Have you ever seen food packages boasting about their dense amounts of certain vitamins or minerals? Think about when you’ve walked down the cereal aisle- so many boxes have “fortified with vitamin D” written across in big bolded letters. Fortified with vitamin D means that food companies have added vitamin D into their food product. Now don’t be fooled, that sugary cereal still isn’t good for you- but what’s the deal with vitamin D? What’s all the hoopla about?
Vitamin D is a fat-soluble vitamin, created in the body when our skin is exposed to UV rays and undergoes two steps of synthesis. The first synthesis step takes place in the liver and converts vitamin D to 25(OH)D (otherwise known as calcidiol). The other synthesis step takes place in the kidney and forms 1,25(OH)2D otherwise known as calcitriol which is the biologically active form of vitamin D. Vitamin D can be stored in adipose tissue, and released in a fasting state (1). However, it should be noted that an abundance of subcutaneous fat can alter vitamin D’s release into the body’s circulation (2,3).
Maintaining optimal amounts of vitamin D prevents many disease states, including osteomalacia, rickets, poor Short Physical Performance Battery, and osteoporosis among others. But beyond that, it plays a significant role in maintaining the calcium levels in your body (5). Vitamin D helps with the absorption of calcium and inorganic phosphorus, also crucial for bone health. Furthermore, it helps with reduction of inflammation and neuromuscular function. Other studies have linked vitamin D levels with cognitive health correlating suboptimal vitamin D levels with reduced hippocampal volume (6-9). So if you needed one more reason to care about your vitamin D levels, it’s imperative for proper brain function!
Unlike other vitamins and minerals which are abundant in our food supply, vitamin D is found in only a few foods, which explains why popular processed foods are fortified with it. Vitamin D has two forms—ergocalciferol (D2), which is found in yeast and plants, and cholecalciferol (D3), which is gained through the ingestion of fatty fish and eggs, as well as vitamin D in fortified products. Fortified products are often heavily processed, making them the less than ideal choice for getting your daily dose of vitamin D. Additionally, the process of fortification does not take into effect the synergistic effect of foods, meaning that nature has packaged vitamins and minerals naturally into foods with all of the compounds needed for absorption and optimal use. Food science has not caught up with mother nature just yet- there is so much about food and nutrition that we still don’t know. This is also why vitamin D supplements, while effective, do not substitute a well balanced, whole foods diet. The good news is that fatty fish like sockeye salmon and sardines (hello, SMASH fish), are great sources vitamin D.
As mentioned, vitamin D synthesis is catalyzed by sun exposure, something often mentioned by those soaking up the sun on hot summer days. However, you also likely know that excessive sun exposure plays a big role in skin cancers (12). So, you need to get your vitamin D, but not at the cost of damaging your skin. How are we supposed to find a happy medium?
The recommended daily allowance of vitamin D for most healthy adults is about 600 IU/day (13). Various findings suggest a daily range of 30-100 ng/mL as a sufficient daily allowance (14,15). This translates to spending 5-30 minutes in the sun without using sunscreen. Sunscreen with an SPF of 30 can absorb ~95-98% of UVB radiation. It is important to take into account the time of day spent in the sun (10am-3pm is ideal), and if there are layers of clouds or haze, which will impair how much UVB reaches your skin. If this recommendation does not seem feasible, oral supplements are available, as well as the foods mentioned above. The important thing to note is that very minimal time is needed in direct sunlight to achieve your daily dose of vitamin D- if you want to bake in the sun all day while lying on the beach, vitamin D can’t be your excuse!
The NIH stresses that older adults are at greater risk of a vitamin D insufficiency than other healthy adults due to inability to synthesize vitamin D efficiently, and secondary to decreased sun exposure and decreased food intake (10, 11). So depending on your age, you may need to be more cautious about maintaining optimal vitamin D levels.
