was 99% in [57]. The two reviews share most of their trials. The abstracts do not report menstrual bleeding. The recurrence trial was a pilot, and its difference in recurrence was not significant [59].
ModerateStudied in women

Fewer fibroids with higher vitamin D levels

Linked to fewer fibroids with higher vitamin D levels. Women with fibroids had about 6 ng/mL less vitamin D than women without, in pooled observational studies.

Compared with women without fibroids [57][60][61]; women with 25-hydroxyvitamin D below 20 or 30 ng/mL [62]

The numbers and sources
Effect
Across 23 observational studies (5,650 participants), women with fibroids had lower serum vitamin D (MD -5.50 ng/mL, 95% CI -6.99 to -4.01, I² 87%) and higher odds of vitamin D deficiency (OR 3.71, 95% CI 1.90 to 7.24) [57]. Across 9 studies (1,730 participants), vitamin D was lower in women with fibroids (SMD -0.67, 95% CI -0.98 to -0.35), and the difference was not significant in the 2 studies from Africa [60]. Across 21 clinical studies, the difference was 5.90 ng/mL (I² 97.4%), and 26 of 29 studies found a link between low vitamin D and fibroids [61]. In a 5-year ultrasound cohort of Black women, 25-hydroxyvitamin D of 20 ng/mL or more was linked to 9.7% slower fibroid growth than below 20 ng/mL (95% CI -17.3% to -1.3%). At 30 ng/mL or more, new fibroids were 22% less common, an imprecise estimate (HR 0.78, 95% CI 0.47 to 1.30) [62].
Population
Premenopausal women in 23 observational studies [57]; 835 women with fibroids and 895 controls in 9 studies [60]; women in 21 pooled clinical studies [61]; 1,610 Black women aged 23 to 35 in Detroit, 73% below 20 ng/mL at enrollment [62].
Sources
[57], [60], [61], [62]
Caveats
Observational. Most studies measured vitamin D once in women with and without fibroids, so they cannot show which came first. Vitamin D levels vary with body weight, skin pigmentation and sun exposure, so confounding is possible. Heterogeneity was high [57][61]. The cohort adjusted for reproductive factors, body mass index and smoking, and only 7% of its women had 30 ng/mL or more [62].
Limited

Preventing autoimmune disease

One trial found about 22% less autoimmune disease over 5 years in older adults, and the difference was gone 2 years after the trial ended.

The numbers and sources
Effect
In VITAL, 2,000 IU a day for a median 5.3 years led to confirmed autoimmune disease in 123 people against 155 on placebo (HR 0.78, 95% CI 0.61 to 0.99, P 0.05). The outcome counted rheumatoid arthritis, polymyalgia rheumatica, autoimmune thyroid disease, psoriasis and others [48]. Two years after the trial ended, the difference was gone (HR 0.98, 95% CI 0.83 to 1.17 at 7 years) [49].
Population
25,871 US men 50 and older and women 55 and older, mean age 67.1 [48]. 21,592 followed for 2 more years [49].
Sources
[48], [49]
Caveats
Both sources are the same trial. Adding 65 newly confirmed cases from the randomized period changed the HR to 0.85 (95% CI 0.70 to 1.04) [49]. Participants were not selected for deficiency.
Why limited
This rests on one trial, of 25,871 people. Strength counts independent studies that agree, so one trial is limited at any size.
Limited

Enamel defects in children after vitamin D in pregnancy

One trial found about half as many enamel defects at age 6 in children of women given vitamin D in pregnancy, in an after-the-fact analysis.

The numbers and sources
Effect
Children of women given 2,400 IU a day of vitamin D3 from week 24 of pregnancy to 1 week after birth, on top of 400 IU standard care, had fewer enamel defects in permanent teeth at age 6 than children of women on placebo (15.1% against 27.5%, OR 0.47, 95% CI 0.27 to 0.81). The same held for baby teeth (8.6% against 15.9%, OR 0.50, 95% CI 0.28 to 0.87). Cavities did not differ [45].
Population
623 pregnant women in Copenhagen and 496 of their children examined at age 6 [45].
Sources
[45]
Caveats
A post hoc analysis of one trial designed for other outcomes [45].
StrongStudied in women

Period pain

Shown in three reviews to lower period pain more than placebo in women with primary dysmenorrhea, by about 1.1 to 1.6 points on a 10-point scale.

