Vitamin D Deficiency in the South: Why Even Sunny State Residents Are Often Deficient

How the Body Makes Vitamin D From Sunlight

Vitamin D is produced in the skin through a photochemical reaction triggered by ultraviolet B radiation, UVB, from sunlight. When UVB rays penetrate the skin they convert a cholesterol precursor called 7 dehydrocholesterol into pre vitamin D3, which is then converted to active Vitamin D3 through a two step process involving the liver and kidneys.

This synthesis pathway is efficient in the right conditions. But it is also subject to a remarkable number of variables that reduce or eliminate Vitamin D production even in environments with abundant sunlight.

Why Southern Sunshine Does Not Guarantee Adequate Vitamin D

Skin pigmentation. Melanin, the pigment that gives skin its color, absorbs UVB radiation and reduces the amount available to drive Vitamin D synthesis. Darker skin requires significantly longer sun exposure to produce the same amount of Vitamin D as lighter skin under the same conditions. Mississippi has a large African American population, and African Americans have substantially higher rates of Vitamin D deficiency than the national average, not because of dietary differences but because of the melanin mediated reduction in cutaneous Vitamin D synthesis.

This is one of the most clinically significant and least publicly discussed aspects of Vitamin D epidemiology in the South. The communities most at risk for Vitamin D deficiency in Mississippi are not those with the least sunlight. They are those with the highest melanin content in a state where UVB exposure is abundant but where melanin significantly reduces its clinical impact on Vitamin D production.

Sunscreen use. Sunscreen with SPF 15 or higher absorbs UVB radiation and reduces Vitamin D synthesis by as much as 99 percent at high SPF levels when applied correctly. This is the intended function of sunscreen, blocking the UV radiation that causes skin cancer. It is also the function that eliminates most cutaneous Vitamin D production.

Patients who appropriately use sunscreen every time they are outdoors, as dermatologists and public health guidelines recommend, are also eliminating the primary pathway for Vitamin D production from sun exposure. This is not a reason to stop using sunscreen. It is a reason to ensure adequate Vitamin D through supplementation or dietary sources.

Time of day and sun angle. UVB radiation reaches the earth’s surface most effectively when the sun is high in the sky, between approximately 10am and 3pm. Outside of this window the sun angle causes UVB to be filtered by the atmosphere before it reaches the skin. During winter months even in Mississippi the sun angle is lower and the UVB reaching the surface is reduced compared to summer months.

Obesity. Vitamin D is a fat soluble vitamin that is sequestered in fat tissue. People with obesity have higher total body fat mass that acts as a reservoir that sequesters Vitamin D and reduces circulating blood levels. Mississippi has the highest obesity rate in the United States. The combination of obesity related Vitamin D sequestration and melanin related reduced synthesis makes the Mississippi population particularly vulnerable to Vitamin D deficiency by two independent mechanisms simultaneously.

Indoor lifestyle. Air conditioning, a Mississippi necessity for most of the year, is one of the most effective tools for keeping people indoors and out of the sun. A person who works indoors, commutes by car, and spends evenings and weekends in an air conditioned home or watching television may spend very little time in direct sunlight despite living in the sunniest state in the country.

Age. Skin’s capacity to produce Vitamin D decreases with age. Older adults produce significantly less Vitamin D from the same sun exposure as younger adults, making age related Vitamin D deficiency a particular concern in Mississippi’s older population.

Why Vitamin D Deficiency Matters

Vitamin D is not a minor micronutrient with a narrow clinical role. It functions as a hormone in virtually every tissue of the body, with documented roles in:

Bone health. Vitamin D is essential for calcium absorption in the intestine. Without adequate Vitamin D, dietary calcium passes through the gut without being absorbed, and the body responds by pulling calcium from bones, producing the bone softening of osteomalacia in adults and rickets in children. In older adults chronic Vitamin D insufficiency contributes to osteoporosis and fracture risk.

Immune function. Vitamin D regulates both innate and adaptive immune responses. Deficiency is associated with increased susceptibility to respiratory infections, including influenza and COVID 19, and with dysregulated immune responses in autoimmune conditions.

Muscle function and fall prevention. Vitamin D receptors are present in muscle tissue and Vitamin D plays a direct role in muscle cell function. Deficiency causes proximal muscle weakness, weakness in the large muscles of the hips and thighs, that contributes to balance problems and fall risk in older adults. Studies have shown that correcting Vitamin D deficiency in older adults reduces fall rates significantly.

Cardiovascular health. Vitamin D receptors are present in cardiac muscle and vascular smooth muscle. Deficiency is associated with increased risk of hypertension, heart failure, and cardiovascular events, conditions that are already epidemic in Mississippi.

Mental health. Vitamin D receptors are present throughout the brain and Vitamin D deficiency is associated with increased rates of depression. In a state with high rates of depression and limited mental health resources, the contribution of Vitamin D deficiency to mood disorders is a clinically meaningful and underaddressed factor.

Cancer risk. Epidemiological data has consistently associated lower Vitamin D levels with higher rates of certain cancers, colorectal cancer in particular, though the causal relationship and the clinical implications for supplementation remain areas of active research.

What the Numbers Actually Look Like in Mississippi

National survey data consistently shows that African Americans have Vitamin D deficiency rates of 40 to 70 percent depending on the threshold used, compared to 20 to 30 percent in non Hispanic white populations. Given Mississippi’s demographic composition and the additional risk factors of obesity and indoor lifestyle, the prevalence of clinically relevant Vitamin D insufficiency in Mississippi is likely among the highest of any state in the country.

What Optimal Vitamin D Looks Like

Blood levels of Vitamin D, measured as 25 hydroxyvitamin D, are classified as:

• Deficient: below 20 ng/mL
• Insufficient: 20 29 ng/mL
• Sufficient: 30 100 ng/mL
• Optimal for most clinical benefits: 40 60 ng/mL according to many functional medicine practitioners, though 30 ng/mL is the widely accepted sufficiency threshold

The daily supplementation doses required to achieve and maintain sufficient levels vary by individual but most adults, particularly those with dark skin, obesity, or limited sun exposure, require between 2,000 and 5,000 IU of Vitamin D3 daily to maintain levels above 30 ng/mL. The standard 400 IU dose found in many multivitamins is inadequate for most adults with risk factors for deficiency.

What to Do

Get your Vitamin D level checked. A 25 hydroxyvitamin D blood test is a standard laboratory test that most physicians can order. If you have never had your Vitamin D level checked, or if it has not been checked in several years, request it at your next appointment.

Choose Vitamin D3 over D2 when supplementing. Vitamin D3, cholecalciferol, is the form produced naturally by human skin and is more effective at raising and maintaining blood levels than Vitamin D2, ergocalciferol, which is derived from plant sources. Look for Vitamin D3 specifically on supplement labels.

Take Vitamin D with your largest meal. Vitamin D is fat soluble and is absorbed significantly better when taken with a meal containing fat. Taking it with breakfast if breakfast includes eggs, dairy, or other fat containing foods improves absorption substantially.

Consider the combination of Vitamin D3 and Vitamin K2. As discussed in our Senior Wellness content, Vitamin K2 directs calcium into bones rather than arteries when Vitamin D is driving calcium absorption. For patients supplementing with high dose Vitamin D3, including Vitamin K2 in the regimen supports the cardiovascular safety of the supplementation.

This article is for general information only and is not a substitute for personalized medical advice. Before starting or changing any medication, including over the counter products and supplements, talk with your pharmacist or physician about your specific situation.