Researchers at the Intermountain Medical Center Heart Institute in Salt Lake City have found that patients are fine from a heart standpoint, and may need no further treatment, if their vitamin D level is anywhere above 15 nanograms per milliliter.
"Although vitamin D levels above 30 were traditionally considered to be normal, more recently, some researchers have proposed that anything above 15 was a safe level. But the numbers hadn't been backed up with research until now," said J. Brent Muhlestein, MD, co-director of cardiovascular research at the Intermountain Medical Center Heart Institute, and lead researcher of the study.
"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. The best way to determine one's vitamin D level is by getting a blood test," he said.
Dr. Muhlestein and his team will present their findings from the study at the 2015 American Heart Association Scientific Session in Orlando on Monday, Nov. 9.
The body naturally produces vitamin D as a result of exposure to the sun, and it's also found in a few foods -- including fish, fish liver oils, and egg yolks as well as some dairy and grain products.
Those who don't have enough exposure to sunlight or vitamin D producing foods often have low vitamin D levels. Low levels are also attributed to race because people with dark skin have a natural protectant against ultraviolet light.
Dr. Muhlestein and his team have studied the effects of vitamin D on the heart for several years, looking at smaller numbers of patients. In this study, thanks to Intermountain Healthcare's vast clinical database, they were able to evaluate the impact of vitamin D levels on more than 230,000 patients.
The 230,000 patients were split up into four groups (<15 ng/ml, 15-29, 30-44, ≥45) and were followed for the next three years by researchers who looked for major adverse cardiac events, including death, coronary artery disease, heart attacks, stroke, and incidents of heart or kidney failure.
Dr. Muhlestein found that for the nine percent of patients in the greater than 15 group, their risk of cardiovascular events increased by 35 percent compared to the other three groups, and the risks faced by the other three groups weren't very different from each other.
"This study sheds new light and direction on which patients might best benefit from taking vitamin D supplements," said Dr. Muhlestein. "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."
Going forward, Dr. Muhlestein hopes to take these findings and perform a randomized trial with patients whose levels are below 15. The idea is to randomly separate them into groups and provide supplements for one but not the other to see what the long-term benefits for combating heart problems really are.
"As we continue to study vitamin D and the heart, we hope to ultimately gain enough information so we can inform all patients specifically what they should do to reduce their cardiac risk as much as possible," he said.