August 6, 2010
Can Vitamin D Help Fight Off A Cold?
Young men may have more sick-free days through the cold and flu season if they take a daily vitamin D supplement, a small study published in the Journal of Infectious Diseases suggests.
Vitamin D has been the center of attention in many research studies of late, with studies linking low vitamin D levels in the blood to elevated risks of type 1 diabetes and severe asthma attacks in children and heart disease, cancer and depression in adults.
But whether the vitamin is the reason for the risks -- and whether taking the supplements can cut the risks -- has yet to be proven.
The body produces vitamin D naturally when the skin is exposed to sunlight. Because vitamin D levels in the human body are generally insufficient during the winter months in many parts of the world, researchers have been interested in whether vitamin D supplements may play a role in people's susceptibility to colds, flu and other respiratory ailments.
Some research has found in the past that people with lower vitamin D levels in their blood tend to have higher rates of respiratory infections than those with higher levels of the vitamin, said lead researcher Dr Ilkka Laaksi of the University of Tampere in Finland.
Recent lab research has shown that vitamin D may also play an "important role" in the body's immune defenses against respiratory pathogens, Laaksi told Reuters Health in an email.
"However, there is a lack of clinical studies of the effect of vitamin D supplementation for preventing respiratory infections," the researcher said.
In the current study, Laaksi and colleagues assigned 164 military recruits to take either 400 international units (IU) of vitamin D or inactive placebo pills every day for six months -- October to March, covering the months when people's vitamin D levels usually decline and when respiratory infections tend to peak.
At the end of the study, researchers found no clear difference between the two groups in the average number of days missed from duty due to a respiratory infection -- which includes bronchitis, sinus infections, pneumonia, ear infections and sore throat.
The team found that, on average, men who took the vitamin D supplement missed about two days from duty due to respiratory infection, compared with three days in the placebo group. The difference was not significant in statistical terms.
However, the team determined that men in the vitamin D group were more likely to have no days missed from work due to respiratory illness.
Overall, 51 percent of the vitamin D group remained "healthy" throughout the six-month study, versus 36 percent of the placebo group, the team reports.
Laaksi said the findings offer "some evidence" of a benefit from vitamin D against respiratory infections.
The extent of these benefits is still not clear, however. While recruits in the vitamin D group were more likely to not miss days from duty, they were no less likely to report having cold-like symptoms at some point during the six-month period.
Some other recent studies have shown conflicting results on the usefulness of vitamin D for lower the risk of respiratory ailments.
A Japanese study of schoolchildren published earlier this year found that those given 1,200 IU of vitamin D each day during the cold and flu season were less likely to contract influenza A. Of 167 children given the supplement, 18 developed the flu, compared to 31 of the 167 who were given placebos.
Another recent study of 162 adults found that those who received 2,000 IU of vitamin D every day for 12 weeks were no less likely to develop respiratory ailments than those who took placebos.
Larger clinical trials looking at different doses of vitamin D are still needed before the vitamin can be recommended for cutting the risk of respiratory infections, said Laaksi.
Health officials in the US recommend that adults up to the age of 50 get 200 IU of vitamin D daily, while older adults should get up to 600 IU. The upper limit is currently set at 2,000 IU per day. Higher amounts may raise the risk of side effects.
Some researchers say that people need more vitamin D than health officials recommend, and that intakes of more than 2,000 IU per day are safe. However, the exact optimal amount of vitamin D one should take remains under debate.
Vitamin D can be found in milk, cereals and orange juice fortified with vitamin D, as well as some fatty fish, like salmon. Experts typically recommend vitamin pills for people who do not get enough vitamins from their food.
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