Natural therapeutics: anti-photoaging.
Ultraviolet radiation (UVR) in sunlight is the most important cause of skin damage and aging. (1-5) This form of radiation causes skin aging by several mechanisms, including free-radical generation, DNA damage, collagen breakdown, the induction of immune defects, and cell death. (1-5) In addition, repeated damage to the skin by sunburn is a primarily risk factor for the development of cutaneous neoplasia, including melanoma.
While photoaging may be considered to be the pivotal cause of skin aging or damage, other factors operate. (1), (6) Cigarette smoking, various environmental pollutants, and synthetic chemicals (including those present in cosmetic products or sunscreens) can all contribute to dermal pathology and perhaps skin aging. (1) These external factors may often combine with "intrinsic propensities" to aging. Intrinsic skin aging is characterized by thinning of dermal and epidermal layers of the skin coincidental with the evolution of "immune senescence." (1), (6) The recognition that photoaging is caused primarily by ultraviolet radiation (UVR) has led to conventional wisdom that excessive exposure to sunshine should be avoided. The risks of cutaneous sun damage have led to the widespread application of techniques to protect the skin from sunlight, most often using sun-screening techniques.
The objectives of this article are to examine factors that propagate skin phototoxicity (photoaging) and look at natural ways to combat this major public health concern.
UVR causes variegate cutaneous damage to the skin. This UVR is classified by wavelength into UVA (320-400nm), UVB (290-320 nm), and UVC (100-290 nm). The atmospheric UVB type of radiation is the main cause of cutaneous damage (sunburn), but UVA may result in deeper penetration of the dermis and cause significant dermal tissue damage. (1) There is relatively little exposure to UVC because it is absorbed efficiently by the ozone layer surrounding the earth. (1) That said, some geographic locations, such as Australia, have a reduced ozone shield. Exposure to UVC can occur from equipment such as mercury arc lamps or light sources used for sterilization. Much less is known about the cutaneous effects of UVC than other types of UVR. The adverse consequences of tissue exposure to UVR are summarized in Table 1. (1)
Table 1: Tissue Changes Induced by UVR Exposure
UVB is the principal culprit.
Damage to cell membranes, mutations in DNA, and activation of metalloproteinase enzymes, resulting in collagen breakdown.
DNA forms cyclobutane dimers and adducts. Alteration of cell repair mechanisms occur with compromise of endonuclease 5 (T4N5).
Cross-linking of collagen, alteration of remodeling ability of metalloproteinase enzymes, and abnormal elastin accumulation. These factors contribute to dermal breakdown and skin wrinkling.
Langerhans cell (antigen-presenting cells) function is compromised, with inflammatory cytokine formation, neuropeptide release from skin sensory nerves, inhibition of histamine release from mast cells, and induction of tolerance by immune-suppressor cells.
Compromise of cell replication with stability of the genome and induction of apoptosis are caused by UVR, with cell proliferation and cancer formation.
Treatment of Photoaging
There are several approaches to the management of sun-damaged skin, but many applied treatments are often time-limited in their clinical outcome (Table2). (7), (8) Dermatological treatment of photoaging often involves attempts to correct the many skin abnormalities seen after long-term exposure to sunlight. (7), (8) These adverse cutaneous reactions to UVR include dry coarse epidermal changes (leathery skin), wrinkles, loss of skin elasticity, vascular changes (senile purpura, telangiectasia, easy bruising, etc.), freckling or lentiginous changes, general tissue thinning, and benign or malignant neoplasia (solar keratosis, basal cell carcinoma, squamous cancer, and melanoma). (7), (8) Popular approaches for the induction of aesthetic improvements in the presence of intrinsic or extrinsic causes of skin aging are summarized in Table 2. (7), (8)
Table 2: Popular Esthetic Treatments for Photoaging of the Skin
Specific skin disorders related to photoaging required specialized interventions. (9)
Chemicals are used to remove the surface layers of the skin with variable improvement in irregular pigmentation and superficial scars. Combined often with intense moisturizing strategies.
Botulinum toxin (type A)
This toxin paralyses muscle groups with prevention or resolution of minor or moderate skin wrinkles.
Collagen injections (fillers)
Injections of purified (bovine) collagen or other "fillers" to correct significant wrinkles, scars, facial lines, and furrows.
