Relationships between Skin Carotenoid Levels and Metabolic Syndrome.

Carotenoids have potential antioxidant and anti-inflammatory effects; their protective roles are of particular interest in the pathogenesis of metabolic syndrome (MetS). The reflection spectroscopy method has been recently developed to noninvasively measure skin carotenoid (SC) levels, which highly correlates with serum concentration of carotenoids. The relationship between SC levels and metabolic syndrome has been investigated. We aimed to identify the differences in patient characteristics and SC levels between participants with and without MetS in a large health examination population. In addition, the relationships between SC levels and various clinical parameters related to MetS were investigated. SC levels were measured using a reflection spectroscopy. A total of 1812 Japanese participants (859 male, 953 female; mean age ± standard deviation (SD), 57.8 ± 11.0 years) comprised the study population, i.e., participants with MetS (n = 151) and those without MetS (n = 1661). Multivariate logistic regression analysis was performed to identify variables associated with MetS. Compared to controls (377.3 ± 122.8), SC indices were significantly lower in patients with MetS (340.7 ± 112.5, p = 0.0004). Multivariate models also suggested that lower SC was significantly associated with MetS after adjustment for age, sex, smoking habit, and other potential risk factors for MetS. Furthermore, male gender (p < 0.0001), smoking habit (p < 0.0001) and worse lipid profiles (i.e., serum triglyceride (r = -0.1039, p < 0.0001), high-density lipoprotein (r = 0.1259, p < 0.0001), and usage of hypolipidemic agents (p = 0.0340)) were significantly associated with lower SC levels. The current study indicated that lower SC levels were significantly associated with MetS. This study highlights the antioxidant capacity of carotenoids in patients with MetS and the clinical utility of non-invasive and cost-effective SC measurement to detect participants who are at risk of developing MetS in a large population.

Skin carotenoids are inversely associated with adiposity in breast cancer survivors.

Carotenoids are antioxidants which may mitigate some of the adverse effects of obesity, a condition associated with poor outcomes in breast cancer patients. We hypothesized that baseline skin carotenoids would be inversely associated with adiposity in breast cancer survivors and would increase with weight loss. Skin carotenoid score (SCS) was assessed by resonance Raman spectroscopy in breast cancer survivors (body mass index ≥25 kg/m2) enrolled in a 6-month randomized controlled weight loss trial (n = 47). Measurements included total body fat using dual-energy X-ray absorptiometry, height, weight, waist and hip circumference, dietary intake, and serum biomarkers. Associations between SCS, adiposity measures, and serum biomarkers were assessed at baseline, as was the change in SCS from baseline to 6 months, in the intervention and usual care groups. At baseline, SCS was inversely correlated with all adiposity measures (P ≤ .05). In multivariate analyses, baseline percent body fat had the strongest association with baseline SCS (partial R2= 0.20). Baseline SCS was significantly inversely associated with log C-reactive protein levels (regression coefficient ß ±â€¯SE: -0.051±â€¯0.019; P = .011) and log leptin (ß ±â€¯SE: -0.019±â€¯0.009; P = .046), but the associations were no longer significant after adjustment for adiposity. Over the 6-month study, the intervention group had a 17.6% increase in SCS compared to a 1.5% decrease in the usual care group (P = .28). In our study of overweight and obese breast cancer survivors, dual-energy X-ray absorptiometry-measured body fat explained a large portion of the variation in skin carotenoids at baseline, suggesting a stronger association than that previously seen in studies using less accurate measures of adiposity.

Concurrent validity of skin carotenoid status as a concentration biomarker of vegetable and fruit intake compared to multiple 24-h recalls and plasma carotenoid concentrations across one year: a cohort study.

