Why do African Americans have lower vitamin D levels?

From the Guidelines

African Americans have lower vitamin D levels primarily due to their darker skin pigmentation, which reduces the skin's ability to produce vitamin D when exposed to sunlight. This biological factor is significant because sunlight exposure is the primary way humans obtain vitamin D 1. According to the studies, the higher melanin content in darker skin can reduce vitamin D production by up to 99% compared to lighter skin. Additionally, genetic factors affecting vitamin D binding proteins and metabolism may contribute to lower levels in African Americans 1. Environmental and lifestyle factors such as living in northern latitudes with less sun exposure, spending more time indoors, dietary habits with lower vitamin D intake, and higher rates of obesity (which can sequester vitamin D in fat tissue) may further compound this issue 1.

Some key points to consider:

• The prevalence of low vitamin D levels is higher in African Americans, with 70.6% having levels of 50 nmol/L (20 ng/mL) or less, compared to 21.7% of white persons 1.
• The geometric mean of 25-(OH)D levels in adults aged 20 years or older ranged from 32.5 to 36.25 nmol/L (13.0 to 14.5 ng/mL) in African Americans, compared to 57.5 to 64 nmol/L (23.0 to 25.6 ng/mL) in white persons 1.
• It is unclear if low 25-(OH)D levels are associated with adverse clinical outcomes in African Americans, as the increased risk for fractures and cardiovascular disease observed in some studies of white persons has not been found in African Americans 1.
• A recent study suggests that although total serum 25-(OH)D levels may be lower in African Americans than in white persons, the concentration of bioavailable 25-(OH)D may be similar between the 2 populations when vitamin D–binding protein is considered 1.

To address the lower vitamin D levels in African Americans, higher vitamin D supplementation, typically 1,000-2,000 IU daily, or more frequent consumption of vitamin D-rich foods like fatty fish, fortified dairy products, and egg yolks may be necessary. Regular monitoring of vitamin D levels through blood tests is recommended, as maintaining adequate levels is important for bone health, immune function, and potentially reducing the risk of certain chronic diseases 1.

From the Research

Factors Contributing to Lower Vitamin D Levels in African Americans

• Pigmentation reduces vitamin D production in the skin 2
• Lower median vitamin D intakes among American blacks, particularly from puberty onwards 2
• Limited sun exposure and inefficient vitamin D photosynthesis due to deep skin pigmentation 3
• Lower use of dietary supplements among African Americans compared to whites 4

Health Implications of Low Vitamin D Levels

• Increased risk of osteoporotic fractures, despite bone-protective adaptations 2
• Potential links to cardiovascular disease, diabetes, and certain cancers, which are prevalent among African Americans 2, 5
• Associations between vitamin D deficiency and hypertension, type 2 diabetes, and cardiovascular disease 5, 3

Vitamin D Supplementation and Bone Health

• Improving vitamin D status may benefit African Americans, particularly in reducing parathyroid hormone concentrations and bone turnover marker concentrations 4
• Vitamin D supplements may decrease the risk of osteoporosis and fractures, especially among older individuals 4, 6
• Recommended intake of vitamin D3 to maintain optimal 25(OH)D concentrations is approximately 1000 IU/d 4