Skin Color Cues to Human Health: Carotenoids, Aerobic Fitness, and Body Fat

Mapping and annotating genomic loci to prioritize genes and implicate distinct polygenic adaptations for skin color

Evidence for adaptation of human skin color to regional ultraviolet radiation suggests shared and distinct genetic variants across populations. However, skin color evolution and genetics in East Asians are understudied. We quantified skin color in 48,433 East Asians using image analysis and identified associated genetic variants and potential causal genes for skin color as well as their polygenic interplay with sun exposure. This genome-wide association study (GWAS) identified 12 known and 11 previously unreported loci and SNP-based heritability was 23-24%. Potential causal genes were determined through the identification of nonsynonymous variants, colocalization with gene expression in skin tissues, and expression levels in melanocytes. Genomic loci associated with pigmentation in East Asians substantially diverged from European populations, and we detected signatures of polygenic adaptation. This large GWAS for objectively quantified skin color in an East Asian population improves understanding of the genetic architecture and polygenic adaptation of skin color and prioritizes potential causal genes.

Chronic and immediate refined carbohydrate consumption and facial attractiveness

The Western diet has undergone a massive switch since the second half of the 20th century, with the massive increase of the consumption of refined carbohydrate associated with many adverse health effects. The physiological mechanisms linked to this consumption, such as hyperglycaemia and hyperinsulinemia, may impact non medical traits such as facial attractiveness. To explore this issue, the relationship between facial attractiveness and immediate and chronic refined carbohydrate consumption estimated by glycemic load was studied for 104 French subjects. Facial attractiveness was assessed by opposite sex raters using pictures taken two hours after a controlled breakfast. Chronic consumption was assessed considering three high glycemic risk meals: breakfast, afternoon snacking and between-meal snacking. Immediate consumption of a high glycemic breakfast decreased facial attractiveness for men and women while controlling for several control variables, including energy intake. Chronic refined carbohydrate consumption had different effects on attractiveness depending on the meal and/or the sex. Chronic refined carbohydrate consumption, estimated by the glycemic load, during the three studied meals reduced attractiveness, while a high energy intake increased it. Nevertheless, the effect was reversed for men concerning the afternoon snack, for which a high energy intake reduced attractiveness and a high glycemic load increased it. These effects were maintained when potential confounders for facial attractiveness were controlled such as age, age departure from actual age, masculinity/femininity (perceived and measured), BMI, physical activity, parental home ownership, smoking, couple status, hormonal contraceptive use (for women), and facial hairiness (for men). Results were possibly mediated by an increase in age appearance for women and a decrease in perceived masculinity for men. The physiological differences between the three meals studied and the interpretation of the results from an adaptive/maladaptive point of view in relation to our new dietary environment are discussed.

Diet and skin health: The good and the bad

The skin protects humans from pathogens, ultraviolet light, chemicals, mechanical, thermal, and physical injuries as well as hazardous substances. Other important roles of the skin include the regulation of several important physiological processes of the body, sensing stimuli, synthesis of vitamin D, and immune surveillance. However, aging, diseases and environmental conditions significantly change the skin's behavior and functioning. The treatment and prevention strategies for various skin diseases especially photoaging usually include topical treatment with medical cosmetology, active ingredients and other physical means of photoprotection. In recent times, however, there is an increasing consciousness about the role of diet and nutrition in skin health with certain dietary components emerging as an adequate alternative approach to alleviate and prevent both endogenous and exogenous aging symptoms. Therefore, this narrative review uniquely discusses the basic structure of the skin and also addresses common dermatological signs of damaged skin, the impacts of unhealthy diet habits on the skin, and the beneficial effects of some healthy diet habits on skin health. The information and data were collated from various literature databases and resources such as Science Direct, PubMed, Wiley, Springer, Taylor and Francis, Inflibnet, Scopus, Google, and Google Scholar using relevant keywords Medical Subject Headings (MeSH). In conclusion, diet and nutrition play essential roles in the optimum functioning of the human body, including the skin. Thus, certain diet habits such as less water intake, high-fat diet, refined sugar, and certain food additives are unhealthy and harmful to the skin while alternative healthy diet habits such as adequate water intake; consumption of antioxidants and polyphenolic-rich fruits, vegetables, nuts, and legumes; a low glycemic index diet; probiotics; and phytoestrogens should be adopted to enhance skin health.