BACKGROUND: Biological markers of vegetable and fruit (VF) intake are needed both for nutrition surveillance and for the evaluation of nutrition interventions. Optically assessed skin carotenoid status (SCS) has been proposed as a marker of intake but there are few published validity studies to date. Therefore, the objective of the study was to examine the concurrent validity of multiple methods of assessing VF intake cross-sectionally and seasonally over one year and to discuss the relative merits and limitations of each method. METHODS: Fifty-two 40-60 y old women completed a 1-year longitudinal study that included 1) SCS assessment using resonance Raman spectroscopy (RRS) and using pressure-mediated reflection spectroscopy (RS) at 12 timepoints, 2) thirty-six 24-h recalls using the Automated Self-Administered 24-Hour Dietary Assessment Tool (ASA24; total 1866 recalls), and 3) plasma carotenoid concentrations measured every 3 months. Pearson correlation coefficients and mixed linear models were used to estimate pairwise correlations between RRS, RS, ASA24, and plasma carotenoids. RESULTS: RS and RRS were strongly correlated at baseline and over the year (r = 0.86 and 0.76; respectively, P < 0.001). RS was strongly correlated with plasma carotenoids at baseline (r = 0.70) and moderately across the year (r = 0.65), as was RRS (r = 0.77 and 0.69, respectively, all P < 0.001). At baseline, self-reported VF was weakly correlated with RRS (r = 0.33; P = 0.016), but not with RS or plasma carotenoids. Across the year, self-reported VF intake was weakly correlated with both RS (r = 0.37; P = 0.008), RRS (r = 0.37; P = 0.007), and with plasma carotenoids (r = 0.36; P < 0.008). CONCLUSIONS: SCS as measured by RS and RRS is moderately to strongly correlated with plasma carotenoid concentrations both cross-sectionally and longitudinally, indicating that it can be a powerful tool to assess carotenoid-rich VF intake in populations. CLINICAL TRIAL REGISTRY: This trial was registered at ClinicalTrials.gov as NCT01674296.

Skin Carotenoid Index in a large Japanese population sample.

Carotenoids are anti-oxidative agents. Human skin and eyes contain specific carotenoid species known to prevent various pathologies caused by oxidative stress. We quantified skin and eye carotenoid levels and investigated their potential correlation in a population including 985 Japanese patients and staff members of an ophthalmology clinic (577 men, 408 women, mean age of 69.7 ± 13.6 [SD]). Skin carotenoid (SC) and macular pigment (MP) levels were measured with reflection spectroscopy and autofluorescence imaging methods, respectively. The mean SC index was 343.1 ± 142.1 (SD). SC indices for women were higher than for men (382 vs 315, p < 0.001). Smokers and overweight subjects (BMI ≥ 25) had lower SC indices. Subjects taking lutein supplements had higher SC indices than non-supplementing subjects (415 vs 325, p < 0.001). SC and MP indices were significantly correlated. The obtained data set can be used for reference purposes by Japanese subjects and researchers interested in tissue responses to diets high in carotenoids and lutein supplementation.

Optical assessment of skin carotenoid status as a biomarker of vegetable and fruit intake.

