A clinical trial of the effects of oral beta-carotene on the responses of human skin to solar radiation

Skin Protection by Carotenoid Pigments

Sunlight, despite its benefits, can pose a threat to the skin, which is a natural protective barrier. Phototoxicity caused by overexposure, especially to ultraviolet radiation (UVR), results in burns, accelerates photoaging, and causes skin cancer formation. Natural substances of plant origin, i.e., polyphenols, flavonoids, and photosynthetic pigments, can protect the skin against the effects of radiation, acting not only as photoprotectors like natural filters but as antioxidant and anti-inflammatory remedies, alleviating the effects of photodamage to the skin. Plant-based formulations are gaining popularity as an attractive alternative to synthetic filters. Over the past 20 years, a large number of studies have been published to assess the photoprotective effects of natural plant products, primarily through their antioxidant, antimutagenic, and anti-immunosuppressive activities. This review selects the most important data on skin photodamage and photoprotective efficacy of selected plant carotenoid representatives from in vivo studies on animal models and humans, as well as in vitro experiments performed on fibroblast and keratinocyte cell lines. Recent research on carotenoids associated with lipid nanoparticles, nanoemulsions, liposomes, and micelles is reviewed. The focus was on collecting those nanomaterials that serve to improve the bioavailability and stability of carotenoids as natural antioxidants with photoprotective activity.

Protective Role of Natural Compounds under Radiation-Induced Injury

In recent years, evidence has shown the potential therapeutic effects of different natural compounds for the prevention and treatment of radiotherapy-induced mucositis (RIOM). RIOM represents one of the most frequent side effects associated with anti-neoplastic treatments affecting patients' quality of life and treatment response due to radiation therapy discontinuation. The innate radio-protective ability of natural products obtained from plants is in part due to the numerous antioxidants possessed as a part of their normal secondary metabolic processes. However, oxygen presence is a key point for radiation efficacy on cancer cells. The aim of this review is to describe the most recent evidence on radiation-induced injury and the emerging protective role of natural compounds in preventing and treating this specific damage without compromising treatment efficacy.

Role of ingestible carotenoids in skin protection: A review of clinical evidence

Carotenoids, a class of phytonutrients, have been well established to boost skin's innate resistance against ultraviolet (UV) B-induced erythema (sunburn). Many of the published clinical studies thus far have focused on the measurement of erythema as the primary clinical indicator of skin protection against UVB radiation. More recent studies have shown that carotenoid supplementation provides even more skin protection than previously shown as new clinical and molecular endpoints beyond UVB-induced erythema have been reported. These recent studies have demonstrated that carotenoids also provide photoprotection against UVA-induced pigmentation and inhibit molecular markers of oxidative stress such as intercellular adhesion molecule 1, heme oxygenase-1, and matrix metalloproteinases 1 and 9. This article provides a comprehensive review of the published clinical evidence on skin benefits of carotenoids in the last five decades and indicates new perspectives on the role of ingestible carotenoids in skin protection.

The Benefits and Risks of Certain Dietary Carotenoids that Exhibit both Anti- and Pro-Oxidative Mechanisms-A Comprehensive Review

Carotenoid pigments, particularly β-carotene and lycopene, are consumed in human foodstuffs and play a vital role in maintaining health. β-carotene is known to quench singlet oxygen and can have strong antioxidant activity. As such, it was proposed that β-carotene might reduce the risk of cancer. Epidemiological studies found inverse relationships between cancer risk and β-carotene intake or blood levels. However, clinical trials failed to support those findings and β-carotene supplementation actually increased lung cancer incidence in male smokers. Early experimental animal studies found dietary β-carotene inhibited UV-induced skin cancers. Later studies found that β-carotene supplementation exacerbated UV-carcinogenic expression. The discrepancies of these results were related to the type of diet the animals consumed. Lycopene has been associated with reduced risk of lethal stage prostate cancer. Other carotenoids, e.g., lutein and zeaxanthin, play a vital role in visual health. Numerous studies of molecular mechanisms to explain the carotenoids' mode of action have centered on singlet oxygen, as well as radical reactions. In cellular systems, singlet oxygen quenching by carotenoids has been reported but is more complex than in organic solvents. In dietary β-carotene supplement studies, damaging pro-oxidant reactivity can also arise. Reasons for this switch are likely due to the properties of the carotenoid radicals themselves. Understanding singlet oxygen reactions and the anti-/pro-oxidant roles of carotenoids are of importance to photosynthesis, vision and cancer.

Carotenoids in human skin

The skin is shielding our organism from exogenous threats including solar radiation. Carotenoids which are ingested with the diet accumulate in the skin with the highest levels occurring in skin of the forehead and in the palms of the hands. Blood and skin levels of carotenoids increase during supplementation and due to their antioxidant properties and UV-absorbing effects carotenoids are used as photoprotective agents. Systemic photoprotection with carotenoids after supplementation or ingestion of a carotenoid rich diet has been demonstrated in several human intervention studies. Although protection is only moderate it may contribute to UV protection in combination with other measures. Beyond photoprotection, ingestion of carotenoids has been postulated to be of additional benefit for cutaneous tissue and influences moisture and texture or elasticity of the skin. However, only a limited number of studies is available yet to substantiate such a claim.

Do We Utilize Our Knowledge of the Skin Protective Effects of Carotenoids Enough?

