Vitamin D therapy may significantly cut the risk of a second heart attack for many patients.New research finds targeted vitamin D3 treatment—where doses are adjusted to reach optimal blood levels—may cut the risk in half.The study included 630 people who had recently survived a heart attack. Most of them had vitamin D levels below the recommended 40 nanograms per milliliter.Half of the participants were given personalized vitamin D3 doses and had their blood levels checked regularly.The goal: to keep their vitamin D above that 40 nanogram mark.To achieve this, many in the treatment group needed high initial doses—5,000 units—compared to the usual 600 to 800.But over time, those who reached and maintained healthy D3 levels were about 50% less likely to have another heart attack.Dr. Heidi May, lead investigator, says they observed no adverse outcomes from the high doses.“I think what the important message about this study is that it's personalized and it is important to test and then dose accordingly that just giving a fixed dose might not be the answer.”The researchers say a larger trial is needed to confirm the results, but the findings offer real promise, especially because up to two-thirds of people worldwide have low vitamin D levels.Results of the TARGET-D study were presented at the American Heart Association Scientific Sessions 2025.Author Affiliations: Intermountain Health.Sign up for our weekly HealthDay newsletter