Shining a light on vitamin D and immune health

In actual fact, one in every four Australians aren’t getting enough vitamin D – and only 5% take a supplement to support healthy vitamin D intake.[1] Our vitamin D levels are often lower in the colder months because we don’t get as much sun exposure compared with the summer months.[1] This is significant, as vitamin D is important for many functions in the body – but its involvement in immune health is where vitamin D really shines.

Quick Overview

• Vitamin D is important for immune health as it plays a supportive role in immune cell function
• Adequate levels of vitamin D play a protective role against mild upper respiratory tract infections, like common colds
• Safe sun exposure and including vitamin D-rich foods into your diet such as oily fish and egg yolk are good ways to boost your vitamin D levels

What is vitamin D?

Although vitamin D is actually a fat-soluble hormone it’s commonly referred to as a vitamin. Vitamin D2 is one of its main forms which is found in plants and is also often synthetically produced and found in fortified foods and dietary supplements. It’s not absorbed and used as well as other types of vitamin D, but is still important.[2]

Vitamin D3 is another form which is found in animal-based foods. It’s also produced by the body when sunlight (or ultraviolet [UV] rays) are exposed to the skin.[2]  

When UVB rays from the sun hit your bare skin, or when you consume vitamin D-rich foods, the kidneys and liver then ‘activate’ vitamin D3. From here, it’s ready to go to work in the body.[2]  

Vitamin D and immune function

The immune system can be broken down into physical barriers (skin, mucous membranes of the airways), innate and adaptive immunity. Vitamin D is vital to the function both innate and adaptive immunity, but in different ways.

Innate immunity

Our innate immunity, which is with us from birth, reacts quickly to ‘threats’ like bacteria and viruses. Its defence system includes the physical barrier (skin and mucous membranes) and immune cells (like white blood cells), as well as chemicals and enzymes.[3]

Vitamin D helps to control how our immune cells respond to bacteria and viruses. Immune cells like monocytes (a type of white blood cell) require plenty of vitamin D to help prevent mild bacterial and viral infections.[3]

Adaptive immunity

Also known as ‘acquired’ immunity, adaptive immunity is a longer lasting, specific type of immunity you develop against bacteria, viruses and fungi over the course of your life.

It relies on two types of immune cells called B and T cells which produce various defences against viruses and bacteria via the ‘antimicrobial pathway’. In order for this pathway to function properly, it requires healthy levels of vitamin D. Vitamin D is also needed by the T cells that influence the function of the pathway.[3]

Vitamin D and respiratory tract infections

Low serum (blood) vitamin D levels have been found to increase susceptibility to mild acute respiratory tract infections, like common colds.[4] A number of studies have also shown that supplementing with vitamin D can help to prevent these mild infections. [4]  Ensuring you’re getting adequate amounts of vitamin D from safe sunlight exposure, vitamin D-rich foods or a supplement (if needed) is important.

How much vitamin D do you need?

As a fat-soluble nutrient, vitamin D3 is present in fatty foods (like oily fish and egg yolk) and also needs dietary fat to be used by the body.[5]

The following are the National Health and Medical Research Council’s recommendations for adequate daily vitamin D intake for both male and females by age:[6]

• 0-12 months: 5mcg (200IU)
• 1-18 years: 5mcg (200IU)
• 19-50 years (including pregnancy and lactation): 5mcg (200IU)
• 51-70 years: 10mcg (400IU)
• 70 years and over: 15mcg (600IU)

Safe sun exposure

For fairer-skinned people in Australia, safe sunlight exposure for 10-15 minutes at around 10am and 3pm three to four times a week from October-March is sufficient for vitamin D production in the body. Longer exposure is needed in the southern states of Australia from April to September.[7]

In January, as little as 2-14 minutes four times per week around midday is all that is needed. Those with dark skin pigmentation are at a greater risk of vitamin D deficiency and require approximately six times more UV exposure.[7]

What foods contain vitamin D?

Here’s a small but seriously nutritious range of foods that you can include in your diet to boost your vitamin D levels:[8]

• Egg yolks: that’s right, folks – don’t throw out the yolks! They’re the most nutritious bit - part of their nutritional profile includes vitamin D3
• Oily fish: sardines, trout, and salmon have a many great health benefits, including high levels of vitamin D3
• Cod liver oil: it may look like a supplement to us, but it is a traditional part of the diet in many northern European countries, such as Norway.[9] Cod liver oil is how some people in this part of the world continue to support their immune systems throughout the winter.
• Mushrooms: For a vegan source, look to the humble mushroom. These fungi have the plant-based form of vitamin D2. One caveat is that these need to be grown with UV-exposure, not in the dark. Wild or UV-exposed mushrooms synthesize vitamin D from the sun – much like humans do.
• Beef liver: if you’re not sure how palatable you’ll find beef liver, ask your butcher to grind it up into some regular beef mince for you. Add some mushrooms to your mince for a Bolognese and you’ve got yourself a vitamin D-rich meal!   

Ensuring you’re on the A-list when it comes to your vitamin D status is not only great for your overall immune function – it’s also easy. Including an early morning or late afternoon walk in the winter and adding a couple of key ingredients to your meals can help to boost your vitamin D levels and keep your immune system in great shape.

For more tips on building a robust immune system for winter, check out this article on traditional Chinese medicine tips for winter wellness.

References:

1. Australian Bureau of Statistics. Last updated 2013, accessed June 2021 from https://www.abs.gov.au/statistics/health/health-conditions-and-risks/australian-health-survey-biomedical-results-nutrients/latest-release
2. Norman AW. The American Journal of Clinical Nutrition 2008;88(2):491S-499S.
3. Tiosano D. The Journal of Clinical Endocrinology & Metabolism 2013;98(4):1685-1693.
4. Martineau AR, et al. BMJ 2017;356:i6583.
5. Nair R, et al. J Pharmacol Pharmacother 2012;3(2):118-126.
6. National Health and Medical Research Council. Last updated March 2014, accessed June 2021 from https://www.nrv.gov.au/nutrients/vitamin-d
7. Samanek AJ, et al. Med J Aust 2006;184(7):338-341.
8. National Institutes of Health. Last updated March 2021, accessed June 2021 from https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#:~:text=An%20FNB%20committee%20established%20RDAs,40%20IU%20(Table%202).
9. Griffing G.T. Medscape J Med 2008;10(1):8.