Resonance Raman spectroscopy (RRS) and reflection spectroscopy (RS) are optical methods applicable to the non-invasive detection of carotenoids in human skin. RRS is the older, more thoroughly validated method, whereas RS is newer and has several advantages. Since collective skin carotenoid levels serve as a biomarker for vegetable and fruit intake, both methods hold promise as convenient screening tools for assessment of dietary interventions and correlations between skin carotenoids and health and disease outcomes. In this manuscript, we describe the most recent optimized device configurations and compare their use in various clinical and field settings. Both RRS and RS devices yield a wide range of skin carotenoid levels between subjects, which is a critical feature for a biomarker. Repeatability of the methods is 3-15% depending on the subject's skin carotenoid level and the uniformity of its local distribution. For 54 subjects recruited from an ophthalmology clinic, we first checked the validity of the relatively novel RS methodology via biochemical serum carotenoid measurements, the latter carried out with high performance liquid chromatography (HPLC). A high correlation between RS skin and serum HPLC carotenoid levels was established (R = 0.81; p < 0.001). Also, a high correlation was found between RS and RRS skin levels (R = 0.94 p < 0.001). Subsequent comparisons of skin carotenoid measurements in diverse age groups and ethnicities included 569 Japanese adults, 947 children with ages 2-5 screened in 24 day care centers in San Francisco, and 49 predominantly Hispanic adults screened at an outdoor health fair event. Depending on the particular subject group, correlation coefficients between the RRS and RS methods ranged between R ∼0.80 and R ∼0.96. Analysis of the Japanese screening showed that, on average, skin carotenoid levels are higher in women compared to men, skin levels do not depend on age, and tobacco smokers have reduced levels versus non-smokers. For the two most ethnically diverse groups with widely varying melanin levels, we investigated the effect of dermal melanin on RS and RRS skin carotenoid levels. The analysis revealed that large variations in skin carotenoid levels remain detectable independent of the particular melanin index. This behavior is consistent with the absence of melanin effects on the skin carotenoid levels generated with the instrument configurations. The RS method has an advantage over RRS in its relative simplicity. Due to its detection of skin reflection over a wide spectral range from the near UV to the near IR, it has the unique ability to quantify each of the major tissue chromophores and take them into account in the derivation of skin carotenoid levels.

Using Skin Carotenoids to Assess Dietary Changes in Students After 1 Academic Year of Participating in the Shaping Healthy Choices Program.

OBJECTIVE: To determine whether fourth-grade students participating in the Shaping Healthy Choices Program (SHCP), a school-based nutrition intervention, would change vegetable and carotenoid intake measured by skin carotenoids and dietary intake. METHODS: Single-group pretest-posttest with a self-selected, convenience sample of students (n = 30) participating in the SHCP, which lasted 1 academic year (9 months). Dietary intake of vegetables and carotenoids as measured by Block food frequency questionnaire and skin carotenoids as measured by Raman spectroscopy were collected at the school preintervention and postintervention. RESULTS: Reported carotenoid intake decreased by 1.5 mg (P = .05) and skin carotenoids decreased by 2,247.9 RRS intensity units (P = .04). Change in reported intake correlated with change in skin carotenoids (r = .43; P = .02). CONCLUSIONS AND IMPLICATIONS: The reported decrease in vegetable and carotenoid intake was unanticipated; nevertheless, the RRS measurements confirmed this. RRS data can help evaluate changes in fruit and vegetable intake.

Evaluating the relationship between plasma and skin carotenoids and reported dietary intake in elementary school children to assess fruit and vegetable intake.

Accurate assessment of dietary intake of children can be challenging due to the limited reliability of current dietary assessment methods. Plasma carotenoid concentration has been used to assess fruit and vegetable intake, but this testing is rarely conducted in school settings in children. Resonance Raman spectroscopy (RRS) is emerging as a useful method to objectively assess fruit and vegetable intake. This methodology has been validated in adults, but limited work has been done in children, particularly in the school setting. The purpose of this research is to further validate the RRS methodology in children. Children (9-12 year) participating in a school-based intervention were recruited. Plasma carotenoids were quantified using HPLC, skin carotenoid status was measured using RRS, and dietary intake of carotenoids was measured with the Block Food Frequency Questionnaire Ages 8-17. Total plasma carotenoid concentrations and skin carotenoid intensities were strongly correlated (r=0.62, p<0.001, n=38). Reported total carotenoid intake correlated with skin carotenoids (r=0.40, p<0.0001, n=128). Skin carotenoid status as measured by RRS can be a strong predictor of plasma carotenoid status and dietary intake of carotenoids in children. RRS may be used as a valid, non-invasive, and useful method to assess fruit and vegetable intakes in this population.

Optical detection methods for carotenoids in human skin.

