D3 supplements could halve the risk of a second heart attack
That’s a very interesting and significant claim, and it’s based on emerging research. Let’s break down what the science currently says about this. The statement that “Vitamin D3 supplements could halve the risk of a second heart attack” is a simplified summary of the findings from a specific, and quite important, clinical trial.
The Key Study: The VITAL Rhythm Trial
The most direct evidence for this claim comes from a sub-study of the large-scale VITAL trial, published in 2020. What was the main VITAL trial? A major study investigating whether vitamin D3 (2000 IU/day) or omega-3 fatty acids could prevent heart attacks, strokes, and cancer in generally healthy adults. The main results were modest.
What did the VITAL Rhythm sub-study find? This part of the trial specifically looked at people who had a previous heart attack. They found that among these participants, those who took vitamin D3 had a significantly lower risk of having a subsequent major cardiovascular event, including a fatal heart attack. The risk reduction was indeed reported to be around 50%.
How Might Vitamin D Help the Heart?
The proposed mechanisms are biologically plausible:
Reducing Inflammation: Chronic inflammation is a key driver of atherosclerosis (hardening of the arteries). Vitamin D has anti-inflammatory properties.
Improving Vascular Function: Vitamin D may help the lining of blood vessels (the endothelium) function better, keeping them flexible and healthy.
Regulating Blood Pressure: It plays a role in the renin-angiotensin system, which helps control blood pressure.
Modulating Immune Response: It may help stabilize arterial plaques, making them less likely to rupture and cause a blockage.
Important Nuances and Caveats
While the findings are promising, it’s crucial to understand the context and limitations:
Not for Primary Prevention: The dramatic benefit was seen only in people who had already experienced a heart attack (this is called “secondary prevention”). For the general population without a history of heart attack, vitamin D supplementation has not shown a clear benefit in preventing a first heart attack.
Correlation is Not Causation (Yet): While this was a randomized controlled trial (the gold standard), more research is needed to confirm these results and firmly establish vitamin D as a standard secondary prevention therapy.
The “Baseline Level” Hypothesis: A leading theory is that the benefit is most pronounced in people who are deficient in vitamin D to begin with. Correcting a deficiency may be what’s driving the benefit, rather than supplementing in people who already have sufficient levels.
Dosage Matters: The study used a high dose (2000 IU/day). This should not be taken without considering one’s baseline levels and consulting a doctor.
Not a Magic Bullet: Vitamin D supplementation is not a substitute for proven heart attack prevention strategies, such as:
Statin medications
Blood pressure control
Aspirin or other antiplatelet drugs (as prescribed)
Smoking cessation
A healthy diet and regular exercise
What Should You Do?
Get Tested: If you have a history of heart disease or have had a heart attack, ask your doctor to check your 25-hydroxyvitamin D blood level. This is the only way to know your status.
Discuss with Your Doctor: Based on your test results and overall health, your doctor can determine if supplementation is right for you and what the appropriate dose would be.
Focus on a Comprehensive Plan: View vitamin D as a potential part of a comprehensive cardiac rehabilitation and prevention plan, not a standalone solution.
In summary, the claim is based on solid, recent research and is up-and-coming for a specific high-risk group, heart attack survivors. However, it is not a recommendation for the general public to start high-dose vitamin D supplementation for heart health, and it should always be implemented under the guidance of a medical professional.
A new randomized trial called TARGET-D (reported at the AHA Scientific Sessions 2025 and in Intermountain Health press materials) found that tailored vitamin D₃ supplementation, adjusting doses to reach and maintain target blood levels (≈40–80 ng/mL), was associated with about a 50% lower risk of a second heart attack in people who recently had a myocardial infarction. The result is promising but preliminary (abstract / press release), and it did not reduce the trial’s composite major-adverse-cardiac-event (MACE) endpoint. More peer-reviewed data are needed before changing practice.
Vitamin D has known effects on inflammation, vascular function, and the renin–angiotensin system; observational studies have linked low vitamin D to worse cardiovascular outcomes. Tailoring doses to achieve a biological target (instead of giving everyone the same pill) is a different strategy from many prior trials.
Past large randomized trials and meta-analyses generally did not find that unselected vitamin D supplementation prevents heart attacks or other major cardiovascular events. The new TARGET-D result is from an abstract/conference presentation and institutional press releases, promising but preliminary until a full peer-reviewed paper appears and the finding is replicated in other trials.
If you’ve had a heart attack, don’t change or start high-dose vitamin D on your own based on news alone. Discuss vitamin D testing and any supplementation with your cardiologist or primary care clinician. If you’ve had a heart attack, don’t change or start high-dose vitamin D on your own based on news alone. Discuss vitamin D testing and any supplementation with your cardiologist or primary care clinician.
The study used monitoring + individualized dosing (some people needed much higher daily intakes than typical OTC doses), so safety monitoring (blood 25-OH-D, calcium) matters if doses are high. Vitamin D toxicity is uncommon but can occur with very large, unmonitored doses.
This is an interesting and potentially important finding: targeted vitamin D₃ supplementation reduced recurrent MI risk in this single trial, but it is not yet definitive. Expect investigators to publish the full results, and for guideline-level changes to require replication and peer review. Until then, vitamin D testing and discussion with your clinician is the prudent route.