Vitamin D is necessary for the proper functioning of your immune system, which is your body’s first line of defense against infection and disease. This vitamin plays a critical role in promoting your immune health. It has both anti-inflammatory and immunoregulatory properties and is crucial for the activation of immune system defenses.
Vitamin D enhances the pathogen fighting effects of monocytes and macrophages — white blood cells that are important parts of your immune defense — and decreases inflammation, which helps promote immune response.
Unfortunately, many people are vitamin D deficient, which may negatively affect immune function. In fact, low vitamin D levels are associated with an increased risk of upper respiratory tract infections, including influenza and allergic asthma.
Some studies show that supplementing with vitamin D may improve immune response. Recent research suggests that taking this vitamin may protect against respiratory tract infections.
In a 2019 review of randomized control studies in 11,321 people, supplementing with vitamin D significantly decreased the risk of respiratory infections in people deficient in this vitamin and lowered infection risk in those with adequate vitamin D levels.
This suggests an overall protective effect of vitamin D on immune health.
Other studies note that vitamin D supplements may improve response to antiviral treatments in people with certain infections, including hepatitis C and HIV.
Depending on blood levels, anywhere between 1,000 and 4,000 IU of supplemental vitamin D per day is sufficient for most people, though those with more serious deficiencies often require much higher doses.