Resonance Raman spectroscopy and reflection spectroscopy are non-invasive optical quantitative methods for the measurement of carotenoid antioxidant levels in human skin in vivo. Since all tissue carotenoids are derived from the diet, optical monitoring in skin may serve as an objective indicator for fruit and vegetable intake, and more broadly also as an effective biomarker for integrative health. The two optical methods have already found enthusiastic application in the Nutritional Supplement Industry where they are used with large populations to measure skin carotenoid uptake upon consumption of carotenoid-containing dietary supplements. Applications in medical fields such as nutrition science and epidemiology have been awaiting rigorous correlation studies between the optical carotenoid detection methods and the established gold standard detection method of high-performance liquid chromatography, which requires excised tissue samples. In this article we review the principles of the methods along with the current status of validations so the reader can assess the merits of the optical methods in their respective fields of interest.

Skin and plasma carotenoid response to a provided intervention diet high in vegetables and fruit: uptake and depletion kinetics.

BACKGROUND: Objective biomarkers are needed to assess adherence to vegetable and fruit intervention trials. Blood carotenoids are considered the best biomarker of vegetable and fruit intake, but collecting blood is invasive and the analyses are relatively expensive for population studies. Resonance Raman spectroscopy (RRS) is an innovative method for assessing carotenoids in skin noninvasively. OBJECTIVE: Our objective was to compare blood carotenoid concentrations with skin carotenoid assessments by RRS during a controlled feeding intervention. DESIGN: Twenty-nine participants consumed low-carotenoid diets (6 wk, phases 1 and 3), a provided diet containing 6-cup equivalents (1046 g/d) of vegetables and fruit (8 wk, phase 2), and usual diet (final 8 wk, phase 4). RESULTS: At baseline, skin and plasma total carotenoid values were correlated (r = 0.61, P < 0.001). Skin and plasma carotenoid values decreased (P < 0.001) 36% and 30%, respectively, from baseline to the end of phase 1 and then increased (P < 0.001) by >200% at the end of phase 2. Plasma carotenoids returned to baseline concentrations by the middle of phase 3 and skin carotenoid concentrations by the middle of phase 4. Skin carotenoid status predicted plasma values by using a mixed linear model including all time points (r = 0.72, P < 0.001), which indicates that changes in skin carotenoid status closely follow changes in plasma across a broad range of intakes. At the individual level, skin carotenoids predicted plasma values (r = 0.70, P < 0.001) over all time points. CONCLUSION: Skin carotenoid status assessed by resonance Raman spectroscopy is a noninvasive, objective biomarker of changes in vegetable and fruit intake.

Optical detection of carotenoid antioxidants in human bone and surrounding tissue.

Carotenoids are known to play an important role in health and disease state of living human tissue based on their antioxidant and optical filtering functions. In this study, we show that carotenoids exist in human bone and surrounding fatty tissue both in significant and individually variable concentrations. Measurements of biopsied tissue samples with molecule-specific Raman spectroscopy and high-performance liquid chromatography reveal that all carotenoids that are known to exist in human skin are also present in human bone. This includes all carotenes, lycopene, ß-cryptoxanthin, lutein, and zeaxanthin. We propose quantitative reflection imaging as a noncontact optical method suitable for the measurement of composite carotenoid levels in bone and surrounding tissue exposed during open surgeries such as total knee arthroplasty, and as a proof of concept, demonstrate carotenoid measurements in biopsied bone samples. This will allow one to establish potential correlations between internal tissue carotenoid levels and levels in skin and to potentially use already existing optical skin carotenoid tests as surrogate marker for bone carotenoid status.

Interrelationships between maternal carotenoid status and newborn infant macular pigment optical density and carotenoid status.