Compared with placebo or standard care [63]; placebo, in trials that had a placebo group [64]; placebo [65]

The numbers and sources
Effect
Across 8 RCTs (695 participants), vitamin D lowered pain more than placebo (SMD -1.404, 95% CI -2.078 to -0.731), with relief at average weekly doses over 50,000 IU [63]. Across 11 studies (687 participants), pain intensity fell 1.64 points more than in controls (95% CI 1.00 to 2.27, I² 79%), with moderate certainty. Pain fell in primary dysmenorrhea (MD -1.90) but not in the 3 trials of secondary dysmenorrhea [64]. A review of registered trials found pain 1.12 points lower than placebo on a visual analogue scale (95% CI 0.07 to 2.16, 5 studies, 308 participants), in the primary dysmenorrhea trials only [65].
Population
Women with primary dysmenorrhea in 8 RCTs [63]; women with regular periods and primary or secondary dysmenorrhea in 11 RCTs, 7 of them in Iran [64]; 7 registered RCTs in primary dysmenorrhea or endometriosis [65].
Sources
[63], [64], [65]
Caveats
Heterogeneity was high [64][65]. Doses and schedules varied widely, and the registered trials had high or some concerns of risk of bias [65]. The three reviews share many trials.
ModerateStudied in women

PMS symptoms

Shown in one review of 5 trials to lower overall PMS severity, physical symptoms and depression, at very low certainty. Anxiety, cravings and water retention did not change.

Compared with placebo or standard care [68]

The numbers and sources
Effect
Across 5 RCTs (436 participants), vitamin D lowered total PMS severity (SMD -0.78, 95% CI -1.30 to -0.26), physical symptoms (SMD -1.00, 95% CI -1.99 to -0.01) and depression (SMD -0.78, 95% CI -1.53 to -0.02). Anxiety, craving and water retention did not change, and no adverse events were reported [68].
Population
5 RCTs with 436 women with PMS [68].
Sources
[68]
Caveats
Certainty was rated very low, and heterogeneity was substantial. Four of the five trials had some concerns for risk of bias [68].
ModerateStudied in women

Ovulation, pregnancy and cycles in PCOS

Shown in one review to raise ovulation and pregnancy rates, and in another to make cycles more regular, in women with PCOS given vitamin D alongside other treatment.

Compared with placebo, metformin, short-acting contraceptives, ovulation drugs or assisted reproduction without vitamin D [69]; controls the source abstract does not describe [70]

The numbers and sources
Effect
Across 20 RCTs (1,961 women), adding vitamin D raised pregnancy rate (RR 1.44, 95% CI 1.28 to 1.62) and ovulation rate (RR 1.42, 95% CI 1.14 to 1.78) and lowered early miscarriage (RR 0.44, 95% CI 0.30 to 0.66) [69]. Across 12 studies (849 women), cycles became more regular (RR 1.35, 95% CI 1.18 to 1.54), with significant effects only above 4,000 IU a day, beyond 8 weeks, or with other supplements. LH fell (SMD -0.41) and FSH did not change [70].
Population
Women with PCOS seeking pregnancy, mean age about 29, most with low vitamin D at baseline [69]; 849 women with PCOS [70].
Sources
[69], [70]
Caveats
12 of the 20 trials in [69] were published in Chinese. In [69], vitamin D was added on top of the control treatment, so it measures an add-on effect. Each outcome rests on one review.
ModerateStudied in women

Blood sugar and insulin in PCOS

Shown in one review to lower fasting glucose and insulin slightly against placebo in women with PCOS. An earlier review found changes mainly with other nutrients.