Due to their potential health-promoting effects, carotenoids have drawn both scientific and public attention in recent years. The primary source of carotenoids in the human skin is diet, mainly fruits, vegetables, and marine product, but they may originate from supplementation and topical application, too. In the skin, they accumulate mostly in the epidermis and act as a protective barrier to various environmental influences. Namely, the skin is exposed to numerous environmental factors, including ultraviolet radiation (UVR), air pollution, and smoking, that cause oxidative stress within the skin with consequent premature (extrinsic) aging. UVR, as the most prominent environmental factor, may cause additional detrimental skin effects, such as sunburn, DNA damage, and skin cancer. Therefore, photoprotection is the first line intervention in the prevention of premature aging and skin cancer. Numerous studies have demonstrated that carotenoids, particularly β-carotene, lycopene, lutein, and astaxanthin, have photoprotective effects, not only through direct light-absorbing properties, but also through their antioxidant effects (scavenging reactive oxygen species), as well as by regulation of UV light-induced gene expression, modulation of stress-dependent signaling, and/or suppression of cellular and tissue responses like inflammation. Interventional studies in humans with carotenoid-rich diet have shown its photoprotective effects on the skin (mostly by decreasing the sensitivity to UVR-induced erythema) and its beneficial effects in prevention and improvement of skin aging (improved skin elasticity and hydration, skin texture, wrinkles, and age spots). Furthermore, carotenoids may be helpful in the prevention and treatment of some photodermatoses, including erythropoietic protoporphyria (EPP), porphyria cutanea tarda (PCT) and polymorphous light eruption (PMLE). Although UVR is recognized as the main etiopathogenetic factor in the development of non-melanoma skin cancer (NMSC) and melanoma, and the photoprotective effects of carotenoids are certain, available studies still could not undoubtedly confirm the protective role of carotenoids in skin photocarcinogenesis.

Engineered nanoceria cytoprotection in vivo: mitigation of reactive oxygen species and double-stranded DNA breakage due to radiation exposure

Cerium oxide nanomaterials are known to absorb ionizing radiation energy, as well as to neutralize free radicals in solution, by undergoing redox changes. We, therefore, proposed that ceria nanoparticles could be used in biomedical applications as an injectable, radio-protectant material. In this study, we examine the effectiveness of engineered nanoparticles in protecting germ cells from the damaging effects of irradiation-induced cell death, in vivo. C57BL/6J male mice were used as a model and irradiation was localized to the scrotal region at 2.5, 5, and/or 10 Gy intensities. Ceria nanoparticles were introduced as 100 μL injections at 100 nM and 100 μM via tail vein injections, weekly, for one month. Following this, the animals were sacrificed and their organs (heart, brain, kidneys) were harvested. Tissues were fixed, sectioned, and stained for instances of cell death, DNA damage (TUNEL assay), and ROS (nitro-tyrosine evolution). Tissues from mice treated with ceria nanoparticles showed significantly less (∼13% decrease; *P < 0.05) tissue damage (per immunohistochemistry) over controls at up to 5 Gy radiation. DNA damage and ROS also decrease substantially with ceria treatment, confirming ceria's capacity as an injectable, radio-protectant material. The study also highlights the ability of ceria nanoparticles to protect cells/tissues from both direct and indirect effects of ionizing radiation.

Enhancing Skin Health: By Oral Administration of Natural Compounds and Minerals with Implications to the Dermal Microbiome

The history of cosmetics goes back to early Egyptian times for hygiene and health benefits while the history of topical applications that provide a medicinal treatment to combat dermal aging is relatively new. For example, the term cosmeceutical was first coined by Albert Kligman in 1984 to describe topical products that afford both cosmetic and therapeutic benefits. However, beauty comes from the inside. Therefore, for some time scientists have considered how nutrition reflects healthy skin and the aging process. The more recent link between nutrition and skin aging began in earnest around the year 2000 with the demonstrated increase in peer-reviewed scientific journal reports on this topic that included biochemical and molecular mechanisms of action. Thus, the application of: (a) topical administration from outside into the skin and (b) inside by oral consumption of nutritionals to the outer skin layers is now common place and many journal reports exhibit significant improvement for both on a variety of dermal parameters. Therefore, this review covers, where applicable, the history, chemical structure, and sources such as biological and biomedical properties in the skin along with animal and clinical data on the oral applications of: (a) collagen, (b) ceramide, (c) β-carotene, (d) astaxanthin, (e) coenzyme Q10, (f) colostrum, (g) zinc, and (h) selenium in their mode of action or function in improving dermal health by various quantified endpoints. Lastly, the importance of the human skin microbiome is briefly discussed in reference to the genomics, measurement, and factors influencing its expression and how it may alter the immune system, various dermal disorders, and potentially be involved in chemoprevention.

Oral Photoprotection: Effective Agents and Potential Candidates

Electromagnetic radiation in the ultraviolet, visible, and infrared ranges produces biologic effects in humans. Where some of these effects are beneficial, others are harmful to the skin, particularly those stemming from ultraviolet radiation (UVR). Pharmacological photoprotection can be topical or systemic. Systemic photoprotection is often administered orally, complementing topical protection. New and classic oral agents (e.g., essential micronutrients as vitamins, minerals, polyphenols, carotenoids) are endowed with photoprotective and anti-photocarcinogenic properties. These substances bear the potential to increase systemic protection against the effects of electromagnetic radiation in the UV, visible, and infrared ranges. Protective mechanisms vary and include anti-oxidant, anti-inflammatory, and immunomodulatory effects. As such, they provide protection against UVR and prevent photo-induced carcinogenesis and aging. In this review, we present state of the art approaches regarding the photoprotective effects of vitamins and vitamin derivatives, dietary botanical, and non-botanical agents. A growing body of data supports the beneficial effects of oral photoprotection on the health of the skin. More studies will likely confirm and expand the positive impact of oral dietary botanicals as complementary measures for photoprotection.

Molecular evidence that oral supplementation with lycopene or lutein protects human skin against ultraviolet radiation: results from a double-blinded, placebo-controlled, crossover study

BACKGROUND

Increasing evidence suggests photoprotection by oral supplementation with β-carotene and lycopene.

OBJECTIVES

To examine the capacity of lycopene-rich tomato nutrient complex (TNC) and lutein, to protect against ultraviolet (UV)A/B and UVA1 radiation at a molecular level.

METHODS

In a placebo-controlled, double-blinded, randomized, crossover study two active treatments containing either TNC or lutein were assessed for their capacity to decrease the expression of UVA1 the radiation-inducible genes HO1, ICAM1 and MMP1. Sixty-five healthy volunteers were allocated to four treatment groups and subjected to a 2-week washout phase, followed by two 12-week treatment phases separated by another 2 weeks of washout. Volunteers started either with active treatment and were then switched to placebo, or vice versa. At the beginning and at the end of each treatment phase skin was irradiated and 24 h later biopsies were taken from untreated, UVA/B- and UVA1-irradiated skin for subsequent reverse transcriptase polymerase chain reaction analysis of gene expression. Moreover, blood samples were taken after the washout and the treatment phases for assessment of carotenoids.