Removing the superficial layers of the skin with an electrical abrasion instrument. Microdermabrasion utilizes particles passed through a vacuum tube to remove skin and stimulate its growth.
Live fish are exposed to skin of an individual in a large tank. The fish nibble away at surface layers of the skin (used mainly in Asia).
Laser skin resurfacing
High-energy thermal ablation (monochromatic light) to remove damaged skin or the use of nonablative resurfacing. Techniques often combine laser light and electrical energy.
Intense pulsed light therapy
A nonablative therapy using light of multiple wavelengths.
Estrogen or progesterone creams, liposome complexes, various cosmeceuticals and antioxidants, etc. A variable evidence base for efficacy.
The concepts of beauty or skin health from "within the body" are dawning in the practice of skin care. Protomorphogens for skin, hair, and nail care, antioxidants, and even "oral sun-blockers" (Polypodium spp.) are being used increasingly. Oral nutraceuticals complement actions of topical cosmeceuticals and vice versa. (10)
Sunlight (UVR) exposure results in many biophysiological changes that result in several types of photodermatosis (Table 3). The clinician should be vigilant in recognizing causes of photosensitivity that require special intervention. Diagnostic applications of "phototesting" utilize local light applications that assist in detecting photosensitizing agents.
Table 3: A General Classification of the Causes of Skin Photosensitivity, with Examples
Increased presence of porpyrins in the skin; e.g., porphyria cutanea tarda.
Bloom syndrome, Rothmund-Thomson syndrome, xeroderma pigmentosum, etc.
Skin disease (unpredictable effects)
Acne, rosacea, lupus, erythematosis (discoid or systemic), atopic dermatitis, psoriasis. Some dermatoses may improve with modest sunlight (a contrarian phenomenon).
Chemical/drug solar interactions
Topical or systemic photosensitizing agents include drugs (e.g., amiodarone, tetracycline); dietary supplements (e.g., St. John's wort); and contact with a variety of botanicals, synthetic chemicals, fragrances, dyes, and germicidal compounds.
Unknown causes of solar hypersensitivity
Solar rashes such as urticaria, actinic prurigo, polymorphic light eruptions, chronic dermatitis, and pseudoporphyria.
The presence of damaging UVR in the environment is often underestimated. Even dull weather in a tropical climate can result in UVR exposures that precipitate significant sunburn. While sunshades or glass enclosures are useful for partial outdoor protection, a significant amount of UVA can penetrate glass or "shutters" that are installed to protect homes. Sunproof clothing (with high UPF values) has been recommended, but this approach is often seen as impractical because it involves wearing relatively thick clothes of dark color, together with clumsy accessories (e.g., sombreros, socks).
The most widespread direct attempts to provide sun protection involve the use of a variety of topical agents (sunscreens). (1-11) These often contain chemical products that absorb UVR and dissipate heat within the dermis. Some topical sunscreens involve the application of physical barriers that reflect sunlight. These products are effective when applied carefully to cover the skin entirely; and they do not carry the same risks of toxicity associated with the use of many synthetic chemical sunscreens (e.g., oxybenzones, benzophenones, methoxy dibenzoylmethane, PABA).(11-14)
While many people espouse the benefits of sunscreens, the safety and efficacy of these products have been questioned in many research studies. Topical sunscreens may cause several medical disorders (Table 4).
Table 4: Clinical Disorders Associated with the Use of Topical Sunscreens
The putative toxicity of many synthetic sunscreens is a public health concern that remains underexplored.(11-14)
* Contact allergy
* Free-radical generation
* Unacceptable esthetics
* Local toxicities
* Vitamin deficiency (D)
* Systemic toxicities
Characteristics and Actions of Topical Sunscreens
The objectives of using sunscreen involve not only the prevention of sunburn, but the avoidance of cumulative cutaneous damage by repeated UVR exposure. Cumulative damage to the skin caused by UVR is dependent on both the magnitude and duration of exposure, but chronic skin damage can occur without obvious or premonitory signs or even a documented history of significant or recurrent sunburn. Broad-spectrum sunscreens block both UVA and UVB, but there is no international standard for UVA blockage. Unfortunately, there are no sunscreen products that block all UVR effectively, and studies of routine or casual users of these products show that sunscreens are often applied patchily, especially to the face. Many sunscreens are easily washed off by swimming; therefore, despite claims of efficacy of topical agents, many of these products are applied in a manner that cannot afford adequate or widespread sun protection. (1), (11), (12)
The concept or "strength" of sun-blocking is described by the sun protection factor (SPF) of a topical agent. This SPF value is defined as the ratio of the energy (UVR) needed to induce a minimal skin reddening (erythema), in the presence of the production of the same skin reaction in the absence of a sunscreen.(1), (13) Theoretically, the higher the SPF, the larger the amount of sun exposure that can occur without sunburn or the percentage of UVB light absorption (dosing) to the skin (e.g., SPF 15 absorbs about 92% of UVB and SPF absorbs about 97.5% of UVB). The concept of "theoretical" SPF or solar protection must be considered in relationship to SPF values, given the inevitable failure of sunscreens to provide complete and lasting coverage. (1), (12) To be effective, the topical sunscreens must be used with careful and repeated interval application. This requires good compliance, which is often absent or compromised during recreational activities. Education about behavioral changes during outdoor recreation is underutilized in society.