Compared with placebo [71][72]

The numbers and sources
Effect
Across 13 RCTs (691 women), vitamin D lowered fasting glucose by 2.91 mg/dL (95% CI 1.04 to 4.78) and insulin by 1.98 µIU/mL (95% CI 0.64 to 3.32) more than placebo, with lower triglycerides, total cholesterol and LDL cholesterol [71]. An earlier review of 11 RCTs (601 women) found lower fasting glucose and HOMA-IR when vitamin D was given with other micronutrients, and lower HOMA-IR at doses under 4,000 IU a day [72].
Population
Women aged 18 and older with PCOS in 13 RCTs [71]; 601 women with PCOS in 11 RCTs [72].
Sources
[71], [72]
Caveats
The changes are small. The earlier review's abstract gives no effect size and does not report a significant effect for vitamin D alone at all doses [72].

Mixed results6

Moderate

Muscle strength

Shown to raise muscle strength slightly in older adults and those with low vitamin D, with no change in younger people. A newer review found no change.

The numbers and sources
Effect
Across 30 RCTs (5,615 people, mean age 61.1), vitamin D raised global muscle strength by an SMD of 0.17. Muscle mass (SMD 0.058) and power (SMD 0.057) did not change. The effect was larger with baseline 25-hydroxyvitamin D below 30 nmol/L and at 65 or older (SMD 0.25, 95% CI 0.01 to 0.48) than in younger people (SMD 0.03, 95% CI -0.08 to 0.14) [23]. Across 7 RCTs in adults 60 and older, vitamin D did not raise skeletal muscle mass index, lean mass or handgrip strength [24]. In 152 postmenopausal women with 25-hydroxyvitamin D below 30 ng/mL, 20 µg calcifediol or 3,200 IU vitamin D3 a day for 6 months did not differ from placebo on gait speed, knee strength and sit-to-stand tests (success in 53.6%, 55.5% and 61.4%) [25].
Population
Adults in 30 RCTs, with or without calcium [23]; adults with mean age 60 to 74 in 7 RCTs of 3 to 36 months [24]; women aged 50 to 70 with osteopenia or osteoporosis [25].
Sources
[23], [24], [25]
Caveats
An SMD of 0.17 is small, and the search for that review ended in January 2014 [23]. The newer review did not find a change in handgrip strength [24].
Moderate

Pregnancy outcomes

Mixed results: in pregnancy, one review found lower gestational diabetes and 53 g higher birth weight, while reviews disagree on preeclampsia and preterm birth.

The numbers and sources
Effect
Across 66 trials (17,276 participants, median dose 2,000 IU a day), vitamin D in pregnancy did not change preeclampsia (RR 0.81, 95% CI 0.43 to 1.53, 6 trials), lowered gestational diabetes (RR 0.65, 95% CI 0.49 to 0.86, 12 trials) and raised birth weight by 53 g (95% CI 16 to 90). Preterm birth, small for gestational age and low birth weight did not change [30]. An umbrella analysis of 35 studies (188,370 participants) found lower gestational diabetes (RR 0.68, 95% CI 0.53 to 0.88), preeclampsia (RR 0.62), preterm delivery (RR 0.77), low birth weight (RR 0.67), stillbirth (RR 0.77) and neonatal death (RR 0.58, 95% CI 0.40 to 0.84) [31].
Population
Pregnant women in RCTs of 400 to 60,000 IU [30]; pregnant women in pooled meta-analyses [31].
Sources
[30], [31]
Caveats
The two reviews disagree on preeclampsia, preterm birth and low birth weight. In the 66-trial review, 25 trials had at least one domain at high risk of bias and heterogeneity was high [30]. The umbrella analysis pooled published meta-analyses, which share trials [31].
Moderate

Multiple sclerosis

Mixed results: a Cochrane review found no change in relapses or disability in MS, while later analyses found modest drops in relapse and disability.

