Question explored with the scientific record
Is it worth taking vitamin d supplements
The short version: vitamin D is worth taking mainly if you are deficient, and the evidence for it preventing disease in healthy adults is weak.
The strongest case is for people with low blood levels. In US adults aged 50 to 79, about 1 in 5 were deficient, and deficiency was tied to higher death rates [9]. In Irish adults over 50, insufficient levels tracked with roughly double the odds of death [10]. But that is correlation, not proof that a pill fixes it.
The trial record is sobering. Mega-trials found no reduction in heart attacks, cancer, or falls from vitamin D [3]. A 2024 meta-analysis of 12 trials found no reduction in respiratory infections in older adults [8]. For fractures, results are mixed: some trials show benefit in deficient elderly [4], others show none [1][2]. Daily dosing at 800 to 1,000 IU was linked to fewer fractures, while higher doses were not [5].
| Outcome | What the trials show |
|---|---|
| Heart disease | No reduction [3] |
| Cancer death | Possible 13 to 17% reduction [3] |
| Falls | Mixed; daily dosing may help [5][6] |
| Fractures | Benefit mainly in deficient elderly [4][5] |
| Respiratory infections | No reduction [8] |
Dose matters. Very high doses caused more hypercalciuria, a calcium-in-urine problem [7]. The safe zone appears to be moderate daily dosing, not giant occasional boluses.
My call: worth it if you are deficient or at high risk (older, dark-skinned, little sun), at a moderate daily dose; not worth it as a blanket supplement for healthy adults expecting disease prevention. Confidence: moderate.
Sources used 10
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Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults
This systematic review and meta-analysis found no significant association between calcium or vitamin D supplementation and fracture incidence in community-dwelling older adults, suggesting that these supplements should not be routinely recommended for fracture prevention in this…
DOI: 10.1001/jama.2017.19344 -
Vitamin D supplementation and the prevention of fractures and falls: results of a randomised trial in elderly people in residential accommodation
This study investigates the effect of vitamin D supplementation on the incidence of fractures and falls among elderly residents in care homes, finding no significant reduction in either outcome compared to a control group.
DOI: 10.1093/ageing/afj080 -
Is There Proof of Extraskeletal Benefits From Vitamin D Supplementation From Recent Mega Trials of Vitamin D?
The review of seven recent vitamin D mega-trials (four published: CAPS, ViDA, VITAL, DO-HEALTH) finds no prevention of hard-disease endpoints such as CVD, cancer, fractures, or falls—aside from a possible 13–17% reduction in cancer mortality—while showing benefits for intermedia…
DOI: 10.1002/jbm4.10459 -
Efficacy and safety of calcium and vitamin D supplementation to prevent osteoporotic fracture
Calcium and vitamin D supplementation may prevent osteoporotic fractures in deficient elderly, but evidence is conflicting; low-dose 800–1,000 mg calcium and 800–1,000 IU vitamin D are recommended, avoiding high-dose harms.
DOI: 10.5124/jkma.2021.64.4.305 -
Effect of Vitamin D Supplementation on Risk of Fractures and Falls According to Dosage and Interval: A Meta-Analysis
In 32 RCTs, daily vitamin D 800-1,000 IU/day was associated with lower osteoporotic fracture and fall risk, and daily administration and vitamin D deficiency were associated with lower fall risk; overall fracture effects were null and falls were reduced.
DOI: 10.3803/enm.2021.1374 -
Efficacy of Vitamin D Supplementation on the Risk of Falls Among Community-Dwelling Older Adults: A Systematic Review and Meta-Analysis
A comprehensive systematic review and meta-analysis of 10 randomized trials (23,211 participants) examining whether vitamin D supplementation reduces falls among community-dwelling adults aged 65 and older, finding no significant overall effect but nuanced subgroup signals by se…
DOI: 10.3390/jcm14176117 -
The complex relationship between vitamin D and kidney stones: balance, risks, and prevention strategies
Vitamin D deficiency and excess may both raise kidney stone risk via calcium–phosphorus metabolism, yet trial evidence on supplementation is contradictory and moderate doses under 4,000 IU/day appear generally safe.
DOI: 10.3389/fnut.2024.1435403 -
Vitamin D supplementation for prevention of acute respiratory infections in older adults: A systematic review and meta-analysis
Meta-analysis of 12 RCTs found that vitamin D supplementation probably does not reduce acute respiratory infection incidence in older adults (RR 0.99; 95% CI 0.97-1.02; moderate certainty), with no significant subgroup effects and no significant safety differences.
DOI: 10.1371/journal.pone.0303495 -
Prevalence of vitamin D deficiency and associated risk of all-cause and cause-specific mortality among middle-aged and older adults in the United States
Among US non-institutional adults aged 50–79, about one-fifth had vitamin D deficiency; deficiency (<50 nmol/L), but not insufficiency (50–75 nmol/L), was associated with higher all-cause and pneumonia mortality.
DOI: 10.3389/fnut.2023.1163737 -
Vitamin D and all-cause mortality in older adults > 50 years - data from The Irish Longitudinal Study of Ageing
Insufficient baseline 25-hydroxyvitamin D is associated with increased odds of all-cause mortality in community-dwelling Irish adults over 50.
DOI: 10.1017/s0029665120000610