Why do people with heavily pigmented skin often have lower levels of vitamin D, and how does sunscreen play a role? These are questions researchers are trying to answer.
Vitamin D is an essential vitamin that is naturally present in some foods and can be produced when sunlight interacts with proteins in the skin. It’s critical to many metabolic functions and plays a crucial role in the immune system. Recent studies have even shown it may help reduce the risk of acute respiratory tract infections.
Adequate vitamin D is essential to a healthy immune system and strong bones. Studies have also shown that insufficient vitamin D levels can increase the likelihood of health concerns such as diabetes, cardiovascular disease, Alzheimer’s disease and dementia, multiple sclerosis, and osteoporosis.
Sources of vitamin D
The level of vitamin D in the body is determined by a variety of factors, including age and consumption of foods rich in vitamin D like sardines, salmon, yogurt and eggs.
But for most people, sun exposure and ultraviolet B, or UVB, rays – the shorter wavelength associated with sunburn – are the main source of vitamin D. For those who still don’t get enough vitamin D, dietary supplements can help; consult a physician to ensure you get the correct amount.
Ultraviolet A, or UVA, rays are responsible for skin aging. UVB rays are associated with sunburn, which increases the risk of melanoma.
Impact of melanin on vitamin D production and synthesis
A person’s vitamin D level is also determined by the amount of melanin in their skin, the pigment that influences skin tone. The more melanin, the darker the skin tone. The less melanin, the lighter the skin.
The amount of melanin in the skin affects vitamin D status because the skin depends on UV rays to synthesize vitamin D, and darker skin inhibits its production. It takes about 15 minutes in the sun for a person with lighter skin to generate enough vitamin D for the day, whereas a person with darker skin needs anywhere from 30 minutes to three hours.
Melanin absorbs harmful UV radiation and therefore protects cells against DNA damage from sun exposure.
Populations with higher levels of melanin who live at high latitude are most likely to have vitamin D deficiency. But that may be only because sun exposure for most people living at higher latitude – in cold weather that requires protective clothing year-round – is very limited.
In one study, for instance, people with darker skin at higher latitude are slower to produce vitamin D and have a higher prevalence of vitamin D deficiencies than lighter-skinned individuals at the same latitudes. The farther the distance from the Equator, the higher the latitude and the less sunlight the area receives – a major reason individuals with higher melanin levels find themselves at risk for vitamin D deficiencies in places like Alaska and Canada.
People with heavily pigmented skin are caught between a rock and a hard place – they have lower risk of skin cancer because of their melanin but they often have a vitamin D deficiency for the very same reason.
Sunscreen and vitamin D
Since populations with high levels of melanin often have insufficient vitamin D levels, and since studies show sunscreen application doesn’t play a role, researchers are exploring how sunscreen may affect those with more melanin.
Like melanin, sunscreen plays an important role in reducing exposure to damaging UV radiation. There’s also a theory that sunscreen may also reduce the body’s generation of vitamin D – one study argues their widespread use has led to the decrease in vitamin D in the skin. But in general, the evidence suggests the risk of getting vitamin D deficiency from everyday sunscreen use is very low.
Some studies of the effect of regular sunscreen use on vitamin D levels, including one in Australia, found that vitamin D levels didn’t change in any of the study participants. And a comparison of self-reported sunscreen use and vitamin D levels found no significant evidence that sunscreen application affected vitamin D levels significantly.
But factors like the amount of time spent outdoors and the types of clothing worn in the sun can affect the amount of UVB rays reaching the skin and therefore the synthesis of vitamin D. These variables make it more difficult to research sunscreen and can lead to contradictory results.
In fact, a 2020 article in the Journal of Cosmetic Science revealed that no study has directly compared protection from the sun by melanin and sunscreens.
While uncertainties remain, use sun protection
We still don’t how much melanin levels affect the need for sunscreen. More research is needed exploring the relationship between sunscreen and the effect on vitamin D synthesis of different melanin levels, particularly in large sample sizes in environments representative of real life.
Until we have definitive answers about melanin and sunscreen, people with high melanin levels are encouraged to use sun protection.