Vitamin D is essential for our bone health. But because people spend most of their times indoors and in air-conditioned environments, they get very little sunshine, which is a primary source of the vitamin D. To make-up for their loss, most of them turn to vitamin D supplements, either on their own or on the advice of their doctors.
However, new research by Johns Hopkins scientists suggests that vitamin D, if taken in excess could actually cause harm. Study leader Muhammad Amer, M.D., an assistant professor in the division of general internal medicine at the Johns Hopkins University School of Medicine, says his findings show that increasing levels of vitamin D in the blood are linked with lower levels of a popular marker for cardiovascular inflammation—c-reactive protein [also known as CRP].
Amer and his colleagues found an inverse relationship between vitamin D and CRP in adults without cardiovascular symptoms but with relatively low vitamin D levels. Healthier, lower levels of inflammation were found in people with normal or close to normal vitamin D levels. But beyond blood levels of 21 nanograms per milliliter of 25-Hydroxyvitamin D — considered the low end of the normal range for vitamin D — any additional increase in vitamin D was associated with an increase in CRP, a factor linked to stiffening of the blood vessels and an increased risk of cardiovascular problems.
“The inflammation that was curtailed by vitamin D does not appear to be curtailed at higher levels of vitamin D,” says Amer. “Clearly vitamin D is important for your heart health, especially if you have low blood levels of vitamin D. 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.”
In the light of the recent findings, Amer warns against taking supplements without consulting the physicians. He also urges and physicians should know the potential risks. Each 100 international unit of vitamin D ingested daily produces about a one nanogram per milliliter increase 25-Hydroxyvitamin D levels in the blood. “People taking vitamin D supplements need to be sure the supplements are necessary,” Amer says. “Those pills could have unforeseen consequences to health even if they are not technically toxic.”