Carotenoids and skin colour: a redox-dependent display of health?

There has been some interesting research recently on carotenoids and skin colour ^1–3, which has also made it into the mainstream media. The potential links between carotenoids, skin colour and health intrigue me, as explained below.

Carotenoids are a large family of over 600 organic pigments found in plants and mainly responsible for yellow-red colours (list of phytochemicals in food). They are fat-soluble molecules which can be absorbed by the body and accumulate in most tissues in a non-uniform manner ⁴. Carotenoids have various biological effects including the ability act as antioxidants, modulate cell signaling pathways, and some have provitamin A activity (e.g. α and β-carotene).

Carotenoid accumulation in the skin plays a role in skin pigmentation. Carotenoids contribute to yellow skin tones (before/after faces), alongside other important determinates of skin colour such as melanin (yellow-brown) and blood flow (redness). Also the carotenoids lutein and zeaxanthin preferentially accumulate in the eye where they are responsible for the yellow pigmentation of the macular. Several studies have shown that carotenoid-based skin colouration is perceived as extremely healthy and attractive, more so even than melanin colouration, which is responsible for the browning induced by sun exposure ^1–3. This is thought to be consistent with a carotenoid-based health signaling system conserved through nature, from plants to animals.

In many animals (e.g. birds) vibrant colours are considered honest indicators of health and reproductive fitness. Animal colouration has been shown to correlate various aspects of current health relating to immunity, redox/antioxidant capacity and chronic disease ^2,3,5. In humans, diets high in colourful plant foods, and tissue levels of carotenoids positively correlate with health under various conditions ^2,6,7. Skin carotenoid levels partially reflect diet (i.e. fruit and veg intake) but are also lowered by other lifestyle/health factors such as sunlight exposure, smoking, alcohol consumption, adiposity, stress/illness ^7–9 and medical conditions (e.g. metabolic syndrome ¹⁰ and schizophrenia ¹¹). Therefore given the connection between carotenoids, health and skin colour, a carotenoid-based signaling system may display health ^1,2.

One of the main ways bad health may lower carotenoid levels is via oxidative stress ^7,5,10–12. Carotenoids readily react with oxidising species enabling them to act as antioxidants ^4,13,14. In this role they are gradually depleted and cannot be resynthesized, rather they must be regenerated by other antioxidants or replaced by diet. For instance skin exposure to sunlight or its components (e.g. IR, UV and blue-violet) induces free radicals and depletes antioxidants/carotenoids ¹². Skin carotenoid levels have also been reported to inversely correlate markers of oxidative stress (urinary MDA) ⁷. In contrast consumption of a high antioxidant capacity diet, while keeping β-carotene levels constant, was found to double the blood levels of β-carotene ¹⁵. Since correlations exist between carotenoid levels in different areas of the body, carotenoid-based skin colouration may be able to signal the general antioxidant status of the body ⁹. Importantly this also illustrates why mono-supplementation with β-carotene has failed to improve human health in many trials, because carotenoids are as much markers as mediators of health ⁶.

Notably, carotenoids have not been assessed in ME/CFS, although given the consistent reports of oxidative stress, they may well be low.

Finally it is interesting to note that while we can absorb carotenoids, we have a more limited capacity to absorb other major plant pigments such as polyphenols (i.e. red-blue-purple colours). Most polyphenols pass through the digestive system and arrive relatively unaltered in the colon, where they are metabolised by the microbiota and increase levels of good bacteria ¹⁶. So even these other plant pigments will contribute to good health. Furthermore, the effects of the gut microbiota extend to the skin, where probiotics can also induce changes in skin and hair quality to display a ‘glow of health’ ¹⁷!

References

1.         Lefevre, C. E. & Perrett, D. I. Fruit over sunbed: carotenoid skin colouration is found more attractive than melanin colouration. Q. J. Exp. Psychol. (Hove). 68, 284–93 (2015).

2.         Stephen, I. D., Law Smith, M. J., Stirrat, M. R. & Perrett, D. I. Facial Skin Coloration Affects Perceived Health of Human Faces. Int. J. Primatol. 30, 845–857 (2009).

3.         Whitehead, R. D., Ozakinci, G. & Perrett, D. I. Attractive skin coloration: harnessing sexual selection to improve diet and health. Evol. Psychol. 10, 842–54 (2012).

4.         Stahl, W. & Sies, H. β-Carotene and other carotenoids in protection from sunlight. Am. J. Clin. Nutr. 96, 1179S–84S (2012).

5.         Simons, M. J. P., Cohen, A. A. & Verhulst, S. What does carotenoid-dependent coloration tell? Plasma carotenoid level signals immunocompetence and oxidative stress state in birds-A meta-analysis. PLoS One 7, e43088 (2012).

6.         Donaldson, M. S. A carotenoid health index based on plasma carotenoids and health outcomes. Nutrients 3, 1003–22 (2011).

7.         Mayne, S. T. et al. Resonance Raman spectroscopic evaluation of skin carotenoids as a biomarker of carotenoid status for human studies. Arch. Biochem. Biophys. 539, 163–70 (2013).

8.         Darvin, M. E., Sterry, W., Lademann, J. & Patzelt, A. Alcohol consumption decreases the protection efficiency of the antioxidant network and increases the risk of sunburn in human skin. Skin Pharmacol. Physiol. 26, 45–51 (2013).

9.         Lademann, J. et al. Cutaneous carotenoids: the mirror of lifestyle? Skin Pharmacol. Physiol. 27, 201 (2014).

10.       Holt, E. W., Wei, E. K., Bennett, N. & Zhang, L. M. Low skin carotenoid concentration measured by resonance Raman spectroscopy is associated with metabolic syndrome in adults. Nutr. Res. 34, 821–6 (2014).

11.       Chow, T. J., Loh, H. C., Tee, S. F. & Tang, P. Y. Evaluation of carotenoid level in schizophrenic patients using non-invasive measurement. Asian J. Psychiatr. 3, 190–3 (2010).

12.       Vandersee, S., Beyer, M., Lademann, J. & Darvin, M. E. Blue-violet light irradiation dose dependently decreases carotenoids in human skin, which indicates the generation of free radicals. Oxid. Med. Cell. Longev. 2015, 579675 (2015).

13.       Böhm, F., Edge, R. & Truscott, T. G. Interactions of dietary carotenoids with singlet oxygen (1O2) and free radicals: potential effects for human health. Acta Biochim. Pol. 59, 27–30 (2012).

14.       Chen, J., Song, Y. & Zhang, L. Effect of lycopene supplementation on oxidative stress: an exploratory systematic review and meta-analysis of randomized controlled trials. J. Med. Food 16, 361–74 (2013).

15.       Del Rio, D. et al. Intervention study with a high or low antioxidant capacity diet: effects on circulating beta-carotene. Eur. J. Clin. Nutr. 63, 1220–5 (2009).

16.       Cardona, F., Andrés-Lacueva, C., Tulipani, S., Tinahones, F. J. & Queipo-Ortuño, M. I. Benefits of polyphenols on gut microbiota and implications in human health. J. Nutr. Biochem. 24, 1415–22 (2013).

17.       Levkovich, T. et al. Probiotic bacteria induce a ‘glow of health’. PLoS One 8, e53867 (2013).