RESULTS

TNC completely inhibited UVA1- and UVA/B-induced upregulation of heme-oxygenase 1, intercellular adhesion molecule 1 and matrix metallopeptidase 1 mRNA, no matter the sequence (anova, P < 0·05). In contrast, lutein provided complete protection if it was taken in the first period but showed significantly smaller effects in the second sequence compared with TNC.

CONCLUSIONS

Assuming the role of these genes as indicators of oxidative stress, photodermatoses and photoageing, these results might indicate that TNC and lutein could protect against solar radiation-induced health damage.

Nutrition and skin

Nutrition has long been associated with skin health, including all of its possible aspects from beauty to its integrity and even the aging process. Multiple pathways within skin biology are associated with the onset and clinical course of various common skin diseases, such as acne, atopic dermatitis, aging, or even photoprotection. These conditions have been shown to be critically affected by nutritional patterns and dietary interventions where well-documented studies have demonstrated beneficial effects of essential nutrients on impaired skin structural and functional integrity and have restored skin appearance and health. Although the subject could be vast, the intention of this review is to provide the most relevant and the most well-documented information on the role of nutrition in common skin conditions and its impact on skin biology.

Oral Polypodium leucomotos increases the anti-inflammatory and melanogenic responses of the skin to different modalities of sun exposures: a pilot study

BACKGROUND

The effects on the inflammatory and tanning responses of sunlight/UVR of several oral antioxidants are still unknown.

OBJECTIVE

Assess intensity, time course of the inflammatory, and tanning responses to increasing dosages of solar-simulated radiation (SSR) at baseline and after oral supplementation of an extract of Polypodium leucotomos (PLE).

METHODS

Ten healthy subjects underwent phototesting with SSR with a visual and spectrophotometrical assessment of the responses with or without daily oral supplementation of two tablets containing 240 mg of PLE for a total of 15 days.

RESULTS

Polypodium leucotomos supplementation induced a significant increase of the minimal erythema dose (MED), a faster recovery of the inflammation following the delivery of super-erythemal doses, and no significant changes of the minimal melanogenic dose (MMD). Spectrophotometric assessment of the Δa* in test areas exposed to equally doses of SSR did not show differences.

CONCLUSIONS

Polypodium leucotomos supplementation increased the MED and induced a faster recovery of the inflammation and a stronger tanning response with no changes in the melanogenic threshold.

Brazilian consensus on photoprotection

Brazil is a country of continental dimensions with a large heterogeneity of climates and massive mixing of the population. Almost the entire national territory is located between the Equator and the Tropic of Capricorn, and the Earth axial tilt to the south certainly makes Brazil one of the countries of the world with greater extent of land in proximity to the sun. The Brazilian coastline, where most of its population lives, is more than 8,500 km long. Due to geographic characteristics and cultural trends, Brazilians are among the peoples with the highest annual exposure to the sun. Epidemiological data show a continuing increase in the incidence of non-melanoma and melanoma skin cancers. Photoprotection can be understood as a set of measures aimed at reducing sun exposure and at preventing the development of acute and chronic actinic damage. Due to the peculiarities of Brazilian territory and culture, it would not be advisable to replicate the concepts of photoprotection from other developed countries, places with completely different climates and populations. Thus the Brazilian Society of Dermatology has developed the Brazilian Consensus on Photoprotection, the first official document on photoprotection developed in Brazil for Brazilians, with recommendations on matters involving photoprotection.

Photoprotective effect of botanicals and vitamins: A systematic review of clinical trials

BACKGROUND

Overexposure to solar radiation is a major contributor to skin cancer development and premature skin aging. Botanical extracts and vitamins may represent novel photoprotective agents.

OBJECTIVE

We sought to systemically review clinical evidence for the use of botanically derived agents and vitamins as photoprotective agents.

METHODS

We systematically searched Embase and PubMed databases. Two independent reviewers reviewed abstracts for inclusion. Additional relevant studies were identified by a manual review of reference lists. Data from eligible studies were extracted independently and discrepancies were resolved by consensus.

RESULTS

A total of 51 studies met inclusion criteria. Limited available evidence indicates that several botanical agents and vitamins in topical or oral forms may have promising photoprotective effects. However, generalizability of results is limited by small sample sizes.

CONCLUSION AND RELEVANCE

Botanical extracts and vitamins may add to the armamentarium of sun-protective agents. Additional high-quality trials are needed to strengthen support for their use.

Mechanisms of Photoaging and Cutaneous Photocarcinogenesis, and Photoprotective Strategies with Phytochemicals

Photoaging and photocarcinogenesis are primarily due to solar ultraviolet (UV) radiation, which alters DNA, cellular antioxidant balance, signal transduction pathways, immunology, and the extracellular matrix (ECM). The DNA alterations include UV radiation induced thymine-thymine dimers and loss of tumor suppressor gene p53. UV radiation reduces cellular antioxidant status by generating reactive oxygen species (ROS), and the resultant oxidative stress alters signal transduction pathways such as the mitogen-activated protein kinase (MAPK), the nuclear factor-kappa beta (NF-κB)/p65, the janus kinase (JAK), signal transduction and activation of transcription (STAT) and the nuclear factor erythroid 2-related factor 2 (Nrf2). UV radiation induces pro-inflammatory genes and causes immunosuppression by depleting the number and activity of the epidermal Langerhans cells. Further, UV radiation remodels the ECM by increasing matrixmetalloproteinases (MMP) and reducing structural collagen and elastin. The photoprotective strategies to prevent/treat photoaging and photocarcinogenesis include oral or topical agents that act as sunscreens or counteract the effects of UV radiation on DNA, cellular antioxidant balance, signal transduction pathways, immunology and the ECM. Many of these agents are phytochemical derivatives and include polyphenols and non-polyphenols. The flavonoids are polyphenols and include catechins, isoflavones, proanthocyanidins, and anthocyanins, whereas the non-flavonoids comprise mono phenolic acids and stilbenes. The natural sources of polyphenols include tea, cocoa, grape/wine, soy, pomegranate, and Polypodium leucotomos. The non-phenolic phytochemicals include carotenoids, caffeine and sulphoraphance (SFN). In addition, there are other phytochemical derivatives or whole extracts such as baicalin, flavangenol, raspberry extract, and Photomorphe umbellata with photoprotective activity against UVB radiation, and thereby carcinogenesis.

