• Vitamin D is an essential nutrient, and researchers are interested in how it may help in several health areas.
• One area of interest is how much vitamin D supplementation is required to achieve potential cardiac benefits.
• An initial analysis in a clinical trial suggests that the current recommended dietary allowance of vitamin D in the United States is too low to achieve optimal vitamin D levels for people with certain cardiac problems.
• Future research in this area will seek to determine if achieving optimal vitamin D levels can decrease the risk for adverse cardiovascular events.

Research is ongoing about the health benefits of vitamin D. One area of interest is how vitamin D may help reduce the risk of heart problems.

Researchers at Intermountain Health are conducting an ongoing clinical trial looking into this topic, and their first analysis is already complete.

Reports shared at the American Heart Association’s Scientific Sessions 2023 suggest that current recommended dietary allowances are inadequate for achieving optimal serum vitamin D levels.

In this trial’s next phase, researchers will examine if optimal vitamin D levels are associated with a decreased risk for adverse cardiovascular events such as heart attack and stroke.

Why do we need vitamin D for heart health?

Vitamin D is an essential nutrient and contributes to proper bone function. Research is ongoing about how vitamin D may promote health in other areas, including cardiovascular health.

However, the National Institutes of Health (NIH) note that current evidence does not seem to support the claim that taking vitamin D supplements helps reduce risks for cardiovascular disease.

Dr. Mary Greene, from Manhattan Cardiology in New York, and contributor to LabFinder, not involved in the current research, explained to Medical News Today that “[m]any studies have failed to demonstrate if supplementation with Vitamin D can prevent major adverse cardiovascular events.”

She added:

“There are several proposed mechanisms by which vitamin D may contribute to cardiovascular health. Having healthy vitamin D levels may promote glucose metabolism and insulin sensitivity, may promote endothelial function in the blood vessels, may regulate blood pressure and blood volume homeostasis and may inhibit inflammation. Due to these effects, vitamin D helps to regulate the underlying dysfunction that causes heart disease.”

Dr. Cheng-Han Chen, a board-certified interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA, also not involved in the current research, further noted that: “Vitamin D deficiency has been considered a possible risk factor in cardiovascular disease. However, studies which examined the effect of vitamin D supplementation have not found a clear benefit of Vitamin D in preventing cardiovascular events.”

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

Currently, the recommended dietary allowance for vitamin D is 600 international units (IU), or approximately 15 micrograms (mcg), for adults under 70 years of age, and 800 IU, or around 20 mcg, for adults over 70.

However, according to the researchers who conducted the current clinical trial, this might not be enough for people to reach appropriate serum levels of vitamin D.

They suggest that participants in other studies were not given high enough doses of vitamin D to achieve a therapeutic response.

How much vitamin D is enough?

The authors of the current clinical trial wanted to understand more about optimal dosing to help people reach appropriate vitamin D levels and whether or not this aids in preventing adverse cardiovascular events.

For this clinical trial — called TARGET-D — they have recruited 632 participants. All of these participants had experienced acute coronary syndrome. This refers to a group of events with decreased blood flow to the heart. For example, someone who experienced a heart attack would have acute coronary syndrome.

Researchers then divided participants into the vitamin D intervention group and the group receiving standard care. Instead of just giving a standard dose of vitamin D, researchers went off of participants’ specific vitamin D levels and provided supplementation as needed.

In the first part of their analysis, they found that most participants required vitamin D supplementation to reach a serum vitamin D level of more than 40 nanograms per milliliter (ng/mL).

When determining what doses to give participants to reach this level, they found that 51% needed between 5,000-8,000 IU, much higher than the recommended dietary allowance. Additionally, 14.6% of participants required 10,000 IU or more to reach optimal vitamin D levels.

It also took time for participants to reach the target vitamin D level. Less than 65% of participants reached the level at three months, and 25% required six months of intervention to reach the level.

The results indicate that higher vitamin D doses are required to reach therapeutic levels in this group.

Study author Dr. Heidi May, a cardiovascular epidemiologist with Intermountain Health, explained some of the key components of the clinical trial to MNT:

“TARGET-D is a randomized clinical trial that is evaluating whether obtaining a blood vitamin D level>40 ng/mL reduces adverse cardiovascular outcomes. We have found this association in prior observational studies, but a randomized clinical study is needed to determine if there is a causation relation. We were not surprised that so many patients had levels [lower than or equal to] 40 ng/mL, but how much vitamin D supplementation was needed to achieve this level.”

Next steps in the vitamin D and heart health trial

The first of these analyses on vitamin D levels is completed. It indicates that higher vitamin D supplementation is needed to reach certain therapeutic levels.

The next part of the research will help determine if achieving vitamin D levels greater than 40 ng/mL in this group helps improve cardiovascular disease outcomes.

Thus, it is unclear what the full research limitations will be. However, the research includes limited participants, so future research will likely be needed. Some participants could not continue vitamin D intervention, which may have impacted some results.

Dr. May detailed some of the future components of this clinical trial:

“If TARGET-D shows that achieving a vitamin D level of [more than] 40 ng/mL reduces the risk of adverse cardiovascular events, clinicians should be more proactive in testing and treating low vitamin D levels. Completing TARGET-D is very important. Currently, we are following participants until there have been enough events that have occurred so we can compare if treating low vitamin D reduces cardiovascular outcomes compared to not actively treating low vitamin D.”

Researchers anticipate the study data collection will end by May 2024.

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