Optimal vitamin D doses halve the risk of recurrent heart attacks

Vitamin D deficiency is widespread, and current health authority recommendations are too low for cardiovascular health. A new U.S. study from Intermountain Healthcare in Salt Lake City shows that high-dosed vitamin D supplements, sufficient to optimize blood levels, can halve the risk of a repeat heart attack in patients who have already experienced one. According to the researchers, heart patients should have their vitamin D levels measured and adjusted with appropriate supplementation. However, this remains an underemphasized area, with many lives lost as a result.

A heart attack typically occurs due to a blood clot in a coronary artery, often caused by atherosclerosis, which blocks blood flow to the heart. Even mild heart attacks can damage the heart muscle, potentially leading to chronic heart failure. While treatments have improved, there remains a risk of recurrent heart attacks, and 20–50% of heart failure patients die within the first year after diagnosis, depending on severity.
Because diet and lifestyle play a crucial role in cardiovascular health and the risk of heart attacks and recurrence, the researchers wanted to investigate the role of vitamin D, given how common deficiencies are and the ongoing debate about the actual requirements.

• Vitamin D deficiency is primarily caused by insufficient sun exposure during summer, lack of sunlight in winter, aging, dark skin, overweight, type 2 diabetes, and other chronic diseases.

The crucial difference between standard and targeted supplementation

The researchers noted that earlier studies had given low-dose vitamin D supplements to heart patients, but these studies did not show positive results in reducing heart disease. In the new study, the researchers first measured patients’ blood vitamin D levels. Then, patients received supplements large enough to optimize their blood levels, with repeated blood tests and adjustments over time.
The study, called the TARGET-D Trial, included 630 patients who had experienced a heart attack within the previous month. The trial ran from April 2017 to May 2023, with participants followed until March 2025 to assess cardiovascular outcomes and survival.
Participants were divided into two groups, with only one group receiving vitamin D supplementation. The goal was for this group to achieve blood vitamin D levels above 100 nmol/L (≈40 ng/mL)—higher than the generally recommended optimal value of 75 nmol/L. At baseline, 85% of participants had blood vitamin D levels below 100 nmol/L, indicating widespread deficiency in relation to cardiovascular health.
During the trial, participants in the treatment group received targeted vitamin D therapy of up to 125 micrograms per day, which is far above the official recommended intake of 10-20 micrograms. Blood levels were regularly monitored and adjusted until the desired target of >100 nmol/L was reached, after which supplementation was continued at a maintenance dose.
Throughout the study, researchers tracked repeat heart attacks, strokes, heart failure, hospitalizations, and deaths. Of the 630 participants, 107 experienced such events. Importantly, the risk of a repeat heart attack was 50% lower in the group receiving targeted vitamin D supplementation.
No participants experienced side effects from the high-dose vitamin D. The researchers conclude that, while further studies are needed, these results are very promising. Heart patients should at least have their vitamin D levels measured so any deficiencies can be corrected with appropriate, targeted supplementation.
The study’s results were presented at the American Heart Association’s Scientific Sessions in New Orleans on November 9, 2025.

How vitamin D may help prevent heart attacks

Most cells in the body have vitamin D receptors, including cells that are important for cardiovascular health. According to a previous review published in Clinical Nutrition, vitamin D has multiple mechanisms that may protect against heart attacks and other cardiovascular diseases:

• Strengthens the immune system, helping prevent bacteria in the bloodstream from causing blood clots
• Regulates inflammation, which can otherwise trigger oxidative stress and atherosclerosis
• Reduces arterial stiffness, lowering the risk of high blood pressure and clot formation
• Regulates blood sugar and insulin levels
• Helps prevent metabolic syndrome and type 2 diabetes, conditions linked to atherosclerosis and cardiovascular disease

References:

Intermountain Healthcare. Vitamin D3 breakthrough halves risk of second heart attack. ScienceDaily. November 10, 2025

Fernando de la Guia-Galipienso et al. Vitamin D and cardiovascular health. Clinical Nutrition. 2021