Despite the recognized disadvantages and limitation of topical sunscreen products, several animal and human studies have demonstrated their preventive benefits for reducing aging changes in the skin (decreased wrinkling, reduction of skin sagging, and abnormal elastin deposition) and decreasing direct or immune damage (reduction of pyrimidine dimer formation and protection of Langerhans cells with reduction of UV-induced cutaneous hypersensitivity.) In addition, the correct use of sunscreens may cause a significant reduction in the prevalence of precancerous skin lesions. (1), (14) While there is good reason to believe that the efficient use of sunscreen products may reduce the incidence of melanoma, this finding has not been demonstrated convincingly or consistently in some controlled clinical observations. Aggregate information links the occurrence of melanoma to UVR exposure. (1), (15)
Effectiveness of Topical Sunscreens
Recent toxicological studies have raised major concerns about the safety and effectiveness of many commercially available topical sunscreens. (1) These studies have uncovered the current limitations of regulatory controls or approvals of chemical sunscreens, especially in the US. A recent landmark study of the safety and effectiveness of 952 topical sunscreen products implies that about four out of five of the most popular sunscreens do not offer efficient sun protection, and many contain ingredients with putative or actual toxicity.
This study was performed by the Environmental Working Group (EWG), with startling outcomes (www. cosmeticsdatabase.com). Leading brands of topical sunscreens appeared to be among the least effective. For example, only 1 of more than 100 products produced by Neutrogena or Banana Boat was recommended as safe and effective for use as a consequence of these studies; and none of the 41 products marketed by Coppertone met standards of safety and efficacy espoused by the EWG. This comprehensive study utilized ratings of products based on a compilation of information derived from technical literature and combined industry, government, or academic data on sunscreens. The findings of the study are summarized in Table 5.
Table 5: Descriptive Comments on the Outcome of the EWG Study on the Safety and Efficacy of Leading Brands of Topical Sunscreen Products (www.cosmeticsdatabase.com)
* Many sunscreen products carry questionable claims; e.g., "all day protection," "blocks all harmful rays," and "mild as water."
* Nanoscale components pose safety concerns, especially in powders or sprays, because of systemic access by accidental inhalation and greater systemic absorption.
* Components of sunscreens (organochemicals) may be absorbed into the body with toxic effects (much toxicity is predicted but unknown).
* Some components of sunscreens release free radicals when they interact with UVR, thereby compounding oxidative damage to the skin (an aging effect).
* Several ingredients are linked to allergic reactions and hormonal effects (xenoestrogens) and may accumulate in body tissues with secondary metabolic effects (perhaps toxic lipogenesis).
* Many sunscreens (about 48%) contain unstable ingredients that decompose in a variable time period (minutes to hours).
* Regulatory controls that govern sunscreen compositions are inadequate; e.g., failure to approve safe sunscreen ingredients, lack of sanction against inflated claims, no requirements for detailed stability data, and a lack of focus on approving agents that block both UVA and UVB forms of radiation. Overall, there is a lack of mandatory sunscreen standards.
There are many published reviews of sunscreen products in books, in magazines, and on the Internet (e.g., www. consumersearch.com). However, the basis for the ratings of certain products is often not clear in consumer reports, and it is perhaps biased by economic influences, most notably advertising revenue obtained by the publications from certain purveyors of cosmetic components. This type of bias plagues the supplement, pharmaceutical, and cosmetics industries. Some claims by editorial staff that reports are "objective" have not been supported by disclosure of the basis of rating systems that are used to make conclusions about the efficacy and safety of cosmetic for nutraceutical) products.
