Customizing vitamin D3 levels for heart attack survivors can cut the risk of another heart attack by 50%, according to new research.

Researchers at Intermountain Health in Salt Lake City found that developing personalized vitamin D3 treatment plans and carefully monitoring blood levels significantly reduced patients’ chances of suffering a second heart attack.

Vitamin D refers to a group of related nutrients, while D3 — known as cholecalciferol — is the specific form the body produces through sunlight exposure and obtains from animal-based foods.

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The study used a “target-to-treat” approach to evaluate how maintaining optimal vitamin D levels affected cardiovascular health. The findings, presented at the 2025 American Heart Association Scientific Sessions in New Orleans, were striking. Researchers reported “no adverse outcomes when giving patients higher doses of vitamin D3 supplementation.”

The team noted that between one-half and two-thirds of people worldwide are deficient in vitamin D. The nutrient is produced in the skin in response to ultraviolet B (UVB) rays from sunlight, but many people avoid sun exposure because of skin cancer concerns. As a result, supplements are often needed to maintain healthy levels.

Previous research has linked low vitamin D levels to poor cardiovascular outcomes, but most studies used standard supplement doses and showed little improvement. The Intermountain Health team took a different approach — customizing vitamin D doses to individual patients and monitoring their blood levels regularly. When adequate levels were achieved, the risk of another heart attack dropped dramatically.

“We found that patients had their risk of another heart attack cut in half,” said Heidi May, a cardiovascular epidemiologist and the study’s principal investigator.

The Intermountain study, known as TARGET-D, ran from 2017 to 2023 and involved 630 patients who had recently experienced a heart attack. Participants were divided into two groups: one received standard care with no vitamin D3 management, and the other received targeted vitamin D3 treatment.

The goal for the treatment group was to maintain blood levels above 40 nanograms per milliliter (ng/mL). At the start of the study, 85% of participants had vitamin D3 levels below that threshold. More than half of those receiving treatment required an initial daily dose of 5,000 international units (IU) — much higher than the current general recommendations of 600 to 800 IU.

Patients in the vitamin D group had their blood levels checked annually once they reached the target range. Those with lower levels were monitored every three months and had their doses adjusted until reaching the goal.

The study found no significant difference in overall risk of major cardiovascular events — including strokes, heart failure, or death — between the two groups.
 However, the risk of a second heart attack was reduced by 50% in patients receiving targeted vitamin D therapy.

The researchers plan to conduct a larger clinical trial to confirm these findings. “A larger study group will allow researchers to adequately evaluate whether targeted vitamin D management reduces the risk of developing or lowering the risk of other cardiovascular diseases,” said May.