Colour information biases facial age estimation and reduces inter-observer variability

Age estimation is a perceptual task that people perform automatically and effortlessly on a daily basis. Colour has been identified as one of the facial cues that contributes to age perception. To investigate further the role of colour in age perception, we manipulated the chromatic content of facial images holistically. In Experiment 1, images were shown in colour or grey scale; in Experiment 2, images were shown with red-green contrast increased or decreased; in Experiment 3, images were shown with modified yellow-blue contrast. We examined whether the presence of chromatic information biases the perception of age and/or affects inter-observer variability in age judgements, and whether specific chromatic information affects the perception of age. We found that the same face tended to be judged as younger with increased red-green contrast compared to decreased red-green contrast, suggesting that red-green contrast directly affects age perception. Inter-observer variability in age ratings was significantly lower when participants were asked to rate colour compared with grey scale versions of images. This finding indicates that colour carries information useful cues for age estimation.

A Cross-Sectional Assessment of Quantitative Epidermal Melanin and Erythema Indices among North Indians

Background

Remarkable diversity of skin tones among Indians ranging from pale pinkish to dark brown appears to be an ideal choice for the assessment of skin pigment variation.

Aim

The present study was designed to assess the variation observed in melanin and erythema indices among north Indians.

Material and Methods

Skin reflectance data (n = 574) was collected from six diverse populations of north India using DermaSpectrometer (DSM II ColorMeter) followed by statistical analysis to investigate the impact of geographical location and gender on constitutive skin pigmentation.

Results

The melanin index (MI) varied between 17.93 and 56.92 (Mean (M) = 35.80 ± 6.26) whereas the erythema index (EI) varied between 4.92 and 18.82 (M = 10.48 ± 2.68). MI and EI of females were found to be significantly lower than males (P < 0.001). Geographical location exhibited a significant association with MI and EI (P < 0.001). Furthermore, we have noted a positive correlation between MI and EI (P < 0.001).

Conclusion

The study has refined our understanding of skin pigmentation variation among north Indians in terms of significant association with geographical location {MI: F _(5,568) = 31.07, P < 0.001; EI: F _(5,568) = 73.37, P < 0.001} and gender {MI: t ₍₃₈₆₎ = -4.06, P < 0.001; EI: t ₍₃₈₆₎ = -11.96, P < 0.001} and rendered opportunities for further studies.

Protective effects of chlorogenic acid on growth, intestinal inflammation, hepatic antioxidant capacity, muscle development and skin color in channel catfish Ictalurus punctatus fed an oxidized fish oil diet

Under oxidative stress condition, the protective effects of dietary chlorogenic acid (CGA) supplementation on liver antioxidant capacity, intestinal inflammation and barrier function, muscle development and skin coloration in channel catfish Ictalurus punctatus were explored in the current study. With that purpose, I. punctatus were fed five experimental diets containing 2% fresh fish oil (FFO, 9.2 meqO₂/kg) or 2% oxidized fish oil (OFO, 897.4 meqO₂/kg) without or with CGA supplementation (0.02%, 0.04% and 0.08%) for 8 weeks. Upon comparative analysis, the oxidized fish oil consumption significantly lowered weight gain rate, decreased intestinal villi length and muscular thickness values and the tight junction proteins mRNA abundance, augmented the intestinal proinflammatory factors, attenuated hepatic antioxidant enzymes activities and related genes mRNA expression levels, influenced the myogenic regulatory factors expression profile and impacted the myocyte density, myocyte area values as well as the skin pigments contents compared to the FFO treatment. Collectively, long-term feeding of the oxidized fish oil diet suppressed the growth performance, destroyed intestinal structural integrity, caused intestinal inflammation and hepatic oxidative stress, impacted the skeletal development and skin color of I. punctatus. Whereas CGA supplementation in oxidized fish oil diets partially counteracted the negative effects of the oxidized fish oil on I. punctatus in terms of increasing the growth performance, improving the intestinal mucosal structure, alleviating hepatic oxidative stress and intestinal inflammation, recompiling the myogenic regulatory factors expression and improving skin color. In conclusion, CGA has great potential to be an aquatic feed additive.

