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 Researchers examined data combined from seven previously published
studies with a total of 955 asthma patients who were randomly
selected to take vitamin D or a placebo pill, in addition to any
other medicines prescribed to manage their symptoms.
When asthma patients took vitamin D supplements, they were 54
percent less likely to have an attack severe enough to require an
emergency room visit or hospital admission, the study found. They
were also 31 percent less likely to have frequent asthma attacks
requiring treatment with corticosteroids.
The apparent benefits of taking vitamin D were significant only in
people who started out with a deficiency, however.
“The take-home message is that asthma patients who suffer with
attacks (exacerbations) should get their vitamin D level checked,
and if it is low, they should take a vitamin D supplement - there is
negligible risk associated with doing this, and there is pretty good
evidence to suggest that this could reduce their risk of having an
attack,” said senior study author Dr. Adrian Martineau of Queen Mary
University of London in the UK.
“It’s very important to emphasize that asthma patients should not
stop taking their usual asthma therapy,” Martineau said by email.
“All of the studies included in our review looked at the effects of
giving vitamin D on top of usual therapy.”
Worldwide, more than 300 million people have asthma, and the disease
is responsible for an estimated 400,000 deaths each year,
researchers note in The Lancet Respiratory Medicine.
In the study, participants lived in six countries on three
continents and ranged in age from 1 to 85 years.
Vitamin D supplement doses varied across all the studies in the
analysis. One study tested a 100,000 IU (international units) dose
every two months; four studies examined daily doses ranging from 500
IU to 2,000 IU; and two studies explored giving patients vitamin D
both daily and once every two months.
Supplements appeared to have the biggest impact on reducing the risk
of asthma attacks in people who started out with blood levels of the
circulating form of vitamin D that were below 25 nanomoles per liter
(nmol/L), which is widely considered deficient. For people who
started with circulating levels of 25 nmol/L or higher, there was
some reduction in asthma attacks, but the difference was too small
to rule out the possibility it was due to chance.
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One potential explanation of the results is that vitamin D boosts
immunity to respiratory viruses that are the major precipitant of
asthma attacks, Martineau said. It also dampens harmful inflammatory
responses in the airway that can contribute to the development of an
asthma attack and may enhance the anti-inflammatory effects of
corticosteroids for some people.
“In addition to benefits in asthma, vitamin D supplementation can
reduce risk of colds and flu in people who don’t have asthma and
protect against rickets in children and osteomalacia (softening of
the bones) in adults,” Martineau said.
“It is possible to take too much vitamin D, and if you do, it can
cause high calcium levels that can result in kidney damage in
extreme cases,” Martineau added. “However, this would not occur at
the doses investigated in the trials that contributed to our
analysis.”
The study didn’t examine the ideal dose of vitamin D or test
possible reasons the supplement might ease asthma symptoms. The
small studies in the analysis also had different methods of
measuring the effectiveness of vitamin D for reducing asthma
attacks, making it hard to say for sure who would benefit most from
supplements.
“This analysis suggests that vitamin D supplementation may be
beneficial in patients with asthma, although the evidence is not yet
strong enough to recommend its use,” said Dr. Richard Beasley of the
Medical Research Institute of New Zealand in Wellington, coauthor of
an accompanying editorial.
“Vitamin D supplementation is potentially an attractive therapeutic
approach as it is relatively cheap, and vitamin D deficiency is
common in many populations where asthma is also common,” Beasley
said by email.
SOURCES: http://bit.ly/2glkQbY and http://bit.ly/2yx8J3q The Lancet
Respiratory Medicine, online October 3, 2017.
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