Sometimes referred to as sunshine in a bottle, vitamin D (a hormone, in actual fact) is a powerful and essential nutrient when it comes to our wellbeing. Almost every single cell in our body contains a vitamin D receptor (VDR) which highlights just how important this UVB-induced nutrient is to our health and cellular function.[1]

One of my favourite properties of vitamin D is how – in sufficient quantities – it enables us to make our own antibiotics.

Our Bodies Can Make Antibiotics

Yes, you read that correctly. No, this is not a drill.

Our bodies are, or more specifically our immune system is, capable of producing specific and not-so-specific responses to various immunological challenges. One of the incredible features of this is, when presented with pathogenic (read disease-causing) microorganisms, we endogenously produce our own antimicrobial medication in response – called antimicrobial peptides.

Antimicrobial peptides (AMPs) are an ancient arm of the human immune system and these various peptides protect us against bacteria, viruses, fungi, and even certain parasites. Virtually all human tissues and cells typically exposed to microbes are able to produce AMPs. Important AMPs belonging to two structurally distinct classes, known as the defensins and the cathelicidins, are produced by neutrophils and epithelial cells.[2] And, these are regulated by vitamin D![3,4,5,6,7]

And the reason I have emphasised epithelial cells is – not only does this include skin, but all mucous membranes including the lungs as well. Very important when it comes to cold and ‘flu.

Our Lungs Can Fight Off Cold + Flu

I want to give a shoutout to cathelicidin LL-37 in particular as this AMP, produced in the lining of the lungs, has been shown to help fight off cold and ‘flu.

Manufactured in the respiratory tract, it has been shown to[8]:

• have a broad spectrum of antimicrobial activity against bacteria, fungi, and viral pathogens
• regulate the inflammatory response
• attract immune cells to the infection site
• promote tissue healing

LL-37 has demonstrated antimicrobial activity against the common cold[9], several seasonal influenza A strains[10,11], respiratory syncytial virus[12] and even tuberculosis[13].

As AMPs are regulated by vitamin D and the supplementation of vitamin D boosts, in turn, LL-37 levels[14,15,16], maintaining optimal vitamin D levels is crucial for a robust defence against cold and ‘flu. It is also worth noting that low vitamin D levels doubles your risk of contracting pneumonia[17].

Many Australians Are Vitamin D Deficient

According to a national population-based study[18], 31% of Australian adults aged 25 years and older are deficient in vitamin D. The same study reported that 73% of these otherwise healthy Australian adults had evidence of vitamin D insufficiency, particularly prevalent year-round from Brisbane down to Hobart.

Given vitamin D deficiency has been correlated with increased rates of infection[19], epidemiological studies demonstrate a link between vitamin D deficiency and increased rates of respiratory infections[20,21,22,23], and we notice a seasonal increase in respiratory infections that coincides with declining vitamin D levels in the population – ensuring your vitamin D levels remain in the optimal range year round is a key strategy for winter wellness.

Are You At Risk Of Vitamin D Deficiency?

Those of us who work in an office – especially full-time – are already at risk of vitamin D deficiency. There simply is not enough opportunity for UVB exposure (late spring, over summer, through early autumn) and therefore endogenous vitamin D manufacture.

However, there are other risk factors to consider as well; the groups considered to be at further risk of vitamin D deficiency in Australia include[24,25,226,27,28]:

• the elderly have a reduced capacity to synthesise vitamin D in skin when exposed to sunlight and this group is also likely to stay indoors or use sunscreen to prevent sun damage (estimates of deficiency range from 15-86% for this group)
• individuals with dark skin synthesise less vitamin D on exposure to sunlight than those with light-coloured skin (s many as 80% may have a mild vitamin D deficiency)
• individuals who cover exposed skin for religious or cultural reasons and those who wear protective clothing or always use sunscreen (up to 80% of this group may have a mild vitamin D deficiency)
• exclusively breast-fed infants as breast milk contains only small amounts of vitamin D (this is much more prevalent for infants of women who are deficient in vitamin D as a result of having dark skin or cover their skin)
• institutionalised adults
• patients with fat malabsorption syndromes, certain kidney and liver disorders, inflammatory bowel disease
• patients on anticonvulsant drugs

How Much Vitamin D Should I Take?

Dr Michael Holick, a world-leading vitamin D expert and Professor of Medicine, Physiology, and Dermatology at Boston University School of Medicine, also recommends maintaining good vitamin D levels* to help reduce the risk of chronic illnesses.

*“We like it to be above 75 nmol/L at a minimum and preferably at 100-150 nmol/L”

According to his research[29]:

• aim for vitamin D levels of 75-125 nmol/L – whilst this may sound high, it’s interesting to note that lifeguards often have levels of 250 nmol/L without any toxicity
• to increase serum vitamin D levels to around 50nmol/L (sub-optimal level), normal healthy adults require 1000IU/day of vitamin D – a dose of 4000IU/day of vitamin D is required to increase serum vitamin D to around 75nmol/L (sufficiency)[30]

Prof. Holick said while adults of a normal weight may be prescribed 1000-4000IU of vitamin D supplementation, overweight individuals may need vitamin D supplementation of up to 9000IU. Research has found that obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D3 because of its deposition in body fat compartments.[31]

References:

