During winter, we often worry about catching seasonal illnesses like the flu or COVID-19. Scrolling social media, you will likely have seen articles pop-up making claims that different supplements can boost the immune system. One common claim is that taking vitamin D supplements can help. But what is vitamin D, and can it really prevent seasonal illness?
With less daylight and more time spent indoors, people’s vitamin D levels can decrease in the winter. In fact, 35% of adults in the US are not getting enough. While getting adequate levels can help your immune system do its job, there is no scientific evidence that it will cure infection. There is also no consensus on the necessary dose to prevent illness. Always talk to your doctor first if you are wondering what your vitamin D levels are or considering taking a supplement.
What is Vitamin D?
Vitamins are nutrients the body requires in small amounts to stay healthy. Vitamin D is one that is vital to bone health, muscle movement, and immune system function. Naturally found in foods like fatty fish, egg yolks, and liver, it is also added to foods such as milk, yogurt, and orange juice. In addition to getting vitamin D from your diet, your body makes small quantities when your skin is exposed to the sun.
Vitamin D and the Immune System
Vitamin D is an immune system modulator. This means it can increase and decrease the activity of the immune system. Vitamin D influences many immune cells, including lymphocytes, dendritic cells, T cells, B cells, and neutrophils. Since it interacts with so many different immune cells, it can both help the body fight infection and reduce inflammation. This means it may help the body respond to viral infections like hepatitis, herpes, and respiratory viruses, and bacterial infections, like tuberculosis. However, vitamin D alone cannot prevent or cure these infections.
More Research is Needed
Laboratory studies using cells and epidemiological studies examining population patterns have established the important relationship between vitamin D and the immune system. However, the exact role it plays in preventing disease and how taking supplements can support immune health remains unclear.
The benefits observed in laboratory research using cells do not always appear in studies involving people. This may be because laboratory studies often use high doses of vitamin D beyond recommended levels. Human studies often use smaller, safer doses. Vitamin D may also be causing subtle changes that lead to its benefit but are difficult to observe in people compared to studying cells in the lab.
Studies in people sometimes leads to different results depending on the person or disease being studied. For example, one study observed that taking vitamin D was protective against respiratory tract infection in adults who were vitamin D deficient, but not children. Other studies found that vitamin D, when given with antibiotics, benefited tuberculosis patients, but it showed no benefit for patients with bacterial pneumonia.
Avoiding vitamin D deficiency is considered beneficial but ongoing research is needed to tease out why it benefits the immune system and whether it can entirely prevent disease. Right now, there just isn’t enough scientific evidence to say that taking vitamin D supplements will fully prevent disease. To learn more about how vitamin D could impact your personal health, it is best to talk to a health care professional.