Edwina Clark, MS, RD, APD (Aus), CSSD
Sun exposure didn't used to be a problem - it was always assumed that you would both get enough, and be protected when outside in the summer. It brightened up any day or event - yet sun exposure has recently been questioned beyond moods. Yes, too much sun is still bad for you but too little comes with problems too. One of those issues is vitamin D status.
Vitamin D and sun exposure
The problem is that not every part of the world enjoys as many sunny days as Sydney or San Diego. Many places experience greater seasonal fluctuations in temperature and sunlight. Cities with long winters like Boston and Stockholm fall into this category. In these places, the intensity of the sun and the duration of exposure during the colder months typically fall short of the requirements for adequate vitamin D, and dietary vitamin D has to fill the gaps.
Yet, even if you live in a sunny party of the world like Sydney you might not get enough vitamin D. UV-B rays are blocked by sunscreen, clothing, windows, and walls, so if you spend large amounts of time indoors or only ever go outside lathered in sunscreen, you may fall short of the recommendations. Skin type, genetics, size and age also influence the amount of vitamin D made by our body [1, 2].
What does vitamin D do?
Vitamin D is most well-known for being a bone-builder, but recent research suggests that it’s involved in much more than that.
- Bone health: Vitamin D increases calcium absorption from the gut and helps maintain blood calcium which is involved in nervous system maintenance, as well as bone health. Studies suggest that consuming adequate vitamin D, in combination with calcium, helps maintain bone as we age . Vitamin D also boosts phosphorous absorption in the gut, which is another important nutrient for strong bones .
- Immunity: Vitamin D is involved in various immune pathways and is an important immune modulator. Poor vitamin D status has been linked with increased risk of autoimmune conditions such as multiple sclerosis and inflammatory bowel disease [4, 5], and may exacerbate symptoms in several others. Furthermore, studies suggest that vitamin D supplementation may ward-off respiratory infection and boost immunity among those frequently battling respiratory illness [6, 7].
- Heart health: Epidemiological studies indicate that low vitamin D status is associated with increased risk of cardiovascular disease [8, 9]. However, it’s unclear if supplemental vitamin D is helpful for managing heart disease risk .
- Cancer risk: Vitamin D plays a role in cell proliferation and differentiation, and appears to influence the development of some--but not all--cancers. Higher vitamin D levels are associated with reduced risk of cancer of the colo-rectum, and breast, and improved prognosis among those diagnosed with these diseases [4,10].
- Brain power: Studies suggest that poor vitamin D status is associated with an increased risk of cognitive disorders such as Alzheimer’s disease . Furthermore, high circulating levels of vitamin D have been associated with increased verbal fluency .
Getting enough of the good stuff
Dietary reference intakes around the world suggest that adults under 70 should aim for 400-600 IU of vitamin D per day however there’s evidence to suggest that up to 2000 IU of vitamin D may be useful to enjoy some of the benefits listed above .
It’s not entirely clear how much sun exposure you need to generate adequate vitamin D however experts recommend 5-30 minutes unprotected between 10am and 3pm, 2-3 days a week . For people living above 40 degrees north and south, the sun is not strong enough to generate adequate vitamin D during the colder months, and dietary/supplemental vitamin D is highly encouraged.
Unlike other nutrients, vitamin D is relatively sparse in food. In fact, unless you’re eating sizeable portions of fatty fish everyday, it’s relatively difficult to get adequate vitamin D exclusively from your diet. Increasingly, foods like cereal are being fortified with vitamin D to boost vitamin D status, and offer some relief to the vitamin D insufficiency pandemic.
 Vitamin D status: multifactorial contribution of environment, genes and other factors in healthy Australian adults across a latitude gradient. Lucas RM, Ponsonby AL, Dear K, Valery PC, Taylor B, van der Mei I, McMichael AJ, Pender MP, Chapman C, Coulthard A, Kilpatrick TJ, Stankovich J, Williams D, Dwyer T. J Steroid Biochem Mol Biol. 2013 Jul;136:300-8. doi: 10.1016/j.jsbmb.2013.01.011. Review.
 Reductions in body weight and percent fat mass increase the vitamin D status of obese subjects: a systematic review and metaregression analysis. Pannu PK, Zhao Y, Soares MJ. Nutr Res. 2016 Mar;36(3):201-13. doi: 10.1016/j.nutres.2015.11.013. Review.
 Effectiveness and safety of vitamin D in relation to bone health. Cranney A, Horsley T, O'Donnell S, Weiler H, Puil L, Ooi D, Atkinson S, Ward L, Moher D, Hanley D, Fang M, Yazdi F, Garritty C, Sampson M, Barrowman N, Tsertsvadze A, Mamaladze V. Evid Rep Technol Assess (Full Rep). 2007 Aug;(158):1-235. Review.
 Vitamin D. Linus Pauling Institute Micronutrient Information Center. Updated 2014. Accessed on December 30, 2016.
 Vitamin D and inflammatory bowel disease. Ardesia M, Ferlazzo G, Fries W.Biomed Res Int. 2015;2015:470805. doi: 10.1155/2015/470805. Review.
 Vitamin D3 Supplementation and Antibiotic Consumption - Results from a Prospective, Observational Study at an Immune-Deficiency Unit in Sweden. Norlin AC, Hansen S, Wahren-Borgström E, Granert C, Björkhem-Bergman L, Bergman P. PLoS One. 2016 Sep 22;11(9):e0163451. doi:10.1371/journal.pone.0163451.
 Vitamin D supplementation to patients with frequent respiratory tract infections: a post hoc analysis of a randomized and placebo-controlled trial. Bergman P, Norlin AC, Hansen S, Björkhem-Bergman L. BMC Res Notes. 2015 Aug 30;8:391. doi: 10.1186/s13104-015-1378-3.
 Circulating 25-hydroxy-vitamin D and risk of cardiovascular disease: a meta-analysis of prospective studies. Wang L, Song Y, Manson JE, Pilz S, März W, Michaëlsson K, Lundqvist A, Jassal SK, Barrett-Connor E, Zhang C, Eaton CB, May HT, Anderson JL, Sesso HD. Circ Cardiovasc Qual Outcomes. 2012 Nov;5(6):819-29. doi: 10.1161/CIRCOUTCOMES.112.967604. Review.
 Does sufficient evidence exist to support a causal association between vitamin D status and cardiovascular disease risk? An assessment using Hill's criteria for causality. Weyland PG, Grant WB, Howie-Esquivel J. Nutrients. 2014 Sep 2;6(9):3403-30. doi: 10.3390/nu6093403. Review.
 Vitamin D and Colorectal, Breast, and Prostate Cancers: A Review of the Epidemiological Evidence. Jacobs ET, Kohler LN, Kunihiro AG, Jurutka PW. J Cancer. 2016 Jan 5;7(3):232-40. doi: 10.7150/jca.13403. Review.
 Vitamin D in dementia prevention. Annweiler C. Ann N Y Acad Sci. 2016 Mar;1367(1):57-63. doi: 10.1111/nyas.13058.
 Vitamin D and executive functioning: Are higher levels better? Pettersen JA. J Clin Exp Neuropsychol. 2016;38(4):467-77. doi: 10.1080/13803395.2015.1125452.
 Vitamin D - effects on skeletal and extraskeletal health and the need for supplementation. Wacker M, Holick MF.Nutrients. 2013 Jan 10;5(1):111-48. doi: 10.3390/nu5010111. Review.