PURPOSE: Deposition of the macular pigment carotenoids lutein and zeaxanthin in the human retina occurs early in life. In this study, we examined the interrelationships of maternal carotenoid status and newborn infant macular pigment levels and systemic carotenoid status. As a secondary measure, we also evaluated the effects of intrauterine growth restriction (IUGR) on carotenoid status in term newborn infants. METHODS: We measured mother and infant skin carotenoids using resonance Raman spectroscopy (RRS), serum carotenoids by HPLC, and mother breast milk carotenoids by HPLC. We measured infant macular pigment levels using noninvasive blue light reflectometry. RESULTS: We enrolled 30 healthy term infants, their mothers, and 10 IUGR infants and their mothers. A subset of 16 infants was imaged for macular pigment optical density (MPOD). Infant serum zeaxanthin levels correlated with MPOD (r = 0.68, P = 0.007). Mother serum zeaxanthin levels correlated with infant MPOD (r = 0.59, P = 0.032). Infant and mother serum lutein did not correlate with MPOD. Mother-infant correlations were found for total serum carotenoids (r = 0.42, P = 0.020) and skin carotenoids (r = 0.48, P = 0.001). No difference was seen between IUGR infants and controls in total serum or skin carotenoids. Mothers of IUGR infants had lower total serum carotenoids (P = 0.019) and breast milk carotenoids than controls (P = 0.006). CONCLUSIONS: Our findings suggest that maternal zeaxanthin status may play a more important role than lutein status in macular pigment deposition in utero. Controlled trials are needed to determine whether maternal zeaxanthin prenatal supplementation can raise infant macular pigment levels and/or improve ocular function.

Resonance Raman spectroscopic evaluation of skin carotenoids as a biomarker of carotenoid status for human studies.

Resonance Raman spectroscopy (RRS) is a non-invasive method that has been developed to assess carotenoid status in human tissues including human skin in vivo. Skin carotenoid status has been suggested as a promising biomarker for human studies. This manuscript describes research done relevant to the development of this biomarker, including its reproducibility, validity, feasibility for use in field settings, and factors that affect the biomarker such as diet, smoking, and adiposity. Recent studies have evaluated the response of the biomarker to controlled carotenoid interventions, both supplement-based and dietary [e.g., provision of a high-carotenoid fruit and vegetable (F/V)-enriched diet], demonstrating consistent response to intervention. The totality of evidence supports the use of skin carotenoid status as an objective biomarker of F/V intake, although in the cross-sectional setting, diet explains only some of the variation in this biomarker. However, this limitation is also a strength in that skin carotenoids may effectively serve as an integrated biomarker of health, with higher status reflecting greater F/V intake, lack of smoking, and lack of adiposity. Thus, this biomarker holds promise as both a health biomarker and an objective indicator of F/V intake, supporting its further development and utilization for medical and public health purposes.

Single v. multiple measures of skin carotenoids by resonance Raman spectroscopy as a biomarker of usual carotenoid status.

Resonance Raman spectroscopy (RRS) is a non-invasive method of assessing carotenoid status in the skin, which has been suggested as an objective indicator of fruit/vegetable intake. The present study assessed agreement and identified predictors of single v. multiple RRS measures of skin carotenoid status. A total of seventy-four participants had their skin carotenoid status measured in the palm of the hand by RRS at six time points over 6 months. Questionnaires were administered to collect information on demographic, lifestyle and dietary data. Mean age of the participants was 36.6 years, 62.2% were female, 83.8% Caucasian and 85.1% were non-smoking at baseline. There was a good agreement between a single measure of skin carotenoids by RRS and multiple measures (weighted κ = 0.80; 95% CI 0.72, 0.88). The same variables were significantly associated with carotenoid status based on single or multiple measures, including a positive association with intake of total carotenoids (P< 0.01) and an inverse association with season of measurement (P≤ 0.05). The exception was recent sun exposure, which emerged as a significant predictor of lower carotenoid status only when using multiple RRS measures (P≤ 0.01). A single RRS measure was reasonably accurate at classifying usual skin carotenoid status. Researchers using RRS may want to take into account other factors that are associated with the biomarker, including season of measurement and recent sun exposure.

Resonance Raman based skin carotenoid measurements in newborns and infants.

