A recent study offers one more reason to layer on the sun block and eat your fruits and veggies. The study, published in the British journal Evolution and Human Behaviour indicates that a diet rich in carotenoids increases skin yellowness, which may be perceived as being more healthful than tanned skin.
A healthy appearance has long been an important influence in mate selection across species in the animal kingdom. Birds and fish, for example, seek out mates with brightly colored markings, as this sends a signal of general health and fertility. For humans, making a connection between skin coloration and physical health has remained largely unexamined.
In humans, melanin and carotenoids are the main components that affect skin yellowness. Melanin contributes to skin darkness/yellowness and is important for photo protection against damaging UV rays. Carotenoids are important antioxidants that offer photo protection, help boost the immune system and also contribute to skin’s yellowness.
In order to determine whether or not humans have any preference for skin yellowness, researchers at the University of Bristol in Bristol, UK created three studies examining different aspects of skin lightness and yellowness and how they affect perceived health.
The first study considered cross-cultural differences in preference for skin lightness and yellowness. A popular belief, especially in Western cultures, is that tanned skin appears healthier. However, in South Africa, skin lightening products are frequently used because individuals with lighter skin are viewed as more affluent, trustworthy and of a higher class.
To see if these fashionable trends affect skin color preference across cultures, researchers allowed 32 UK-based Caucasian participants and 31 black South African participants to alter skin tones on 50 color-corrected facial images of the same ethnicity. Each participant was instructed to “make the face as healthy as possible”. Interestingly, both groups chose to increase the yellow coloring of the skin and, to a lesser extent, also increased skin lightness. These results established that there is no cross-cultural difference in preference for increased skin yellowness and lightness despite fashionable trends.
Researchers then checked for a correlation between yellow skin pigments and carotenoid intake – either from dietary intake of fruits and vegetables or through supplementation with beta carotene.
Using one group of participants, the researchers compared levels of yellowness on multiple body sites to their self-reported levels of daily fruit and vegetable consumption. In a second group, the researchers recorded baseline skin pigmentation and checked for increased skin yellowness following 8 weeks of daily supplementation with 15 mg of beta-carotene.
In the end, the participants with the highest fruit and vegetable intake and those that supplemented had the most yellow skin pigments. The authors were able to determine that increasing carotenoid consumption (either through diet or supplementation) leads to increased skin yellowness.
Finally, the researchers conducted a study investigating how Caucasian participants perceive melanin and carotenoid skin pigmentation with regard to health. Using a color pigment axis, participants were allowed to alter facial coloring on 51 color-calibrated images by increasing or decreasing the melanin and/or the carotenoid color pigments.
Of the 70 recruited participants, 22 were allowed to manipulate only the carotenoid axis; 26 were allowed to manipulate only melanin axis; 22 were allowed to manipulate both the carotenoid and melanin axis. The participants were then shown Caucasian facial images, one at a time, and asked to “make the face as healthy as possible”.
For the single-axis faces, all the faces were increased in carotenoid and melanin color pigmentation, although the participants consistently increased the carotenoid pigments more than the melanin.
For the double-axis faces, 68% of the faces were increased in melanin while every face was increased in carotenoid coloration. As a result, this study suggests that carotenoid skin pigments are more strongly associated with perceived health in humans than the tanned appearance caused by melanin.
As Dr. Ian Stephen, the lead researcher on the study, notes, “Most people think the best way to improve skin colour is to get a suntan, but our research shows that eating lots of fruit and vegetables is actually more effective.”
The Bottom Line
While these preliminary findings warrant further research into the links between appearance and health, they can certainly have a positive impact on many people’s diet. Especially for young men and women, whose dietary choices are often motivated by their desires for improved physical appearance, this research could provide a much needed reminder to wear sunscreen and increase the amount of fruits and vegetables in their diet.
David H. Rahm, M.D. is the founder and medical director of The Wellness Center, a medical clinic located in Long Beach, CA. Dr. Rahm is also president and medical director of VitaMedica. Dr. Rahm is one of a select group of conventional medical doctors who have education and expertise in functional medicine and nutritional science. Over the past 20 years, Dr. Rahm has published articles in the plastic surgery literature and educated physicians about the importance of good peri-operative nutrition.