The numbers and sources
Effect
A Cochrane review of 12 RCTs (933 participants) found vitamin D3 did not change annualized relapse rate (rate difference -0.05, 95% CI -0.17 to 0.07), disability scores (EDSS MD -0.25, 95% CI -0.61 to 0.10) or MRI lesions at 52 weeks, from very low-quality evidence [33]. A later meta-analysis of 21 studies (1,903 patients) found lower EDSS (MD -0.17), fewer patients relapsing (OR 0.66) and fewer new T2 lesions, and no change in annualized relapse rate, fatigue or quality of life [34]. A network meta-analysis of 32 RCTs (2,254 patients) found lower relapse risk (RR 0.80) and EDSS (MD -0.22) with long-term supplementation [35]. In 316 people with a first episode typical of MS, 100,000 IU every 2 weeks for 24 months lowered disease activity (60.3% against 74.1%, HR 0.66, 95% CI 0.50 to 0.87), driven by MRI findings. Relapse did not differ (17.9% against 21.8%, HR 0.69, 95% CI 0.42 to 1.16) [36].
Population
Adults with MS, mostly on standard treatment [33][34][35]. Untreated adults with clinically isolated syndrome in France [36].
Sources
[33], [34], [35], [36]
Caveats
The Cochrane review and the later analyses disagree. The later analyses include more and newer trials, and their authors describe the effects as modest [34].
Moderate

Inflammatory bowel disease

Mixed results: one review found about 36% fewer relapses in inflammatory bowel disease, mostly Crohn's in remission, while another found no change in relapse or activity.

The numbers and sources
Effect
Across 7 RCTs (458 patients), vitamin D lowered clinical relapse against placebo (RR 0.64, 95% CI 0.46 to 0.89). In Crohn's disease in remission the RR was 0.47 (95% CI 0.27 to 0.82), and ulcerative colitis had only 2 studies (67 patients) [37]. In adults, the Harvey Bradshaw Index for Crohn's disease fell by 1.47 points (95% CI -2.47 to -0.47) and hs-CRP fell by 1.58 mg/L [38]. A meta-analysis of 17 trials (1,127 patients) found lower CRP (SMD -0.33) and no change in disease activity (SMD -0.13, 95% CI -0.66 to 0.39) or relapse (RR 0.59, 95% CI 0.19 to 1.86) [39].
Population
Adults with Crohn's disease or ulcerative colitis [37][38][39].
Sources
[37], [38], [39]
Caveats
The reviews disagree on relapse. Evidence for ulcerative colitis is thin [37].
Moderate

Lupus disease activity

Mixed results: an earlier review found no significant change in lupus activity, while later reviews found modestly lower activity in adults with lupus.

The numbers and sources
Effect
Across 5 RCTs (490 participants), SLEDAI disease activity scores did not differ significantly from placebo (SMD -0.507, 95% CI -1.055 to 0.041), and fatigue scores fell in 2 trials (SMD -1.179) [40]. Later meta-analyses found lower disease activity: SMD -0.54 across 10 RCTs (847 participants) [41], and SLEDAI MD -1 (95% CI -2 to -0.43) in a review of 21 studies [42].
Population
Adults with systemic lupus erythematosus [40][41][42].
Sources
[40], [41], [42]
Caveats
The earlier and later reviews disagree.
ModerateStudied in women

Endometriosis pain

Mixed results: three reviews found no significant drop in endometriosis pain on vitamin D, while one found less period pain in its vitamin D trials.

Compared with placebo [64][65][66][67]

The numbers and sources
Effect
Pain did not fall significantly in the 3 trials of secondary dysmenorrhea [64] or in the registered endometriosis trials [65]. A review of 13 RCTs found vitamin D lowered pelvic pain in endometriosis, a difference that was not significant against placebo [66]. A review of antioxidant supplements found less endometriosis-related period pain in the vitamin D trials (SMD -0.59, 95% CI -1.13 to -0.06, I² 70%) [67].
Population
3 RCTs in secondary dysmenorrhea [64]; registered RCTs in endometriosis [65]; 13 RCTs with 589 women with endometriosis [66]; 10 RCTs of antioxidant supplements in endometriosis [67].
Sources
[64], [65], [66], [67]
Caveats
Trials were few and small, and heterogeneity was high [67].

Not shown to help9

Strong

Fractures, falls and bone density

Not shown to lower fractures, hip fractures or falls in adults mostly not deficient or at high risk. Calcium with vitamin D had little to no effect.