Toxic Consequences of Topical Sunscreens
Mineral-based sunscreens containing zinc oxide (and perhaps calcium compounds or titanium dioxide) are quite effective and safe because they are not absorbed to a significant degree by normal skin. Certainly, zinc oxide is to be preferred because it has intrinsic healing properties and other potential benefits. At present, there are many synthetic chemicals that are approved by the Food and Drug Administration (FDA) for use as active ingredients in sunscreens. However, some brands of sunscreen sold in the US contain chemicals that have not yet been approved in the US but may be used overseas. This "loophole" involves the addition of "unapproved" sunscreen chemicals without any claims for their activity on the label of the product. This practice makes it important for individuals to review the toxicity profiles of many chemical sun-blockers that are used to absorb and disperse UVR (Table 6; see also www.cosmeticsdatabase.com).
Table 6. Examples Of Chemical Ingredients That Are Used to Block UVR, with Their Putative Toxicity
These chemical agents are used often in variable combination with incomplete knowledge of their interactions and cumulative biological activity or toxicity.
Reference: Environmental Working Group (EWG; www.cosmeticsdatabase.com).
Photoallergic tendencies, xenoestrogen with interference of thyroid function and CNS signaling.
Photoallergic tendencies and common, significant transcutaneous absorption.
"Seems safe" but facilitates absorption of other compounds through the skin (carrier properties).
Unstable in sunlight with uncertain end products. Octinoxate reduces stability of avobenzene in mixtures.
Produces oxygen radicals when exposed to UVR.
Hormonal activity, and may facilitate absorption of herbicides. Metabolized to toxic compounds?
Possible carcinogen that generates free radicals in presence of sunlight.
Releases free radicals, xenoestrogens, and allergens.
Releases free radicals.
Poorly absorbed, but unstable in sunlight (about 40% degradation in 2 h).
Sulisobenzone/benzophenone-2 and -4
Irritates skin, eyes, and mucus membranes, with carrier properties. May have endocrine actions.
The data presented in Table 6 may make health-care givers and consumers think twice in their selection of a popular sunscreen product. Among the most perplexing observations in modern medical literature is the presence of "benzones" or related chemicals in the body in more than 90% of the population. A study that analyzed the umbilical cords of 10 newborn babies detected an average of 100 chemicals in newborn blood. Of considerable concern is the association between the presence of the sunscreen chemicals (oxybenzone) and low birth weight (www. cosmeticsdatabase.com). The jury remains out on many synthetic sunscreen chemicals.
Tanning Lamps and Parlors
The quest for a year-round tan in industrialized nations has spawned the tanning industry. This industry has tended to imply that "artificial tanning" is safer than natural sunlight tanning. However, it is recognized that the increase in melanin pigmentation in the skin as a consequence of UVR exposure (artificial or natural) is a body defense mechanism against dermal damage. (1), (10) Tanning lamps often use high-intensity UVA light that does not result in natural tanning in the same manner as from sunlight. Furthermore, increases in melanin formation during artificial tanning are often preceded by evidence of DNA damage in skin cells. (1) These observations start to dispel the notion that there is a readily definable "safe level" of UVR exposure.
It is known that tanning achieved with the use of effective topical sunscreens has a greater margin of safety. In this circumstance, modest dosages of UVR reach the skin with the induction of "slower "melanin pigmentation (tanning). This pigmentation protects the skin in a secondary manner, leading to the suggestion that modest tanning has an additive protective benefit to the sunscreen (a contrarian thought?). In simple terms, the act of sunbathing without sunscreens may result in more cutaneous damage than is experienced with their use.
If an individual is intent on using a tanning parlor, then the routine use of sunscreens is advisable, together with the benefits that can be derived from natural ways to diminish skin damage; for example, the use of antioxidants, orally effective sun-blockers, or protomorphogens for skin repair.
Natural and Optimal Ways to Protect from Solar Skin Damage
A general consensus supports the use of several techniques (applied synergistically) to minimize exposure to UVR for skin health. However, exposure to the sun is an inevitable and enjoyable life experience for many people. Clearly, this dictates the need to use safe (nontoxic), effective topical sunscreen products. The use of zinc as a primary ingredient appears to be an acceptable choice because of negligible toxicity, stability, and secondary benefit of zinc on skin structure and function (e.g., healing tendencies and immune support).
