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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.
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