Providing heart attack survivors with a tailored vitamin D3 treatment that relied on frequent monitoring and dosage adjustments to achieve an optimal vitamin D3 status drastically reduced heart attack survivors’ risk of having a second heart attack, concluded a new study by Intermountain Health researchers. The findings, which have not yet been published, were presented on Nov. 9 at the American Heart Association’s Scientific Sessions in New Orleans.

Through this “target-to-treat” approach, the likelihood that a heart attack survivor would experience a second heart attack were cut by 50%.

“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,” stated Heidi May, PhD, cardiovascular epidemiologist at Intermountain Health and the principal investigator of the study. “We’re excited with these results but know we have further work to do to validate these findings.”

Globally, between one half and two-thirds of people have low levels of vitamin D, the researchers noted. And while past observational studies have linked poor cardiovascular outcomes to low vitamin D levels, standard supplementation treatments haven’t made a significant difference in cardiovascular risk in past intervention trials.

“Previous studies just gave patients supplementation without regularly checking blood levels of vitamin D to determine what supplementation achieved,” stated May.

The Intermountain study, called TARGET-D, ran from April 2017 to May 2023 and included 630 patients who suffered a heart attack within a month of enrolling. Participants were followed to March 2025 to continue monitoring cardiovascular outcomes.

One group received no vitamin D management, while the other was administered the nutrient with the aim of keeping blood levels above 40 nanograms per milliliter. At the start, 85% of participants had vitamin D levels below that threshold.

More than half in the treatment arm needed initial dosages of 5,000 IU to reach the threshold, compared to typical supplement recommendations of 600-800 IU. For those that were able to maintain adequate levels, they were tested annually. Patients with lower levels were tested every three months, and had their dosage adjusted until reaching the 40 ng/mL target.

Out of 630 participants, 107 experienced a major cardiac event (MACE), defined as heart attacks, strokes, heart failure hospitalizations, or deaths. While there wasn’t a significant difference in MACE, the risk of a second heart attack was cut in half among those taking vitamin D.