Researchers linked vitamin D levels below 15 ng/mL to increased risk for cardiovascular events, such as heart disease, heart attack and stroke
Lead investigator Dr. J. Brent Muhlestein, of the Intermountain Medical Center Heart Institute in Salt Lake City, UT, and colleagues recently presented their findings at the American Heart Association's Scientific Sessions 2015 in Orlando, FL.
Individuals who do not get enough vitamin D through dietary sources or sun exposure often have vitamin D deficiency - when the levels of the vitamin in the body are too low, which is determined by measuring levels of 25-hydroxyvitamin D (25-OHD) in the blood.
It is well established that vitamin D is important for bone health, promoting calcium absorption, but studies have increasingly suggested the vitamin may also play an important role in heart health, linking vitamin D deficiency to increased risk for high blood pressure, heart attack and heart disease.
But what specific level of vitamin D deficiency poses a risk to heart health? According to Dr. Muhlestein and colleagues, a 25-OHD level of 30 nanograms/milliliter (ng/mL) or above is considered normal, though some researchers claim a level of 15 ng/mL or above is safe.
Vitamin D levels below 15 ng/mL linked to poor heart health
To investigate further, the team assessed how vitamin D levels affected the health of more than 230,000 patients who were on Intermountain's database.
The team allocated each patient into one of four groups dependent on their 25-OHD levels: less than 15 ng/mL, 15-29 ng/mL, 30-44 ng/mL and more than 45 ng/mL.
Over the next 3 years, the researchers monitored the patients for any incidence of major cardiac events, including coronary heart disease, heart attack, stroke and heart failure, as well as incidence of kidney failure and death.
The researchers found that patients whose 25-OHD levels were less than 15 ng/mL were 35% more likely to experience a cardiovascular event in the subsequent 3 years than participants in the other three groups.
The risk for cardiovascular events was the same for participants whose 25-OHD levels were 15-29 ng/mL, 30-44 ng/mL or more than 45 ng/mL, according to the results.
According to the researchers, these findings indicate that if a person's 25-OHD levels are 15-29 ng/mL or above, they should not be concerned about the effect their vitamin D levels may have on their heart, and vitamin D supplementation is unlikely to improve heart health any further.
Commenting on the results, Dr. Muhlestein says:
"This study sheds new light and direction on which patients might best benefit from taking vitamin D supplements. Even though there's a possibility that patients may benefit in some way from achieving higher blood levels of vitamin D, this new information tells us the greatest benefit to the heart will likely occur among patients whose vitamin D level is below 15 ng/mL."
The researchers stress, however, that a lot of people in the US have vitamin D levels below 15 ng/mL, putting them at significantly higher risk for cardiovascular events.
"Even if any level above 15 is safe, one out of 10 people still have vitamin D levels lower than that. This equates to a very large percentage of our population," notes Dr. Muhlestein. "The best way to determine one's vitamin D level is by getting a blood test."
The team now plans to conduct further research assessing the effects of vitamin D supplementation on the heart health of individuals with vitamin D levels below 15 ng/mL.
Medical News Today recently reported on a study suggesting vitamin D supplementation may lower the risk for heart disease.