Taking a supplement of vitamin D — the so-called 'sunshine vitamin' — could help fight off colds and flu, according to a new study from Finland.

Researchers at the University of Tampere gave 164 male military recruits either 400IU of vitamin D or a placebo every day over the course of six months, from October to March — a period chosen because of the lower sunlight levels in the Northern Hemisphere at that time of year.

Vitamin D, which is produced in the body when skin is exposed to the sun's rays, has been linked with immune boosting benefits and scientists have hypothesized that shorter and darker days during colder months may explain higher incidences of cold and flu in the winter.

At the end of the study, the research team found no significant difference between the two groups in terms of the average number of days subjects missed from work as a result of respiratory illnesses. However, the soldiers that had taken the vitamin D supplements were more likely to have missed no days at all from work as a result of respiratory infections compared with those in the control group.

Overall, 51 percent of subjects who took vitamin D remained completely healthy during the six months compared with 36 percent of those who took the placebo.

Illkka Laaski, who led the study, told Reuters Health that the results indicated "some evidence" that vitamin D helped to prevent cold and flu-type illnesses.

The 400IU dose, it should be noted, is the current Dietary Reference Intake in the United States and is based on epidemiological research on the deficiency disease rickets dating back to the 1940s. But it is widely believed that when the revised U.S. Dietary Guidelines are released in October that level could rise significantly, to as much as 1000 IU/day or more.