It’s not just genetics, nor sunlight: the diet also works on tanning.
120 years ago, anthropologist and doctor Felix Von Luschan created a color scale to characterize different skin tones. This scale included 36 different shades, with the aim of proving that the further away from the equator a person’s ancestors were, the lighter their skin should be.
However, the “tans” Inuitwith dark hair and warmed under animal skin coats in the freezing cold with little sun of northeast Asia, northern Canada and Alaska, always defied the Austrian doctor’s logic.
Almost 100 years later, at the turn of the century, anthropologists Nina Jablonski and George Chaplin published a study in the journal Science in which they demonstrated that there is a correlation between skin color and exposure to ultraviolet (UV) rays over more than 500 years in a given region. The two scientists even created an equation capable of estimating the pigmentation of a population based on the intensity of solar radiation and the time spent in the location. But research still could not explain the Inuit’s natural tan.
Today, we know as a fact that the key to understanding this phenomenon lies in the interaction between the skin and UV radiation.
Skin color is genetically determined: genes tell the body how much of each type of melanin to produce. In this process, eumelanin is responsible for darker brown tones, while pheomelanin generates reddish or yellowish pigments. But the genetics is not the only factor taken into account: exposure to the sun increases the production of melanin, which makes us more tanned.
UV rays stimulate the optic nerve to send signals to the pituitary gland, which in turn increases pigment production. It is a process that protects the skin against sun damage by preventing the degradation of folic acid, essential for DNA synthesis. It also reduces the risk of burns and skin cancer.
Despite being most often associated with , UV rays also have beneficial effects: they help convert cholesterol into vitamin D, essential for bone health, and prevent some types of cancer, heart disease, diabetes and even mental disorders.
When humans’ earliest ancestors split from primates, they were still almost as hairy as primates. They were therefore little exposed to direct sunlight, and their skin remained lighter. As humans evolved and their fur became thinner, their skin became more exposed to radiation from the equator. To protect itself, the body started to produce more melanin, making the skin darker.
As groups of humans migrated to higher latitudes, such as Europe and Asia, intense pigmentation became a problem: dark skin made it difficult to synthesize vitamin Dnecessary for bone health. The adaptation consisted of reducing melanin production, making the skin lighter.
Food works the bronze
But this is where the Inuit take a different path. The group’s vitamin D intake did not depend on the sun, but on food.
The traditional diet, rich in fatty fish like salmon and codprovided vitamin D in abundant quantities, avoiding the need to reduce melanin. Before the fortification of milk with vitamin D, populations in regions with little sunlight also turned to marine products, such as cod liver oil, to supplement the vitamin.
The Inuit’s naturally tanned skin is not an effect of sun exposure, but rather a reflection of diet and genetic inheritance. Even in the cold and dark environment of the Arctic, foods rich in vitamin D allowed them to maintain their original pigmentation: sometimes, it is not the Sun that dictates the color of the skin, but rather what is on the plate.
Furthermore, dark skin “protects them from very, very high levels of reflected ultraviolet radiation – long wavelength ultraviolet radiation – from snow” explained Nina Jablonski in 2009. This is what also explains the more intense pigmentation in maritime people, who receive incident radiation from the water surface.
