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You’ve probably heard of vitamin D. It’s the sunlight vitamin, and you’re an Australian, which means it’s the one vitamin you don’t have to worry about.
Right?
Well, that’s not entirely accurate. In fact, up to 36% of Australians are deficient in vitamin D.
Vitamin D is essential for both bone and immune health, so getting enough of it is incredibly important for a healthy body. In this article, we’re going to look at the role vitamin D plays in the immune system, what happens when we don’t get enough of it, and the best ways to increase your vitamin D intake.
Let’s get into it.
Vitamin D is a vitamin that humans get from food and sunlight. About 80% of our intake comes from synthesising sunlight, with just 20% coming from our diet [1]. Also known as ‘calciferol’, vitamin D is essential for a functioning immune system and strong bones.
As more and more people eat processed foods and lead indoor lifestyles, the rate of vitamin D is growing globally [2]. In Australia, though, our vitamin D levels are actually pretty good – 77% of Australians have levels above 50 nanamoles per litre, which is considered the minimum healthy amount of vitamin D an average person needs.
Since more exposure to sunlight generally means higher levels of vitamin D, it shouldn’t surprise you that 94% of Queenslanders have sufficient vitamin D in summer (compared to just 81% of New South Wales residents). Over winter, the average number of Aussies with enough vitamin D drops to 64%, spiking back up to 86% in summer, and there are similar results for city-dwellers versus people in regional communities.
In short, if you work indoors, live in the city, and live in a colder part of Australia, you’re more likely to have suboptimal levels of vitamin D.
So why does vitamin D actually matter for our health?
Well, it’s used for two main functions in our body: maintaining strong bones and supporting our immune systems. The interaction between vitamin D and calcium is pretty complex, so, in this article, we’ll stick with talking about the second topic: immune health.
Almost all the cells in your immune system – including neutrophils, macrophages, dendritic cells, B cells, and T cells – have vitamin D-metabolising enzymes in them [3].
Through these enzymes, vitamin D helps support our innate immune system (the first line of defence against germs) [1]. It does this by increasing cells’ production of antimicrobial proteins and peptides, which helps our bodies fight diseases and sickness more effectively [1].
Vitamin D also has a role in how our adaptive immune systems work. Your adaptive immune system is your second line of defence against infection – unlike the innate immune system, which is designed to fight germs generally, the adaptive immune system actually learns about specific germs when it encounters them, allowing it to respond more effectively next time.
Although studies have shown that vitamin D could have a negative impact on T cells, it’s also been shown have a positive impact on dendritic cells, which can actually reverse the effects on T cells [1, 3]. The end result? There isn’t a clear-cut answer as to whether vitamin D is helpful for our adaptive immune systems.
Overall, though, vitamin D’s role in the innate immune system makes it extremely important for healthy immune function. Without enough of the sunshine vitamin, your body could be in serious trouble.
So how much vitamin D should you be getting if you want to stay healthy?
There isn’t a definitive answer. Vitamin D levels are measured by the amount of its hydroxylated form, 25(OH)D3, in your blood [1]. Most countries and health systems believe that the ‘sufficiency threshold’ is somewhere between 50–75 nanomoles per litre; the Australian government, for example, holds that less than 50 nanomoles per litre is ‘insufficient’ [1, 4].
That doesn’t mean you should start downing handfuls of vitamin D pills, though. Newer research indicates that levels over 150 nanomoles per litre are actually toxic and can increase mortality rates [1]. To avoid excessive amounts of vitamin D in your body, many leading health authorities recommend consuming no more than 4,000 IU of dietary vitamin D per day [5].
Here are the NIH guidelines on the recommended dietary allowances (RDAs) for vitamin D. Keep in mind that your needs may vary depending on your health and your exposure to sunlight.
Age | Male | Female | Pregnancy | Lactation |
0-12 months* | 10 mcg | 10 mcg | ||
1–13 years | 15 mcg | 15 mcg | ||
14–18 years | 15 mcg | 15 mcg | 15 mcg | 15 mcg |
19–50 years | 15 mcg | 15 mcg | 15 mcg | 15 mcg |
51–70 years | 15 mcg | 15 mcg | ||
>70 years | 20 mcg | 20 mcg |
*Adequate Intake (AI)
For context, most vitamin D pills contain 1,000 IU per pill; if you eat a balanced diet and lead a semi-outdoors lifestyle, you probably don’t need that much vitamin D.
AdVital Powder, on the other hand, contains 108 IU per scoop, making it the perfect way to enhance your existing intake. With two to three scoops of AdVital per day, you’ll potentially be getting up to 324 IU of vitamin D per day from your supplements – add in intake from the rest of your diet, and you’ll probably achieve your RDA.
If you love learning about nutrition as much as us, you may already know that there are different forms of vitamin D. Let’s take a look at what each form is, where it comes from, and how effective it is for your immune system.
Vitamin D3 (also known as ‘cholecalciferol’) is the most common form of vitamin D. When our skin is exposed to sunlight, we synthesise vitamin D3 from a compound in our bodies known as 7-DHC [5].
We can also get vitamin D3 naturally from egg yolks and fatty fish like salmon and sardines [5].
Vitamin D2 (also known as ‘ergocalciferol’) is a synthetic form of vitamin D that comes from ergosterol, a steroid found in fungi and some plants [6, 7].
Vitamin D3 is generally considered to be superior for use as a supplement [6]. It’s absorbed by our cells more effectively, which means it becomes less concentrated in our blood [6]. It’s also more potent, so we don’t need as much to get the benefits [6]. Don’t stress, though – both D3 and D2 are ultimately pretty similar, and it probably won’t matter which form you supplement with.
