Vitamin D supplements may help to reduce the severity and frequency of the common cold

The common cold has returned after a couple of years of mask-wearing, social isolation, and hand sanitising. Vitamin D supplementation, fortunately, may be able to shorten the length of a cold.

Because we spend more time indoors during the winter, we may be more susceptible to common colds. 

Vitamin D levels, on the other hand, may influence the likelihood of catching a cold. When vitamin D levels are lowest in the winter, there are more chances of getting cold, and when vitamin D levels are highest in the summer, there are less chances of getting cold.

The majority of our vitamin D comes from the sun's rays (80–100%), with only a minor amount coming from our diet. In the winter, those living at latitudes are more likely to have low vitamin D levels (vitamin D insufficiency). 

Vitamin D deficiency is also more common in people who spend most of their time indoors or with their skin covered. In the winter, more than half of the world population is thought to be deficient in vitamin D.

Between October and March, the sun's beams are too feeble to supply enough vitamin D. This means that people's vitamin D levels are likely to drop from October to March.

Vitamin D has been shown to influence the likelihood of developing common colds and other respiratory illnesses in studies. People with low vitamin D levels are more likely to have a cold, whereas those who take vitamin D supplements are less likely to catch one.

During 12 weeks of basic military training, research discovered that vitamin D-sufficient military recruits were less likely than vitamin D-deficient recruits to catch a cold. Then they also looked at how vitamin D supplementation affected common colds during the winter. 

Recruits were given either simulated sunlight (UV radiation via a whole-body irradiation cabinet) or oral vitamin D3 tablets as a supplement (1,000 IU per day for four weeks to restore vitamin D to normal levels and then 400 IU per day for eight weeks to maintain healthy vitamin D levels). Almost all recruits were vitamin D sufficient after taking supplements.

Research found that Vitamin D supplementation helped to lower the intensity of common cold symptoms by 15%.

Between October and March, it's difficult to obtain enough sunlight, therefore it's a good idea to take a daily vitamin D supplement of 10 micrograms (this value is sometimes shown as 400 IU on the label). If you don't get enough sunlight or haven't taken vitamin D supplements since October, you may need to take 25 micrograms (1,000 IU) of vitamin D for four weeks to get your vitamin D levels back to normal.

Make sure you get regular sunshine exposure during the summer to ensure you get enough vitamin D. The safe solar exposure is 15 minutes in the sun between 10 a.m. to 3 p.m.