Vitamin D is an essential vitamin involved in bone, muscle, nerve and immune functions. You can get vitamin D from fortified foods, and your body can make vitamin D when exposed to the sun for a certain amount of time during the day. However, those with darker skin can't produce vitamin D as quickly as those with lighter skin, according to the National Institutes of Health.
Function
When ultraviolet rays touch the skin, your body makes vitamin D. However, the color of your skin affects how much sun exposure is necessary to make enough vitamin D to meet your body's needs. While a light-skinned person can make sufficient vitamin D with approximately 15 minutes of sun exposure, it can take a dark-skinned person 45 minutes to make the same amount of vitamin D, according to the University of Maryland Medical Center.
Considerations
Skin color is not the only factor that affects the body's ability to make vitamin D. Glass, cloudy days, smog, sunscreen use, clothing and latitude also limit the necessary exposure to the sun and make it harder to meet your vitamin D needs.
Even though covering up your skin with clothing and sunscreen limits your body's ability to make vitamin D, it is still recommended by the National Institutes of Health because vitamin D is available from other sources and excessive sun exposure can cause skin cancer.
Theories/Speculation
Theories about the differences in skin color and how vitamin D is made abound, including one posted on the University of Pennsylvania website. It states that over time, northern peoples developed lighter skin to allow the body to use the sun to synthesize vitamin D, while southerners evolved to have darker skin to keep UV rays from stopping the production of folic acid, while still allowing in enough to get sufficient vitamin D.
Prevention/Solution
In one study it was found that 4.2 percent of non-Hispanic white women were vitamin D-deficient, compared to 42.2 percent of non-Hispanic black women of the same age group, according to the Centers for Disease Control, or CDC. Darker-skinned people, especially those living in northern climates, should make sure to get enough vitamin D from food and supplements. Fortified foods are one of the most common food sources of vitamin D.
Warning
Take care when taking vitamin D supplements, as it is possible to get too much vitamin D. This vitamin can also interact with some medications, so talk to your doctor to determine whether supplements are recommended in your case and how much vitamin D you should take each day. According to the CDC, some medications also either raise or lower the amount of vitamin D in your blood, so this needs to be taken into consideration.
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