Data from the TARGET-D randomized clinical trial showed that 85% of participants started the study with vitamin D levels below 40 ng/mL and used personalized doses of the sunshine vitamin to achieve the optimal range of 40-80 ng/mL.
Just over 50% of the study’s 630 participants needed to take more than 5,000 IU per day of vitamin D to reach the optimal blood level range. The current daily recommended amount of vitamin D for adults is 600 IU.
“Previous clinical trial research on vitamin D tested the potential impact of the same vitamin D dose for all participants without checking their blood levels first,” said Heidi May, PhD, principal investigator of TARGET-D and an epidemiologist and professor of research at Intermountain Health in Salt Lake City, Utah, where the study took place.
“We took a different approach. 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.”
Vitamin D
Vitamin D refers to two biologically inactive precursors: D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25(OH)D, the non-active ‘storage’ form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
While the human body does manufacture vitamin D on exposure to sunshine (UV-B radiation with a wavelength between 290 and 315 nm), the levels in some northern countries are so weak during the winter months that the body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
In addition, darker skin is known to limit a person’s ability to produce vitamin D, and various surveys have reported that as much as 90% of African Americans may be vitamin D deficient, defined as having 25(OH)D levels below 30 ng/mL.
Study details
The Utah-based scientists recruited 630 adults with acute coronary syndrome with an average age of 63 to participate in their study. Seventy-eight percent were men, and 48% were heart attack survivors. Ninety percent self-identified as white.
Participants were randomly assigned to receive either the targeted vitamin D supplementation to achieve optimal levels (doses were adjusted every three months), or to standard care with no vitamin D monitoring or dose-tailoring.
Over the course of four years, the researchers recorded 107 major cardiac events, including heart attack, heart failure hospitalization, stroke or death. Close to 16% of the incidents occurred in the tailored vitamin D group and 18.4% occurred in the standard care group.
Results showed that the personalized vitamin D group had a 52% lower risk of heart attack compared to participants in the standard care group.
Dr. May stated that these results could improve patient care by focusing on blood tests for vitamin D levels and tailoring doses.
“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,” she added.
The researchers cautioned that the study only included adults with heart disease and therefore the results may not apply to people without heart disease.
Source: American Heart Association Scientific Sessions 2025, Abstract 4382525