The numbers and sources
Effect
Across 81 RCTs (53,537 participants), vitamin D had no effect on total fracture (RR 1.00, 95% CI 0.93 to 1.07), hip fracture (RR 1.11, 95% CI 0.97 to 1.26) or falls (RR 0.97, 95% CI 0.93 to 1.02). Results were similar for doses above 800 IU a day, and bone density differences ranged from -0.16% to 0.76% over 1 to 5 years [1]. A 2026 review of 69 trials (153,902 participants) found vitamin D alone did not change the risk of any fracture (RR 1.00, 95% CI 0.95 to 1.06, 36 trials, 92,045 participants, high certainty). Calcium with vitamin D gave RR 0.91 (95% CI 0.84 to 0.99, 15 trials), which the authors rated as little to no effect by absolute risk thresholds. Other fracture and fall outcomes showed little to no effect [2]. In VITAL, 2,000 IU a day for a median 5.3 years did not change total fractures (HR 0.98, 95% CI 0.89 to 1.08), nonvertebral fractures (HR 0.97) or hip fractures (HR 1.01, 95% CI 0.70 to 1.47) [3]. In the Finnish Vitamin D Trial, fractures were more frequent on 1,600 IU a day than placebo (HR 1.52, 95% CI 1.06 to 2.18) and did not differ on 3,200 IU a day (HR 1.07, 95% CI 0.72 to 1.58) over a mean 4.1 years [4]. Fall risk was 55% and fall-injury risk 11% in all three arms over 5 years [5].
Population
Adults in 81 trials [1]; adults not on osteoporosis drugs in 69 trials, 87% community dwelling and 73% not at high risk of fractures or falls [2]; 25,871 US men 50 and older and women 55 and older not selected for deficiency, low bone mass or osteoporosis [3]; 2,495 men 60 and older and women 65 and older in Finland, mean baseline 25-hydroxyvitamin D 75 nmol/L [4][5].
Sources
[1], [2], [3], [4], [5]
Caveats
Most participants were not selected for deficiency or high fracture risk, and evidence for high-risk people and residential care was limited [2]. The higher fracture count at 1,600 IU in the Finnish trial did not appear at 3,200 IU [4]. The bone density figures come from one review [1]. Trials that gave calcium with vitamin D were counted in [1] only where the groups differed by vitamin D alone.
Strong

Psoriasis severity

Not shown to lower psoriasis severity with oral vitamin D in adults. One small pooled effect lost significance after adjustment.

The numbers and sources
Effect
Across 3 trials, oral vitamin D lowered PASI at 6 months (MD -0.92, 95% CI -1.72 to -0.11), and the result lost significance after Hartung-Knapp adjustment (95% CI -2.21 to 0.38) [9]. Across 4 studies (333 patients), PASI, DLQI and CRP changes did not differ from control [10]. In 122 adults in Norway with low vitamin D, 100,000 IU then 20,000 IU a week for 4 months did not change PASI against placebo (adjusted difference 0.11, 95% CI -0.23 to 0.45) [11].
Population
Adults with plaque psoriasis [9][10][11].
Sources
[9], [10], [11]
Caveats
Baseline severity was low in the Norwegian trial (mean PASI 3.1) [11]. This concerns oral vitamin D, not topical vitamin D analogue creams.
Moderate

Respiratory infections

Not shown to clearly lower respiratory infections in people. An earlier review found one point fewer, which lost significance in a 2025 update.

