including
hospitalizations for asthma, use of
inhaled steroids and total IgE levels,
according to a study that will appear in
the first issue for May of the
American Journal of Respiratory and
Critical Care Medicine.
While previous in
vitro studies have suggested that
vitamin D may affect how airway cells
respond to treatment with inhaled
steroids, this is the first in vivo
study of vitamin D and disease severity
in children with asthma.
Juan Celedon, M.D.,
Dr. P.H. and Augusto Litonjua, M.D.,
M.P.H. of Harvard Medical School and
colleagues recruited 616 children with
asthma living in the Central Valley of
Costa Rica, a country known to have a
high prevalence of asthma. Each child
was assessed for allergic markers,
including both allergen-specific and
general sensitivity tests, and assessed
for lung function and circulating
vitamin D levels. Children whose forced
expiratory volume in one second (FEV1)
exceeded 65 percent of the predicted
value were also tested for airway
reactivity.
They found that
children with lower vitamin D levels
were significantly more likely to have
been hospitalized for asthma in the
previous year, tended to have airways
with increased hyperreactivity and were
likely to have used more inhaled
corticosteroids, all signifying higher
asthma severity. These children were
also significantly more likely to have
several markers of allergy, including
dust-mite sensitivity.
"To our knowledge this
is the first study to demonstrate an
inverse association between circulating
levels of vitamin D and markers of
asthma severity and allergy," wrote Drs.
Celedon and Litonjua "While it is
difficult to establish causation in a
cross-sectional study such as this, the
results were robust even after
controlling for markers of baseline
asthma severity."
"This study suggests
that there may be added health benefits
to vitamin D supplementation" said Dr.
Celedon. Current recommendations for
optimal vitamin D levels geared toward
preserving bone health, such as
preventing rickets in children and
osteoporosis in adults.
"This study also
provides epidemiological support for a
growing body of in vitro evidence that
vitamin D insufficiency may worsen
asthma severity, and we suspect that
giving vitamin D supplements to asthma
patients who are deficient may help with
their asthma control" wrote Drs. Celedon
and Litonjua, noting that a clinical
trial should be the next step in this
research. "Whether vitamin D
supplementation can prevent the
development of asthma in very young
children is a separate question, which
will be answered by clinical trials that
are getting under way," he said.
A complication is that
vitamin D, unlike most other nutrients,
is primarily synthesized in the body
rather than consumed. Because about 90
percent of circulating vitamin D is
produced by the body in response to sun
exposure, deficiency is often related to
behavioral issues rather than an
inadequate dietary intake. Increased
time spent indoors, increased use of
sunscreen and sun-protective clothing
all lead to decreased levels of vitamin
D. Dietary sources of vitamin D,
primarily fortified foods and fatty fish
or fish oils, and vitamin D in current
multivitamin preparations are unlikely
to make up the deficiency.
"Ultimately, it is
only by investigating the effects of
vitamin D in doses at, and above, those
currently recommended that decisions can
be made on the optimal intake of vitamin
D and the possible prevention and
treatment of asthma," wrote Graham
Devereux, M.D., of the Department of
Environmental and Occupational Medicine
at the University of Aberdeen in the
accompanying editorial in the same issue
of the journal. |