Depending on your skin type and risk factors for cancer, moderate sun exposure may be a good way to optimize your vitamin D levels. However, even without major skin cancer risk, keep your sun exposure to the recommended amount and incorporate vitamin D rich foods into your diet, such as fatty fish and pasture raised eggs. Make sure to have your vitamin D levels checked regularly, and speak to your registered dietitian if your levels are suboptimal.
 Razzaque, Mohammed S. Sunlight exposure: Do health benefits outweigh harm? Journal of Steroid Biochemistry and Molecular Biology. 175 (2018): 44-48. Web. 8 Sep 2018.
 Ann Epidemiol. 2014 Oct;24(10):781-4. Epub 2014 Aug 6. The effect of body mass index on adequacy of serum 25-hydroxyvitamin D levels in US adults: the National Health and Nutrition Examination Survey 2001 to 2006. Samuel L1, Borrell LN2.
 National Institutes of Health. (2018, March 2). Vitamin D: Fact Sheet for Health Professionals. Retrieved from https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
 Osteoporos Int. 2014 Oct;25(10):2347-57. Epub 2014 May 21. Skeletal and nonskeletal effects of vitamin D: is vitamin D a tonic for bone and other tissues? Reid IR1, Bolland MJ.
 J Bone Miner Metab. 2018 Jun 14. Low serum 25-hydroxyvitamin D increases cognitive impairment in elderly people. Sakuma M1,2, Kitamura K3, Endo N4, Ikeuchi T5, Yokoseki A6, Onodera O7, Oinuma T8, Momotsu T8, Sato K8, Nakamura K3, Narita I9.
 Hum Brain Mapp. 2018 Sep 25. [Epub ahead of print] Vitamin D deficiency is associated with reduced hippocampal volume and disrupted structural connectivity in patients with mild cognitive impairment. Al-Amin M1, Bradford D1,2, Sullivan RKP1, Kurniawan ND3, Moon Y4, Han SH4, Zalesky A5, Burne THJ1,6.
 Autoimmun Rev. 2013 Aug;12(10):976-89. Epub 2013 Mar 28. Vitamin D effects on musculoskeletal health, immunity, autoimmunity, cardiovascular disease, cancer, fertility, pregnancy, dementia and mortality-a review of recent evidence. Pludowski P1, Holick MF, Pilz S, Wagner CL, Hollis BW, Grant WB, Shoenfeld Y, Lerchbaum E, Llewellyn DJ, Kienreich K, Soni M.
 Hoel, D. G., M. Berwick, F. R. de Grujil. The risks and benefits of sun exposure 2016. Dermatoendocrinol. 8(1). NCBI. Web. 8 Sep 2018.
 Nutr Res. 2011 Jan;31(1):48-54. Prevalence and correlates of vitamin D deficiency in US adults. Forrest KY1, Stuhldreher WL.
 Annu Rev Nutr. 1988;8:375-99. The role of sunlight in the cutaneous production of vitamin D3. Webb AR1, Holick MF.
 Arch Dermatol. 1994 Aug;130(8):1018-21. The role of sunlight and DNA repair in melanoma and nonmelanoma skin cancer. The xeroderma pigmentosum paradigm. Kraemer KH1, Lee MM, Andrews AD, Lambert WC.
 Cochrane Database Syst Rev. 2014 Jan 10;(1):CD007470. Vitamin D supplementation for prevention of mortality in adults. Bjelakovic G1, Gluud LL, Nikolova D, Whitfield K, Wetterslev J, Simonetti RG, Bjelakovic M, Gluud C.
 Am J Clin Nutr. 2010 Apr;91(4):985-91. Epub 2010 Feb 3. Once-weekly dose of 8400 IU vitamin D(3) compared with placebo: effects on neuromuscular function and tolerability in older adults with vitamin D insufficiency. Lips P1, Binkley N, Pfeifer M, Recker R, Samanta S, Cohn DA, Chandler J, Rosenberg E, Papanicolaou DA.
 Adv Exp Med Biol. 2014;810:500-25. Optimal serum 25-hydroxyvitamin D levels for multiple health outcomes. Bischoff-Ferrari HA.