Low Vitamin D Levels Associated with Colds and Flu
A new study has found that vitamin D may play a role in helping the immune
system ward off respiratory diseases like the common cold.
Vitamin D helps your body absorb calcium, which keeps your bones strong. But
the vitamin is naturally present in few foods. It’s added to some, such as milk,
and also available as a dietary supplement. Vitamin D is produced by the body
when sunlight strikes the skin, but most people in the U.S. don’t get enough
sunlight to make sufficient amounts, particularly in winter months.
Some recent studies suggest that taking extra vitamin D can have health
benefits beyond building bone, but the evidence hasn’t been conclusive. Several
studies, for example, have linked low levels of vitamin D with the risk for
respiratory tract infections. However, these studies looked at small,
non-diverse groups of patients.
To investigate, a research team led by Dr. Adit Ginde of the University of
Colorado at Denver and Dr. Carlos A. Camargo at Massachusetts General Hospital
looked at data from the Third National Health and Nutrition Examined Survey
(NHANES III), which was conducted between 1988 and 1994. NHANES is a periodic
survey of the U.S. population by CDC's National Center for Health Statistics.
Participants in the survey went through physical and laboratory tests, submitted
information on household characteristics and documented their health
histories.
Using data from almost 19,000 people, the researchers examined the
relationship between blood serum levels of 25-hydroxyvitamin D (25[OH]D)—a
recognized indicator of the body’s vitamin D stores—and respiratory tract
infections like colds and flus. Their analysis adjusted for other factors, such
as the season of the year, age, body mass index and smoking history. Their work
was funded by NIH’s National Heart, Lung and Blood Institute (NHLBI).
The team reported in the February 23, 2009, issue of the
Archives of
Internal Medicine that 24% of the participants with the lowest levels of
25[OH]D in their serum (less than 10ng/mL) had recent upper respiratory tract
infections. In contrast, only 17% of those with the highest levels in their
serum (greater than 30ng/mL) had recent infections. Of those with serum levels
in between, 20% reported recent upper respiratory tract infections. These
associations held regardless of the season. Notably, the relationship between
vitamin D and respiratory tract infections seemed to be even stronger in people
with asthma and chronic obstructive pulmonary disease.
The important discovery of a possible association between vitamin D and
respiratory tract infections provides a strong rationale for clinical trials to
confirm this finding.
"We are planning clinical trials to test the effectiveness of vitamin D to
boost immunity and fight respiratory infection, with a focus on individuals with
asthma and chronic obstructive pulmonary disease, as well as children and older
adults—groups that are at higher risk for more severe illness," Ginde says.
"While it's too early to make any definitive recommendations, many Americans
also need more vitamin D for its bone and general health benefits."
—by William Duval, Ph.D.