Potential role of carotenoids as antioxidants in human health and disease

Carotenoids constitute a ubiquitous group of isoprenoid pigments. They are very efficient physical quenchers of singlet oxygen and scavengers of other reactive oxygen species. Carotenoids can also act as chemical quenchers undergoing irreversible oxygenation. The molecular mechanisms underlying these reactions are still not fully understood, especially in the context of the anti- and pro-oxidant activity of carotenoids, which, although not synthesized by humans and animals, are also present in their blood and tissues, contributing to a number of biochemical processes. The antioxidant potential of carotenoids is of particular significance to human health, due to the fact that losing antioxidant-reactive oxygen species balance results in “oxidative stress”, a critical factor of the pathogenic processes of various chronic disorders. Data coming from epidemiological studies and clinical trials strongly support the observation that adequate carotenoid supplementation may significantly reduce the risk of several disorders mediated by reactive oxygen species. Here, we would like to highlight the beneficial (protective) effects of dietary carotenoid intake in exemplary widespread modern civilization diseases, i.e., cancer, cardiovascular or photosensitivity disorders, in the context of carotenoids’ unique antioxidative properties.

Wrinkle reduction in post-menopausal women consuming a novel oral supplement: a double-blind placebo-controlled randomized study

Objective

The maintenance of youthful skin appearance is strongly desired by a large proportion of the world's population. The aim of the present study was therefore to evaluate the effect on skin wrinkling, of a combination of ingredients reported to influence key factors involved in skin ageing, namely inflammation, collagen synthesis and oxidative/UV stress. A supplemented drink was developed containing soy isoflavones, lycopene, vitamin C and vitamin E and given to post-menopausal women with a capsule containing fish oil.

Method

We have performed a double-blind randomized controlled human clinical study to assess whether this cocktail of dietary ingredients can significantly improve the appearance of facial wrinkles.

Results

We have shown that this unique combination of micronutrients can significantly reduce the depth of facial wrinkles and that this improvement is associated with increased deposition of new collagen fibres in the dermis.

Conclusion

This study demonstrates that consumption of a mixture of soy isoflavones, lycopene, vitamin C, vitamin E and fish oil is able to induce a clinically measureable improvement in the depth of facial wrinkles following long-term use. We have also shown, for the first time with an oral product, that the improvement is associated with increased deposition of new collagen fibres in the dermis.

Résumé

β-Carotene and other carotenoids in protection from sunlight

Protection against skin damage from sunlight by nutritional means has been examined. Likewise, there has been work on the topical application of phytochemicals to the skin. This review focuses on the nutritional aspect of phytochemicals in humans-ie, the provision of carotenoid micronutrients by dietary means to the skin and their role in protection. Human intervention studies have documented protective effects for β-carotene or for lycopene provided either by a carotenoid-rich diet or by supplementation. In exposed tissues, light induces primary and secondary photooxidative processes. Scavenging of reactive oxygen species is considered to be a mechanism of action underlying the protective activity of carotenoids. However, food comprises a complex mixture of numerous constituents, so that other components may also contribute to the observed activity. Molecules with suitable structures absorb UV light and prevent direct damage of cellular targets. Phytoene and phytofluene are precursor molecules of higher unsaturated carotenoids and occur in various fruit and vegetables. Their absorption spectra cover the UVB and UVA range, respectively, thus potentially contributing to photoprotective effects of carotenoid-rich food. Because of the physiologic turnover time of skin, several weeks are required for protective effects to appear. Photoprotection through individual dietary components such as β-carotene or lycopene in terms of sun protection factor is considerably lower than that achieved by using topical sunscreens. However, an optimal supply of antioxidant micronutrients in the skin increases basal dermal defense against UV irradiation, supports longer-term protection, and contributes to maintenance of skin health and appearance.

Discovering the link between nutrition and skin aging

Skin has been reported to reflect the general inner-health status and aging. Nutrition and its reflection on skin has always been an interesting topic for scientists and physicians throughout the centuries worldwide. Vitamins, carotenoids, tocopherols, flavonoids and a variety of plant extracts have been reported to possess potent anti-oxidant properties and have been widely used in the skin care industry either as topically applied agents or oral supplements in an attempt to prolong youthful skin appearance. This review will provide an overview of the current literature "linking" nutrition with skin aging.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Our systematic review has demonstrated that antioxidant supplements may increase mortality. We have now updated this review.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements for prevention of mortality in adults.

SEARCH METHODS

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index Expanded, and Conference Proceedings Citation Index-Science to February 2011. We scanned bibliographies of relevant publications and asked pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention.