Zinc may be formulated in natural topical creams, lotions, or ointments that avoid the use of potentially toxic ingredients such as oxybenzone. Other natural ingredients that have been recommended for use in sun-blocking topical preparation include minerals, tea polyphenols, and coral calcium, but the evidence base for their use is quite variable. Unfortunately, natural agents used as sun-blockers are not often as cosmetically appealing as synthetic chemicals, but the health-conscious may believe that this minor drawback is worthwhile.
The increasingly accepted concept that "beauty or health lies within the body" has stimulated great interest in the use of nutrients, herbals, or botanicals that can be given in oral formats (dietary supplements) for cutaneous health, with some significant advantages over topical cosmecuticals. (10) The logical approach to creating a safe balance between obligatory sunlight exposure and general health is to use agents that can affect the pathophysiology of solar cutaneous damage. This can be achieved by combining oral and topical agents together.
In brief, this combined approach utilizes the use of skin-supporting substances (protomorphogens or building blocks of health skin), antioxidants, and DNA-protectors. The use of these nutritional approaches can be amplified by oral agents that have sun-blocking properties when given orally (e.g., Polypodium spp.).
There are many influences on cutaneous repair. For example, estrogen deficiency in postmenopause has been correlated with dermal (collagen) thinning that may be corrected in part by topical estrogen (estradiol). However, recent research implies that the stimulation of collagen production by estrogen is only observed in skin that has not been repeatedly exposed to sunlight. (1) The same circumstance may apply to the use of topical progesterone. These finding underscore the difficulty that exists in reversing structural skin damage caused by UVR and reinforce the need for comprehensive preventive strategies. (1)
There have been several attempts to examine the evidence base that exists for the use of dietary supplements in sun protection. An important review of this issue implied that antioxidants, carotenoids, and polyunsaturated fatty acids (omega-3 fatty acids) can prevent sunburn damage. Several studies using nutrients or botanicals have looked at the occurrence of cells that form or accumulate in the skin as a consequence of a minimal erythema-inducing dose (MED) of UV radiation. (16), (17)
The value of fish oils (eicosapentanoic and doaasahexanoic acid, EPA and DHA, respectively) in photoprotection has been reported in several studies. (17), (18) The use of these essential fatty acids is based upon their role in cell membrane formation and their intrinsic anti-inflammatory effects. In brief, the administration of omega-3 fatty acids in relatively high dosages (1.8-2.8 grams of EPA and 1.2-plus grams of DHA, requiring up to 10 grams of "regular" fish oil intake) has significant effects on increasing MED of UV radiation. (17)
Two issues arise in this area of "fish oil therapeutics." First, compliance is a challenge because of dosage requirements, but this may be overcome by using enteric-coated fish oil (targeted delivery with enhanced bioavailability). Second, liquid peroxidation end products may occur in UV-exposed skin. This oxidation may be countered by the stabilizing influence of antioxidants on fatty acids (e.g., vitamin E). It is prudent to consider the omega-6 to omega-3 fatty acid ratio in the diet of an individual. (18) An optimal but perhaps unattainable ratio is 1:1 (omega-6 to -3), but many Western diets provide a ratio of up to 15:1.
Supplement combinations (synergistic approaches) in sun protection have been studied in a manner ranging from observational to double-blind, parallel, placebo-controlled trials. Such studies highlight the specific value of vitamin E (d-alpha-tocopherol), vitamin C retinol, trace minerals, selenium, copper, and mixed carotenoids. In some circumstances, protective effects, measured by MED, were found to be dose dependent. (16), (17)
The Natural Anti-Photoaging Protocol
It is possible to create an evidence-based approach to address anti-photoaging. In brief, this would involve factors that are shown in Table 7.
Table 7: A Basis for a Natural Approach to Anti-Photoaging with Emphasis on Prevention of Sun Damage Positive lifestyle change
Support from many studies and reviewed recently (19)
Recreational behavior change, with selection of safe topical sunscreens. Use orally effective sunscreens; e.g., Polypodium
An evidence base for many nutrients (vitamins, minerals, carotenoids and omega-3 fatty acids). Use of vitamin/mineral, fruit, vegetable, berry powder blends, with enteric coated fish oil for compliance (www.naturalclinician.com)
Topical antioxidants, protomorphogens, etc.
