Melanin is a natural substance that gives color to your hair, skin and eyes. Melanin is the primary determinant of skin pigmentation; the more melanin you have in your skin, the darker your skin color will be. The amount of melanin in your skin also determines your body's capacity to produce vitamin D, an essential nutrient, from ultraviolet light exposure. As vitamin D deficiency can cause serious health consequences, it is important for individuals aged 1 to 70 to get at least 600 IU of vitamin D from sun exposure or foods each day.

Relationship

Acting as a natural sunscreen, melanin in skin absorbs ultraviolet-B, or UVB, light -- the same kind of light that initiates vitamin D synthesis. Thus, the higher concentration of melanin in your skin, the longer it will take for you to absorb UVB rays from sun exposure. According to University of Pennysylvania, in one experiment, a light-skinned person experienced a 50-fold increase in blood levels of vitamin D within 8 hours of UVB exposure, while it took a darker-skinned person at least five times as long, or at least 40 hours, to register a 30-fold increase in vitamin D concentrations.

Consequences

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Because a person with darker skin -- that is, high melanin concentrations in the skin -- has a limited capacity obtain vitamin D from sun exposure, darker-skinned people are at a higher risk for vitamin D deficiency than are lighter-skinned individuals. According to a 2008 report by Public Radio International, African Americans are twice as likely to develop vitamin D deficiency than whites. Vitamin D deficiency can cause rickets, a condition causing the bones to become soft and bend, and it may also increase your risk for developing osteoporosis, certain cancers and diabetes.

Other Risk Factors

Besides melanin, other factors also determine your risk for vitamin D deficiency. In addition to people with dark skin, other groups at risk for vitamin D deficiency include breastfed infants, older adults, obese people, and people with disorders that affect fat absorption, such as Crohn's disease and celiac disease. Amount of time spent in the sun, as well as the strength of the sunlight you're exposed to, also determine how much vitamin D your skin is able to make from sun exposure. For example, sunlight that is filtered by clouds, a window, or sunscreen is less conducive to vitamin D production than direct sunlight. Most importantly, inadequate vitamin D intake from foods can put you at risk for vitamin D deficiency.

Vitamin D Deficiency Prevention

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While having more melanin in the skin reduces your capacity to obtain vitamin D from sun exposure, UV rays likely aren't the safest source of vitamin D anyway. It is prudent to avoid spending time in the sun in order to reduce your risk of skin cancer. Instead, you can obtain vitamin D from dietary sources. The best sources of vitamin D are fortified milk and fatty fish such as tuna and salmon. Breakfast cereals and other foods are also sometimes fortified with vitamin D, and some vitamin D is found in mushrooms, cheese, egg yolks and beef liver. People at risk for D deficiency may also benefit from taking vitamin D supplements, under a doctor's supervision.