Your ultimate guide to Vitamin D: a review of the evidence

How common is vitamin D deficiency?

Vitamin D deficiency has been recognised as a global public health concern with nearly a third of Australians over the age of 25 shown to have low levels of vitamin D. This finding was demonstrated in a large population-based study conducted in 2012 which assessed vitamin D levels in more than 11,000 Australians. Vitamin D deficiency was found to affect 31% of Australians, with the highest incidence in women (39% were deficient in vitamin D overall). Even more astounding was the finding that nearly sixty percent of women were found to be deficient in vitamin D over the period of winter to spring. The study also found that 73% of Australians had vitamin D levels less than 75 nmol/L - the level classified as ‘vitamin D insufficiency’.

Why is vitamin D deficiency so common?

There are many plausible reasons to explain why such large proportions of the population are afflicted by suboptimal vitamin D status including:

  • Greater amount of time spent indoors at work and home
  • Increased adherence to sun protection (SPF 15+ sunscreen blocks 99% of vitamin D synthesis in the skin)
  • Higher proportion of people adhering to plant-based diets (vitamin D levels are higher in animal products overall)
  • Lower levels of vitamin D in conventional diets (mushrooms for example are typically grown in dark growing rooms precluding exposure to sunlight which is essential for vitamin D synthesis)
  • A growing elderly and institutionalised population with lower exposure to sunlight

Rising rates of obesity are also likely to be partially responsible for suboptimal vitamin D status. Given that vitamin D is soluble in fat, people tend to store vitamin D in adipose tissue (body fat). Historically, this vitamin D would be released over winter as our hunter-gatherer ancestors were starved of high density caloric diets over the winter period. Nowadays, people tend to maintain their belly fat over winter, preventing release of vitamin D from their fat stores. In addition, people tend to spend more time indoors over winter. The reduced exposure to sunlight combined with a lower UVB index over winter contributes further to vitamin D insufficiency.

What is the link between vitamin D and immunity?

Vitamin D plays an important role in the immune response as an immune modulator. The role of vitamin D in regulating immune function has been described in various literature reports. Vitamin D receptors have been identified on various immune cells including macrophages, monocytes, dendritic cells, and T and B lymphocytes. These cells are vital to enable direct killing of bacteria and viruses along with the development of long-standing immunity through production of antibodies.

What is ‘acute respiratory infection’ and how common is it?

Acute Respiratory Infection (ARI) is defined as any episode of cold or flu with at least one of the following symptoms: fever, chills, sore throat, runny nose, or cough over four consecutive weeks. In 2008 to 2009 an Australian National Survey was conducted to extrapolate the prevalence of ARI by season and state, and to estimate the incidence of ARI in the Australian community. 19.9% (1505/7578) of respondents reported an ARI in the previous 4 weeks, suggesting an incidence of 68.9 million cases of ARI occurring in Australia each year.

What evidence is there to support vitamin D supplementation for the prevention of acute respiratory infection?

Routine vitamin D3 supplementation has been shown to be safe and effective in preventing acute respiratory tract infection. A large meta-analysis of 25 high quality, double-blind randomised control trials involving 10,933 individuals showed that daily and weekly vitamin D supplementation was safe and effective in reducing the incidence of respiratory infection in all participants, including those with 'adequate' levels of vitamin D. The study also demonstrated a profound effect in those who were vitamin D deficient. Those with vitamin D levels less than 25 nmol/L who received daily or weekly supplementation with vitamin D experienced a 70% reduction in incidence of cold and flu. It is important to know that daily and weekly supplementation is effective, but larger infrequent doses (e.g. once a month) are not effective. The body of evidence contributing to this meta-analysis was considered to be of high quality, meaning the randomised trials were well designed, therefore increasing the power of these results.

Another meta-analysis published in 'The Lancet' in May 2021 also found that vitamin D supplementation was associated with a lower risk of acquiring acute respiratory infection, further backing up findings from the 2017 study. This meta-analysis included 43 randomised controlled trials and analysed results from more than 43,000 participants. It concluded a pronounced effect of vitamin D supplementation in children aged 1 to 18 years taking doses of 400 to 1000 IU vitamin D3 on a daily basis. This level of supplementation resulted in a 30% reduction in risk of experiencing at least 1 respiratory tract infection over the study period.

At what level are people considered ‘deficient’?