It is important to note that a multipronged approach is required in management strategies for photoaging. Change of negative to positive lifestyle is a key initiative, combined with avoidance of excessive sunlight exposure.
Nutraceutical and cosmeceutical protection from sun damage or its treatment are a vast area of modern research. At this stage, evidence would support the use of mixed vitamins, minerals, and phytonutrient antioxidants (powder blends as a baseline clinical daily prevention strategy or nutritional insurance). Enteric-coated fish oil can be added (at least 2 g per day, containing 600 mg EPA and 400 mg DHA, approximately). The coated and targeted delivery of fish oil to its site of maximal absorption in the small intestine improves bioavailability and compliance (digestive upset, halitosis, and "fishy burps").
Topical cosmeceutical products have variable contents and advantages. Popular ingredients Include coenzyme Q10, polyphenols, physiological lipids for barrier repair, antioxidant vitamins or derivatives (e.g., vitamins A, E, and E with selenium and zinc), peptides, resveratrol, melatonin, and a variety of botanicals.
Matching topical cosmeceutical products to specific clinical circumstance involves complex therapeutic decisions. Perhaps the biggest issue in topical treatments is whether the therapeutic agents are absorbed to a degree that can result in benefits. The natural clinician must consider these factors, which may be addressed with novel delivery systems including nanotechnology, liposomes, carrier oils (emu oil), or perhaps safe synthetic transfer agents (if we knew what is readily safe).
Strategies to combat photoaging are key public health initiatives for our "graying" population.
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(2.) Harman D. Aging: overview. Ann NY Acad Sci. 2001;928:1-21.
(3.) Yaar M, Gilchrest BA. Skin aging: postulated mechanisms and consequent changes in structure and function. Clin Geriatr Med. 2001;17:617-630.
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(11.) Environ. Working Grp. Skin Deep: cosmetic safety database. www.cosmeticsdatabase.com.
(12.) Foley P, Nixon R, Marks R, Frowen K, Thompson S. the frequency of reactions to sunscreens: results of a longitudinal population-based study on the regular use of sunscreens in Australia. Br J Dermatol. 1993;128:512-518.
(13.) Diffey BL. Sunscreens, suntans, and skin cancer: people do not apply enough sunscreen for protection. Br J Dermatol. 1996;313:942.
(14.) Hawk JL. Cutaneous photoprotection. Arch Dermatol. 2003;139:527-530.
(15.) Bastuji-Garin S, Diepgen T. Cutaneous malignant melanoma, sun exposure, and sunscreen use: epidemiological evidence. Br J Dermatol. 2002;146(suppl 1):24-30.
(16.) Klotter J. Sun protection and supplements. Townsend Lett. October 2008.
(17.) Boelsma E, Hendriks HFJ, Roza L. Nutritional skin care: health effects of micronutrients and fatty acids. Am J Clin Nutr, 2001;73:853-864.
(18.) Simopoulos AP. The importance of the ratio of omega-6/omega-3 essential fatty acids [abstract]. Biomed Pharmacother. 2002 Oct;56(8):365-379.
(19.) Null G, Feldman M. Comprehensive lifestyle intervention improves hair and skin status and mental and physical functioning. Townsend Lett. 2008.
Stephen Holt, MD; is a Distinguished Professor of Medicine (emeritus), and a medical practitioner in New York state. He has published many peer-reviewed papers in medicine and is the best-selling author of 20 books. He has received many awards for teaching and research. Dr Holt is a frequent lecturer at scientific meetings and health-care facilities throughout the world.
Ester S. Mark, MD, is an honors graduate of La Sapienza University in Rome, Italy, where she became certified in gastroenterology. After completing her internship and residency at UCLA/Kern Medical Center, she became board certified in internal medicine and subsequently completed her fellowship training in anti-aging and functional medicine. She practices in Newport Beach, California, and specialized in anti-aging and aesthetic medicine, with a special focus on the comprehensive management of obesity and metabolic syndrome.
by Stephen Holt, MD, and Ester S. Mark, MD
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|Author:||Holt, Stephen; Mark, Ester S.|
|Date:||Oct 1, 2010|
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