'No evidence' that vitamin D protects against colds

There is “no proof vitamin D stops colds,” BBC News has reported, as “scientists say they can find no convincing evidence to show that taking vitamin D supplements will fend off a cold”.

This news comes from a well-designed trial into whether vitamin D reduced the incidence or severity of upper respiratory tract infections (URTIs) in healthy adults. URTIs are infections that affect the nose, sinuses and throat and include the common cold and flu.

Some have argued that vitamin D may play a role in protecting against cold. This is because natural levels of vitamin D drop during the winter (vitamin D is primarily produced when the skin is exposed to sunlight). This drop in vitamin D levels may lead to a drop in immune function, making people more vulnerable to URTIs. It has been suggested that taking supplements is a way to boost immune function and protect against infection.

To test this theory, researchers gave vitamin D to 161 healthy adults for 18 months while a further 161 were given a dummy pill (placebo). Every month the study participants were asked about the number and severity of URTIs they had. The results showed there was no difference in the number of URTI episodes, or the severity of the infection, between the groups during this period.

Significantly, the study mainly included people with normal or near-normal levels of vitamin D, so there may still be a role for supplements in those who are already deficient in vitamin D.

For most of us, there remains no easy way to avoid getting winter sniffles other than washing our hands regularly to avoid germs.