Vitamine D tegen luchtwegeninfecties*
Uit een studie onder 250 kinderen blijkt dat goede bloedwaarden vitamine D
belangrijk zijn ter voorkoming van luchtwegeninfecties in de winter. Gemiddeld
hadden de kinderen aan het begin van de studie veel te lage bloedwaarden van 7
ng/ml. Zeven weken lang kregen de kinderen melk de ene helft aangevuld met 7,5
mcg vitamine D/dag en de andere helft zonder aanvulling. Na zeven weken waren
de bloedwaarden vitamine D in de groep met aanvulling van vitamine D nog laag
doch duidelijk gestegen tot 19 ng/ml. In deze groep bleken nu de kinderen wel
de helft minder luchtwegeninfecties te hebben.
Vitamin D Supplementation Can Decrease Risk of
Respiratory Infections in Children
A study conducted in Mongolian schoolchildren supports the possibility that
daily vitamin D supplementation can reduce the risk of respiratory infections
in winter. In a report that will appear in the journal Pediatrics and has
received early online release, an international research team found that
vitamin D supplementation decreased the risk of respiratory infections among
children who had low blood levels of vitamin D at the start of the study.
"Our randomized controlled trial shows that vitamin D has important
effects on infection risk," says Carlos Camargo, MD, of Massachusetts
General Hospital (MGH), the study's corresponding author. "In almost 250
children with low blood levels of vitamin D during winter, we found that taking
a daily vitamin D supplement cut in half the risk of a respiratory infection."
Several recent investigations have suggested that vitamin D -- best known for
its role in the development and maintenance of strong bones -- has additional
important roles, including in immune function. Studies led by Camargo and other
researchers have associated higher vitamin D levels with reduced risk of
respiratory infections such as colds or flu, but such observational studies
cannot prove that the vitamin actually protects against infection. That kind of
evidence must come from randomized controlled trials comparing two similar
populations that either do or do not receive an intervention such as vitamin D
supplementation. The first such trial, in Japanese schoolchildren, had
equivocal results, showing a reduction in the risk of one type of influenza but
no effect on another type, so many organizations have called for further
randomized trials to settle the issue.
Since vitamin D is naturally produced by the body in response to sunlight,
maintaining adequate levels in winter is particularly challenging in areas such
as the northern U.S. and Canada that have significant seasonal variations in
daily sunlight. The current study analyzed data from the Blue Sky Study,
conducted in Ulaanbaatar, Mongolia, by a team led by Harvard investigators in
collaboration with local health researchers. Mongolians are known to be at high
risk for vitamin D deficiency, especially during winter, and the Blue Sky Study
followed schoolchildren, all of whom were found to have low blood levels of
25-hydroxyvitamin D (25OHD), which is considered the best measure of vitamin D
status, at the study's outset.
In the current study, Camargo and colleagues compared the number of winter
respiratory infections among a group of children who received daily doses of
vitamin D added to locally produced milk with that of a control group receiving
the same milk without added vitamin D. The supplement was undetectable so that
children, teachers, and local researchers could not tell which group received
vitamin D. While blood samples taken at the outset of the study revealed
vitamin D deficiency in all participants, with average 25OHD levels around 7 ng/ml
(17 nmol/L) in both groups, at the end of the seven-week treatment period,
differences between the two groups were significant, with those receive vitamin
D averaging 19 ng/ml (47 nmol/L), which although still low was significantly
higher than at the start of the trial. Based on reports from their parents, the
children receiving vitamin D had about half the incidence of respiratory
infections that the control group had.
"Our study design provides strong evidence that the association between
low vitamin D and respiratory infections is causal and that treating low
vitamin D levels in children with an inexpensive and safe supplement will
prevent some respiratory infections," says Camargo, a professor of
Medicine at Harvard Medical School. "The large benefit was undoubtedly
related to the low baseline vitamin D levels of these children, so I would not
expect the supplement to provide similar benefit in children who start with
healthy levels of vitamin D. The key question for future research is at what
initial vitamin D level would children no longer receive benefit from winter
supplementation?"
The researchers note that while the vitamin D dosage used in this study (300 IU
daily) was higher than the recommended daily dosage at the time the study was
launched, since then the U.S. Institute of Medicine has raised the recommended
dose for children to 400 IU, and other groups recommend daily dosages as high
as 1,000 IU for children at risk for vitamin D deficiency. The authors also
point out that, while Mongolia may appear to have little in common with the
U.S., the low baseline vitamin D levels seen in study participants are
relatively common in some groups of Americans, such as African-American
children living in northern states.
De studie.
(November 2012)
Reacties: