by Mia Syn, M.S., R.D.

Vitamin D has long been referred to as the ‘sunshine vitamin.’ Vitamin D researchers suggest that 5-30 minutes of sun exposure at least twice a week between 10 a.m. and 3 p.m. to exposed skin without sunscreen will result in sufficient vitamin D synthesis. (1) However, research suggests that almost 50 percent of the world population has vitamin D insufficiency – an estimated 1 billion people. (2) This has been attributed to populations staying indoors more and environmental factors like air pollution, which can obstruct the sun’s rays. (2)

Vitamin D is important for not only brain health but bone mineralization as well. Women are more likely to suffer from a bone fracture than men. (3) Roughly 40 percent of white women 50 years old or older in the United States will experience a bone fracture in their lifetime. (3) With International Women’s Day in early March, it is important to shed light on this key nutrient and elucidate the best ways to obtain adequate amounts.

All about vitamin D

Vitamin D is a fat-soluble vitamin obtained from food and dietary supplements, or made by the body. It is produced endogenously when skin is exposed to ultraviolent rays. This vitamin, however, is not active upon consumption. It must be activated through hydroxylation in the body, which occurs first in the liver, followed by the kidney. In the kidney, the activated form of vitamin D is produced in response to serum calcium and phosphorous concentrations. This is a reminder that several nutrients work synergistically with one another. Once vitamin D is activated, it acts as a hormone in the body.

Why your brain loves vitamin D

While the link between vitamin D and bone health has been largely explored, research just recently began illuminating the importance of vitamin D when it comes to brain health. Neuropsychiatric disorders such as cognitive impairment and dementia have been linked to vitamin D deficiency across the last decade of research. (4) The presence of vitamin D receptors in the brain implies that this vitamin plays a role in the functioning of this organ. (5) These receptors are largely located in areas associated with cognition and memory including the hippocampus and prefrontal cortex. (6) Additionally, the central nervous system has been identified as a target for vitamin D. Vitamin D metabolites have been found present in cerebrospinal fluid (CSF), which surrounds the brain. (7)

There is evidence that vitamin D and its metabolites act to protect the brain through several mechanisms including promoting nerve growth and clearing amyloid plaques. (8) Because several neurodegenerative diseases are characterized by amyloid plaque buildup, this may be particularly beneficial.

Neurocognitive decline characterizes a large portion of the aging population. This population is especially at a high risk for vitamin D deficiency due to decreased synthesis and dietary intake. (9) Additionally, malnutrition is common in the elderly, which often accompanies other diseases that afflict these populations including diabetes and kidney disease.

How much do you need?

The recommended dietary intake for a healthy adult is 600 IU (15 mcg). However, elderly individuals over the age of 70 should aim for 800 IU (20 mcg). These intakes are established as sufficient to maintain bone health and normal calcium metabolism in healthy individuals.

Dark-skinned individuals are more prone to vitamin D deficiency since dark skin is higher in melanin and requires more sunlight to synthesize the vitamin. Research shows that vitamin D insufficiency is more prevalent among African Americans than other Americans. (10)

How can you get it?

There are few food sources that contain vitamin D which makes it that much more important to balance the need of sun exposure in moderation and supplementation where needed. Fatty fish including salmon, tuna and mackerel are known sources. Additionally, fortified foods provide a large portion of vitamin D in the American diet, including certain dairy products and breakfast cereals.

Sun exposure is an obvious answer when it comes to ways we can obtain vitamin D. However, there are several factors that determine the sufficiency including the season, time of day, cloud coverage, sunscreen and melanin content in the skin. The balance of sun exposure and skin protection from UV rays is a fine line. Ultra violet radiation is responsible for an estimated 1.5 million skin cancers yearly in America. (11)

Because of the few natural food sources of vitamin D coupled with the need to protect skin from the suns rays, dietary supplementation may be viable option to fill in gaps. Most dietary supplements contain vitamin D3, which has been considered the more efficacious form in its ability to raise active vitamin D levels in the serum while supplements containing the D2 form have been mostly considered less efficacious. (12)

References

1. Holick MF. Vitamin D deficiency. N Engl J Med 2007;357:266-81
2. Nair R, Maseeh A, et al: Vitamin D: The “sunshine” vitamin. J Pharmacol Phrmacother 2016; April-June.
3. United States. (2004). Bone health and osteoporosis: A report of the Surgeon General. Rockville, Md: U.S. Dept. of Health and Human Services, Public Health Service, Office of the Surgeon General.
4. Soni M, Kos K, et al. Vitamin D and cognitive function. Scand J Clin Lab Invest Suppl 2012.
5. Harms L, Burne, THJ, et al. Vitamin D and the brain. Best Practice and Research Clinical Endocrinology and Metabolism. 2011.
6. Eyles DW, Smith S, Kinobe R, Hewison M, McGrath JJ. Distribution of the vitamin D receptor and 1 alpha-hydroxylase in human brain. J Chem Neuroanat. 2005;29:21–30.
7. Balabanova S, Richter HP, Antoniadis G, Homoki J, Kremmer N, Hanle J, Teller WM. 25-Hydroxyvitamin D, 24, 25-dihydroxyvitamin D and 1,25-dihydroxyvitamin D in human cerebrospinal fluid. Klin Wochenschr. 1984;62:1086–90.
8. Schlog M. Holick MF. Vitamin D and neurocognitive function. Clin Inter Aging. 2014.
9. Harris SS, Soteriades E, Coolidge JA, Mudgal S, Dawson-Hughes B. Vitamin D insufficiency and hyperparathyroidism in a low income, multiracial, elderly population. J Clin Endocrinol Metab. 2000;85(11):4125-4130
10. Harris S. Vitamin D and African Americans. The Journal of Nutrition. April 2006.
11. Wolpowitz D, Gilchrest BA. The vitamin D questions: how much do you need and how should you get it? J Am Acad Dermatol 2006;54:301-17.
12. Tripkovic L, Lambert H, Hart K, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. 2012;95(6):1357-1364.