Vitamin D - known to be important for bone health and for heart protection - can also cause harm if it exceeds normal levels, a new research has warned.
Johns Hopkins scientists suggested that vitamin D may stop conferring cardiovascular benefits and could actually cause harm as levels in the blood rise above the low end of what is considered normal.
The findings found 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), said study leader Muhammad Amer, M.D., an assistant professor in the division of general internal medicine at the Johns Hopkins University School of Medicine.
Amer and his colleague Rehan Qayyum, M.D., M.H.S., examined data from more than 15,000 adult participants in the continuous National Health and Nutrition Examination Survey, a nationally representative sample, from 2001 and 2006.
They 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," stated 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," he added.