The role of vitamin D in racial health disparities in the United States (4723 hits)
Skin color, vitamin D, inflammation and chronic disease by William F. Supple, Jr., Ph. D. and Laura Supple
Racial health disparities in the United States are well documented, but the common explanations may overlook an important element that could improve health outcomes for racial minorities.
Excessive rates of chronic disease among racial minorities are widespread, dramatic, and tragic. The U.S. Centers for Disease Control and Prevention (CDC) reports that nearly 44 percent of African American men and 48 percent of African American women have some form of cardiovascular disease. The incidence of various autoimmune diseases is also higher among African Americans.
African Americans also experience rates of hypertension, diabetes, and obesity that are 25 percent, 49 percent, and 59 percent higher, respectively, than those experienced by white counterparts. At the same time, recent African immigrants to the United States also show significantly lower rates of risk factors for heart attacks, strokes, hypertension and other cardiovascular diseases compared to African Americans, according to the American Heart Association.
Along with the numerous environmental, social, and economic factors known to contribute to these stark health disparities, research suggests chronic vitamin D deficiency may play a critical role in exacerbating health inequalities and vulnerabilities to many chronic diseases among African American populations.
The Adaptive Role of Skin Color Variations
Variations in skin color help regulate the degree of ultraviolet (UV) radiation penetration into the skin. Melanin, the body’s natural sunscreen, efficiently absorbs ultraviolet-B (UV-B) radiation, protecting the body’s cells from DNA damage caused by excessive exposure to UV radiation. In fact, the process of tanning, when skin darkens after exposure to sunlight, reflects an on-the-fly, temporary mutation. Skin increases melanin content when exposed to sunlight, specifically UV-B radiation, with greater amounts of melanin producing darker, more pigmented skin.
Melanin plays a critical role in protecting cells against excessive sunlight exposure. Skin cancer is seventy times less likely to occur in individuals with dark skin compared to individuals with lighter skin. In equatorial regions, this protective effect is critical to prevent harmful cellular damage and DNA mutation. However, UV-B radiation is also essential in the production of vitamin D, an essential vitamin necessary for bone growth and mineralization, modulation of cell growth, neuromuscular and immune function, and control of inflammation. Of the nearly 40 trillion cells in the human body, nearly every one contains a vitamin D receptor, indicating a nearly ubiquitous role of vitamin D in almost all of the body’s systems.
One of the most important functions for vitamin D is immune system regulation. Without adequate vitamin D, the immune system can’t differentiate harmful invading cells from healthy cells and may inadvertently attack those healthy cells – the hallmark of an autoimmune condition. This autoimmune attack on healthy cells results in a state of chronic inflammation. Vitamin D deficiency, and the resultant increase in chronic inflammation, has been associated with increased risks of autoimmune disease, various cardiovascular diseases, cancers of epithelial origin (breast, prostate, lung and colon), and many other debilitating conditions.
African-Americans have a markedly higher prevalence of vitamin D insufficiency, and higher incidence and worse outcomes for cardiovascular disease, certain cancers, diabetes mellitus, and renal disease, all of which have been linked to vitamin D insufficiency. Chronic and widespread inflammation, which may be exacerbated by exposure to environmental pollution, socioeconomic stressors, experiences of violence and racial discrimination, and inadequate access to health care and health resources, plays a critical role in the pathology and progression of cardiovascular disease and hypertension. African-Americans have higher levels of inflammation as measured by greater levels of inflammatory markers compared to whites. Most importantly, low-grade systemic inflammation plays a critical role in the pathology and progression of cardiovascular disease and hypertension.
To illustrate the important role of chronic inflammation and vitamin D deficiency in health disparities and health outcomes, consider three very different conditions: infant mortality, cardiovascular disease, and COVID-19, the disease caused by the novel coronavirus, that have all severely impacted the African American community. Examining previously unidentified or underappreciated roles of vitamin D in each of these conditions can help individuals, medical professionals, and public health officials begin to address some of the underlying risk factors contributing to racial health disparities.
