Vitamin D and Heart Attacks: The Science Keeps Changing

Doctors don’t know what to make of vitamin D. Low levels of this essential nutrient have been linked to a greater risk for heart attacks. A meta-analysis of 34 studies with more than 180,000 volunteers revealed that people with higher levels of vitamin D were less likely to have heart attacks or strokes. On the other hand, a large study published in the New England Journal of Medicine (VITAL) reported that Vitamin D₃ supplements did not protect against heart attacks, strokes or other cardiovascular complications. But a study presented at the 2025 American Heart Association [AHA] Scientific Sessions on November 9, 2025, demonstrated that there is good news when it comes to vitamin D and heart attacks.

Contradictions in Medicine About Vitamin D and Heart Attacks:

Many people get frustrated when new results challenge older research. Do not despair! That is the nature of science. It becomes critical to analyze the data and try to make sense out of what seems like contradiction.

We can say with good evidence that low levels of 25-hydroxyvitamin D are associated with an increased risk of cardiovascular disease mortality and overall death rate (European Journal of Nutrition, Feb. 2016). In case you are wondering, 25-hydroxyvitamin D levels are how researchers measure vitamin D in the body. Anything below 20 ng/mL is considered low. Many doctors believe that anything over 20 is adequate. They could be wrong, based on the new data from the AHA recent meeting.

A prospective study involving nearly 20,000 American adults with high blood pressure found that low levels of 25-hydroxyvitamin D were associated with cardiovascular disease deaths and “all-cause mortality” (Nutrition Journal, March 9, 2024).

Vitamin D3 Supplements Did Not Protect in the VITAL Trial:

One of the biggest clinical trials involving vitamin D supplementation was published in the New England Journal of Medicine (Jan. 3, 2019). We described the results in this article:

“Vitamin D Strikes Out Against Heart Attacks and Cancer”
In the VITAL trial, vitamin D strikes out for preventing heart disease and cancer. Are such supplements completely useless?

Here was our summary of the VITAL results when it came to vitamin D and heart attacks:

“The VITAL study demonstrates conclusively that vitamin D pills do not reduce the risks of cancer or heart disease (NEJM, Nov. 10, 2018). Nearly 26,000 people were randomized to take 2000 international units of vitamin D3 or placebo every day for more than five years.”

The Envelope, Please:

“Overall, there was no significant difference between the two groups when it came to survival. There were no fewer heart attacks, strokes or other cardiovascular complications in the vitamin D group. They were also equally likely to die from invasive cancer.”

We even interviewed the lead investigator, JoAnn Manson, DrPH. Should you wish to listen to Dr. Aaron Carroll and Dr. JoAnn Manson discussing changing nutritional guidelines on our nationally syndicated radio show, here is a link to the podcast for Show 1200:

Show 1200: Making Sense of Changing Nutritional Guidelines
Is fish oil helpful or useless? Does eating red meat make any difference for heart health? Can you keep up with changing nutritional guidelines?

To listen, click on the arrow inside the green circle under the photo of Dr. Aaron Carroll.

New Data About Vitamin D and Heart Attacks:

First, what do we know about vitamin D and heart attacks?

1. Low levels of vitamin D in the body (less than 20 ng/mL) are linked to cardiovascular complications.
2. Low levels of vitamin D are linked to other health problems including depression and some cancers.
3. A new study presented at the Nov. 9, 2025, American Heart Association Scientific Sessions reports that vitamin D reduced the likelihood of another heart attack in high risk patients. 

Dose Matters When Studying Vitamin D and Heart Attacks:

Perhaps you missed the dose of vitamin D₃ in the VITAL trial. It was 2,000 international units (IUs) of vitamin D₃. The study (TARGET-D) presented to the AHA Scientific Sessions meeting involved 630 people who had suffered a heart attack less than a month before entering the trial. These were high-risk patients! The chances of having another heart attack are substantially greater in people who have already had one “myocardial infarction.”

What made the TARGET D trial especially interesting was that the investigators randomly assigned the high-risk volunteers to either no vitamin D management or an “intervention” group. This latter group had their 25-hydroxyvitamin D levels measured at the start of the study. The goal was to get these people to a target level of 40 ng/mL.

