The Largest Vitamin D Trial Found No Fracture Benefit at All

TODAY'S TOPIC

Calcium, Vitamin D, and Your Bones

If you are a woman over 40, someone has almost certainly told you to take calcium and vitamin D for your bones. It is one of the most automatic pieces of health advice in America. The evidence behind it is not as automatic as you think.

CLAIM 01

A vitamin D supplement will protect your bones from fractures as you age.

VERDICT: MYTH

Vitamin D helps the body absorb calcium, and calcium is the main mineral in bone. For decades, doctors told women after menopause to take vitamin D to prevent fractures. The logic was airtight: more vitamin D, better calcium absorption, stronger bones, fewer breaks.

The VITAL trial, published in the New England Journal of Medicine, enrolled 25,871 participants and found that 2,000 IU per day of vitamin D3 had no effect on total fractures, hip fractures, or nonvertebral fractures over 5.3 years. No benefit appeared in any subgroup, whether researchers sorted by age, sex, or baseline vitamin D level. In December 2024, the U.S. Preventive Services Task Force, the independent panel that grades preventive health measures, issued a draft recommendation against supplementing with vitamin D for fracture prevention in community-dwelling adults 60 and older, based on well-established evidence from 20 randomized controlled trials.

For a generally healthy woman without diagnosed osteoporosis or documented vitamin D deficiency, adding a supplement specifically to prevent fractures is not supported by the trial data. Women already diagnosed with osteoporosis or deficiency should follow their doctor's guidance. The recommendation is a draft, not yet finalized, but it reflects where the largest and most rigorous evidence points.

The logic was clean, but the data were not.

THE RESEARCH

Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults

Draft Recommendation: Vitamin D, Calcium, or Combined Supplementation for the Primary Prevention of Falls and Fractures in Community-Dwelling Adults

Endocrine Society Guideline recommends healthy adults under the age of 75 take the recommended daily allowance of vitamin D

CLAIM 02

Calcium supplements can raise your risk of a heart attack.

VERDICT: IT'S COMPLICATED

In 2010, a widely covered meta-analysis reported a 27% increase in heart attack risk among calcium supplement users. The proposed explanation: a large dose of supplemental calcium spikes blood calcium levels, potentially speeding up arterial calcification. The finding made headlines, and many women stopped their supplements.

A 2021 review that pooled 13 randomized controlled trials and 28,935 participants found that calcium supplements significantly increased cardiovascular disease risk in healthy postmenopausal women, with a relative risk of 1.15, meaning the supplement group was 15% more likely to develop heart disease. But in 2016, the National Osteoporosis Foundation and the American Society for Preventive Cardiology published a joint position finding moderate-quality evidence of no harmful relationship. The disagreement depends partly on which trials are included and whether calcium was taken alone or with vitamin D: some analyses suggest calcium-only supplementation may carry higher risk, though findings vary.

The cardiovascular question is not settled, and the evidence is mixed. The risk, where it appears, seems specific to supplements rather than calcium from food. Most expert bodies now agree on one practical point: get calcium from food first and use supplements only to fill the gap.

WHERE THE EVIDENCE SPLITS

Calcium Supplements and Risk of Cardiovascular Disease: A Meta-Analysis of Clinical Trials

Lack of Evidence Linking Calcium With or Without Vitamin D Supplementation to Cardiovascular Disease in Generally Healthy Adults

CLAIM 03

Taking your full daily calcium in one big dose works just as well as splitting it up.

VERDICT: MYTH

Calcium supplements often come in 500 to 600mg tablets, and the daily target for women over 50 is 1,200mg. Taking two tablets at once feels efficient. Most supplement labels list a daily dose without specifying when or how to take it.

The NIH Office of Dietary Supplements confirms that calcium absorption decreases as the dose gets larger. The body absorbs roughly 36% of a 500mg dose but only about 28% of a 1,000mg dose. Absorption is highest at doses of 500mg or less per sitting, a finding confirmed across decades of research and repeated in clinical guidelines.

Taking 500mg at breakfast and 500mg at dinner delivers more usable calcium than 1,000mg swallowed at once. Calcium carbonate, the most common and cheapest form, also needs food in the stomach to absorb properly. Calcium citrate can be taken with or without food.

The pill went in, but that does not mean the calcium did.

THE RESEARCH

Calcium - Health Professional Fact Sheet

Office of Dietary Supplements - Frequently Asked Questions

THE BOTTOM LINE

The supplements many women take on autopilot deserve a second look: the vitamin D evidence has shifted, calcium's cardiovascular story is still being written, and how you take a supplement matters as much as whether you take it.