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Random-effects and fixed-effect model meta-analyses were conducted. Risk of bias was considered in order to minimise the risk of systematic errors. Trial sequential analyses were conducted to minimise the risk of random errors. Random-effects model meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Seventy-eight randomised trials with 296,707 participants were included. Fifty-six trials including 244,056 participants had low risk of bias. Twenty-six trials included 215,900 healthy participants. Fifty-two trials included 80,807 participants with various diseases in a stable phase. The mean age was 63 years (range 18 to 103 years). The mean proportion of women was 46%. Of the 78 trials, 46 used the parallel-group design, 30 the factorial design, and 2 the cross-over design. All antioxidants were administered orally, either alone or in combination with vitamins, minerals, or other interventions. The duration of supplementation varied from 28 days to 12 years (mean duration 3 years; median duration 2 years). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects model meta-analysis (21,484 dead/183,749 (11.7%) versus 11,479 dead/112,958 (10.2%); 78 trials, relative risk (RR) 1.02, 95% confidence interval (CI) 0.98 to 1.05) but significantly increased mortality in a fixed-effect model (RR 1.03, 95% CI 1.01 to 1.05). Heterogeneity was low with an I(2)- of 12%. In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. Meta-regression analysis did not find a significant difference in the estimated intervention effect in the primary prevention and the secondary prevention trials. In the 56 trials with a low risk of bias, the antioxidant supplements significantly increased mortality (18,833 dead/146,320 (12.9%) versus 10,320 dead/97,736 (10.6%); RR 1.04, 95% CI 1.01 to 1.07). This effect was confirmed by trial sequential analysis. Excluding factorial trials with potential confounding showed that 38 trials with low risk of bias demonstrated a significant increase in mortality (2822 dead/26,903 (10.5%) versus 2473 dead/26,052 (9.5%); RR 1.10, 95% CI 1.05 to 1.15). In trials with low risk of bias, beta-carotene (13,202 dead/96,003 (13.8%) versus 8556 dead/77,003 (11.1%); 26 trials, RR 1.05, 95% CI 1.01 to 1.09) and vitamin E (11,689 dead/97,523 (12.0%) versus 7561 dead/73,721 (10.3%); 46 trials, RR 1.03, 95% CI 1.00 to 1.05) significantly increased mortality, whereas vitamin A (3444 dead/24,596 (14.0%) versus 2249 dead/16,548 (13.6%); 12 trials, RR 1.07, 95% CI 0.97 to 1.18), vitamin C (3637 dead/36,659 (9.9%) versus 2717 dead/29,283 (9.3%); 29 trials, RR 1.02, 95% CI 0.98 to 1.07), and selenium (2670 dead/39,779 (6.7%) versus 1468 dead/22,961 (6.4%); 17 trials, RR 0.97, 95% CI 0.91 to 1.03) did not significantly affect mortality. In univariate meta-regression analysis, the dose of vitamin A was significantly associated with increased mortality (RR 1.0006, 95% CI 1.0002 to 1.001, P = 0.002).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.

Photoprotection by dietary carotenoids: concept, mechanisms, evidence and future development

Carotenoids are micronutrients present mainly in fruits and vegetables, and they are ingested from these sources with the diet. They exhibit specific antioxidant activity but also influence signaling and gene expression at the cellular level. β-Carotene and lycopene, the colorants of carrots and tomatoes, respectively, are among the most prominent members of this group of lipids, and they are usually the dominating carotenoids in human blood and tissues. Both compounds modulate skin properties when ingested as supplements or as dietary products. There is evidence that they protect the skin against sunburn (solar erythema) by increasing the basal defense against UV light-mediated damage. Their photoprotective efficacy, however, is not comparable to the use of a sunscreen. In vitro data show that also other carotenoids are efficient photoprotectors. Among them are lutein and structurally unusual phenolic polyenes like 3,3'-dihydroxyisorenieratene.

Beta-carotene is an important vitamin A source for humans

Experts in the field of carotenoids met at the Hohenheim consensus conference in July 2009 to elucidate the current status of β-carotene research and to summarize the current knowledge with respect to the chemical properties, physiological function, and intake of β-carotene. The experts discussed 17 questions and reached an agreement formulated in a consensus answer in each case. These consensus answers are based on published valid data, which were carefully reviewed by the individual experts and are justified here by background statements. Ascertaining the impact of β-carotene on the total dietary intake of vitamin A is complicated, because the efficiency of conversion of β-carotene to retinol is not a single ratio and different conversion factors have been used in various surveys and following governmental recommendations within different countries. However, a role of β-carotene in fulfilling the recommended intake for vitamin A is apparent from a variety of studies. Thus, besides elucidating the various functions, distribution, and uptake of β-carotene, the consensus conference placed special emphasis on the provitamin A function of β-carotene and the role of β-carotene in the realization of the required/recommended total vitamin A intake in both developed and developing countries. There was consensus that β-carotene is a safe source of vitamin A and that the provitamin A function of β-carotene contributes to vitamin A intake.

The role of phytonutrients in skin health

Photodamage is known to occur in skin with exposure to sunlight, specifically ultraviolet (UV) radiation. Such damage includes inflammation, oxidative stress, breakdown of the extracellular matrix, and development of cancer in the skin. Sun exposure is considered to be one of the most important risk factors for both nonmelanoma and melanoma skin cancers. Many phytonutrients have shown promise as photoprotectants in clinical, animal and cell culture studies. In part, the actions of these phytonutrients are thought to be through their actions as antioxidants. In regard to skin health, phytonutrients of interest include vitamin E, certain flavonoids, and the carotenoids, β-carotene, lycopene and lutein.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Animal and physiological research as well as observational studies suggest that antioxidant supplements may improve survival.

OBJECTIVES

To assess the effect of antioxidant supplements on mortality in primary or secondary prevention randomised clinical trials.

SEARCH STRATEGY

We searched The Cochrane Library (Issue 3, 2005), MEDLINE (1966 to October 2005), EMBASE (1985 to October 2005), and the Science Citation Index Expanded (1945 to October 2005). We scanned bibliographies of relevant publications and wrote to pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention. Included participants were either healthy (primary prevention trials) or had any disease (secondary prevention trials).