The numbers and sources
Effect
Across 37 trials with primary outcome data (48,488 participants aged 0 to 95), 61.3% on vitamin D and 62.3% on placebo had one or more acute respiratory infections (OR 0.92, 95% CI 0.86 to 0.99, I² 35.6%) [12]. A 2025 update by the same group added 3 trials with 16,085 participants. Across 40 studies (61,589 participants), the effect was no longer statistically significant (OR 0.94, 95% CI 0.88 to 1.00, P 0.057, I² 26.4%), and age, baseline vitamin D status, dosing frequency and dose size did not modify it [13]. In 17 pediatric RCTs (18,372 children), infections did not fall significantly (RR 0.82, 95% CI 0.64 to 1.06), and daily doses of 1,000 IU or less had RR 0.42 (95% CI 0.27 to 0.66) [14]. A Cochrane review of children up to 5 found RR 0.95 (95% CI 0.91 to 1.00) for the share making infection-related healthcare visits, and no change in visits per child [15]. Across 6 RCTs (15,677 participants), tuberculosis infection (OR 0.95, 95% CI 0.79 to 1.14) and active tuberculosis (OR 0.77, 95% CI 0.56 to 1.05) did not differ from placebo [16]. In 1,747 adults newly diagnosed with COVID-19, a 4-week course did not change healthcare visits or death (28% against 29%, OR 0.97, 95% CI 0.75 to 1.24) [17].
Population
46 double-blind RCTs, 75,541 participants [12]; 40 placebo-controlled studies, 61,589 participants [13]; children in 17 RCTs [14] and 107 RCTs from pregnancy to age 5 (31,521 participants) [15]; people without active tuberculosis [16]; adults in the US and Mongolia [17].
Sources
[12], [13], [14], [15], [16], [17]
Caveats
The 2021 and 2025 analyses come from the same group and share most trials. The 2021 absolute difference was one percentage point [12]. The 2025 funnel plot was asymmetric (Egger P 0.002) [13]. The Cochrane result rests on low-certainty evidence [15].
Moderate

Cancer, cardiovascular disease and death

Not shown to lower cancer, cardiovascular disease or death in adults. Reviews disagree on cancer death, which one found about 16% lower.

The numbers and sources
Effect
In VITAL, invasive cancer did not differ (HR 0.96, 95% CI 0.88 to 1.06), nor did major cardiovascular events (HR 0.97, 95% CI 0.85 to 1.12) or death from any cause (HR 0.99, 95% CI 0.87 to 1.12). Cancer death had HR 0.83 (95% CI 0.67 to 1.02) [18]. Across 52 trials (75,454 participants), all-cause mortality did not change (RR 0.98, 95% CI 0.95 to 1.02) and cancer death fell (RR 0.84, 95% CI 0.74 to 0.95) [19]. Across 9 RCTs (114,379 participants), cardiovascular events (RR 0.95, 95% CI 0.88 to 1.04), cardiovascular death (RR 1.04, 95% CI 0.87 to 1.24) and heart attack (RR 0.96, 95% CI 0.83 to 1.11) did not differ from placebo [20]. Across 5 RCTs (56,901 participants), melanoma incidence (RR 0.94, 95% CI 0.71 to 1.24) and recurrence (HR 1.23, 95% CI 0.29 to 5.18) did not differ [21]. In 455 people starting chemotherapy for metastatic colorectal cancer, 4,000 IU a day after a loading dose did not change progression-free survival against 400 IU a day (median 11.8 against 10.3 months, P 0.25) or overall survival (25.6 against 27.0 months) [22].
Population
25,871 US adults over a median 5.3 years [18]; adults in 52 RCTs [19]; adults in 9 placebo-controlled RCTs [20]; adults in 5 RCTs, with or without calcium [21]; US adults with untreated metastatic colorectal cancer, median follow-up 20 months [22].
Sources
[18], [19], [20], [21], [22]
Caveats
The sources disagree on cancer death. VITAL's interval crossed 1.0 [18] and the pooled analysis did not [19]. Melanoma was a secondary endpoint in some trials and events were few [21].
ModerateStudied in men

Testosterone in men

Not shown to change testosterone in adult men.

The numbers and sources
Effect
Across 11 trial comparisons, vitamin D did not change total testosterone (MD 0.47 nmol/L, 95% CI -0.50 to 1.44, I² 24.1%), SHBG (MD 0.27 nmol/L, 95% CI -2.14 to 2.68) or free androgen index (MD -0.37, 95% CI -4.28 to 3.55) [32].
Population
Adult men in RCTs [32].
Sources
[32]
Caveats
GRADE certainty was low for total testosterone, SHBG and free androgen index, and very low for calculated free testosterone [32].
Moderate

Periodontitis alongside gum treatment

Not shown to change gum pocket depth when added to periodontal treatment in adults. One review found more benefit in people with low vitamin D.