Remember, many health professionals only worry if patients have 25-hydroxyvitamin D levels below 20 ng/mL. The researchers running the TARGET D study wanted those in the intervention group to achieve levels of 40 ng/mL or higher. Here is the kicker. About 85% of the volunteers were below that threshold at the start of the trial. They received extra vitamin D₃ until they reached 40 ng/mL or higher. Some needed as much as 5,000 IUs of vitamin D₃ daily to achieve the goal.

And the Envelope Please RE: Vitamin D and Heart Attacks:

After follow-up, the difference was striking: those who took vitamin D were about 50% less likely to suffer a second heart attack compared to those who didn’t receive supplements.

Why is there a discrepancy between the TARGET D study presented November 9, 2025, and the VITAL study published in the January 3, 2019 issue of the New England Journal of Medicine? Participants in the VITAL trial were randomly assigned to take 2,000 IU of vitamin D₃ or placebo daily for more than five years. The conclusion: vitamin D did not reduce the risk of heart attacks, strokes, or cancer.

That study made headlines and prompted many experts to declare that vitamin D had “struck out” as a preventive therapy for major chronic diseases. But the new data suggest the story may not be over—especially for people who are deficient or already at high cardiovascular risk.

The Dose and Details Matter When It Comes to Vitamin D and Heart Attacks:

One possible explanation for the conflicting results lies in the details. The VITAL trial tested a moderate daily dose of 2,000 IU in people who were mostly healthy at baseline, many of whom already had adequate vitamin D levels. The new study, by contrast, focused on heart attack survivors—patients at very high risk for another cardiac event—and adjusted their supplement doses to achieve a specific blood level goal.

That difference is crucial. It suggests that vitamin D may not act like a “magic pill” for everyone but could make a meaningful difference for those who start out deficient and vulnerable. It also highlights an emerging idea in nutrition research: it’s not just the pill that matters, but whether your body actually reaches the target level of the nutrient.

Many of the volunteers in the TARGET D trial were 1) at high risk and 2) were well below the desired goal of 40 ng/mL. The scientists tested frequently and upped the dose of vitamin D₃ until the target was reached. That was not the case in the VITAL trial.

A Word of Caution

Before you start taking high doses of vitamin D on your own, remember that more isn’t always better. Excess vitamin D can raise blood calcium levels and lead to kidney stones or other complications. Most experts recommend checking your blood level of 25-hydroxyvitamin D before deciding whether to supplement—and how much to take.

You will want to read our article titled:

“Can You Overdose on Vitamin D?”

In it you will learn about the RDA for vitamin D as well as the “tolerable upper limit.” We also describe what can happen if you overdose on vitamin D.

For many people, safe sun exposure remains an important source of vitamin D, though that depends on geography, skin tone, and time of year. Dietary sources—like salmon, sardines, cod liver oil, fortified milk, and eggs—can also help maintain healthy levels.

The Bottom Line:

The science on vitamin D and heart attacks is evolving. After years of disappointing results, the latest study suggests that restoring vitamin D to optimal levels may help prevent a second heart attack in those who’ve already had one. The key takeaway: vitamin D might not be a cure-all, but deficiency could be a hidden risk factor worth correcting.

As researchers continue to untangle vitamin D’s complicated relationship with heart health, one thing is clear—this is a story still being written, and the final chapter may not be as simple as “vitamin D works” or “vitamin D fails.”

The Bottom Line on Vitamin D and Heart Attacks:

• Do not guess when it comes to vitamin D levels. Get your healthcare provider to order a blood test to determine your 25-hydroxyvitamin D levels.
• Anything below 20 ng/mL is clearly inadequate!
• Optimal levels may be somewhere between 40-60 ng/mL but check with your healthcare provider to determine what would be safe for you.
• More is not better. Please do not overdose on vitamin D.
• Get some sunshine, even in the winter.

You will find this article of great interest if that last point resonates:

Is Sunshine the Best Source for Vitamin D?

One of our most interesting radio shows was titled “The Surprising Secrets of Sunlight’s Health Benefits.” We think you will find Show 1397 with Dr. Richard Weller quite intriguing. He is a dermatologist who puts sun exposure into perspective.  You may also find our eGuide to Vitamin D and Optimal Health useful. It can be found under the Health eGuides tab.

We hope you have found this article about heart attacks and vitamin D of interest. Please share it with friends and family. Starting about this time of the year, a lot of people reduce their sun exposure. That could easily mean lower levels of 25-hydroxyvitamin D for your acquaintances. This article could make a difference for their health. Thank you for supporting our work.