Caught a cold Don’t bother taking vitamin D – scientists say no evidence supplement will fend of the sniffles
Volunteers who took sunshine vitamin had as many colds as those taking placeboThere was also no difference in how long colds lasted or in their severity
13:08 GMT, 3 October 2012
Loading up on vitamin D is unlikely to prevent the common cold this winter, according to new research.
The study found those given large doses of the sunshine vitamin developed as many coughs and sniffles as those given placebo pills.
'In the population we studied, we can be very confident that it has no effect on prevention or severity (of colds),' said lead author Dr David Murdoch, from the University of Otago in Christchurch, New Zealand.
Can't shake that virus Vitamin D didn't do anything to shorten the length of colds in a recent study
The study included adults who were healthy to begin with, so Dr Murdoch said it was possible the vitamin could have a different impact on those who were deficient.
In the latest research they randomly assigned 322 adults either to receive a monthly dose of vitamin D – starting at 5mg nternational units for the first couple of months, then dropping to 2.5mg – or to get a placebo.
Over the next year and a half, people taking vitamin D had an average of 3.7 colds and other respiratory infections, versus 3.8 in the comparison group – a difference so small it could have been due to chance.
There was also no difference in how long colds lasted or in their severity, according to the report published in the Journal of the American Medical Association.
Dr Murdoch said: 'There's been quite a lot of hype around vitamin D for infection and all sorts of things.
'A lot of people are making a lot of
money out of promoting these substances, but… there's not a lot to back
He added that the only convincing evidence so far has linked extra vitamin D to better bone health.
Vitamin D can be found naturally in salmon, swordfish and eggs, as well as fortified milk, yogurt and orange juice.
Vitamin D is also manufactured in the skin in response to sunlight, but away from the equator, winter sun is too weak to supply enough of the vitamin to meet all the body's needs.
Participants in the new study started with an average vitamin D level of 29 nanograms per millilitre and in those who got the D supplements, levels rose to 48 ng/mL or more for the duration of the study.
The U.S. National Institutes of Health considers a level of 20 ng/mL and above adequate for overall health, with vitamin D deficiency occurring at less than 12 ng/mL.
'If you have a good diet and definitely if you're taking vitamin D, taking more is not going to help,' said Dr Jeffrey Linder from Brigham and Women's Hospital in Boston, who wrote a commentary accompanying the new study.
He said some research has suggested vitamin D helps support the immune system of children in the developing world who are deficient.
Past studies have suggested the sunshine vitamin could help clear bacteria and boost immune health.