Definitions of vitamin D status (based on blood test results) are as follows:

  • Vitamin D deficiency = blood level less than 50 nmol/L (<20ng/mL)
  • Vitamin D insufficiency = 50 to 75 nmol/L (20 to 30 ng/mL)
  • Vitamin D sufficiency = greater than 75 nmol/L (30 ng/mL)
  • Multiple studies cite optimal levels at more than 100 nmol/L (40 ng/mL)

Your optimal vitamin D level may be higher than you think. How much do you really need?

Attaining optimal levels of vitamin D has been shown to optimise immune function and neuromuscular function; optimise intestinal calcium absorption; improve breast milk vitamin D concentration for infant health; and reduce chronic musculoskeletal pain. The suggested general target for optimal beneficial effects of vitamin D is greater than 100 nmol/L on serum blood test. This is twice the level that most doctors consider people to be vitamin D deficient (50 nmol/L).

The following table featured in a review article published in the Australian Journal of General Practice (formerly Australian Family Physician) in 2008. It describes the minimum levels of vitamin D that should be achieved to optimise health benefits.

In Australia, vitamin D deficiency refers to levels lower than 50 nmol/L, with levels greater than 100 nmol/L considered optimal. The total daily requirement of vitamin D (from sunlight and diet) is around 4000 IU to maintain levels above 100 nmol/L. Evidence suggests that exposure to the sun to obtain these levels may increase skin cancer risk, and therefore dietary supplementation is largely considered a safer option. An Australian study of 11,247 individuals found that 73% had vitamin D levels less than 75 nmol/L. In the United States of America, it is estimated that only 10% of the US population has vitamin D levels greater than 100 nmol/L.

Daily vitamin D3 doses of 1000 IU (25 mcg) per day can maintain people in the healthy range provided they are not already deficient in vitamin D. There is some evidence that the dosing requirement to achieve optimal vitamin D levels in the range of 100 to 150 nmol/L may require daily dosing of 4000 to 6000 IU per day. Toxicity from excessive oral intake of vitamin D is possible, however, no evidence of vitamin D toxicity has been shown with doses of up to 4000IU per day. The tolerable upper limit of daily vitamin D is debated, but may be as high as 10,000IU daily. In Australia, the maximum daily dose of vitamin D recommended for general use is 1000IU per day unless advised otherwise by your doctor. The safest way to optimise your vitamin D level is to consider seeing your GP for a blood test and to supplement accordingly to attain levels of at least 100 nmol/L.

Is it safe to get vitamin D from sunlight?

It’s common knowledge now that sunlight plays an important role in vitamin D synthesis. It does this by facilitating the synthesis of vitamin D in the skin. However, apart from being an important source of vitamin D, UV radiation from the sun also causes skin cancer.

The Cancer Council of Australia recommends people limit their sun exposure to reduce skin cancer risk. As the skin can only absorb a limited amount of sunlight, excessive exposure to sunlight does not help boost vitamin D levels and only increases skin cancer risk. In some parts of Australia, sunburn can occur in as little as eight minutes. Regular sunburn increases the risk of skin cancer. Sun exposure guidelines exist for various parts of Australia, and generally recommend limiting exposure of the upper limbs and face to no more than 2 to 10 minutes per day for most areas of Australia over summer, taking extreme care to avoid reddening of the skin. For some parts of Australia, exposure to the sun for more than 5 minutes per day might be putting people at higher risk. For this reason, dietary supplementation is largely considered a safer option.

Can vitamin D be obtained from dietary sources?

Sunlight remains the most important natural source of vitamin D, but smaller amounts can be obtained from select food sources. Animal foods are higher in vitamin D content compared to plants with oily fish like salmon and trout containing around 600 IU of vitamin D per serve. Foods other than fish and mushrooms are generally scarce in vitamin D content, containing less than 200 IU per serve.

Mushrooms are the richest natural plant source of vitamin D. In fact, they are the only non-animal food product that contains a considerable amount of bioavailable vitamin D, making them the primary source of dietary vitamin D for vegans and vegetarians. However, if mushrooms are grown indoors and not exposed to the sun or UV light they will not contain any vitamin D. Most fresh mushrooms sold in grocery stores in Australia, New Zealand, North America and the UK are grown in atmospherically controlled growing rooms in complete darkness leaving them with little to no vitamin D.

Are vitamin D supplements suitable for vegans or those who prefer plant-sourced products?

Select vitamin D3 supplements are available for those who prefer plant-based products, but many forms of vitamin D3 are obtained from animal sources. Vitamin D3 is more effective at boosting blood vitamin D levels than the usual plant sources of vitamin D known as ergocalciferol or Vitamin D2.