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Trials with adequate randomisation, blinding, and follow-up were classified as having a low risk of bias. Random-effects and fixed-effect meta-analyses were performed. Random-effects meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Sixty-seven randomised trials with 232,550 participants were included. Forty-seven trials including 180,938 participants had low risk of bias. Twenty-one trials included 164,439 healthy participants. Forty-six trials included 68111 participants with various diseases (gastrointestinal, cardiovascular, neurological, ocular, dermatological, rheumatoid, renal, endocrinological, or unspecified). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects meta-analysis (relative risk [RR] 1.02, 95% confidence interval [CI] 0.99 to 1.06), but significantly increased mortality in a fixed-effect model (RR 1.04, 95% CI 1.02 to 1.06). In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. In the trials with a low risk of bias, the antioxidant supplements significantly increased mortality (RR 1.05, 95% CI 1.02 to 1.08). When the different antioxidants were assessed separately, analyses including trials with a low risk of bias and excluding selenium trials found significantly increased mortality by vitamin A (RR 1.16, 95% CI 1.10 to 1.24), beta-carotene (RR 1.07, 95% CI 1.02 to 1.11), and vitamin E (RR 1.04, 95% CI 1.01 to 1.07), but no significant detrimental effect of vitamin C (RR 1.06, 95% CI 0.94 to 1.20). Low-bias risk trials on selenium found no significant effect on mortality (RR 0.91, 95% CI 0.76 to 1.09).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Vitamin A, beta-carotene, and vitamin E may increase mortality. Future randomised trials could evaluate the potential effects of vitamin C and selenium for primary and secondary prevention. Such trials should be closely monitored for potential harmful effects. Antioxidant supplements need to be considered medicinal products and should undergo sufficient evaluation before marketing.

Protection from sunburn with beta-Carotene--a meta-analysis

Nutritional protection against skin damage from sunlight is increasingly advocated to the general public, but its effectiveness is controversial. In this meta-analysis, we have systematically reviewed the existing literature on human supplementation studies on dietary protection against sunburn by beta-carotene. A review of literature until June 2007 was performed in PubMed, ISI Web of Science and EBM Cochrane library and identified a total of seven studies which evaluated the effectiveness of beta-carotene in protection against sunburn. Data were abstracted from these studies by means of a standardized data collection protocol. The subsequent meta-analysis showed that (1) beta-carotene supplementation protects against sunburn and (2) the study duration had a significant influence on the effected size. Regression plot analysis revealed that protection required a minimum of 10 weeks of supplementation with a mean increase of the protective effect of 0.5 standard deviations with every additional month of supplementation. Thus, dietary supplementation of humans with beta-carotene provides protection against sunburn in a time-dependent manner.

Carotenoids and flavonoids contribute to nutritional protection against skin damage from sunlight

The concept of photoprotection by dietary means is gaining momentum. Plant constituents such as carotenoids and flavonoids are involved in protection against excess light in plants and contribute to the prevention of UV damage in humans. As micronutrients, they are ingested with the diet and are distributed into light-exposed tissues, such as skin or the eye where they provide systemic photoprotection. beta-Carotene and lycopene prevent UV-induced erythema formation. Likewise, dietary flavanols exhibit photoprotection. After about 10-12 weeks of dietary intervention, a decrease in the sensitivity toward UV-induced erythema was observed in volunteers. Dietary micronutrients may contribute to life-long protection against harmful UV radiation.

Dietary Lutein/Zeaxanthin Partially Reduces Photoaging and Photocarcinogenesis in Chronically UVB-Irradiated Skh-1 Hairless Mice

Lutein and zeaxanthin are xanthophyll carotenoids with potent antioxidant properties protecting the skin from acute photodamage. This study extended the investigation to chronic photodamage and photocarcinogenesis. Mice received either a lutein/zeaxanthin-supplemented diet or a standard nonsupplemented diet. Dorsal skin of female Skh-1 hairless mice was exposed to UVB radiation with a cumulative dose of 16,000 mJ/cm(2) for photoaging and 30,200 mJ/cm(2) for photocarcinogenesis. Clinical evaluations were performed weekly, and the animals were sacrificed 24 h after the last UVB exposure. For photoaging experiments, skin fold thickness, suprapapillary plate thickness, mast cell counts and dermal desmosine content were evaluated. For photocarcinogenesis, samples of tumors larger than 2 mm were analyzed for histological characterization, hyperproliferation index, tumor multiplicity, total tumor volume and tumor-free survival time. Results of the photoaging experiment revealed that skin fold thickness and number of infiltrating mast cells following UVB irradiation were significantly less in lutein/zeaxanthin-treated mice when compared to irradiated animals fed the standard diet. The results of the photocarcinogenesis experiment were increased tumor-free survival time, reduced tumor multiplicity and total tumor volume in lutein/zeaxanthin-treated mice in comparison with control irradiated animals fed the standard diet. These data demonstrate that dietary lutein/zeaxanthin supplementation protects the skin against UVB-induced photoaging and photocarcinogenesis.

[Systemic photoprotection through carotenoids]

Nutritional supplements are increasingly used to protect human skin against environmentally-induced damage, most importantly as a consequence of ultraviolet radiation exposure. beta-carotene is a major constituent of comercially available products administered for systemic photoprotection. Studies on the systemic use of beta-carotene provide evidence that 15-30 mg/d over a period of about 10-12 wk produces a protective effect against UV-induced erythema. Similar effects have been attributed to mixtures of carotenoids or after long-term intake of dietary products rich in carotenoids. Supplementation with carotenoids contributes to basal protection of the skin but is not sufficent to obtain complete protection against severe UV irradiation.

Beneficial long-term effects of combined oral/topical antioxidant treatment with the carotenoids lutein and zeaxanthin on human skin: a double-blind, placebo-controlled study

BACKGROUND

The skin is exposed to numerous environmental assaults that can lead to premature aging. Of these agents, perhaps none is more ubiquitous than the ultraviolet (UV) wavelengths of sunlight. The primary immediate defense against environmental skin damage is the antioxidant capacity of the skin. However, this defense system can be compromised by moderate exposure to UV light. Therefore, bolstering the antioxidant defense system of the skin is a potentially important strategy for reducing environmentally induced skin damage.

AIM OF THE STUDY

This clinical trial was designed to study the efficacy of lutein and zeaxanthin, two potentially important antioxidants found naturally in the skin, upon five skin physiology parameters (surface lipids, hydration, photoprotective activity, skin elasticity and skin lipid peroxidation - malondialdehyde) of human subjects. These xanthophyllic carotenoids were administered either orally, topically, or in combination (both oral and topical routes).

RESULTS

The results obtained indicate that the combined oral and topical administration of lutein and zeaxanthin provides the highest degree of antioxidant protection. However, oral and topical administration of these antioxidants individually also provides significant activity in the skin. In addition, oral administration of lutein may provide better protection than that afforded by topical application of this antioxidant when measured by changes in lipid peroxidation and photoprotective activity in the skin following UV light irradiation.

