Vitamin D and Human Skin Color


Human skin color is primarily determined by the content of melanin in the skin.  Melanin is found in the skin, hair, and iris, giving humans their coloration.  Melanin is present in other areas of the human body as well, but these are the most easily observed (21). 

Melanin in the skin is produced by melanocytes.  These are found in the stratum basale of the epidermis, which is the lowest layer of the dermis.  Most humans have a similar concentration of melanocytes within their skin; however, expression of melanin-producing genes varies greatly within individuals and ethnicities.  Humans who produce no melanin have a condition called albinism (21). 

Melanin Location Within the Skin (

The two main types of melanin found in human skin and hair are pheomelanin and eumelanin, with eumelanin being the most abundant.  Pheomelanin provides a red tone, while eumelanin lends a dark brown to black color (2, 12, 21, 23).  

Melanin is essentially a natural sunscreen found within the skin.  It absorbs UV B light, the same light that initiates the production of vitamin D3.  Because the light gets absorbed by the melanin, it actually requires a longer exposure time for people with a higher concentration of melanin in their skin to manufacture vitamin D3.  For example, in one experiment, a light-skinned person experienced a 50-fold increase in blood concentrations of vitamin D3 within 8 hours, whereas a dark skin person exposed to the same dose did not exhibit any changes in the blood concentrations of vitamin D3.  In fact, the darker skinned person required 5-10 times the exposure than the light skinned person, and still only had a 30-fold increase in their blood concentrations.  (sunlight and vitamin D for health)  Thus, the additional melanin which causes the darker skin can also be blamed for vitamin D deficiency (1, 2, 5, 11, 12) . 

Melanin Absorbance Closely Matches that of 7-dehydrocholesterol (

Melanin also protects against skin cancers.  The melanin absorbs not only UV-B radiation, but also UV-A.  Light skinned people have approximately a 10 times greater risk of dying from skin cancer than darker skinned people when exposed to the same sun conditions (5). 


Human skin can vary from an extremely light pigmentation (no color at all is a genetic mutation called albinism) to a very dark brown.  The color is dictated by the amount of melanin in the skin.  However, the question of what caused this skin tone variation was a puzzle for quite some time.  The production of vitamin D in relation to the amount and quality of sunlight received is part of the answer to this puzzle (1, 2, 11, 12, 17, 18, 21, 23). 

It has been stated that the default human skin color is most closely related to that of Ethiopians (a light brown shade).  However, as stated above, there is a large variation in colors.  Obviously, there is a factor that alters the default situation to other tones.  Essentially, there is an adaptation that causes a lighter skin color and an adaptation that creates a darker skin color than the default (17, 18). 

The darker adaptation seems to come from a need for folate.  If there is not enough melanin in the skin at lower latitudes (near the equator), too much UV radiation is able to penetrate the skin.  The intense UV causes a halt to the folic acid synthesis - the result of the lack of folate can cause neural tube defects in unborn fetuses.  A higher level of melanin allows normal folate synthesis by absorbing the UV radiation, and can allow for normal gestation and fetal development.  Essentially, evolution allowed for a feature (darker skin) that would allow healthy and successful reproduction.

The lighter adaptation allows for a greater quantity of vitamin D synthesis.  A greater amount of epidermal melanin blocks UV penetration which is needed for the transformation of 7-dehydrocholesterol to calciferol (vitamin D3).  Vitamin D deficiency can result in multiple issues such as rickets and other skeletal deformations.  This was primarily discovered as it became evident that darker skinned people who moved to higher latitudes began to suffer from vitamin D deficiencies, while lighter skinned people at the same latitudes had no such issues. 

Therefore, human skin color evolved via natural selection for each latitude to block enough UV to allow for folate synthesis, yet allow enough UV to penetrate the skin to allow for sufficient vitamin D production (1, 2, 11, 12, 17, 18, 21, 23).

This picture demonstrates the skin color that should occur at various latitudes due to the concentration of melanin necessary to both prevent folate destruction and promote adequate vitamin D synthesis.