How does Vitamin D affect the immune system?

Key Points

• Some studies show a connection between vitamin D and immune health.
• Safe sun exposure is the best way to increase vitamin D levels.
• If you think you’re vitamin D deficient, talk to your healthcare professional.

Many of us grew up with adults who were often trying to get us outside to soak up some sunshine, and it seems they were onto something. 

While the ‘slip, slop, slap, seek, slide’ message remains — you can never be too sun-smart in Australia — it turns out a little ray of sunshine may be good for you. Vitamin D (essential for strong bones and muscles) is produced by the body when we are exposed to the sun’s UV radiation. 

But does vitamin D affect the immune system? The science is still evolving; however, we do have evidence that links the two.

How does vitamin D impact the immune system? 

What’s the relationship between vitamin D and the immune system? Emergency department doctor, researcher, and Healthylife Advisory Board member Dinesh Palipana says while the importance of vitamin D for good bone health is known, studies are now exploring vitamin D’s effect on immunity.

“Many cells in the immune system are thought to have vitamin D receptors. However, we’re still learning the details of these interactions,” Dr Dinesh says.

“We’ve seen evidence of vitamin D impacting various diseases relevant to the immune system. A 2019 analysis found that vitamin D supplementation was safe and it may protect against respiratory infections. Vitamin D deficiency has also been linked to autoimmune disorders like rheumatoid arthritis.”

Vitamin D deficiency: who’s most at risk? 

Dr Dinesh says Australians’ vitamin D levels vary depending on the season and location, with deficiency most prevalent in winter and in the nation’s southern regions. 

“The groups with the greatest risk of vitamin D deficiency are those who are housebound, community-dwelling older people, those with a disability or in residential care, people with darker skin tones, and others who regularly avoid the sun or work indoors.”

He says, “The best way to know if you’re vitamin D deficient and need supplementation is to talk to your healthcare professional.”

Foods like salmon, mackerel, tuna and shiitake mushrooms are good dietary sources of vitamin D

Getting vitamin D

How can we obtain natural immune system support with vitamin D? You could take a look at your diet. Dr Dinesh says some foods, such as milk, breads and cereals, are fortified with added vitamin D.

“Foods like salmon, cod liver oil, mackerel, tuna and shiitake mushroom have comparatively higher levels of vitamin D.”

Fun fact: did you know that putting your mushrooms in the sun increases their vitamin D content? Just 15 minutes of ‘mushroom tanning’ is enough to increase the vitamin D concentration. 

“There are also vitamin D supplements you can consult your healthcare professional about,” Dr Dinesh says. “However, tailoring vitamin D intake should be done with the guidance of a health professional.”

Don’t forget to also move your body. Exercise has been shown to reduce the risk of illness and improve immunity. A healthy diet is also important for a strong immune system.

The sun is the main source of vitamin D production for our body, which may help support immunity

Catch the sun: how to safely soak up vitamin D for immune system support

“The sun is the main source of vitamin D production for our body,” says Dr Dinesh, adding that only 5 to 10% of our vitamin D requirements are met through our diet. 

“The Cancer Council of Australia highlights that the best source of vitamin D is UVB radiation from the sun. For many, regular, incidental sun exposure generates enough vitamin D.” 

Those levels of UV radiation will depend on where you are in Australia, the time of year and day, and the cloud cover.

“The Cancer Council advises that when the UV Index is three or more, as it often is in summer, most of us can get enough exposure for vitamin D by just a few minutes outdoors on most days of the week. When the UV Index drops below three, we can spend time outdoors in the middle of the day with some uncovered skin.”

But we need to be sun-smart. “Sun protection should be applied when the UV Index is three or more; or when spending a long time outdoors,” Dr Dinesh adds. 

You’ll find information on the UV index where you are on the Cancer Council's SunSmart app and the Bureau of Meteorology’s website.

We’re just beginning to understand the importance of vitamin D for immunity

Natural immune system support: discover more

The role that vitamin D plays in our immune health is subject to ongoing study, but we do know that safe sun exposure is the best way to increase our vitamin D levels. If you’re concerned about your immune system health or have more questions about vitamins and immunity, consult your healthcare professional. 

Related:

• 15 foods that may help support your immune system
• How does exercise affect the immune system?
• The time-tested power of adaptogens for stress relief

Dinesh Palipana is a doctor in the emergency department, lawyer, spinal cord injury researcher, and disability advocate who has a spinal cord injury. Dinesh sits on the advisory board at Healthylife.

Reviewed by the Healthylife Health Advisory Board October 2023