Sleep Deprivation Increases Facial Skin Yellowness

Sleep shortage is a major concern in modern life and induces various psycho-physical disorders, including skin problems. In cosmeceutics, females are aware that sleep deprivation worsens their facial skin tone. Here, we measured the effects of sleep deprivation on facial skin yellowness and examined yellow chromophores, such as bilirubin and carotenoids, in blood serum as potential causes of yellowness. Total sleep deprivation (0 h sleep overnight, N = 28) and repeated partial sleep deprivation (4 h sleep for 5 consecutive days, N = 10) induced significant increases in facial skin yellowness. The higher yellowness was sustained even after both sleep deprivation types stopped. However, circulating levels of yellow chromophores were unchanged in the total sleep deprivation study. Neither circulating interleukin-6 nor urinary biopyrrin levels were affected by total sleep deprivation, suggesting that apparent oxidative stress in the body was not detected in the present total deprivation protocol. Facial redness was affected by neither total nor repeated partial sleep deprivation. Therefore, blood circulation may play a limited role in elevated yellowness. In conclusion, facial skin yellowness was indeed increased by sleep deprivation in our clinical studies. Local in situ skin-derived factors, rather than systemic chromophore change, may contribute to the sleep deprivation-induced elevation of facial skin yellowness.

In search of the perfect tan: Chemical activity, biological effects, business considerations, and consumer implications of dihydroxyacetone sunless tanning products

As the desire and popularity of a tanned appearance continues, the social effects of UV-free tanning are becoming more important. Dihydroxyacetone (DHA) has seen extensive use as the main tanning agent in sunless tanners. The DHA-induced tan is a result of brown melanoidins formed by a non-enzymatic Maillard reaction between DHA and amino acid species found in the stratum corneum. DHA, thereby, provides a safer route to a tanned appearance compared with exposure to ultraviolet radiation. However, DHA is a highly reactive molecule, posing a multitude of challenges for potential product formulations. With their increased use, the safety considerations of topically applied DHA tanners have been investigated. Many different vehicles have been used for topical delivery of DHA, and they are becoming increasingly multifunctional. This review provides a holistic overview of dihydroxyacetone sunless tanning products.

Using Computer Vision to Track Facial Color Changes and Predict Heart Rate

The current technological advances have pushed the quantification of exercise intensity to new era of physical exercise sciences. Monitoring physical exercise is essential in the process of planning, applying, and controlling loads for performance optimization and health. A lot of research studies applied various statistical approaches to estimate various physiological indices, to our knowledge, no studies found to investigate the relationship of facial color changes and increased exercise intensity. The aim of this study was to develop a non-contact method based on computer vision to determine the heart rate and, ultimately, the exercise intensity. The method was based on analyzing facial color changes during exercise by using RGB, HSV, YCbCr, Lab, and YUV color models. Nine university students participated in the study (mean age = 26.88 ± 6.01 years, mean weight = 72.56 ± 14.27 kg, mean height = 172.88 ± 12.04 cm, six males and three females, and all white Caucasian). The data analyses were carried out separately for each participant (personalized model) as well as all the participants at a time (universal model). The multiple auto regressions, and a multiple polynomial regression model were designed to predict maximum heart rate percentage (maxHR%) from each color models. The results were analyzed and evaluated using Root Mean Square Error (RMSE), F-values, and R-square. The multiple polynomial regression using all participants exhibits the best accuracy with RMSE of 6.75 (R-square = 0.78). Exercise prescription and monitoring can benefit from the use of these methods, for example, to optimize the process of online monitoring, without having the need to use any other instrumentation.

Different colour predictions of facial preference by Caucasian and Chinese observers

Facial colour characteristics convey vital personal information and influence social interactions and mate choices as contributing factors to perceived beauty, health, and age. How various colour characteristics affect facial preference and whether there are cultural differences are not fully understood. Here, we provide a useful and repeatable methodology for skin colour research based on a realistic skin model to investigate the effect of various facial colour characteristics on facial preference and compare the role of colour predictors in Caucasian (CA) and Chinese (CN) samples. Our results show that, although the average skin colour of facial areas plays a limited role, together with colour variation and contrast, there are stronger links between colour and facial preference than previously revealed. We also find large cultural differences in facial colour perceptions; Chinese observers tend to rely more heavily on colour and lightness cues to judge facial preference than Caucasian observers.

Oral Supplementation with Z-Isomer-Rich Astaxanthin Inhibits Ultraviolet Light-Induced Skin Damage in Guinea Pigs

The effect of oral supplementation with astaxanthin of different Z-isomer ratios on ultraviolet (UV) light-induced skin damage in guinea pigs was investigated. Astaxanthin with a high Z-isomer content was prepared from the all-E-isomer via thermal isomerization. Intact (all-E)-astaxanthin and the prepared Z-isomer-rich astaxanthin were suspended in soybean oil and fed to guinea pigs for three weeks. The UV-light irradiation was applied to the dorsal skin on the seventh day after the start of the test diet supplementation, and skin parameters, such as elasticity, transepidermal water loss (TEWL), and pigmentation (melanin and erythema values), were evaluated. The accumulation of astaxanthin in the dorsal skin was almost the same after consumption of the all-E-isomer-rich astaxanthin diet (E-AST-D; total Z-isomer ratio = 3.2%) and the Z-isomer-rich astaxanthin diet (Z-AST-D; total Z-isomer ratio = 84.4%); however, the total Z-isomer ratio of astaxanthin in the skin was higher in the case of the Z-AST-D supplementation. Both diets inhibited UV light-induced skin-damaging effects, such as the reduction in elasticity and the increase in TEWL level. Between E-AST-D and Z-AST-D, Z-AST-D showed better skin-protective ability against UV-light exposure than E-AST-D, which might be because of the greater UV-light-shielding ability of astaxanthin Z-isomers than the all-E-isomer. Furthermore, supplementation with Z-AST-D resulted in a greater reduction in skin pigmentation caused by astaxanthin accumulation compared to that of E-AST-D. This study indicates that dietary astaxanthin accumulates in the skin and appears to prevent UV light-induced skin damage, and the Z-isomers are more potent oral sunscreen agents than the all-E-isomer.

Integrative Analysis of Metabolomic and Transcriptomic Data Reveals the Antioxidant Potential of Dietary Lutein in Chickens

Lutein can increase the body's skin color and has antioxidant potential. However, how it affects lipid metabolism and oxidative stress in chickens remains unknown. In this study, 74-day-old male chickens raised on feed supplemented with lutein had higher hip, back, breast, leg, shin and abdominal fat yellowness than the control group, and the livers of chickens in the lutein group had higher superoxide dismutase and glutathione peroxidase and lower malondialdehyde activities. To clarify the potential regulatory network regulated by lutein, we used RNA-seq and nontargeted metabolomics to detect changes in the male chicken liver and plasma, respectively. A total of 243 differentially expressed genes were significantly enriched in cytokine–cytokine receptor interaction signaling pathways, among others. A total of 237 significantly different metabolites were enriched in lysine biosynthesis and degradation and glycerophospholipid metabolism signaling pathways, among others. Finally, we comprehensively analyzed metabolome and transcriptome data and found that many differentially expressed genes and significantly different metabolites play crucial roles in lipid metabolism and oxidative stress. In summary, dietary lutein can improve male chicken skin yellowness and antioxidant indices and affect liver gene expression and plasma metabolites and may help improve the health of chickens.

Skin coloration is a culturally-specific cue for attractiveness, healthiness, and youthfulness in observers of Chinese and western European descent

