2007-07-18 10:56:46
Oranges
Vitamin C, found naturally in citrus fruit, might not help prevent colds
Taking a daily supplement of vitamin C will not protect most people from common
colds, scientists say.
A review of 30 studies, involving 11,350 people, also found doses of at least
200mg per day did little to reduce the length or severity of colds.
But people exposed to periods of high stress, like marathon runners, could
reduce their risk of catching colds by half if they took the vitamin daily.
The Australian and Finnish team's study is published in the Cochrane Library.
It doesn't make sense to take vitamin C 365 days a year to lessen the chance of
catching a cold
Professor Harri Hemil
Researchers at the Australian National University and the University of
Helsinki concluded that, for most people, the benefits of taking vitamin C
daily were so slight that they were not worth the effort or expense.
Although they found it could reduce the duration of colds by up to 8% in adults
and 13.6% in children, as most people only have two or three colds every year,
this benefit is only very small.
Useful effects
Author Professor Harri Hemil , said: "It doesn't make sense to take vitamin C
365 days a year to lessen the chance of catching a cold."
However, they say it may be justified in those exposed to severe cold or
physical stresses, where vitamin C doses reduced the risk of getting a cold by
half.
Furthermore, they say there is "tantalising" evidence from one study that very
large doses of vitamin C taken at the beginning of a cold might have a useful
effect.
But more research would be needed to evaluate this possibility.
In the 1970s, Nobel Prize-winning chemist Linus Pauling encouraged people to
take 1,000mg of vitamin C daily to ward off colds.
But since then the effects of the vitamin on colds has remained controversial.
Fighting infection
The current recommended daily allowance of vitamin C is just 60mg, and
Catherine Collins, a registered dietician with the British Dietetic
Association, says an optimum amount would be 200mg every day.
But she said most people could easily obtain this amount through eating five
portions of fruit and vegetables every day.
Furthermore, eating too much vitamin C means it cannot be absorbed and so is
removed from the body.
Although infection-fighting white blood cells do use vitamin C, Ms Collins said
there was very little evidence to suggest that it could help fight off colds.
She said: "It sounds biologically plausible because vitamin C does help improve
our immune systems, but it only seems to work if people are deficient in it in
the first place, which is very rare."
However, she added that the study was useful in adding to the existing body of
evidence concerning Vitamin C.