By Caroline Kanzaiza
Skin malignancy is on increase all over the world particularly among Caucasians. Melanoma (squamous cell carcinoma) and nonmelanoma (basal cell carcinoma) skin cancers are the most common forms of malignancy in the Caucasian population. A major risk factor for both skin cancer types is sun exposure. More intense exposure to the ultra violet (UV) radiation and extended sun exposure habits are associated with high incidences of skin malignancy. UV radiation, from the sun and other sources, aggravates formation of reactive oxygen species (free radicals ) known to be one of the causes of skin cancer. Though the skin has a very efficient interlinked antioxidant defense system for counteracting UV-induced oxidative stress, the above risk factors reduce its antioxidant capacity.
Some studies indicate that the damage caused by excessive UV exposure may be prevented by oral intake of antioxidant vitamins and minerals which boost the endogenous antioxidant properties of the skin.
Antioxidant supplements are commonly taken by consumers in the western countries to prevent sunburns and other damages to the skin.
Several clinical trials also suggest that oral antioxidant pills with photoprotective properties can be used in prevention of sunburns. Nutrients recommended for prevention of harmful effects from UV exposure include beta-carotene, ascorbic acid, vitamin E , selenium , and zinc. The antioxidant property inherent in these nutrients is attributed for their preventative role against UV-induced harmful effects. Conversely, other clinical trials testing the benefits of supplementation with high doses of antioxidants over long periods have not produced evidences to support the beneficial effects of antioxidant supplements on skin cancer. For example, a double blind randomized trial evaluating whether daily intake of 200 mg selenium could prevent non melanoma skin cancer reported an association between the selenium supplementation and increased risk of non melanoma skin cancer.
Another double blind, randomized, placebo controlled, study by French researchers***, published in the Journal of Nutrition, also compared medium term (5-10 years) outcome of antioxidants supplementation on skin cancers. The study was carried on 7876 women (35–60 years olds) and 5141 men (45–60 years olds) and representatives of the French population. The study subjects were randomly assigned a capsule containing a combination of antioxidants [120 mg vitamin C (sodium ascorbate), 30 mg vitamin E (dl-alpha-tocopherol), 6 mg beta-carotene, 100 mg selenium (selenium enriched yeast) or a matching placebo. The treatment was administered daily and taken orally in a single capsule. Two questionnaires on sun exposure were administered to participants in 1997 and 2001.
In this study, the effect of antioxidant supplementation on skin cancer appeared to differ between men and women. The incidence of skin cancer and melanomas was not significantly different between the group of men who received antioxidant supplements and the placebo group. The number of women with skin cancer and melanomas was however significantly greater in the antioxidant supplements group than the placebo group. The researchers suggested that the variation in the effect of the antioxidant supplements intake on skin cancer between men and women could be due to the difference in gender biology. According to the same authors, women are likely to have higher serum antioxidant status because of larger storage cellular compartments and also higher intake of antioxidants.
The researchers concluded that antioxidant vitamin and mineral supplements may not always benefit women. They cautioned that intake of antioxidant supplements at the current frequency and dosage by some consumers in the northern hemisphere may be associated with harmful effects in women, especially those already at risk of skin cancer.
***Serge H, Khaled E, Christiane G, Paul P, Pilar G, Sandrine B, Carla E, Serge B, Alain F, Julie L,Denis M, Antioxidant Supplementation Increases the Risk of Skin Cancers in Women but Not in Men. J. Nutr. 137: 2098–2105, 2007.
Additional References
Byers T, Perry G. Dietary carotenes, vitamin C, and vitamin E as protective antioxidants in human cancers. Annu Rev Nutr. 12:139–59, 1992.
Clark LC, Combs GF Jr, Turnbull BW, Slate EH, Chalker DK, Chow J, Davis LS, Glover RA, Graham GF, et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. A randomized controlled trial. Nutritional Prevention of Cancer StudyGroup. JAMA. ;276:1957–63, 1996.
English DR, Armstrong BK, Kricker A, Fleming C. Sunlight and cancer.Cancer Causes Control. 8:271–83, 1997.
Hercberg S, Galan P, Preziosi P, Bertrais S, Mennen L, Malvy D, Roussel AM, Favier A, Briancon S. The SU.VI.MAX study: a randomised, placebo-controlled trial of the health effects of antioxidant vitamins and minerals. Arch Intern Med. 164:2335–42, 2004.
Preston DS, Stern RS. Non melanoma cancers of the skin. N Engl J Med. 327:1649–62, 1992.
Sander CS, Chang H, Hamm F, Elsner P, Thiele JJ. Role of oxidative stress and the antioxidant network in cutaneous carcinogenesis. Int J Dermatol. 43:326–35, 2004.
Urbach F. Incidence of nonmelanoma skin cancer. Dermatol Clin. 9:751–5, 1991.