VITAMIN D AFTER 50: WHAT THE BIG TRIALS ACTUALLY FOUND

Vitamin D was supposed to be the easy one. Cheap, safe, nearly universal — a pill that fixed bones, muscle, falls, and mortality all at once. Then the large randomized trials came in, and the story got a lot more specific and a lot less generous.

The claim that broke first: fractures

The single largest test of vitamin D for bone health is an ancillary study of the VITAL trial, published in the New England Journal of Medicine in 2022. It followed 25,871 adults — men 50 and older, women 55 and older — randomized to 2,000 IU of vitamin D3 daily or placebo, and tracked fractures.

The result was flatly null. Total fractures occurred in 769 of 12,927 participants on vitamin D and 782 of 12,944 on placebo — a hazard ratio of 0.98 (95% CI 0.89 to 1.08). Nonvertebral fractures: no effect. Hip fractures: no effect (HR 1.01). And critically, there was no subgroup that did better — not by age, not by sex, not by BMI, and not by baseline vitamin D level.

That last detail is the one most people skip. The usual defense of a null supplement trial is "they enrolled people who weren't deficient." VITAL looked, and the answer did not change.

What VITAL doesn't say: it enrolled a generally healthy population that was not selected for deficiency, low bone density, or osteoporosis. It is strong evidence against blanket supplementation in healthy adults for fracture prevention. It is not evidence about a genuinely deficient patient, or someone being treated for osteoporosis under a physician's care.

The claim that got stranger: falls

Falls looked like vitamin D's most defensible use case. The evidence there is now shaped like an upside-down U — and the top of the curve is lower than the supplement aisle would suggest.

The clearest single trial is STURDY, published in Annals of Internal Medicine in 2021. It enrolled 688 adults aged 70 and older who were at elevated fall risk and had 25(OH)D levels between 25 and 72.5 nmol/L, then randomized them to four daily doses: 200 IU as the control, or 1,000, 2,000, or 4,000 IU.

Higher doses did not prevent falls. They looked worse. Compared with 1,000 IU, the 2,000 and 4,000 IU arms had higher event rates (hazard ratios 1.86 and 1.68). And serious falls — including falls resulting in hospitalization — occurred more often in everyone assigned 1,000 IU or more than in the 200 IU control group.

The dose-response relationship for vitamin D and falls appears to be J-shaped: low doses do nothing measurable, moderate doses may help, and high doses appear to cause harm.

Meta-analyses land in the same place from the other direction. Pooled data associate roughly 800 to 1,000 IU per day with lower fall risk, while intakes above 1,000 IU per day have been associated with an increased risk of first-time falls with fracture in community-dwelling older adults. High-dose intermittent regimens — the monthly or quarterly mega-dose approach — have not reduced falls, fractures, or all-cause mortality.

The practical translation for anyone over 50 currently taking 5,000 or 10,000 IU because more seemed safer: that is not a conservative choice. It is the arm of the trial that did worse.

The claim athletes care about: strength and performance

Low vitamin D genuinely is common in athletes — a systematic review found 56 percent had inadequate levels, and prevalence rises sharply in winter (one review of para-athletes found 74 percent insufficient in winter versus 57 percent in summer). Indoor training, northern latitude, and diligent sunscreen use all push the same direction.

Common is not the same as consequential, though. The most relevant test is a 2024 systematic review and meta-analysis in Frontiers in Nutrition: 10 randomized controlled trials, 318 athletes, measuring vitamin D3 supplementation against four strength outcomes.

• Overall strength: SMD 0.18 (95% CI −0.02 to 0.37), p = 0.08 — not significant.
• 1-RM bench press: SMD −0.15, p = 0.47 — nothing.
• Handgrip: SMD 0.21, p = 0.35 — nothing.
• Vertical jump: SMD 0.21, p = 0.17 — nothing.
• Quadriceps contraction: SMD 0.57, p = 0.04 — the one significant finding.

The authors' own conclusion is worth reading carefully: supplementation reliably raised blood levels, but "cannot warrant significant overall enhancements in muscle strength when athletes attain adequate serum 25(OH)D levels through supplementation."

A separate 2024 meta-analysis of active vitamin D analogues in older adults found the same narrow pattern — no improvement in global muscle strength, handgrip, or back extensor strength, but a real effect on quadriceps strength. Two independent evidence bases converging on quadriceps specifically is interesting. It is also a long way from "vitamin D makes you stronger."

What the evidence actually supports

Strip out the overreach and a defensible position remains — it is just much narrower than the marketing.

Correcting a measured deficiency is worth doing. That is a different intervention from supplementing a normal level and expecting a bonus. Nearly all the disappointing trial results above involve the second thing.

Test before you dose. A 25(OH)D level is an inexpensive, widely available blood test, and it converts this entire question from guesswork into a number. If you train indoors, live at northern latitude, or are reading this in winter, your prior probability of being low is genuinely high — and you can stop guessing for the price of one lab panel.

If you supplement without a test, stay modest. The dose range with support in the fall literature is roughly 800 to 1,000 IU per day. That is also the range that shows up in mainstream intake guidance for older adults. The 5,000+ IU habit has no trial supporting it and one good trial suggesting harm.

Skip the mega-dose schedule. Monthly or quarterly bolus dosing has repeatedly failed to help and is the pattern most associated with harm signals.

Do not expect it to replace the thing that actually works. For strength, falls, and bone loading after 50, the intervention with the deep evidence base is resistance training. Vitamin D is, at best, making sure a deficiency is not holding that work back.

The Protocol

• Ask for a 25(OH)D level at your next blood draw — it is often not on a standard panel unless requested.
• If you are deficient, treat it with your doctor, and retest rather than assuming the dose worked.
• If you are supplementing blind, cap it around 1,000 IU per day and take it daily rather than in large intermittent boluses.
• If you are currently on 5,000 IU or more without a documented deficiency, raise it with your physician — that is a conversation, not a self-directed change, and high-dose vitamin D interacts with calcium and kidney status.
• Keep two to three resistance sessions a week regardless. That is the part of this list with the strongest evidence behind it.

For educational purposes only. Not medical advice. Consult your physician before making changes to your health regimen — including before starting, stopping, or changing the dose of any supplement.