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The last time I visited the dermatologist for my annual skin-cancer check, she started the checkup with a surprise recommendation: Sensible sun exposure—without sunscreen—to support vitamin D production (FYI, a sunscreen with an SPF of 15 reduces the production of vitamin D in the skin by 99%).1 The surprise wasn’t that I should get some unprotected sun exposure to optimize vitamin D production; the shocker was that it came from my very conventional dermatologist, who would normally admonish me for not wearing sunscreen.
I first wrote about vitamin D, aka, the sunshine vitamin, 12 years ago, and it’s just as important to health today as it was then. And now, with the lingering threat of COVID-19, optimizing our levels of the nutrient has become even more urgent. But unfortunately, we are still experiencing an epidemic of insufficient and deficient levels—data from the National Health and Nutrition Examination Survey found that out of 4,495 people sampled, 41 percent were deficient in vitamin D (defined as less than 20 ng/mL). Race was a significant risk factor, with African Americans and Latinos having the highest prevalence of deficiency, at 82 percent and 69 percent, respectively.2 Native Americans have also been found to have high deficiency rates.3 Other risk factors for deficiency include smoking, obesity, having diabetes, and general “poor health,”4 as well as geographical location (think Colorado and farther north), sunscreen use and limiting sun exposure, advanced age, and magnesium deficiency.
These days, immunity is on everyone’s mind, and if you are still doubtful about vitamin D, consider this: Preliminary research is showing that when it comes to COVID-19, vitamin D status can be a matter of life or death. For example, a study in Indonesia compared two groups of patients (those who died, and those who survived; 780 patients total) diagnosed with SARS-CoV-2 and found that vitamin D status was strongly associated with COVID-19 mortality outcome. More specifically, nearly 90 percent of those patients who were deficient in vitamin D died (levels < 20 ng/mL), 87 percent of patients who had insufficient levels died (levels between 20-30 ng/mL), while only 4 percent of patients with normal vitamin D levels died (levels > 30 ng/ mL). The researchers wrote that, “When compared to cases with normal Vitamin D status, death was approximately 10.12 times more likely for Vitamin D deficient cases.”5
A growing number of researchers and clinicians are calling for vitamin D supplementation to potentially reduce the severity of COVID-19, with the goal of increasing vitamin D levels to 40-60 ng/mL.6
Long before COVID-19, vitamin D was known to profoundly affect immunity, and deficiency has consistently been associated with an increased susceptibility to respiratory infections, while sufficient levels have been shown to be protective against influenza and other respiratory illnesses. Vitamin D receptors are found in most immune cells, where vitamin D directly acts as an immune system modulator, helping the immune system respond appropriately, without over-or under-reacting. It has also been shown to support general lung health, reduce the expression of pro-inflammatory cytokines, and stimulate the expression of potent antiviral peptides like cathelicidin. Vitamin D’s role in immune function inhibits the development of autoimmune diseases as well.7 8 9 10 11
While supporting immunity is top-of-mind these days, we shouldn’t forget about the importance of supporting whole-body health, and the cardiovascular system is one of the best places to start. Just as vitamin D receptors are found in most immune cells, they are also found in all the major cardiovascular cells and studies have “demonstrated an independent association between vitamin D deficiency and various manifestations of degenerative cardiovascular disease including vascular calcification.”12 When you have optimal levels of vitamin D, it is able to influence cardiovascular health—via gene expression—in a number of ways, some of which include reducing endothelial inflammation; improving arterial dilation, endothelial repair, and vascular tone; reducing the risk of thrombosis; and supporting healthy blood pressure.13
Vitamin D receptors are found throughout the central nervous system, where vitamin D plays a critical role in brain development and cognitive function. Clinical studies have found that low serum vitamin D levels are associated with reduced cognitive function, dementia, autism, anxiety, and depression.14 15 In a study of seniors, with an average vitamin D level of 18 ng/mL, those with the lowest levels had the most depression and the worst performance on dementia and cognitive function tests.16 In a separate study, the same researchers investigated whether neurological manifestations of vitamin D deficiency were more common in African Americans, who have a higher prevalence of vitamin D deficiency in general. The researchers compared 30 African Americans with 30 white Americans (the subjects were all older than 50) and found that African Americans had an average serum level of 18 ng/ mL compared to 25 ng/mL in white Americans. Among African Americans, vitamin D deficiency was associated with worse cognitive performance compared to those African Americans who had normal vitamin D levels, leading the researchers to write, “This significant finding suggests that African Americans may be at a particular increased risk for cognitive impairment as a result of their vitamin D deficiency.”17
Vitamin D is involved in the biosynthesis of neurotrophic factors such as nerve growth factor (which support the growth, survival, and differentiation of neurons), neurotransmitter production, and increased glutathione levels in the brain (important for detoxification and antioxidant protection). It has also been shown to have a neuroprotective effect, including clearing amyloid plaques, a hallmark of Alzheimer’s disease, as well as support synaptic plasticity, or the brain’s ability to grow and change. Recent research has shown that deficiencies of vitamin D in pregnant women may lead to disabilities in their o spring, including learning and memory problems, while sufficient levels decrease the risk for their children developing mental illness later in life. And finally, studies have also found that supplementation with vitamin D improves symptoms of depression and anxiety.18 19 20 21 22 23
Vitamin D also plays important roles in muscle strength, balance, and decreasing the risk of falls;24 25 26 insulin sensitivity and blood sugar regulation;27 28 and reducing inflammation and oxidative damage in the body, two major factors in disease development and poor aging. A scientific review published in 2019 underscored vitamin D’s importance for healthy aging: “Vitamin D is one of the key controllers of systemic inflammation, oxidative stress and mitochondrial respiratory function [i.e., energy production], and thus, the aging process in humans …Vitamin D adequacy leads to less oxidative stress and improves mitochondrial and endocrine functions, reducing the risks of disorders, such as autoimmunity, infections, metabolic derangements, and impairment of DNA repair; all of this aids a healthy, graceful aging process.”29
Vitamin D is unique in the nutrient world in that it is the only vitamin made in the human body from exposure to sunlight, specifically from UVB rays. Our bodies developed based on a need for high levels of the nutrient. Like plants, humans need the sun—and the vitamin D it produces—for normal growth and optimal health. There are thousands of vitamin D receptors (VDR) located throughout the body, and vitamin D directly influences hundreds of genes, including those associated with autoimmune diseases like multiple sclerosis, type-1 diabetes, and Crohn’s disease, as well as genes related to cancer, immune function, stress response, and DNA repair. In one study, researchers concluded that, “Our data suggest that any improvement in vitamin D status will significantly affect expression of genes that have a wide variety of biologic functions of more than 160 pathways linked to cancer, autoimmune disorders and cardiovascular disease which have been associated with vitamin D deficiency.”30 31
It is difficult to be rooted in health without first achieving optimal vitamin D levels. But what is optimal? Researchers are still trying to answer that question, but most experts agree that levels between 40 and 60 ng/mL will best support whole-body health, and many health care practitioners now routinely recommend 5,000 IUs of vitamin D3 daily to reach those levels. A simple blood test, called the 25-hydroxy-vitamin D test, can determine your levels. It is also important to note that a deficiency, or even insufficiency, is not reversed immediately; it may take months of supplementation to increase your D levels to the optimal range.