Do you need a vitamin D supplement?

Large trials find vitamin D pills rarely prevent fractures, colds, heart events or early death. Who might benefit, and where the limits are.

Published October 2026

Short answer

In large trials of mostly healthy adults, vitamin D showed no clear gain for bones, heart, infections or early death. The clearest benefit is in prediabetes. Evidence grade B (Moderate). Meta-analyses of randomised trials on fractures, deaths and heart events; downgraded for inconsistency because cancer and mood results vary between reviews.

Key takeaways

Across 36 trials of vitamin D alone, with 92,045 people, fracture risk was unchanged [1].
Across 52 trials with 75,454 people, vitamin D did not lower overall death risk [2].
In five trials, vitamin D did not significantly reduce major cardiovascular events, stroke or cardiovascular death [3].
Taking 3,200 to 4,000 IU a day for six months or longer raised the risk of high blood calcium, falls and hospital stays [4].

The short version

Large trials have not shown that vitamin D supplements prevent fractures, heart events, infections or early death [1] [2] [3] [5]. The clearest benefit so far is a lower chance of developing type 2 diabetes in people with prediabetes [6]. Whether a supplement makes sense depends on your health and blood level, so talk to a doctor.

What the studies show

Fractures and falls. Across 36 trials of vitamin D alone, with 92,045 people, fracture risk was unchanged [1]. Calcium, vitamin D or both had little to no effect on falls [1].

Death and cancer. Across 52 trials with 75,454 people, vitamin D did not lower deaths from any cause, but it reduced cancer deaths by 16% in that review [2]. A later review of 14 trials (104,727 people) found a smaller, non-significant 6% reduction overall, and about 12% in the 10 trials that used daily dosing [7].

Heart and blood vessels. Five randomised trials found no significant reduction in major cardiovascular events, stroke or cardiovascular death [3].

Infections. A 2025 meta-analysis of 40 trials with 61,589 people found no statistically significant protection against acute respiratory infections (odds ratio 0.94, 95% confidence interval 0.88 to 1.00) [5].

Blood sugar. In three trials of people with prediabetes, vitamin D lowered the risk of type 2 diabetes by 15%, a 3.3 percentage-point absolute reduction over three years [6].

Autoimmune disease. In the VITAL trial of 25,871 people (men aged 50 and older, women aged 55 and older), 2,000 IU a day for a median of 5.3 years reduced confirmed autoimmune diseases by 22% (hazard ratio 0.78, 95% confidence interval 0.61 to 0.99) [8]. This is one trial, and its confidence interval nearly includes no effect.

Mood. Across 31 trials with 24,189 people, vitamin D3 produced a slight reduction in depressive symptoms [9].

The nuances

Who is short. A pooled analysis of 308 population studies, covering 7.9 million people in 81 countries, estimated that about 16% of people had a blood level below 30 nmol/L and about 48% were below 50 nmol/L [10]. Low levels were more common at high latitudes, in winter and spring, and in women [10]. The study reports several cut-offs, so the share called deficient depends on which one is used [10].

Doses and blood levels. The diabetes trials gave vitamin D3 at 4,000 IU a day or 20,000 IU a week, and one used eldecalcitol, a related compound [6]. In a post hoc comparison within the vitamin D group, people whose levels stayed at 50 ng/mL or above had a 76% lower diabetes risk than those at 20 to 29 ng/mL. That was not a randomised comparison [6].

Body weight. An earlier review of eight trials found the diabetes benefit in people without obesity (risk ratio 0.73), but not in people with obesity (risk ratio 0.95) [11].

Mood effects fade. The mood effect was larger in people with depression, but trials lasting longer than a year showed no effect [9].

Large occasional doses. In women aged 70 and older at high fracture risk, one 500,000 IU dose each year increased falls and fractures compared with placebo (fracture rate ratio 1.26) [12].

What this means for you

The benefits above came from doses of 2,000 IU a day [8] or 4,000 IU a day, or 20,000 IU a week [6]. The upper tolerable intake for the general population is 4,000 IU a day [4]. In a review of 22 trials lasting six months or longer, 3,200 to 4,000 IU a day raised the risk of high blood calcium (risk ratio 2.21, about 4 cases per 1,000 people), and also raised falls and hospital stays [4]. The authors judged safety reporting in these trials to be incomplete [4].

In adults with chronic kidney disease, vitamin D therapy raised blood calcium and did not reduce deaths from any cause [13]. A 2024 Cochrane review of 10 pregnancy trials found the evidence on pre-eclampsia and preterm birth very uncertain [14].

This article does not cover interactions with medicines; check with a pharmacist or doctor. The Vitamin D page lists the wider safety picture.

Go deeper

Vitamin D — In people with prediabetes, vitamin D supplements lower the chance of developing type 2 diabetes.