Chemoprevention of nonmelanoma skin cancer

Skin cancer is the most common cancer in human beings. The increased incidence of skin cancer has brought much attention to the process by which these tumors develop and how they can be prevented. Efforts have been made to educate the public about the importance of protecting skin from excessive ultraviolet light. Despite this work, the incidence of skin cancer continues to increase. Available compounds may be useful in the chemoprevention of skin cancer. Chemoprevention is defined as oral or topical use of dietary or pharmacologic agents to inhibit or reverse the development of cancer. Potential agents included are the retinoids; difluoromethylornithine; T4 endonuclease V; polyphenolic antioxidants, such as (-)-epigallocatechin gallate, found in green tea and grape seed extract; silymarin; isoflavone genestein; nonsteroidal anti-inflammatory drugs; curcumin; lycopene; vitamin E; beta-carotene; and selenium. Many of these agents are available over the counter as topical or oral preparations.

LEARNING OBJECTIVE

At the conclusion of this activity, participants should be familiar with the chemopreventive agents and their efficacy, as well as any significant side effects associated with them.

Lycopene-rich products and dietary photoprotection

Plant constituents such as carotenoids and flavonoids are involved in the light-protecting system in plants and contribute to the prevention of UV damage in humans. As micronutrients they are ingested with the diet and are distributed into light-exposed tissues where they provide systemic photoprotection. beta-Carotene is an endogenous photoprotector, and its efficacy to prevent UV-induced erythema formation has been demonstrated in intervention studies. Lycopene is the major carotenoid of the tomato and is a very efficient singlet oxygen quencher in the group of carotenoids. Following ingestion of lycopene or tomato-derived products rich in lycopene, photoprotective effects have been demonstrated. After 10-12 weeks of intervention a decrease in the sensitivity towards UV-induced erythema was observed in volunteers. Dietary carotenoids may contribute to life-long protection against harmful UV radiation.

beta-Carotene interferes with ultraviolet light A-induced gene expression by multiple pathways

Ultraviolet light A (UVA) exposure is thought to cause skin aging mainly by singlet oxygen ((1)O(2))-dependent pathways. Using microarrays, we assessed whether pre-treatment with the (1)O(2) quencher beta-carotene (betaC; 1.5 microM) prevents UVA-induced gene regulation in HaCaT human keratinocytes. Downregulation of growth factor signaling, moderate induction of proinflammatory genes, upregulation of immediate early genes including apoptotic regulators and suppression of cell cycle genes were hallmarks of the UVA effect. Of the 568 UVA-regulated genes, betaC reduced the UVA effect for 143, enhanced it for 180, and did not interact with UVA for 245 genes. The different interaction modes imply that betaC/UVA interaction involved multiple mechanisms. In unirradiated keratinocytes, gene regulations suggest that betaC reduced stress signals and extracellular matrix (ECM) degradation, and promoted keratinocyte differentiation. In irradiated cells, expression profiles indicate that betaC inhibited UVA-induced ECM degradation, and enhanced UVA induction of tanning-associated protease-activated receptor 2. Combination of betaC-promoted keratinocyte differentiation with the cellular "UV response" caused synergistic induction of cell cycle arrest and apoptosis. In conclusion, betaC at physiological concentrations interacted with UVA effects in keratinocytes by mechanisms that included, but were not restricted to (1)O(2) quenching. The retinoid effect of betaC was minor, indicating that the betaC effects reported here were predominantly mediated through vitamin A-independent pathways.

Influence of oral antioxidants on ultraviolet radiation-induced skin damage in humans

Ultraviolet radiation (UVR) causes a range of acute and chronic adverse cutaneous effects, in addition to some beneficial effects. In present times, the skin is generally exposed to higher levels of UVR, such that inherent defence mechanisms become overwhelmed. Complications, notably skin malignancies, show a serious rise in incidence. Since many effects of UVR are mediated through generation of reactive oxygen species, antioxidant supplementation provides a strategy to combat their excess generation, and hence reduce the clinical consequences. Human supplementation studies examining the potential of a range of oral agents to protect against UVR-induced skin effects show mixed results; further studies should examine whether certain subgroups of the population may show augmented benefit.

Oral Polypodium leucotomos extract decreases ultraviolet-induced damage of human skin

BACKGROUND

UV radiation induces damage to human skin. Protection of skin by an oral photoprotective agent would have substantial benefits. Objective We investigated the photoprotective effect of oral administration of an extract of the natural antioxidant Polypodium leucotomos (PL).

METHODS

A total of 9 healthy participants of skin types II to III were exposed to varying doses of artificial UV radiation without and after oral administration of PL (7.5 mg/kg). At 24 hours after exposure the erythema reaction was assessed and paired biopsy specimens were obtained from PL-treated and untreated skin.

RESULTS

A significant decrease in erythema was found in PL-treated skin (P < .01). Histologically, PL-treated biopsy specimens showed less sunburn cells (P < .05), cyclobutane pyrimidine dimers (P < .001), proliferating epidermal cells (P < .001), and dermal mast cell infiltration (P < .05). A trend toward Langerhans cell preservation was seen.

CONCLUSION

Oral administration of PL is an effective systemic chemophotoprotective agent leading to significant protection of skin against UV radiation.

Nutritional protection against skin damage from sunlight

The concept of systemic photoprotection by dietary means is gaining momentum. Skin is continuously exposed to ultraviolet (UV) radiation, the major cause of skin disorders such as sunburn, photodamage, and nonmelanoma skin cancer. Most of the erythemal annual UV dose is encountered under nonvacation conditions, when no sunscreen is applied. In the absence of topically added compounds, skin protection depends solely on endogenous defense. Micronutrients can act as UV absorbers, as antioxidants, or can modulate signaling pathways elicited upon UV exposure. UV-induced erythema is a suitable parameter to assess photoprotection. Dietary protection is provided by carotenoids, tocopherols, ascorbate, flavonoids, or n-3 fatty acids, contributing to maintenance resistance as part of lifelong protection.