Facial skin coloration signals information about an individual and plays an important role in social interactions and mate choice, due its putative association with health, attractiveness, and age. Whether skin coloration as an evolutionary significant cue is universal or specific to a particular culture is unclear and current evidence on the universality of skin color as a cue to health and attractiveness are equivocal. The current study used 80 calibrated, high-resolution, non-manipulated images of real human faces, either of Chinese or western European descent, which were rated in terms of attractiveness, healthiness, and perceived age by 44 observers, 22 western European (13 male; mean age ± SD = 24.27 ± 5.30) and 22 Chinese (7 male; mean age ± SD = 26.05 ± 3.96) observers. To elucidate the associations between skin coloration and these perceptual ratings and whether these associations are modulated by observer or image ethnicity, a linear mixed-effect model was setup with skin lightness (L*; CIELAB), redness (a*) and yellowness (b*), observer and image ethnicity as independent variables and perceived attractiveness, healthiness, and estimated age as dependent variables. We found robust positive associations between facial skin lightness (L*) and attractiveness, healthiness, and youthfulness, but only when Chinese observers judge facial images of their own ethnicity. Observers of European descent, on the other hand, associated an increase in yellowness(b*) with greater attractiveness and healthiness in Chinese facial images. We find no evidence that facial redness is positively associated with these attributes; instead, an increase in redness (a*) is associated with an increase in the estimated age of European facial images. We conclude that observers of both ethnicities make use of skin color and lightness to rate attractiveness, healthiness, and perceived age, but to a lesser degree than previously thought. Furthermore, these coloration cues are not universal and are utilized differently within the Chinese and western European ethnic groups. Our study adds to the growing body of work demonstrating the importance of skin color manipulations within an evolutionary meaningful parameter space, ideally using realistic skin models based on physical parameters.

GWAS Identifies Multiple Genetic Loci for Skin Color in Korean Women

Human skin color is largely determined by genetic factors. Recent GWASs have reported several genetic variants associated with skin color, mostly in European and African populations. In this study, we performed GWAS in 17,019 Korean women to identify genetic variants associated with facial skin color, quantitatively measured as CIELAB color index. We identified variants in three, one, and six genomic loci associated with facial skin color index L∗, a∗, and b∗ values, respectively, and replicated the associations (combined analysis P-value < 5.0 × 10^-8). The significant loci included variants in known genes (OCA2 rs74653330, BNC2 rs16935073, rs72620727 near KITLG, and SLC6A17 rs6689641) and to our knowledge previously unreported genes (SCARB1 rs10846744, SYN2 rs12629034, and LINC00486 rs6543678). This is GWAS to elucidate genetic variants of facial skin color in a Korean female population. Further functional characterizations of the investigated genes are warranted to elucidate their contribution to skin pigmentation-related traits.

Redox and autonomic responses to acute exercise-post recovery following Opuntia ficus-indica juice intake in physically active women

BACKGROUND

The aim of this study was to investigate if the supplementation with Opuntia ficus-indica (OFI) juice may affect plasma redox balance and heart rate variability (HRV) parameters following a maximal effort test, in young physically active women.

METHODS

A randomized, double blind, placebo controlled and crossover study comprising eight women (23.25 ± 2.95 years, 54.13 ± 9.05 kg, 157.75 ± 0.66 cm and BMI of 21.69 ± 0.66 kg/m2) was carried out. A juice containing OFI diluted in water and a Placebo solution were supplied (170 ml; OFI = 50 ml of OFI juice + 120 ml of water; Placebo = 170 ml beverage without Vitamin C and indicaxanthin). Participants consumed the OFI juice or Placebo beverage every day for 3 days, before performing a maximal cycle ergometer test, and for 2 consecutive days after the test. Plasma hydroperoxides and total antioxidant capacity (PAT), Skin Carotenoid Score (SCS) and HRV variables (LF, HF, LF/HF and rMSSD) were recorded at different time points.

RESULTS

The OFI group showed significantly lower levels of hydroperoxides compared to the Placebo group in pre-test, post-test and 48-h post-test. PAT values of the OFI group significantly increased compared to those of the Placebo group in pre-test and 48-h post-test. SCS did not differ between groups. LF was significantly lower in the OFI group 24-h after the end of the test, whereas rMSSD was significantly higher in the OFI group 48-h post-test.

CONCLUSION

OFI supplementation decreased the oxidative stress induced by intense exercise and improved autonomic balance in physically active women.