1. Bouillon R, Carmeliet G, Verlinden L, et al. Vitamin D and Human Health: Lessons from Vitamin D Receptor Null Mice. Endocr Rev. 2008; 29(6): 726–776.
2. Wiesner J, Vilcinskas A. Antimicrobial peptides: the ancient arm of the human immune system. Virulence. 2010;1(5):440-64.
3. Liu PT, Stenger S, Li H, et al. Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response. Science. 2006;311(5768):1770–1773.
4. Gombart AF, Borregaard N, Koeffler HP. Human cathelicidin antimicrobial peptide (CAMP) gene is a direct target of the vitamin D receptor and is strongly up-regulated in myeloid cells by 1,25-dihydroxyvitamin D3. FASEB J. 2005;19(9):1067–1077.
5. Wang TT, Nestel FP, Bourdeau V, et al. Cutting edge: 1,25-dihydroxyvitamin D3 is a direct inducer of antimicrobial peptide gene expression. J. Immunol. 2004;173(5):2909–2912.
6. Weber G, Heilborn JD, Chamorro Jimenez CI, et al. Vitamin D induces the antimicrobial protein hCAP18 in human skin. J. Invest. Dermatol. 2005;124(5):1080–1082.
7. Zasloff M. Fighting infections with vitamin D. Nat. Med. 2006;12(4):388–390.
8. Dürr UHN, Sudheendra US,Ramamoorthy A, et al. LL-37, the only human member of the cathelicidin family of antimicrobial peptides. Biochimica et Biophysica Acta (BBA) – Biomembranes 2006 Volume 1758, Issue 9, P1408–1425.
9. Schögler A, Muster RJ, Kieninger E, et al. Vitamin D represses rhinovirus replication in cystic fibrosis cells by inducing LL-37. Eur Respir J 2015;47 (2), 520-530.
10. Tripathi S, Tecle T, Verma A, et al. The human cathelicidin LL-37 inhibits influenza A viruses through a mechanism distinct from that of surfactant protein D or defensins. J Gen Virol. 2013; 94(Pt 1): 40–49.
11. Barlow PG, Svoboda P, Mackellar A, et al. Antiviral Activity and Increased Host Defense against Influenza Infection Elicited by the Human Cathelicidin LL-37. PLoS ONE 2011; 6(10): e25333.
12. Harcourt JL, McDonald M, Svoboda P, et al. Human cathelicidin, LL-37, inhibits respiratory syncytial virus infection in polarized airway epithelial cells. BMC Res Notes. 2016; 9: 11.
13. Liu PT, Stenger S, Tang DH, et al. Cutting edge: vitamin D-mediated human antimicrobial activity against Mycobacterium tuberculosis is dependent on the induction of cathelicidin. J Immunol 2007;179, 2060–2063.
14. Zhang C, Zhao L, Ding Y, et al. Enhanced LL-37 expression following vitamin D supplementation in patients with cirrhosis and spontaneous bacterial peritonitis. Liver Int. 2016;36(1):68-75.
15. Gombart AF, Borregaard N, Koeffler HP. Human cathelicidin antimicrobial peptide (CAMP) gene is a direct target of the vitamin D receptor and is strongly up-regulated in myeloid cells by 1,25-dihydroxyvitamin D3. FASEB J. 2005;19(9):1067–1077
16. Wang TT, Nestel FP, Bourdeau V, et al. Cutting edge: 1,25-dihydroxyvitamin D3 is a direct inducer of antimicrobial peptide gene expression. J. Immunol. 2004;173(5):2909–2912.
17. Aregbesola A, Voutilainen S, Nurmi T, Jet al. Serum 25-hydroxyvitamin D3 and the risk of pneumonia in an ageing general population. J Epidemiol Community Health. 2013;67:533-536.
18. Daly RM, Gagnon C, Lu ZX, et al. Prevalence of vitamin D deficiency and its determinants in Australian adults aged 25 years and older: a national, population-based study. Clin Endocrinol (Oxf). 2012;77(1):26-35.
19. Gombart AF. The vitamin D–antimicrobial peptide pathway and its role in protection against infection. Future Microbiol. 2009; 4: 1151.
20. Laaksi I, Ruohola JP, Tuohimaa P, et al. An association of serum vitamin D concentrations < 40 nmol/l with acute respiratory tract infection in young Finnish men. Am. J. Clin. Nutr. 2007;86(3):714–717.
21. Karatekin G, Kaya A, Salihoglu O, et al. Association of subclinical vitamin D deficiency in newborns with acute lower respiratory infection and their mothers. Eur. J. Clin. Nutr. 2009;63(4):473–477.
22. Walker VP, Modlin RL. The vitamin D connection to pediatric infections and immune function. Pediatr. Res. 2009
23. Ginde AA, Mansbach JM, Camargo CA., Jr Vitamin D, respiratory infections, and asthma. Curr. Allergy Asthma Rep. 2009;9(1):81–87.
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25. Nowson CA et al.  Vitamin D in Australia.  Issues and recommendations.  Reprinted from Australian Family Physician Vol. 33, No.3, March 2004.
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27. National Health and Medical Research Council.  Nutrient Reference Values for Australia and New Zealand including Recommended Dietary Intakes. 2006;127-135.
28. Ebeling PR.  Megadose therapy for vitamin D deficiency. MJA. 2005;183(1):4-5.
29. Holick MF. Vitamin D Deficiency. N Engl J Med 2007; 357:266-281.
30. Vieth R, Chan PC, MacFarlane GD. Am J Clin Nutr 2001;73(2):288-94.
31. Wortsman J, Matsuoka L Y, et al. Decreased bioavailability of vitamin D in obesity. American Society for Clinical Nutrition 2000.