(RxWiki News) Though many people are deficient in vitamin D, it's possible to go too far to make up the difference. The "sunshine vitamin" may only protect the heart if you have the right amount.
People with normal levels of vitamin D in their blood are likely gaining the benefits of stronger bones and low levels of inflammation around the heart, but when they have too much, the benefits may reverse, according to a new study.
"Be sure you have a deficiency before taking vitamin D supplements."
Investigating data from over 15,000 adults from the National Health and Nutrition Examination Survey, from 2001 to 2006, lead author Muhammad Amer, MD, of the Johns Hopkins University School of Medicine, and his colleague found that high levels of vitamin D are actually associated with more cardiovascular problems.
They discovered that vitamin D blood levels are linked with a protein called c-reactive protein, or CRP, which is associated with blood vessel stiffening and cardiovascular inflammation.
Generally, people with normal vitamin D levels have a lower level of CRP and cardiovascular inflammation while people with low levels of vitamin D had more CRP.
But this was only true up until 21 nanograms per milliliter of of the vitamin, the low end of normal. As vitamin D levels increased 21, CRP also increased, which could be increasing cardiovascular inflammation as well.
"Clearly vitamin D is important for your heart health," said Dr. Amer. "It reduces cardiovascular inflammation and atherosclerosis, and may reduce mortality, but it appears that at some point it can be too much of a good thing."
Eve Pearson, a registered and licensed dietitian, told dailyRx it's still unclear why Americans tend to be deficient in vitamin D, as researchers have discovered in recent years.
But it's important that a person makes sure they actually have low levels of vitamin D before they start buying bottles of it.
"It's easy to ask for Vitamin D levels when going in for a annual physical," Pearson said. "This will ensure that if you're going to supplement with D or try to address a deficiency, you know there is one first."
Every 100 IU of vitamin D translates to one nanogram per milliliter of the compound levels in the blood. So a 400 IU tablet raises levels 4 nanograms, and a 1000 IU tablet raises levels 10 nanograms.
That means taking a 2000 IU supplement of vitamin D could be pushing the limits unless you're completely deficient of the vitamin. The most abundant natural source of vitamin D is sunlight, though milk is usually fortified with it as well.
Dr. Amer and his colleague, Rehan Qayyum, MD, said it's uncertain why higher levels become a risk to the heart, but they caution that patients should check with a doctor before taking supplements.
The study appears online in the American Journal of Cardiology. No information regarding funding or financial interests of the researchers was provided.