A new study from Intermountain Health in Salt Lake City reports that a personalized vitamin D3 treatment plan for patients who have suffered a heart attack can greatly reduce their chances of another one.
In a large randomized clinical trial, researchers found that managing patients’ vitamin D levels through a “target-to-treat” approach — where blood levels were monitored and dosages were adjusted to reach an optimal range — cut the likelihood of a second heart attack by 50%.
The findings were presented on Nov. 9 at the 2025 American Heart Association Scientific Sessions in New Orleans.
Encouraging Early Results from Intermountain Researchers
These results are very encouraging, said Heidi May, PhD, cardiovascular epidemiologist at Intermountain Health and the study’s principal investigator. “We observed no adverse outcomes when giving patients higher doses of vitamin D3 supplementation, and to significantly reduce the risk of another heart attack, which are exciting results,” said Dr. May. “We’re excited with these results but know we have further work to do to validate these findings.”
According to researchers, the results carry global importance, as between one-half and two-thirds of people worldwide have low levels of vitamin D.
In the past, most individuals received sufficient vitamin D through sunlight exposure. Today, with lifestyle changes and medical advice aimed at reducing skin cancer risk, people spend less time in the sun and must rely more on dietary supplements such as vitamin D3 to maintain healthy levels.
From Observation to Precision Treatment
Low vitamin D levels have long been linked to poor cardiovascular outcomes in observational studies. However, earlier clinical trials that provided standard supplementation doses failed to show measurable reductions in heart disease risk. Intermountain scientists wanted to test a different idea: rather than giving everyone the same dose, what if supplementation was adjusted to reach a specific, healthy vitamin D level?
“Previous studies just gave patients supplementation without regularly checking blood levels of vitamin D to determine what supplementation achieved,” said Dr. May. “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.”
Inside the TARGET-D Clinical Trial
The Intermountain study, called the TARGET-D trial, ran from April 2017 to May 2023 and included 630 patients who had suffered a heart attack within a month of enrolling. Participants were followed until March 2025 to monitor cardiovascular outcomes.
Patients were randomly assigned to one of two groups: one received no vitamin D management, and the other underwent active, targeted vitamin D3 treatment.
The goal for the treatment group was to raise blood vitamin D levels to above 40 nanograms per milliliter (ng/mL). At the start, 85% of participants had vitamin D3 levels below that threshold (<40 ng/mL).
Dosing, Monitoring, and Results
More than half of the patients receiving targeted therapy required an initial dose of 5,000 international units (IU) of vitamin D3, compared to typical supplement recommendations of 600-800 IU.
Vitamin D blood levels were checked annually for those maintaining healthy levels. Patients with lower levels were tested every three months and had their dosage adjusted until reaching the 40 ng/mL target. Afterward, their levels were monitored once a year.
Researchers tracked major cardiac events (MACE), including heart attacks, strokes, heart failure hospitalizations, or deaths. Out of 630 participants, 107 experienced such events. While there was no significant difference in the overall risk of MACE between the two groups, the chance of having a second heart attack was cut in half among those receiving targeted vitamin D treatment.
Next Steps for Heart and Vitamin D Research
Researchers plan to expand their work with a larger clinical trial to confirm and build upon these findings.
A larger study group will allow us to more fully evaluate whether targeted vitamin D management can reduce not only repeat heart attacks but also other forms of cardiovascular disease, said Dr. May.
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