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1.) genetic factors;
2.) telomere shortening and chromosomal alterations;
3.) free radical generation (in excess of free radicals necessary for normal metabolism);
4.) UV light-induced skin damage.
Each of these are discussed in more detail below.
Genetic factors that contribute to skin aging
Skin aging is the result of genetic, as well as environmental, factors. In several lower species, genes that contribute to aging have been identified, and it is believed that corresponding genes may play a role in aging of humans. For instance, studies in mice have shown that caloric restriction increases the life of the mice and the expression of sirt1 genes, which code for sirtuins that may be responsible for prolonging the life of cells by turning off unnecessary gene expression. For human skin, caloric restriction has also been proposed to decrease contact dermatitis, decrease free radical formation, and potentially preserving the softened, youthful state of collagen by decreasing the formation of advanced glycation endproduct glucosepane. More on caloric restriction and human skin is available here.
Telomere shortening and chromosomal alterations
Telomeres are repeated patterns of DNA sequences (TTAGGG) found at the end of chromosomes. With each round of DNA replication, telomeres shorten. Older adults have shorter telomeres compared with younger adults and children; when telomeres reach a certain shortened length, the cell is no longer able to divide, and cell death occurs. In fact, according to this study, the size of telomeres found in adrenal (kidney) chromosomes shortens by about 0.24% per year of human life. The telomere theory of aging is also supported by patients with Werner’s Syndrome, a rare disease in which aging is accelerated. Although an enzyme, telomerase, is able to make telomeric sequences to replace shortened sequences, and the introduction of telomerase into retinal epithelial cells and fibroblasts has been shown in this 1994 study by Bodnar et. al. to regenerate telomeres, telomerase is also reactivated in cancer cells, and so the introduction of telomerase into normal human cells to fight aging is not in fact a sound therapy at all.
Other chromosomal alterations reported by Dr. Susan C. Taylor in Cosmetic Dermatology include a defective DNA helicase, which is the enzyme used to uncoil DNA prior to each round of replication. It has been found that a mutation in DNA helicase is responsible for Werner’s Syndrome and the premature aging symptoms that result. In another disease resulting in accelerated aging, progeria, a misregulation of mitosis has been identified as the major cause.
Free radical generation
The free radical theory of aging has existed since the 1950’s by Denham Harman. The theory essentially states that free radical processes cumulatively lead you to age. Free radical generating processes include UV exposure, environmental pollutants, and smoking, and also mandatory processes, like respiration and metabolism. As respiration and metabolism are necessary for life to continue, it is impossible to eradicate free radical production in the body completely. For this reason, it has been proposed by deGrey in Ending Aging (amongst others) that free radicals are a natural byproduct of life that should not necessarily be neutralized with antioxidants. According to Dr. Jeannette Graf in Cosmetic Dermatology, newfound technologies like “spin traps” have been developed to eradicate only the rare free radicals that are created when an aberrant electron “spins” out of its orbit. (Spin traps, being developoed by Dr. J. Carney and his associates, are not yet available in skin care products.)
Despite this, most experts emphatically recommend the use of topical antioxidants, with support from numerous nutritional studies that demonstrate eating antioxidant-rich fruits and vegetables helps to prevent aging and certain diseases. As topical application of an ingredient results in a maximal absorption of about 33% of the ingredient, according to this 2002 study by Briggs et. al., so applying topical antioxidants and consuming them through the diet should have synonymous effects. In addition, while studies at MIT have suggested that oxygen free radicals do not contribute to a shortened lifespan, another study has demonstrated that oxygen free radicals can damage the DNA of cultured skin cells. As such, free radical-induced aging seems to be one of the only causes we can treat: eat a diet rich in antioxidants and apply a multitude of topical antioxidants to eradicate free radical production.
To eat as many antioxidant-rich vegetables as possible, you may like to know vegetables were found to retain 80% of their raw antioxidant capacity when steamed, but just 30% when boiled. Also, of 27 vegetables, those with the highest antioxidant capacity were artichokes, beetroot, cabbage, broccoli, red chicory, red chili, and yellow pepper, so eat up!
To maximize the benefit of topically applied antioxidants, use products with network antioxidants (vitamin C, vitamin E, lipoic acid, coenzyme Q10 and glutathione), and/or strong antioxidants, such as coffeeberry, idebenone, vitamin E and kinetin.
UV radiation generates free radicals, which turn on matrix metalloproteinases (enzymes). In a 1996 study by Fisher et al., it was found that UV exposure increase MMPs (and hence collagen production) in three steps, as mentioned in Dr. Leslie Baumann’s Cosmetic Dermatology. One, UV exposure increases the production of the transcription factor c-jun. Two, the “extra” c-jun combines with another transcription factor already present in high concentration, c-fos, to produce activator protein, AP-1. Three, AP-1 activates the MMP genes, which produce collagenase, gelatinase, and stromelysin-1. It may further be noted that there are twenty-three human MMPs, and MMP-1 has been found in studies to be the MMP responsible for collagen degradation. And, similar to how natural antioxidants keep free radicals in check, the body naturally produces Tissue Inhibitors (TMPs) to keep levels of MMPs down. Unfortunately, however, as people age, MMP activity increases, while levels of Tissue Inhibitors (TMPs) decrease.
Matrix metalloproteinase activity can be stopped in two ways. The first is to prevent their production. This is best done with a sunscreen with high UVB protection (UVB has been directly liked to MMP production by Fisher et al.) Fortunately, the best UVB protection is easy to find: look for the sunscreen with the highest sun protection factor (SPF), a direct measure of UVB protection. The second method is to stop the degrading activities of the MMPs. According to Dr. Wexler, there are several substances that act as MMP inhibitors (MMPis): epigallocatechin-3-gallate (a derivative of green tea), retinoic acid, eicosapentaenoic acid (an omega-3 fatty acid), beta-carotene, DHEA (though this is controversial), polysaccharides, vitamin E, and vitamin C, and flavonoids. Research has shown all of these inhibit MMPs and increase TIMPs. Patricia Wexler’s MMPi Skin Regeneration Serum, available at Bath and Body Works stores, uses MMPis to inhibit MMP activity in skin cells by more than 80% (statistic from drpatriciawexlermd.com).
In short, what should I do to prevent skin aging?
First and foremost, wear a broad-spectrum (UVA/UVB) sunscreen and avoid the sun with protective hats, clothing, and sunglasses, particularly when the sun’s rays are the strongest, between 9 AM and 4 PM. However, according to a 2007 study from the University of Pittsburgh, there is a nationwide vitamin D deficiency, so make sure that you get 10-15 minutes of sunscreen-free exposure per week between hours of 9 AM and 4 PM to areas like your face, hands, back, and feet.
Second, try to eat a diet filled with steamed (not boiled) antioxidant-rich vegetables like artichokes, beetroot, cabbage, broccoli, red chicory, red chili, and yellow pepper. Use topical antioxidants with documented independent research behind them as well, particularly vitamin C, vitamin E, lipoic acid, coenzyme Q10, glutathione, idebenone, coffeeberry and kinetin (of course you don’t have to use them all!).
Lastly, be healthy. The skin is often an early indicator of disease, so what’s good for your body is ultimately good for your skin. Take care of yourself! 🙂