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Researchers say the current vitamin D dosing recommendations are insufficient to protect against a cardiac event. Westend61/Getty Images
  • Preliminary results from an ongoing clinical trial suggest the current vitamin D dosing recommendations are insufficient to protect against heart attack and stroke.
  • Prior studies on vitamin D supplementation and heart disease prevention have been inconclusive.
  • Researchers of the new trial say that increasing vitamin D dosages could improve heart health outcomes in future studies.

Low vitamin D affects nearly 42% of the adult population in the United States and is considered a potential risk factor for heart disease.

Research investigating vitamin D supplementation to prevent heart attack and stroke in people with vitamin D deficiency is ongoing, and it remains unclear whether there are any benefits.

Two new studies recently presented at the American Heart Association’s Scientific Sessions in Philadelphia, PA, examined the effectiveness of vitamin D in preventing a cardiac event.

The findings suggest that current dosage recommendations should be revised to help people meet their optimal vitamin D levels.

The studies are part of TARGET-D, a randomized clinical trial conducted at Intermountain Health in Salt Lake City, UT. According to the researchers, people enrolled in prior trials were not taking high enough doses of vitamin D, which may have led to inaccurate results.

“Our findings here show that just giving patients some vitamin D does not help them achieve optimal levels,” said lead author Heidi May, PhD, an epidemiologist at Intermountain Health, in a news release.

“If researchers are going to further look at vitamin D dosing as a possible way to improve heart health, patients need to be given the right doses to reach those ideal levels.”

In both studies, researchers evaluated whether achieving optimal vitamin D levels through personalized supplementation management could reduce the risk of a cardiac event.

They found that achieving ideal levels required giving patients more than the daily Recommended Dietary Allowance (RDA) of 600–800 International Units (IU) of vitamin D.

“Our research group has performed many observational studies evaluating the association of vitamin D with adverse cardiovascular outcomes,” May told Healthline. “Based on past observational studies, we were not at all surprised that participants’ levels were so low and that so many received supplementation at higher doses than is typically thought is needed.”

May explained that lower levels of vitamin D were associated with an increase in cardiac events in a “stepwise manner.”

“Because of this stepwise association, we evaluated at what level did the risk no longer increase,” she said.

May noted the current recommendation for vitamin D levels for bone and overall health is 20 nanograms per milliliter (ng/mL), which she said may be insufficient for reducing cardiovascular outcomes.

“Our observational data has suggested that a level of >40 ng/mL be optimal for preventing cardiovascular events. However, since TARGET-D is a randomized clinical trial and not an observational study, TARGET-D should be able to tell us if achieving a level >40 ng/mL prevents cardiovascular events,” she said.

A total of 632 patients were divided into one of two groups:

  • 316 received a recommendation to discuss their vitamin D treatment with their clinician
  • 316 received a targeted vitamin D treatment

Of the treatment participants, almost 90% required vitamin D dosing, with 86.5% requiring more than 2,000 IU daily and 14.6% requiring more than 10,000 IU daily.

At three months, fewer than 65% of subjects reached the 40 ng/mL threshold. Another 25% of subjects needed six months or more of vitamin D supplementation.

In the second study, researchers reviewed whether participants had a cardiovascular event within 30 days of enrollment. This study is ongoing and will continue until 104 patients experience another heart event or death due to heart disease.

“These two studies showed that the generally recommended levels of vitamin D supplement are not sufficient to raise the levels of vitamin D to a level thought to be beneficial,” said Dr. Cheng-Han Chen, board certified interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA. Chen was not involved in the studies.

“Because of this, it might be necessary for us to rigorously monitor blood vitamin D levels in future clinical trials that look at Vitamin D supplementation for cardiovascular health,” Cheng added.

Vitamin D deficiency is considered a risk factor for heart disease, but prior research on whether vitamin D treatment can offer a protective benefit has been inconclusive.

“Past observational studies have noted an association between low vitamin D levels and increased risk of a cardiovascular event such as heart attack or stroke. However, the reasons behind this association are not clear,” Cheng said.

“It is hypothesized that vitamin D receptors in cells throughout the vascular system are involved in blood vessel inflammation, which could promote heart disease.”

Dr. Robert Segal, founder of Manhattan Cardiology, Medical Offices of Manhattan, and co-founder of LabFinder, agreed the relationship between vitamin D and heart disease is complicated and not fully understood. Segal was not involved in the new research.

“There may be a link between not getting enough vitamin D and a higher chance of heart disease, but evidence isn’t always strong, and more research is needed to prove a clear cause-and-effect link,” he told Healthline.

“Vitamin D helps keep blood pressure, inflammation, and the functioning of the endothelium (the walls of blood vessels) in check. Deficiency may make diseases like high blood pressure and cholesterol worse, both of which raise the risk of heart disease.”

Segal explained that unhealthy cholesterol levels and insulin resistance are also associated with low vitamin D, which may contribute to heart disease.

Vitamin D supplements may be an option for people with low vitamin D, regardless of their health status, but always check with your doctor first.

“We generally recommend that all patients with vitamin D deficiency take a supplement, and not just patients at higher risk of heart attack or stroke,” Cheng said.

Segal explained that a medical professional can evaluate your unique needs and make suggestions for vitamin D supplementation based on your health and lifestyle.

“Supplement choices should be based on each person’s unique situation, which could include their food, how much sun they get, and their health,” he noted.

“Self-prescribing high amounts of vitamin D without medical advice is not a good idea because too much or too little can be harmful. Hypercalcemia (high calcium levels in the blood), which can happen if you consume too much vitamin D, can harm the heart and other organs,” Segal cautioned.

New research recently presented at the AHA’s Scientific Sessions suggests the current dosing recommendations and targets for vitamin D are insufficient.

The researchers say this may explain why results from prior trials involving vitamin D supplementation to prevent cardiac events have been inconclusive.

Though the exact relationship between vitamin D and heart health is not yet fully known, it may be helpful to supplement with vitamin D if your levels are low.

Talk with your doctor about your current vitamin D intake and whether you’d benefit from additional treatment.