We describe Resonance Raman based skin carotenoid measurements in newborns and infants. Skin- and serum carotenoid levels correlate with high statistical significance in healthy newborns and infants, and with reduced accuracy also in prematurely born infants, who in general feature very low carotenoid levels and thin transparent skin giving rise to large background absorption effects. Skin carotenoid levels can be easily compared among subjects and/or tracked in longitudinal studies with the highly molecule-specific Raman method. It therefore holds promise as a rapid, non-invasive, carotenoid antioxidant assessment method for newborns and infants in the field of pediatrics.

Dermal carotenoid measurements via pressure mediated reflection spectroscopy.

We describe a reflection-based method for the quantitative detection of carotenoid antioxidants in living human skin. The skin tissue site of interest is illuminated with broad-band white light spanning the spectral range from 350-850 nm and the spectral composition of the diffusively reflected light is analyzed in real time. Topical pressure is applied to temporarily squeeze blood out of the illuminated tissue volume. In this way the influence of oxy-hemoglobin on the reflection spectra is effectively reduced. After a short optical clearing time the carotenoid absorption becomes easily discernable in a 460-500 nm spectral window and its optical density can be calculated with high accuracy. Our empirical methodology provides a non-invasive rapid determination of skin carotenoid levels, can be used to monitor skin carotenoid concentration changes over time in response to carotenoid containing natural or supplemental diets, and is easily adaptable for applications in clinical and field settings.

Validation model for Raman based skin carotenoid detection.

Raman spectroscopy holds promise as a rapid objective non-invasive optical method for the detection of carotenoid compounds in human tissue in vivo. Carotenoids are of interest due to their functions as antioxidants and/or optical absorbers of phototoxic light at deep blue and near UV wavelengths. In the macular region of the human retina, carotenoids may prevent or delay the onset of age-related tissue degeneration. In human skin, they may help prevent premature skin aging, and are possibly involved in the prevention of certain skin cancers. Furthermore, since carotenoids exist in high concentrations in a wide variety of fruits and vegetables, and are routinely taken up by the human body through the diet, skin carotenoid levels may serve as an objective biomarker for fruit and vegetable intake. Before the Raman method can be accepted as a widespread optical alternative for carotenoid measurements, direct validation studies are needed to compare it with the gold standard of high performance liquid chromatography. This is because the tissue Raman response is in general accompanied by a host of other optical processes which have to be taken into account. In skin, the most prominent is strongly diffusive, non-Raman scattering, leading to relatively shallow light penetration of the blue/green excitation light required for resonant Raman detection of carotenoids. Also, sizable light attenuation exists due to the combined absorption from collagen, porphyrin, hemoglobin, and melanin chromophores, and additional fluorescence is generated by collagen and porphyrins. In this study, we investigate for the first time the direct correlation of in vivo skin tissue carotenoid Raman measurements with subsequent chromatography derived carotenoid concentrations. As tissue site we use heel skin, in which the stratum corneum layer thickness exceeds the light penetration depth, which is free of optically confounding chromophores, which can be easily optically accessed for in vivo RRS measurement, and which can be easily removed for subsequent biochemical measurements. Excellent correlation (coefficient R=0.95) is obtained for this tissue site which could serve as a model site for scaled up future validation studies of large populations. The obtained results provide proof that resonance Raman spectroscopy is a valid non-invasive objective methodology for the quantitative assessment of carotenoid antioxidants in human skin in vivo.

Production of deuterated zeaxanthin by Flavobacterium multivorum and its detection by resonance Raman and mass spectrometric methods.

Flavobacterium multivorum, a zeaxanthin-producing organism, was grown aerobically in a medium prepared with deuterated water. Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and resonance Raman spectroscopy (RRS) analysis revealed approximately 75% replacement of hydrogen by deuterium atoms as indicated by the molecular mass cluster at around m/z 600. Deuterated zeaxanthin upon excitation with a 488 nm laser exhibited characteristic resonance Raman vibrational modes at 1,161 and 1,504 cm(-1) as compared to 1,007, 1,159 and 1,525 cm(-1 )for undeuterated zeaxanthin. HPLC/APCI-MS and HPLC/RRS were specific and sensitive with limits of detection of 2.5 pg and 50 ng, respectively.