Beta-carotene inhibits UVA-induced matrix metalloprotease 1 and 10 expression in keratinocytes by a singlet oxygen-dependent mechanism

UVA exposure causes skin photoaging by singlet oxygen (1)O(2)-mediated induction of, e.g., matrix metalloproteases (MMPs). We assessed whether pretreatment with beta-carotene, a (1)O(2) quencher and retinoic acid (RA) precursor, interferes with UVA-induced gene regulation. HaCaT keratinocytes were precultured with beta-carotene at physiological concentrations (0.5, 1.5, and 3.0 microM) prior to exposure to UVA from a Hönle solar simulator (270 kJ/m(2)). HaCaT cells accumulated beta-carotene in a time- and dose-dependent manner. UVA irradiation massively reduced the cellular beta-carotene content. Beta-carotene suppressed UVA-induction of MMP-1, MMP-3, and MMP-10, three major matrix metalloproteases involved in photoaging. We show that regulation by not only MMP-1, but also MMP-10, involves (1)O(2)-dependent mechanisms. Beta-carotene dose-dependently quenched (1)O(2)-mediated induction of MMP-1 and MMP-10. Thus, as in chemical solvent systems, beta-carotene quenches (1)O(2) also in living cells. Vitamin E did not cooperate with beta-carotene to further inhibit MMP induction. HaCaT cells produced weak retinoid activity from beta-carotene, as demonstrated by mild upregulation of RAR beta and activation of an RARE-dependent reporter gene. Beta-carotene did not regulate the genes encoding other RARs, RXRs, or the two beta-carotene cleavage enzymes. These results demonstrate that beta-carotene acts photoprotectively, and that this effect is mediated by (1)O(2) quenching.

Chemoprevention of skin cancer and photoaging

Skin cancer and photoaging are thought to be the result of ultraviolet radiation exposure. "Chemoprevention" refers to the prevention of photoaging and skin cancer through the use of pharmacologic agents that inhibit or reverse the process of photoaging or carcinogenesis. As both carcinogenesis and photoaging are multi-step processes, tumor development may be halted at several prospective points of intervention. A wealth of research aimed at chemoprevention is emerging. In this article, a variety of potential chemopreventive agents are discussed, including vitamins, diet, aspirin and non-steroidal anti-inflammatory drugs, and topical agents. Although further studies are warranted to identify and determine the safety and efficacy of new chemotherapeutic agents, it is expected that both systemic and topical agents may soon be available that effectively prevent photoaging and skin cancer development.

Pro-carcinogenic activity of β-carotene, a putative systemic photoprotectant

Beta-carotene is a strong singlet oxygen quencher and antioxidant. Epidemiologic studies have implied that an above average intake of the carotenoid might reduce cancer risks. Earlier studies found that the carotenoid, when added to commercial closed-formula rodent diets, provided significant photoprotection against UV-carcinogenesis in mice. Clinical intervention trials found that beta-carotene supplementation evoked no change in incidence of nonmelanoma skin cancer. However, when smokers were supplemented with the carotenoid a significant increase in lung cancer resulted. Recently, employing a beta-carotene supplemented semi-defined diet, not only was no photoprotective effect found, but significant exacerbation of UV-carcinogenesis occurred. Earlier, a mechanism, based upon redox potential of interacting antioxidants, was proposed in which beta-carotene participated with vitamins E and C to efficiently repair oxy radicals and, thus, thought to provide photoprotection. In this schema, alpha-tocopherol would first intercept an oxy radical. In terminating the radical-propagating reaction, the tocopherol radical cation is formed which, in turn, is repaired by beta-carotene to form the carotenoid radical cation. This radical is repaired by ascorbic acid (vitamin C). As the carotenoid radical cation is a strongly oxidizing radical, unrepaired it could contribute to the exacerbating effect on UV-carcinogenesis. Thus, vitamin C levels could influence the levels of the pro-oxidant carotenoid radical cation. However, when hairless mice were fed beta-carotene supplemented semi-defined diet with varying levels of vitamin C (0-5590 mg kg(-1) diet) no effect on UV-carcinogenesis was observed. Lowering alpha-tocopherol levels did result in further increase of beta-carotene exacerbation, suggesting beta-carotene and alpha-tocopherol interaction. It was concluded that the non-injurious or protective effect of beta-carotene found in the closed-formula rations might depend on interaction with other dietary factors that are absent in the semi-defined diet. At present, beta-carotene use as a dietary supplement for photoprotection should be approached cautiously.

Determinants of skin sensitivity to solar irradiation

BACKGROUND

Acute effects of UV irradiation include UV-induced erythema. Sunlight plays an important role in the development of skin cancer. Several predictive factors of UV-induced erythema could also be predictive for skin cancer.

OBJECTIVE

Our objective was to quantitatively assess phenotypical and nutritional determinants of sensitivity to UV irradiation, as assessed by the minimal erythema dose (MED).

DESIGN

We conducted a cross-sectional study among 335 volunteers. Sensitivity to UV irradiation was established through assessment of the MED. Phenotypical determinants, including skin melanin content, hair color and iris color were determined by skin reflectance spectrometry, a subjective questionnaire and an objective classification system, respectively. Furthermore, dietary exposure was measured by carotenoids, vitamin C, retinol and alpha-tocopherol in serum.

RESULTS

Male subjects were found to be more sensitive to UV irradiation; that is, the MED was significantly lower compared to female subjects. Skin melanin content, which was positively associated with iris color in both sexes and with hair color in men, was the main phenotypical determinant of sensitivity to UV irradiation. No associations were found between serum carotenoids and MED in the total study group. Vitamin C was inversely associated with MED. However, associations between carotenoids concentrations and MED showed a positive trend in subjects with melanin values above and a negative trend in subjects below the median after adjustment for gender and total cholesterol.

CONCLUSIONS

Skin melanin content and gender are important determinants of sensitivity to UV irradiation. No relation was found between serum carotenoids and MED in the total study group. The inverse association between vitamin C and MED was against our hypothesis. For the modifying effect of melanin on the association between carotenoids and MED, we do not have a clear biological explanation.