Influenza, more commonly known as the flu, is a respiratory infection that is caused by a virus infecting the nose, throat, and lungs. Influenza is most common during winter and can cause fever, chills, sore throat, cough, body aches, and fatigue
What is vitamin D ?
Vitamin D is an important part of the immune system. Some studies have shown that there is a link between vitamin D levels and the risk of getting influenza. People who have low vitamin D levels may have a higher chance of developing influenza.
Influenza epidemics occur in the winter, and vitamin D levels are dramatically lower in the winter as well. Since influenza is seasonal, it is thought that vitamin D might be a factor that can affect your chances of getting the flu.
Many studies that have been done about influenza have shown that people who have lower levels of vitamin D are more likely to get influenza. Not many studies have been done about treating influenza with vitamin D, but some research has shown a relationship between higher levels of vitamin D and shorter duration of the influenza infection.
On the other hand, some experiments have shown that taking vitamin D supplements can reduce your chances of getting influenza in the first place. Some researchers recommend getting more vitamin D to protect against influenza, but more experiments are needed to say whether or not taking a vitamin D supplement can for sure prevent influenza.
If you want to take vitamin D to prevent influenza, it is unlikely to cause you any harm, as long as you take less than 10,000 IU per day. However, it’s not proven that taking vitamin D will help to prevent or treat influenza.
If you have influenza, you shouldn’t take vitamin D in place of your treatment medications. Talk to your physician for more advice about taking supplements (4).
What does recent research say about vitamin D and influenza?
An experiment done in the United States gave African-American women either 800 IU vitamin D per day for 2 years, then 2,000 IU per day for the 3rd year, or a dummy pill. The researchers looked at how many times those women got influenza over the 3 years. They found that (3):
The vitamin D group had fewer influenza symptoms compared to the dummy pill group.
Only one person in the vitamin D group had influenza when the dose was at 2,000 IU per day.
The dummy pill group had influenza symptoms mostly in the winter, whereas the people who got influenza in the vitamin D group had symptoms year round.
This experiment suggests that vitamin D, especially at higher doses, may help to protect against seasonal influenza. The researchers conclude that vitamin D supplements might be useful to prevent the flu, but that more experiments are needed.
An experiment done with Japanese schoolchildren looked at the effects of vitamin D supplements on their chances of getting influenza. The researchers gave children either 1,200 IU vitamin D per day for 3 months during the winter, or a dummy pill. They found that (2):
More children in the dummy pill group got influenza A than children in the vitamin D group.
There was a preventive effect of 1,200 IU
vitamin D per day on children getting influenza A.
The researchers conclude that taking 1,200 IU of vitamin D in children can help to protect against seasonal influenza A.
In this study, there was no effect of vitamin D on influenza B, possibly because vitamin D may respond in different ways to the inflammatory proteins in the viruses.
A study done in 2011 looked at vitamin D levels and respiratory infections, like influenza, in a large group of British adults. The researchers found that (1):
For each 4 ng/ml increase in vitamin D levels in the body, there was a 7% lower chance of developing influenza.