Vitamin D
Vitamin D supplementation is strongly supported for deficiency correction: supplemental D3 reliably raises serum 25(OH)D in deficient individuals, with roughly 100 IU per day raising levels by approximately 1 ng/mL; this relationship is mechanistic, dose-dependent, and not contested (Grade A; PMID 26183416). For bone health and fracture reduction, vitamin D alone shows no consistent fracture-risk reduction; combined with adequate calcium (400-800 IU D3 plus 1,000-1,200 mg calcium), the evidence supports a modest 6% reduction in any fracture and 16% reduction in hip fracture in older deficient populations (PMID 31860103; Grade B). Primary prevention of cancer and cardiovascular disease is NOT supported by the best available evidence: the VITAL trial (25,871 participants, 5.3-year follow-up, PMID 30415629) found no reduction in cancer incidence (HR 0.96, p=0.47) or major cardiovascular events (HR 0.97, p=0.69) at 2,000 IU D3 per day; this is a pre-specified primary endpoint result, not a post-hoc analysis (Grade D). Falls prevention evidence is mixed and dose-dependent: high-dose daily vitamin D (at least 700 IU) combined with calcium reduced fall risk by 17% in a 38-RCT meta-analysis (PMC 9399608), but low-dose and bolus dosing show no significant effect; benefit is primarily relevant to older adults with baseline deficiency (Grade C). Label accuracy is a specific concern: the LeBlanc 2013 JAMA Internal Medicine study (PMID 23400578) found OTC cholecalciferol products ranged from 52% to 135% of labeled dose, and ConsumerLab 2024 testing found products delivering up to 200% of labeled dose, which raises hypercalcemia risk for consumers already taking multiple D-containing supplements.
Vitamin D is fat-soluble and accumulates in body fat; unlike water-soluble vitamins, excess is not readily excreted. The NIH Tolerable Upper Intake Level for adults is 4,000 IU per day. Chronic high-dose supplementation above this level raises hypercalcemia risk. Hypervitaminosis D causes hypercalcemia, hypercalciuria, and at extreme levels (serum 25(OH)D above approximately 375 nmol/L or 150 ng/mL) can lead to soft tissue calcification, cardiac arrhythmia, and renal failure. Toxicity is almost always supplement-driven rather than diet- or sun-driven. The risk is compounded when consumers take multiple D-containing products (multivitamins, calcium+D combinations, standalone D3) without tracking aggregate daily intake, and when products deliver more than their labeled dose. Serum 25(OH)D testing before starting supplementation is the most defensible approach to dosing. Not a treatment for any disease.
Full safety details belowEvidence by use
Each use graded independently. A strong grade for one use does not carry over to others.
Strong, consistent human trials.
Moderate evidence; some gaps remain.
Preclinical or weak. Not established in people.
Emerging and mixed. Not settled.
Vitamin D is fat-soluble and accumulates in body fat; unlike water-soluble vitamins, excess is not readily excreted. The NIH Tolerable Upper Intake Level for adults is 4,000 IU per day. Chronic high-dose supplementation above this level raises hypercalcemia risk. Hypervitaminosis D causes hypercalcemia, hypercalciuria, and at extreme levels (serum 25(OH)D above approximately 375 nmol/L or 150 ng/mL) can lead to soft tissue calcification, cardiac arrhythmia, and renal failure. Toxicity is almost always supplement-driven rather than diet- or sun-driven. The risk is compounded when consumers take multiple D-containing products (multivitamins, calcium+D combinations, standalone D3) without tracking aggregate daily intake, and when products deliver more than their labeled dose. Serum 25(OH)D testing before starting supplementation is the most defensible approach to dosing. Not a treatment for any disease.
Who takes it and why
Each expert's dose and stated reason, linked to their own words. Attribution only; no endorsement implied.
Photo: Jamesbrianbounds, CC BY-SA 4.0, via Wikimedia Commons ↗Blood level testing is the correct approach; dose should be calibrated to individual serum 25(OH)D levels rather than universally prescribed. Covers vitamin D with bloodwork guidance.
www.hubermanlab.com ↗Attribution only; no endorsement implied.
Photo: Jop van Velthuis, CC BY-SA 4.0, via Wikimedia Commons ↗Critiques standard trials for using insufficient doses (2,000 IU) that may not meaningfully shift blood levels; advocates individualized measurement-driven dosing rather than universal supplementation. Either no supplementation (if levels are adequate) or 5,000 IU if supplementation is warranted.
peterattiamd.com ↗Attribution only; no endorsement implied.
Vitamin D functions as a steroid hormone, not a simple nutrient. Genetic variation in vitamin D metabolism makes testing essential. 70% of U.S. population has inadequate levels (below 30 ng/mL). Blood level target of 40-60 ng/mL based on all-cause mortality meta-analyses. 2,000 IU prevents and treats deficiency per large RCT review.
www.foundmyfitness.com ↗Attribution only; no endorsement implied.
Photo: M Robertson, CC BY 4.0, via Wikimedia Commons ↗Blueprint focuses on biomarker-driven dosing rather than universal recommendations; Johnson has documented interest in vitamin D monitoring as part of his longevity protocol. Note: his personal daily dose is not explicitly stated in the public protocol document; 2,000 IU appears for a specific sub-population.
blueprint.bryanjohnson.com ↗Attribution only; no endorsement implied.
Which Vitamin D should you buy?
The short version: plain vitamin d is the most-studied and least-expensive form, and any product that is third-party certified is a safe bet. Certification (NSF Certified for Sport or USP Verified) screens for banned substances and confirms the label matches what is in the bottle. Here are recognizable brands that carry it. We do not certify products and take no payment to list them.
16 Vitamin D products are third-party certified in total. See the full list →
Published lab tests on Vitamin D
These studies test the ingredient category, not a single branded product. All attributed to their original source. We do not run the tests.
OTC vitamin D pills contained 52% to 135% of the labeled dose. Compounded tablets ranged from 9% to 146% of label. Just over half of OTC pills and only one-third of compounded pills met USP Convention potency standards. Variation occurred not only across brands but across individual pills within the same bottle. The single bottle from a USP-verified manufacturer was substantially more accurate than all others.
Two products contained up to twice the vitamin D amount listed on the label, raising hypercalcemia risk at high chronic doses. Doses across tested products ranged from 960 IU to 6,760 IU per serving; cost per 25 mcg dose ranged from 1 cent to $1.75.
Sources
- Over-the-counter and compounded vitamin D: is potency what we expect? (2013) observational
- Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease (2019) rct
- Vitamin D and Calcium for the Prevention of Fracture: A Systematic Review and Meta-analysis (2019) review
- Supplementation of vitamin D isolated or calcium-associated with bone remodeling and fracture risk in postmenopausal women without osteoporosis: A systematic review of randomized clinical trials (2023) review
- Effect of Vitamin D on falls: a meta-analysis (2004) review
- Association Between Vitamin D Supplementation and Fall Prevention (2022) review