Most consumers and prescribers are unaware that vitamin D3 commonly found in health supplements and marketed as 'vegetarian' is typically derived from lanolin, which is obtained from sheep's wool. Other forms of vitamin D may rely on farming fish for the relatively high vitamin D content that is found in fish oil.

For those that prefer to avoid animal-sourced products (e.g. those adhering to plant-based diets or looking to live an ethically responsible lifestyle), some specialised vitamin D3 supplements are available using vegan-friendly Vitamin D3 obtained from lichens - an animal-free, sustainable, eco-friendly, and clean source of vitamin D3. Lichens are small unique plant species consisting of a symbiotic association of a fungus with an algae. This gives them unique attributes such as surviving in extreme climates and having the ability to grow and accumulate meaningful levels of useful nutrients, including Cholecalciferol.

What type of vitamin D is used in IMUNI products?

All IMUNI products that contain vitamin D use a specialised ingredient called Vitashine, which is the world’s only vegan society and vegetarian society registered plant-sourced vitamin D3. All Vitashine products use responsibly sourced lichen which is obtained from sustainable growing sites under organic growing conditions. No pesticides are used in the creation of Vitashine vitamin D products, making them suitable for those looking to avoid pesticides and potentially harmful additives.

QUICK FACTS:

  • Nearly a third of Australians over 25 have low vitamin D
  • Did you know? Vitamin D receptors have been identified on various immune cells including macrophages, monocytes, dendritic cells, and T and B lymphocytes
  • The optimal level of vitamin D is 100 to 150 nmol/L on serum blood test
  • It is estimated there are more than 60 million cases of acute respiratory tract infection in Australia each year.
  • Our vitamin D is responsibly sourced from a small unique plant species called Lichen
  • Our vitamin D products use Lichen obtained from sustainable growing sites under organic growing conditions
  • If mushrooms are grown indoors and not exposed to the sun or UV light they will not contain any vitamin D
References:
  1. Daly R, Gagnon C, Lu Z, Magliano D, Dunstan D, Sikaris K et al. Prevalence of vitamin D deficiency and its determinants in Australian adults aged 25 years and older: a national, population-based study. Clinical Endocrinology [Internet]. 2012;77(1):26-35. Available from: https://pubmed.ncbi.nlm.nih.gov/22168576/

  2. Charoenngam N, Holick M. Immunologic Effects of Vitamin D on Human Health and Disease. Nutrients [Internet]. 2020;12(7):2097. Available from: https://www.mdpi.com/2072-6643/12/7/2097/htm

  3. Martineau A, Jolliffe D, Hooper R, Greenberg L, Aloia J, Bergman P et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ [Internet]. 2017:i6583. Available from: https://www.ncbi.nlm.nih.gov/

  4. RCPA - Vitamin D [Internet]. Rcpa.edu.au. 2020 [cited 4 December 2020]. Available from: https://www.rcpa.edu.au/Manuals/RCPA-Manual/Pathology-Tests/V/Vitamin-D

  5. Vitamin D deficiency in adults [Internet]. NPS Medicinewise. 2010 [cited 4 December 2020]. Available from: https://www.nps.org.au/australian-prescriber/articles/vitamin-d-deficiency-in-adults-1

  6. Cancer Council NSW. Sun exposure and vitamin D. Available from: https://www.cancercouncil.com.au/melanoma/after-cancer-treatment/sun-exposure-and-vitamin-d/

  7. Office of Dietary Supplements - Vitamin D [Internet]. Ods.od.nih.gov. 2021 [cited 1 April 2021]. Available from: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

  8. Nowson, C., & Mason, R. (2013). Vitamin D and health in adults in Australia and New Zealand. Medical Journal of Australia, 199(6), 394-394.

  9. Epidemiology and Infection: Incidence of acute respiratory infections in Australia. Available from: https://pubmed.ncbi.nlm.nih.gov/24103382/

  10. Stroud et al. 2008. Vitamin D: a review. Australian Family Physician. Vol 37, No. 12. Available from: https://www.racgp.org.au/

  11. Samanek A et al. 2006. Estimates of beneficial and harmful sun exposure times during the year for major Australian population centres. Medical Journal of Australia. Available from: https://pubmed.ncbi.nlm.nih.gov/16584368/

    Your ultimate guide to Vitamin D: a review of the evidence

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