Vitamin D supplements unlikely to reduce risk of colds

By Kathy Oxtoby

BMJ Group News

What do we know already?

Your body uses vitamin D to help make strong, healthy bones. Most of the vitamin D in our bodies is made in the skin, when it is exposed to sunlight. You can also get it from such foods as egg yolks, oily fish, and some dairy products, or by taking supplements.

Some people think that taking extra vitamin D might help with a cold. But there’s little research about this.

To find out more, researchers studied 322 healthy adults aged 18 or over. They were randomly chosen to take an initial high dose of vitamin D, the same dose one month later, then a lower dose every month for 18 months, or a dummy pill (placebo) for the same period.

What does the new study say?

During the 18-month study period, there were 593 colds among those who took vitamin D, and 611 among those who took the dummy treatment. This difference is small enough to be down to chance. Taking vitamin D did not seem to make much difference in reducing people’s chances of getting a cold.

Researchers also found that taking vitamin D did not seem to lessen the length or severity of cold symptoms. People who had colds during the study had symptoms for an average of 12 days, whether or not they took vitamin D.

Taking the supplement appeared to make little difference when it came to people taking time off work. Nearly half (41%) people of who had colds during the study took sick leave, whether they had been taking supplements or not.

How reliable is the research?

This is a randomised controlled trial, which is one of the best types of studies to find whether a treatment works. It was also carried out over a longer period of time and involved a larger group of people than previous research into vitamin D and cold prevention. And its findings are consistent with other studies that showed that taking vitamin D is unlikely to reduce people’s risk of catching a cold or to ease their symptoms.

However, more research is needed to see whether the level and frequency of the dosage of vitamin D has any impact on whether it can help to prevent colds and reducing symptoms.

What does this mean for me?

The little research that is available shows that taking vitamin D will not help to prevent you getting a cold or reduce your symptoms.

But it is important to have vitamin D in your diet as your body needs it to make strong, healthy bones. The Department of Health advises that most people should get enough vitamin D by eating a varied diet and by getting some sun. However, certain groups - including pregnant and breastfeeding women, young children, older people, and black and ethnic minority groups - may not get enough of this nutrient and need to take supplements.

You need to be careful not to take too much vitamin D from supplements, as the side effects include not feeling hungry, losing weight, feeling sick, vomiting, diarrhoea, headache, being thirsty, and feeling dizzy.

If you’re concerned about your vitamin D levels, you can talk to your GP about having a blood test.