Heart disease remains the leading cause of death in the United States, with someone experiencing a heart attack every 40 seconds. While lifestyle changes and medications are standard ways to reduce risk, a new study suggests a surprisingly simple yet often overlooked strategy that could dramatically cut the chance of a second heart attack: optimizing vitamin D levels.

The study comes from heart specialists at Intermountain Health in Salt Lake City and was presented at the American Heart Association’s Scientific Sessions 2025. It examined 630 adults with heart disease, many of whom had already experienced a heart attack. Researchers found that adults with heart disease who took vitamin D tailored to reach optimal blood levels had a 52 percent lower risk of a repeat heart attack compared to those whose levels weren’t monitored.

For reference, more than 85 percent of the analyzed adults began with vitamin D levels below 40 nanograms per milliliter, a level most experts consider too low for heart health.

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The trial used a “target-to-treat” approach, checking vitamin D every three months and adjusting doses as needed. About half of the participants required daily doses above 5,000 IU to reach optimal levels. That’s more than six times the FDA’s standard recommendation of 800 IU, according to the American Heart Association.

“Previous studies just gave patients supplementation without regularly checking blood levels of vitamin D to determine what supplementation achieved,” cardiovascular epidemiologist and principal investigator of the study, Heidi May, PhD, told SciTech Daily. “With more targeted treatment, when we checked exactly how supplementation was working and made adjustments, we found that patients had their risk of another heart attack cut in half.”

Experts advise adults with heart disease to discuss vitamin D testing and individualized supplementation with their healthcare providers before making any changes to their regimen. But, researchers assert the study’s results are promising.

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This story was originally reported by Men’s Journal on Nov 17, 2025, where it first appeared in the Health & Fitness section. Add Men’s Journal as a Preferred Source by clicking here.