People with low vitamin D have more heart disease. That association is consistent across many studies. But when vitamin D supplements were tested in large randomized trials, they did not reduce heart attacks, strokes or cardiovascular deaths.
The fairest reading is that low vitamin D is mostly a marker of health, not a cause of heart disease. A vitamin D level is not a heart risk test, and a supplement is not a heart treatment.
Key takeaways
- Lower vitamin D levels go along with more cardiovascular events in observational studies.
- The largest US trial found no reduction in major cardiovascular events with a daily supplement.
- A pooled analysis of 21 trials reached the same result, whatever the starting vitamin D level.
- Endocrine experts advise against routine vitamin D testing in healthy adults.
- Treating a true deficiency is still worthwhile for bone health, which is a separate question.
What the test measures
The blood test measures 25-hydroxyvitamin D, the form that circulates in your blood. US labs report it in nanograms per milliliter (ng/mL).
What counts as "low" is argued over more than you might expect. The Institute of Medicine concluded that a level of at least 20 ng/mL meets the needs of at least 97.5% of the population, a figure based on bone health.1
Some labs use higher cut-offs. The same committee concluded that vitamin D inadequacy in North America had been overestimated, and called for laboratory ranges to be reassessed. So a result marked low on your report is not always a deficiency.
The association with heart disease
The link shows up reliably when researchers measure vitamin D and then follow people over time. A pooled analysis of 34 publications with 180,667 participants found that each 10 ng/mL higher vitamin D level was linked with a 10% lower risk of cardiovascular events and a 12% lower risk of cardiovascular death.2
An association like this can mislead. Vitamin D is made in skin exposed to sunlight, so a level may partly reflect how much time someone spends outdoors and being active. It may also reflect body weight or existing illness. Each of those affects heart risk by itself.
In other words, low vitamin D may simply travel with the things that harm the heart. The only way to find out whether vitamin D itself matters is to give it to some people and not others, at random, and count what happens.
What the trials found
That experiment has now been done several times, in very large numbers.
The VITAL trial. This US trial assigned 25,871 men aged 50 or older and women aged 55 or older to daily vitamin D or a placebo. After a median of 5.3 years, major cardiovascular events had occurred in 396 people taking vitamin D and 409 taking placebo, a difference no larger than chance would produce.3
The pooled trials. A meta-analysis of 21 randomized trials with more than 83,000 participants found that vitamin D supplements did not reduce major cardiovascular events, heart attack, stroke, cardiovascular death or death from any cause.4
The result held regardless of sex, starting vitamin D level, the amount given, and whether it was taken daily or in large occasional amounts. The authors concluded that vitamin D supplementation does not provide cardiovascular protection.
One partial exception. An Australian trial of 21,315 adults aged 60 to 84 found slightly fewer major cardiovascular events with monthly vitamin D than with placebo, 6.0% compared with 6.6%, a difference that did not reach statistical significance.5
Heart attacks alone were less frequent in the vitamin D group in that trial. The authors described the overall finding cautiously: a possible small benefit, with results also consistent with no effect. It is a reason for more research, not a reason to take vitamin D for your heart.
What expert bodies say
The guidance follows the trials. The Endocrine Society's 2024 guideline suggests against routine vitamin D testing in people without an established reason for it, and against supplements above the standard recommended intake to lower disease risk in healthy adults under 75.6
That guideline does suggest vitamin D for some groups for reasons unrelated to heart attacks, including adults aged 75 and older and people who are pregnant. If you are in one of those groups, talk with your clinician.
The Institute of Medicine reached a similar view years earlier. It found the evidence for benefits beyond bone, including for cardiovascular disease, inconsistent and insufficient to set requirements.
So is a low level worth knowing about?
Sometimes. A truly low level matters for bone health, and treating it is standard care. That is separate from heart protection.
As a heart signal, low vitamin D is best read as a nudge to look at the bigger picture: activity, weight, blood sugar, inflammation and kidney health. Our program page lists low vitamin D among the risk factors that can make a cardiovascular evaluation worthwhile. That fits the association data. It does not mean that taking vitamin D lowers the risk.
More is not better, either. The Institute of Medicine noted that for some outcomes risk was higher at both low and high vitamin D levels.1 Do not start or raise a supplement on the basis of a heart concern without talking to your clinician.
What to measure instead, and how Cardio Res-Q fits
If your real question is "what is my heart risk?", other tests answer it far better. ApoB and Lp(a) measure the particles that build plaque. A1c and insulin show how your body handles sugar. A coronary calcium score looks for plaque itself.
The Cardio Res-Q Comprehensive Assessment ($775) includes ApoB, Lp(a), hs-CRP, homocysteine, insulin, glucose and A1c, the Cleveland Heart cardiac panel and Dr. Varano's clinical evaluation. The Enhanced Assessment ($999) adds a CIMT ultrasound and a coronary calcium score. Vitamin D is not named in the published lab list, so ask our team if you want it checked.
For a candid look at who gains the most from this kind of testing, read is preventive heart testing worth the money? You can book from the Cardio Res-Q program page.
Are You a Candidate for Cardio Res-Q?
Three quick questions about the risk factors we screen for. Your answers stay between you and the clinic.
Frequently asked questions
Should I take vitamin D to protect my heart?
The trial evidence does not support it. Large randomized trials found no reduction in heart attacks or strokes. Whether you need vitamin D for another reason, such as bone health or a confirmed deficiency, is a separate decision to make with your clinician.
My vitamin D is low. Does that mean my heart risk is high?
Not by itself. Low vitamin D is linked with higher risk across large groups, but it often reflects other things, such as less time outdoors, less activity or more body fat. Your blood pressure, cholesterol particles, blood sugar and family history say much more.
Should I have my vitamin D tested as part of a heart check?
It is not needed for estimating heart risk, and endocrine experts advise against routine testing in healthy adults. Testing makes sense when your clinician has a specific reason for it.
Why did the studies and the trials disagree?
Observational studies show which things occur together. They cannot show which one causes the other. Randomized trials can, and when vitamin D was tested that way the heart benefit did not appear.
Related reading
This article is for general education and is not medical advice. Decisions about testing and medication should be made with your clinician. If you have chest pain or other symptoms of a heart attack, call 911.