Once your body absorbs either vitamin D3 or D2, your liver transforms it into a bioactive form through a process called ‘hydroxylation’ [3]. This hydroxylated type of vitamin D is known as ‘25(OH)D3’, which is the main form of vitamin D circulated through your body [3].
25(OH)D3 is then transported to your kidneys, where it gets converted into 1,25(OH)2D3 – the form of vitamin D useful for our immune health [3]. Interestingly, our immune cells can also receive and metabolise 25(OH)D3 into 1,25(OH)2D3 [3].
If that was all getting a bit complex, here’s the plain English breakdown: any vitamin D you get from sunlight or food gets processed a few different times by your body before it can be used by your immune system.
If you have less than 50 nanomoles per litre of vitamin D in your blood, you’re generally considered to have a vitamin D deficiency [8].
Effects of a vitamin D deficiency include [8, 5, 3]:
Low vitamin D can definitely cause a weak immune system, which is why getting enough sunlight, eating a balanced diet, and exercising regularly is important. If you think you might not be absorbing vitamin D properly, consult your GP for advice.
Although anyone can have a vitamin D deficiency, you’re especially at risk if you [9, 10]:
Sunlight is the best source of vitamin D, but your diet can also contribute to about 20% of your total vitamin D intake. Here are some foods that contain vitamin D [11, 12, 13]:
In Australia, it’s currently mandatory for edible oil spreads like margarine to be fortified with vitamin D. Other dairy products, like milks, yoghurts, table confections, and cheeses, may also be fortified – check the packaging if you’re not sure.
Getting enough vitamin D is essential for a healthy immune system, but, despite our climate, it’s one nutrient that many Aussies are deficient in.
And, no, we’re not recommending that you ditch the Bunnings hat and sun-bake on the beach. Sun safety is still incredibly important, so the best way to up your vitamin D intake is through a balanced diet that incorporates lots of fish or supplements like AdVital Powder.
Making sure your vitamin D levels are right can help prevent a broad variety of health conditions, including common colds, and can seriously improve your quality of life. If you think you might not be absorbing vitamin D properly, consult your GP for advice.
Medical information on AdVital.com.au is merely information and is not the advice of a medical practitioner. This information is general advice and was accurate at the time of publication. For more information about nutrition and your individual needs, see your GP or an Accredited Practising Dietitian.
[1] Sassi, F., Tamone, C., & D’Amelio, P. (2018). Vitamin D: Nutrient, Hormone, and Immunomodulator. Nutrients, 10(11), 1656–1670. DOI: 10.3390/nu10111656
[2] Zmijewski, Michal (2019). Vitamin D and Human Health. International Journal of Molecular Sciences, 20(1), 145–150. DOI:10.3390/ijms20010145
[3] Vanherwegen, A.-S., Gysemans, C., & Mathieu, C. (2017). Regulation of Immune Function by Vitamin D and Its Use in Diseases of Immunity. Endocrinology and Metabolism Clinics of North America, 46(4), 1061–1094. DOI: 10.1016/j.ecl.2017.07.010
[4] Charoenngam, N., & Holick, M. F. (2020). Immunologic Effects of Vitamin D on Human Health and Disease. Nutrients, 12(7), 2097. DOI: 10.3390/nu12072097
[5] Prietl, B., Treiber, G., Pieber, T., & Amrein, K. (2013). Vitamin D and Immune Function. Nutrients, 5(7), 2502–2521. DOI: 10.3390/nu5072502
[6] Dereje, S., Muradov, I., Nazzal, S., & Nguyen, T. (2017). Cholecalciferol (D3) Versus Ergocalciferol (D2) in Older Adults. The Consultant Pharmacist, 32(6), 337–339. DOI: 10.4140/TCP.n.2017.337
[7] Tripkovic, L., Lambert, H., Hart, K., Smith, C. P., Bucca, G., Penson, S., Chope, G., Hyppönen, E., Berry, J., Vieth, R., & Lanham-New, S. (2012). Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. The American Journal of Clinical Nutrition, 95(6), 1357–1364. DOI: 10.3945/ajcn.111.031070
[8] Bartley, J. (2010). Vitamin D: emerging roles in infection and immunity. Expert Review of Anti-infective Therapy, 8(12), 1359–1369. DOI: 10.1586/eri.10.102
[9] Holick, M. F. (2017). The vitamin D deficiency pandemic: Approaches for diagnosis, treatment and prevention. Reviews in Endocrine and Metabolic Disorders, 18(2), 153–165. DOI: 10.1007/s11154-017-9424-1
[10] Wyskida, M., Wieczorowska-Tobis, K., & Chudek, J. (2017) Prevalence and factors promoting the occurrence of vitamin D deficiency in the elderly. Postepy higieny i medycyny doswiadczalnej, 71, 198–204. DOI: 10.5604/01.3001.0010.3804
[11] Lu, Z., Chen, T. C., Zhang, A., Persons, K. S., Kohn, N., Berkowitz, R., Martinello, S., & Holick, M. F. (2009). An Evaluation of the Vitamin D3 Content in Fish: Is the Vitamin D Content Adequate to Satisfy the Dietary Requirement for Vitamin D? The Journal of Steroid Biochemistry and Molecular Biology, 103(3–5), 642–644. DOI: 10.1016/j.jsbmb.2006.12.010
[12] Browning, L. C., & Cowieson, A. J. (2014). Vitamin D fortification of eggs for human health. Journal of the Science of Food and Agriculture, 94(7), 1389–1396. DOI: 10.1002/jsfa.6425
[13] Cardwell, G., Bornman, J. F., James, A. P., & Black, L. J. (2018) A Review of Mushrooms as a Potential Source of Dietary Vitamin D. Nutrients, 10(10), 1498. DOI: 10.3390/nu10101498
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