The numbers and sources
Effect
In 3 studies that added vitamin D to non-surgical periodontal therapy, pocket depth did not change (MD 0.0023 mm, 95% CI -0.0378 to 0.0424) [46]. A review of 4 RCTs found limited added benefit in people with sufficient vitamin D, and greater pocket depth reduction, attachment gain and lower plaque and bleeding scores in deficient people whose levels were raised above 30 ng/mL [47].
Population
13 RCTs and 1 controlled trial, 3 of them pooled [46]. Adults with periodontitis in 4 RCTs [47].
Sources
[46], [47]
Caveats
Evidence was limited and heterogeneous [46]. The second review did not pool results [47].
Limited

Preventing depression

One trial found no change in the risk of depression over 5 years in adults 50 and older.

The numbers and sources
Effect
In VITAL, 2,000 IU a day for a median 5.3 years did not change the risk of depression or clinically relevant depressive symptoms (12.9 against 13.3 per 1,000 person-years, HR 0.97, 95% CI 0.87 to 1.09). Mood scores did not change (PHQ-8 difference 0.01 points, 95% CI -0.04 to 0.05) [50].
Population
18,353 US adults 50 and older, mean age 67.5, 16,657 of them with no history of depression [50].
Sources
[50]
Caveats
One trial. Participants were not selected for deficiency or for current depression [50].
Why limited
This rests on one trial, of 18,353 people. Strength counts independent studies that agree, so one trial is limited at any size.
Limited

Dementia

One trial found no clear difference in dementia over about 4 years in mostly vitamin D sufficient older adults, from few cases.

The numbers and sources
Effect
In the Finnish Vitamin D Trial, dementia was diagnosed in 18 people on placebo, 14 on 1,600 IU a day (HR 0.77, 95% CI 0.38 to 1.55) and 13 on 3,200 IU a day (HR 0.72, 95% CI 0.35 to 1.48) over a mean 4.2 years [51].
Population
2,492 adults in Finland free of dementia, mean age 68.2 [51].
Sources
[51]
Caveats
There were 45 cases in all, so the intervals are wide. Participants were largely vitamin D sufficient, with a mean baseline of 74.8 nmol/L [51].
Why limited
This rests on one trial, of 2,492 people. Strength counts independent studies that agree, so one trial is limited at any size.
ModerateStudied in women

Excess hair and androgens in PCOS

Not shown to change hair growth scores or SHBG in women with PCOS in one review. Total testosterone fell slightly against placebo.

Compared with placebo [73]; placebo, metformin, short-acting contraceptives, ovulation drugs or assisted reproduction without vitamin D [69]

The numbers and sources
Effect
Across 13 RCTs (840 women), modified Ferriman-Gallwey hair scores (MD 0.04, 95% CI -0.79 to 0.86) and SHBG (MD 1.33, 95% CI -2.70 to 5.36) did not differ from placebo. Total testosterone fell by 0.17 (95% CI 0.05 to 0.29) and serum vitamin D rose by 17.81 [73]. A review of add-on vitamin D in women seeking pregnancy also found lower androgen levels (MD -2.31, 95% CI -3.51 to -1.11) [69].
Population
840 women with PCOS in 13 RCTs [73]; 1,961 women with PCOS in 20 RCTs [69].
Sources
[73], [69]
Caveats
The abstract of [73] does not give units for testosterone or vitamin D. The hair score result rests on one review.

Doses studied

VITAL gave 2,000 IU a day [3][18]. The Finnish Vitamin D Trial gave 1,600 or 3,200 IU a day for 5 years [4]. The 2021 respiratory infection subgroup with an effect used daily equivalents of 400 to 1,000 IU [12], and the 2025 update found no difference by dose size [13]. The prediabetes trials used 20,000 IU a week or 4,000 IU a day [28]. A Calgary trial compared 400, 4,000 and 10,000 IU a day for 3 years [52]. An Australian trial gave a single 500,000 IU dose each autumn or winter for 3 to 5 years [53]. The MS trial in France gave 100,000 IU every 2 weeks for 24 months [36], and the Norwegian psoriasis trial gave 100,000 IU once and then 20,000 IU a week [11].