The Expressive Triad: Structure, Color, and Texture Similarity of Emotion Expressions Predict Impressions of Neutral Faces

Previous research has demonstrated how emotion resembling cues in the face help shape impression formation (i. e., emotion overgeneralization). Perhaps most notable in the literature to date, has been work suggesting that gender-related appearance cues are visually confounded with certain stereotypic expressive cues (see Adams et al., 2015 for review). Only a couple studies to date have used computer vision to directly map out and test facial structural resemblance to emotion expressions using facial landmark coordinates to estimate face shape. In one study using a Bayesian network classifier trained to detect emotional expressions structural resemblance to a specific expression on a non-expressive (i.e., neutral) face was found to influence trait impressions of others (Said et al., 2009). In another study, a connectionist model trained to detect emotional expressions found different emotion-resembling cues in male vs. female faces (Zebrowitz et al., 2010). Despite this seminal work, direct evidence confirming the theoretical assertion that humans likewise utilize these emotion-resembling cues when forming impressions has been lacking. Across four studies, we replicate and extend these prior findings using new advances in computer vision to examine gender-related, emotion-resembling structure, color, and texture (as well as their weighted combination) and their impact on gender-stereotypic impression formation. We show that all three (plus their combination) are meaningfully related to human impressions of emotionally neutral faces. Further when applying the computer vision algorithms to experimentally manipulate faces, we show that humans derive similar impressions from them as did the computer.

Reactions to an Online Demonstration of the Effect of Increased Fruit and Vegetable Consumption on Appearance: Survey Study

Background

Inadequate fruit and vegetable consumption causes a considerable disease burden and premature mortality. Despite public health promotion of a healthy diet, the average consumption is still below recommended levels. Fruit and vegetable consumption influences human skin color, increasing red/yellow/orange pigment in the skin. Given that this color is deemed attractive and healthy-looking, the appearance benefit may motivate to eat more fruit and vegetables. Such appearance motivation could be particularly useful in young individuals who currently eat the least fruit and vegetables.

Objective

Our objectives were to assess how widely the impact of diet on skin color is known within the UK and to compare the strength of motivation to eat fruit and vegetables based on health and appearance benefits among different demographic groups.

Methods

Four groups of UK residents (N=200 per group) were recruited through the Prolific online platform. Groups comprised younger (aged 18-24) and older adults (aged 40-60) of low and high self-reported socioeconomic status (1-5 and 6-10 on a 10-point rating scale). Facial images simulating the skin color associated with low and high fruit and vegetable diets were shown to participants. Questionnaires were used to assess (1) background knowledge of the health and skin color effects of dietary fruit and vegetables, (2) the specific motivational impact of the skin color illustration, and (3) the relative importance of motivation to consume fruit and vegetables arising from health and skin color appearance benefits.

Results

We found that 61% (n=487) of all participants were unaware of the dietary–skin color association. We also found that 57% (n=457) of participants found the simple demonstration of the dietary impact on skin color positively motivating to eat more fruit and vegetables. The visual demonstration was equally motivating for participants of high and low self-reported socioeconomic status (P=.63) and different ethnic backgrounds (White N=453, Black N=182, Asian N=87, P=.22). Health benefits from a diet high in fruit and vegetables were regarded as more motivating than skin color appearance benefits. The appearance-changing benefits of a high fruit and vegetable diet (compared to the health benefits) were relatively more important for the younger participants (Mann-Whitney U=96,263, P<.001) and for women (N=489) than for men (N=310, U=83,763, P=.01).

Conclusions

These findings indicate that the promotion of the skin color effects of diets high in fruit and vegetables could provide additional motivation for a healthier diet. Our study indicates the broad appeal of appearance benefits from dietary fruit and vegetable (across ethnicity and socioeconomic status) and particularly amongst young adults where an inadequate diet is most prevalent.

Misperceptions of opposite-sex preferences for thinness and muscularity

Thin and muscular have been characterized as ideals for women and men, respectively. Little research has investigated whether men and women have accurate perceptions of opposite-sex preferences of thinness and muscularity. Further, no study has explored whether opposite-sex perceptions of thinness and muscularity preferences differ for short-term and long-term relationships. The present study set out to address these questions. We used interactive 3D human models to represent bodies varying in size (body mass index/BMI weight scaled by height) and body composition. University-aged (18-31) White European heterosexual men and women were asked to choose their own and ideal body shape, the ideal body shape for a short- and a long-term partner, and the body shape they thought the opposite-sex would most like for short- and long-term partners. Women overestimated the thinness that men prefer in a partner and men overestimated the heaviness and muscularity that women prefer in a partner. These misperceptions were more exaggerated for short-term relationships than for long-term relationships. The results illustrate the importance of investigating misperceptions of opposite-sex preferences and raise the possibility that correcting misperceptions might have utility in reducing body dissatisfaction or eating disorders.