Infant Mortality: African American mothers are 2.3 times as likely as white mothers to experience an intrauterine fetal death (11.1 vs. 4.8 fetal deaths at 20 weeks gestation or greater per 1000 live births). Compared with white women, African American women are at 1.5- to 2.5-times greater risk of delivering a preterm (<37 weeks gestation; 18.5 percent vs. 11.7 percent) or very preterm infant (<32 weeks gestation; 4.1 percent vs. 1.7 percent) as well as a term low birth weight infant (<2500 g birth weight at ≥37 weeks; 5.6 percent vs. 2.6 percent). African American women are also more likely to develop preeclampsia and have more severe complications of the disorder than white women, even after excluding women with chronic hypertension. Maternal vitamin D deficiency may predispose to the increased inflammatory response that characterizes preeclampsia. Again, the relationship between vitamin D, immune function and dark skin being a risk factor for exacerbating vitamin D deficiencies on measures of health are clear.
Cardiovascular Disease (CVD): National Health and Nutritional Examination Survey data demonstrated a high prevalence CVDs, including coronary heart disease, heart failure, stroke and peripheral artery disease, among all groups with vitamin D deficiency, which is further magnified with respect to vitamin D deficiency and CVD prevalence among the African American population. Vitamin D’s protective effects against CVD revolve around maintaining healthy vascular endothelial tissue (the inside walls of blood vessels) through nitric oxide availability. Nitric oxide is critical to maintaining healthy endothelial vascular function through the suppression of inflammation-induced vascular dysfunction.
In a provocative study on the effects of vitamin D on blood pressure in African Americans, Forman et al.(2013) found that vitamin D daily doses of 1000 IU, 2000 IU or 4000 IU for three months significantly lowered systolic pressure in a dose-dependent manner compared to a group receiving placebo. These promising results indicate that vitamin D supplementation could be a simple, low-cost preventative therapy to reduce risk factors for hypertension and other CVDs. Again, the relationship between vitamin D, immune function and dark skin being a risk factor for exacerbating vitamin D deficiencies on measures of health, in this instance CVD, are clear.
COVID-19: The current COVID-19 crisis has severely impacted African American communities across the country. A recent analysis by the Washington Post found that counties with African American majorities have three times the rate of COVID-19 infections, and six times the rate of death compared to predominately white communities . Furthermore, a new study published April 22nd in the Journal of the American Medical Association described the symptoms, comorbidities, and clinical outcomes of 5,700 patients hospitalized due to COVID-19 in the New York area. 94 percent of those hospitalized had at least one chronic health problem, or comorbidity, and 88 percent had two or more. The three most prevalent conditions were hypertension (57 percent), obesity (42 percent), and diabetes (34 percent) – three conditions with documented relationships to chronic vitamin D deficiency. Given the documented chronic vitamin D deficiency among African Americans, vitamin D deficiency being a risk factor for these comorbidities, and the role of vitamin D in immune system function, perhaps enhancing the vitamin D status of the African American community is warranted. Furthermore, a recent paper describing low population mortality rates in countries closer to the equator, where populations experience greater sunlight exposure and tend to suffer lower rates of chronic vitamin D deficiency, suggested that vitamin D is ‘very important in preventing the cytokine storm and subsequent acute respiratory distress syndrome that is commonly the cause of mortality’ in COVID-19.
What to do? While the many factors contributing to racial health disparities in the United States are incredibly complex, addressing chronic vitamin D deficiency is one step individuals can take immediately that may reduce their own risk of chronic disease and improve immune system functioning. Consult with your doctor and ask to have your vitamin D [25(OH)] blood levels tested. 50-100 ng/ml is optimal. If you are vitamin D deficient and getting sunlight year-round is a problem (as it is for most of us living in northern latitudes), supplement with vitamin D3 (cholecalciferol) the most bioavailable form of vitamin D. If you have dark skin, you most likely need to supplement. Start to build up your blood levels of vitamin D now, and keep them there from now on.
Considering the important contribution of vitamin D to general health and the demonstrated vitamin D deficiencies among African Americans, it makes practical common sense to address the vitamin D status of this group immediately. Vitamin D is an inexpensive, safe and easy to obtain substance that represents a very easy fix to a number of serious problems. Indeed, filmmaker Tyler Perry recently urged fellow African Americans to increase their intake of vitamin D to strengthen their immune system. All should realize and take comfort knowing that there is very little risk and tremendous, perhaps life-saving, upside to following his advice.