Risks

Reported risks3

ModerateHow often is not known

Hypercalcemia and hypercalciuria

Shown to raise high blood calcium about 54% and high urine calcium about 64% in long-term trials of adults. Kidney stones did not rise.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In 48 studies (19,833 participants) lasting 24 weeks or more, vitamin D raised the risk of hypercalcemia (RR 1.54, 95% CI 1.09 to 2.18, 37 studies) and hypercalciuria (RR 1.64, 95% CI 1.06 to 2.53, 14 studies). Kidney stones did not rise (RR 0.66, 95% CI 0.41 to 1.09, 9 trials). The risk was not modified by dose, duration, baseline level or calcium co-supplementation [54]. In 11 RCTs of 10,000 IU a day or more in people with MS, calcium disturbances were rare and transient [55]. In children up to 5, hypercalcemia did not differ from placebo (RR 0.81, 95% CI 0.53 to 1.24, very low certainty) [15].
Population
Adults in long-term RCTs [54]; adults with MS [55]; pregnant women and young children [15].
Sources
[54], [55], [15]
Caveats
VITAL reported no excess hypercalcemia at 2,000 IU a day [18].
LimitedStudied in womenHow often is not known

Falls and fractures with annual mega-doses

One trial found a yearly 500,000 IU dose raised falls about 15% and fractures about 26% in women aged 70 and older.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In 2,256 women aged 70 and older, an annual oral dose of 500,000 IU raised falls (rate 83.4 versus 72.7 per 100 person-years, IRR 1.15, 95% CI 1.02 to 1.30) and fractures (IRR 1.26, 95% CI 1.00 to 1.59). The fall rate ratio was 1.31 in the first 3 months after dosing [53].
Population
Community-dwelling older women at high fracture risk, 3 to 5 years [53].
Sources
[53]
Caveats
One trial of a single large yearly dose. It does not test daily dosing.
LimitedHow often is not known

Lower bone density at 4,000 and 10,000 IU a day

One trial found lower forearm bone density after 3 years at 4,000 and 10,000 IU a day than at 400 IU, in adults 55 to 70. Strength did not differ.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Compared with 400 IU a day, radial volumetric bone density after 3 years was lower with 4,000 IU (-3.9 mg HA/cm³, 95% CI -6.5 to -1.3) and 10,000 IU (-7.5 mg HA/cm³, 95% CI -10.1 to -5.0). Tibial density was lower only at 10,000 IU. Bone strength did not differ [52].
Population
311 healthy adults aged 55 to 70 without osteoporosis, Calgary [52].
Sources
[52]
Caveats
One single-center trial. Bone strength, the co-primary outcome, did not change.

Claims tested and not found

  1. That vitamin D prevents fractures in the general population. Total fracture did not change across 36 trials (RR 1.00) [1], in a 2026 review of 36 vitamin D trials (RR 1.00) [2] or in VITAL (HR 0.98) [3].
  2. That vitamin D prevents falls. Falls did not change in pooled trials (RR 0.97) [1], and fall risk was 55% in every arm of the Finnish trial [5].
  3. That vitamin D prevents cancer or heart disease. Invasive cancer and major cardiovascular events did not differ from placebo in VITAL [18], and cardiovascular events did not differ across 9 RCTs (RR 0.95) [20].
  4. That vitamin D builds muscle. Muscle mass did not change in pooled trials (SMD 0.058) [23], nor did muscle mass index or lean mass in adults 60 and older [24].
  5. That oral vitamin D lowers psoriasis severity. PASI did not change against placebo in a 122-person trial [11] or in a meta-analysis of 4 studies [10].
  6. That vitamin D raises testosterone. Total testosterone did not change across 11 trial comparisons (MD 0.47 nmol/L, 95% CI -0.50 to 1.44) [32].
  7. That vitamin D prevents depression in older adults. Depression risk did not differ from placebo in 18,353 adults over 5.3 years (HR 0.97) [50].
  8. That vitamin D in pregnancy prevents cavities in children. Cavities in baby teeth did not differ between high and low doses [44], and cavities at age 6 were not associated with high-dose supplementation [45].

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