When it comes to cardiovascular
health, more Vitamin D may not necessarily be better
New research by Johns Hopkins scientists
suggests that vitamin D, long known to be important for bone health
and in recent years also for heart protection, 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.
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 (CRP).
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," says
Amer, whose newest finding appears in the Jan. 15 issue of the American
Journal of Cardiology. "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."
Amer says consumers should exercise caution before taking supplements
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."
Amer and Qayyum, also an assistant professor in the division of
general internal medicine at Hopkins, say the biological and molecular
mechanisms that account for the loss of cardiovascular benefits
are unclear.
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