A major new finding from Intermountain Health suggests that a personalized approach to vitamin D may dramatically change the outlook for heart attack survivors. In a series of studies presented at the 2025 American Heart Association Scientific Sessions, researchers reported that tailoring vitamin D3 doses to achieve optimal blood levels reduced the risk of a second heart attack by about 50 percent. The evidence points to a breakthrough in precision heart care that could reshape how doctors prevent repeat cardiac events.
The work was led by Dr. Heidi May, a cardiovascular epidemiologist at Intermountain Health in Salt Lake City. Her team ran a large randomized clinical trial known as TARGET-D, following 630 adults with heart disease who had recently experienced a heart attack. Most participants entered the study with low vitamin D levels, and nearly half had already suffered at least one heart attack.
Instead of giving all patients the same supplement dose, the researchers checked blood vitamin D levels and adjusted each person’s intake to reach an optimal range above 40 nanograms per milliliter. Many patients needed far higher doses than those typically recommended. Roughly 52 percent required more than 5,000 IU per day, which is more than six times the FDA’s standard daily intake.
Patients receiving the tailored treatment cut their chance of a second heart attack by more than half. “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,” Dr. May said. She also emphasized that more studies are needed to further validate the findings.
How Vitamin D May Protect the Heart
For years, low vitamin D has been linked to worse heart health, but earlier clinical trials failed to show improvements because they did not track blood levels. The new research suggests that vitamin D may influence heart attack risk through several possible mechanisms. These include improved calcium regulation, better immune function, reduced inflammation and healthier blood vessel activity. All of these processes play important roles in preventing plaque instability, blood clots and other triggers of heart attacks.
By raising vitamin D levels into a healthy range and keeping them there, researchers believe the body may function in a more stable, less inflammatory state, lowering the chances of repeat cardiovascular events.
How the TARGET-D Trial Worked
The trial followed patients for more than four years. Participants were split into two groups. One group received standard care with no vitamin D level management. The other group underwent targeted vitamin D therapy, with frequent blood tests and adjustments every three months until they reached the optimal range.
Once levels were stable, blood tests were done yearly. Throughout the study, calcium levels were also monitored to prevent vitamin D toxicity. Levels above 80 ng/mL triggered a dose reduction to ensure safety. Despite the higher dosing, the research team did not observe dangerous side effects such as abnormal heart rhythms or kidney problems.
A total of 107 major heart-related events occurred during the study. While vitamin D did not reduce the overall rate of stroke, heart failure or death, it showed a dramatic benefit for preventing heart attacks specifically.
The Outlook for Patients
The implications for heart attack survivors are promising. Many people worldwide have low vitamin D levels, partly because of reduced sun exposure and modern indoor lifestyles. This means a large portion of the population may be within reach of a simple, low-cost intervention that could improve long-term heart health.
Dr. May encourages patients with heart disease to speak with their cardiologists about vitamin D testing and personalized dosing. The findings could lead to changes in clinical practice, particularly for individuals who have already had a heart attack and are at high risk for another.
Researchers now plan a larger trial to confirm whether targeted vitamin D therapy can also prevent other types of cardiovascular events. More diversity in study participants will also help determine whether the benefits apply across different populations.
Early public and scientific reactions have been optimistic but cautious. Experts note that the findings are preliminary until they appear in a peer-reviewed journal. Still, many researchers see this as an important step toward a more personalized approach to vitamin supplements. The precision strategy appears to solve a long-standing problem in earlier studies, which never tested whether standard supplement doses were actually correcting deficiencies.
Dr. May summed it up plainly. “We checked each participant’s vitamin D levels at enrollment and throughout the study, and we adjusted their dose as needed to bring and maintain them in a range of 40 to 80 ng/mL.” That, she explained, was the difference that earlier research had missed.
If future studies confirm these results, targeted vitamin D therapy could become a powerful new tool in preventing second heart attacks, providing millions of patients with a safer and more hopeful outlook after their first cardiac event.
