Not worth it for strength and health.
The label shows how strong the evidence is, not how big the effect is. Tap a claim to see its papers.
Small at best: effects were larger below 30 nmol/L and in people 65+, but in deficient young men lifting weights, 8000 IU/day added no strength or lean mass over 12 weeks.[1][2][3][4]
A 30-trial meta-analysis (mean age 61.1) found a small strength effect (SMD 0.17) concentrated in very deficient and older people; in deficient athletes the effect was small and not significant, and an RCT in deficient young trainees was null. Evidence mainly in other populations is Grade C.
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Vitamin D had a small positive effect on muscle strength, larger below 30 nmol/L and in people 65+, with no effect on muscle mass or power.
Vitamin D did not significantly improve maximal strength or power in athletes; effects were small below 75 nmol/L and trivial at or above it.
Many athletes risk vitamin D insufficiency; 800-2000 IU/day maintains status, higher short-term doses restore it in deficient athletes, and adequate status may lower stress-fracture risk.
In vitamin D deficient young men, 8000 IU/day during 12 weeks of resistance training did not add strength or lean mass versus placebo; placebo gained more on two exercises.
Promising: female navy recruits given 2000 mg calcium plus 800 IU vitamin D had 20% fewer stress fractures (5.3% vs 6.6%) during 8 weeks of basic training.[4][5]
One large RCT (5201 recruits) supports this and the IOC cites it, but it tested calcium and vitamin D together, in one population, and has not been replicated in athletes. A single trial is Grade C.
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Many athletes risk vitamin D insufficiency; 800-2000 IU/day maintains status, higher short-term doses restore it in deficient athletes, and adequate status may lower stress-fracture risk.
Female navy recruits given 2000 mg calcium and 800 IU vitamin D daily had 20% fewer stress fractures during basic training than those on placebo.
Not clearly: the updated 2025 meta-analysis of 40 trials (61,589 people) found OR 0.94 (95% CI 0.88-1.00), no longer statistically significant, with no added effect in deficient people.[4][6]
The earlier small protective effect lost significance once large new trials were added, and a funnel plot suggested small-study bias. The IOC gives it moderate support for athletes in winter. Mixed evidence is Grade C.
Each plate is one paper. Taller = stronger study design, wider = more studies pooled. Tap one.
With new large trials added, vitamin D no longer significantly reduced acute respiratory infections, with no stronger effect in deficient people or by dose.
Many athletes risk vitamin D insufficiency; 800-2000 IU/day maintains status, higher short-term doses restore it in deficient athletes, and adequate status may lower stress-fracture risk.
No meaningful effect: in athletes starting at or above 75 nmol/L the effect on power was trivial (SMD 0.15, not significant), and pooled strength across athlete trials was not significantly improved.[2][7][8][9][10]
Three meta-analyses of athlete RCTs found no significant overall strength effect, and a 54-trial meta-analysis in non-athletes found no benefit (with slightly worse knee-flexion strength). One isolated quadriceps result (SMD 0.57) does not change the overall null. Grade D.
Each plate is one paper. Taller = stronger study design, wider = more studies pooled. Tap one.
In non-athletes, vitamin D did not improve muscle strength, mass or physical performance, including in low-vitamin-D subgroups, and slightly worsened two measures.
Vitamin D did not significantly improve maximal strength or power in athletes; effects were small below 75 nmol/L and trivial at or above it.
In athletes, vitamin D3 raised blood 25(OH)D, but overall strength across four measures did not improve significantly; quadriceps contraction did improve.
Vitamin D3 brought athletes' blood levels to sufficiency, but bench press, quadriceps strength and overall strength did not improve significantly.
Vitamin D has a clear indication when deficiency is present, but limited evidence supports routine use in replete athletes.
No effect in the general population: vitamin D did not lower total fractures (RR 1.00), hip fractures or falls, or meaningfully change bone density, at high or low doses.[11][12]
A meta-analysis of 81 RCTs (53,537 people) and the 25,871-person VITAL trial both found no fracture benefit in adults not selected for deficiency. Good null trials is Grade D for this population.
Each plate is one paper. Taller = stronger study design, wider = more studies pooled. Tap one.
Vitamin D did not prevent total or hip fractures or falls, or meaningfully change bone density, with no difference between high and low doses.
In healthy adults 50+ not selected for deficiency, 2000 IU/day vitamin D3 for a median 5.3 years did not lower total, nonvertebral or hip fractures, regardless of baseline vitamin D level.
Vitamin D is a fat-soluble vitamin made in the skin from sunlight, which normally supplies about 90% of it; few foods are rich in it. In North America, average intake from food tends to be under 400 IU/day. Blood 25-hydroxyvitamin D (25(OH)D) is the marker of status.
Vitamin D regulates gene transcription in most tissues and is central to calcium absorption and bone health. Muscle cells respond to it too, so deficiency was expected to impair strength. In practice, giving vitamin D to people who already have adequate levels does not improve muscle function, and data on muscle and recovery are equivocal, probably because of differing starting levels.[4][9][13]
Reviewed 03 Oct 2026 · every PubMed ID checked against PubMed
RDA 600 IU/day (ages 1-70) and 800 IU/day (71+); the IOC suggests 800-2000 IU/day to maintain status. Do not exceed 4000 IU/day without medical supervision.
RDA; meets the needs of at least 97.5% of people (blood level of at least 20 ng/mL / 50 nmol/L).[13]
IOC range to maintain status in the general population.[4]
Raised insufficient athletes to 31.7 ng/mL without significant strength gains.[8]
Raised deficient young men from 36.3 to 142.4 nmol/L with no extra strength or lean mass.[3]
No difference in fracture, fall or bone-density effects.[11]
The stress-fracture reduction in recruits came from calcium (2000 mg) plus vitamin D (800 IU) together.[5]
Mega-dosing vitamin D builds strength.
8000 IU/day raised blood levels nearly fourfold in deficient lifters but added no strength or muscle.[3]
Everyone should get their vitamin D tested.
The Endocrine Society found no trial evidence supporting routine 25(OH)D screening and suggests against it without an established indication.[14]
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