For heart attack survivors, there might be an unexpected way to cut in half the risk of a second heart attack: a simple blood test and a customized vitamin D plan.
"We took a different approach," said Heidi T. May, Ph.D., M.S.P.H., FAHA, principal investigator of the TARGET-D study and an epidemiologist at Intermountain Health in Salt Lake City. "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 40-80 ng/mL."
This challenges the way doctors have thought about vitamin D for decades. In the past, researchers tested vitamin D by giving everyone identical doses and hoping it would help—without actually measuring whether people's levels improved. Those experiments didn't show much benefit, making the medical world skeptical about whether vitamin D even mattered for the heart, researchers said.
The real problem is bigger than most people realize. When researchers started the study, 85 percent of participants had dangerously low vitamin D levels—below 40 nanograms per milliliter. And this isn't just an American issue: between one-half and two-thirds of people worldwide have insufficient vitamin D, the researchers said.
The reason so many people are deficient is straightforward. Years ago, people got enough vitamin D naturally from the sun. But as skin cancer awareness grew and people spent more time indoors, that natural source was less used. Now, more people need to get vitamin D from pills and food, according to Intermountain Health’s announcement.
Nearly half the patients in the study needed to take more than 5,000 international units of vitamin D daily to reach healthy levels. That's more than six times what the FDA recommends. This might explain why earlier studies using smaller doses didn't work, the researchers noted.
The study was straightforward in design. Researchers randomly split participants—all of whom had suffered recent heart attacks—into two groups. One group received standard care with no vitamin D monitoring. The other group had their blood tested every three months and their vitamin D doses adjusted as needed to stay in the healthy range.
Researchers checked both vitamin D and calcium levels to make sure no one developed toxic levels of either nutrient. If vitamin D climbed above 80 nanograms per milliliter, doctors reduced or stopped the supplements to prevent dangerous side effects like kidney problems or irregular heartbeats.
Over the average 4.2-year follow-up period, 107 major cardiac events occurred across the study group—heart attacks, strokes, heart failure hospitalizations, or deaths. While targeted vitamin D management didn't significantly reduce the overall number of such major events, it specifically prevented repeat heart attacks with impressive results.
The typical study participant was a 63-year-old man; about 48 percent had already suffered a previous heart attack. Around 90 percent identified as white, which researchers acknowledged as a limitation—more diverse research is needed to see if such results apply to everyone.
Though these are preliminary findings awaiting peer review and publication in a scientific journal, the implications could reshape how doctors care for heart patients.
"We encourage people with heart disease to discuss vitamin D blood testing and targeted dosing with their health care professionals to meet their individual needs," May said.
Researchers are already planning larger studies to confirm such findings and determine whether this personalized vitamin D approach might even prevent first heart attacks before they happen.