Simple Raman instrument for in vivo detection of macular pigments.

Raman spectroscopy holds promise as a novel noninvasive technology for the quantification of the macular pigments (MP) lutein and zeaxanthin. These compounds, which are members of the carotenoid family, are thought to prevent or delay the onset of age-related macular degeneration, the leading cause of irreversible blindness in the elderly. It is highly likely that they achieve this protection through their function as optical filters and/or antioxidants. Using resonant excitation in the visible region, we measure and quantify the Raman signals that originate from the carbon double bond (C=C) stretch vibrations of the pi-conjugated molecule backbone. In this manuscript we describe the construction and performance of a novel compact MP Raman instrument utilizing dielectric angle-tuned band-pass filters for wavelength selection and a single-channel photo-multiplier for the detection of MP Raman responses. MP concentration measurements are fast and accurate, as seen in our experiments with model eyes and living human eyes. The ease and rapidity of Raman MP measurements, the simplicity of the instrumentation, the high accuracy of the measurements, and the lack of significant systematic errors should make this technology attractive for widespread clinical research.

Resonance Raman detection of carotenoid antioxidants in living human tissue.

Increasing evidence points to the beneficial effects of carotenoid antioxidants in the human body. Several studies, for example, support the protective role of lutein and zeaxanthin in the prevention of age-related eye diseases. If present in high concentrations in the macular region of the retina, lutein and zeaxanthin provide pigmentation in this most light sensitive retinal spot, and as a result of light filtering and/or antioxidant action, delay the onset of macular degeneration with increasing age. Other carotenoids, such as lycopene and beta-carotene, play an important role as well in the protection of skin from UV and short-wavelength visible radiation. Lutein and lycopene may also have protective function for cardiovascular health, and lycopene may play a role in the prevention of prostate cancer. Motivated by the growing importance of carotenoids in health and disease, and recognizing the lack of any accepted noninvasive technology for the detection of carotenoids in living human tissue, we explore resonance Raman spectroscopy as a novel approach for noninvasive, laser optical carotenoid detection. We review the main results achieved recently with the Raman detection approach. Initially we applied the method to the detection of macular carotenoid pigments, and more recently to the detection of carotenoids in human skin and mucosal tissues. Using skin carotenoid Raman instruments, we measure the carotenoid response from the stratum corneum layer of the palm of the hand for a population of 1375 subjects and develop a portable skin Raman scanner for field studies. These experiments reveal that carotenoids are a good indicator of antioxidant status. They show that people with high oxidative stress, like smokers, and subjects with high sunlight exposure, in general, have reduced skin carotenoid levels, independent of their dietary carotenoid consumption. We find the Raman technique to be precise, specific, sensitive, and well suitable for clinical as well as field studies. The noninvasive laser technique may become a useful method for the correlation between tissue carotenoid levels and risk for malignancies or other degenerative diseases associated with oxidative stress.

Resonance Raman measurement of macular carotenoids in the living human eye.

There is growing evidence that high levels of the macular xanthophyll carotenoids lutein and zeaxanthin may be protective against visual loss from age-related macular degeneration. To study this protective effect further, it is important to measure macular carotenoid levels noninvasively in a wide variety of subjects. We have developed and validated resonance Raman spectroscopy as a sensitive and specific objective method to measure macular carotenoid levels in the living human eye. In this minireview, the principles and implementation of ocular carotenoid resonance Raman spectroscopy are reviewed, and the results of observational cross-sectional studies and of prospective supplementation studies on subjects with and without macular pathology are summarized. We have recently extended this technology to an imaging mode which will further enhance our understanding of the roles of lutein and zeaxanthin in normal macular function and in the prevention of age-related visual loss.