Oral Intake of Soy Isoflavone Aglycone Improves the Aged Skin of Adult Women

Abstract

Summary A double-blind, placebo-controlled trial was conducted to clinically evaluate the effect of soy isoflavone aglycone on the aged skin of middle-aged women. Twenty-six women volunteers in their late 30s and early 40s were randomly assigned to receive either a test food (13 women, the test food group) or a placebo food (13 women, the control group). These groups were given the test food (40 mg of soy isoflavone aglycone per day) and placebo, respectively, for 12 wk. The extent of linear and fine wrinkles at the lateral angle of the eyes was selected as the major evaluation criterion to assess the effects of foods, and the wrinkles' area ratio was used as the evaluation parameter. The extent of skin microrelief at the lateral angle of eyes and that of malar skin elasticity were used as secondary evaluation criteria, and the skin microrelief 's area ratio and recovery of skin elasticity were used as the respective evaluation parameters. These parameters were assessed 4, 8, and 12 wk after the start of the test food or placebo intake. The test food group showed a statistically significant improvement of fine wrinkles at week 12 ( p Ͻ 0.05) and of malar skin elasticity at week 8 ( p Ͻ 0.05), compared with the control group. Although there was no significant difference between the test food group and the control group regarding effects on skin microrelief at lateral angle of the eyes, a significant intragroup improvement was observed at week 8 in the test food group ( p Ͻ 0.05). As for the test food safety, none of the subjects presented adverse symptoms during the study period or discontinued the intake of the test food. These data indicate that the oral intake of 40 mg soy isoflavone aglycones per day improves the aged skin of middle-aged women. Key Words isoflavone, aglycone, skin, wrinkle, elasticity Soy isoflavone has been reported to have an estrogenlike effect ( 1 , 2 ). Such an effect suggests that soy isoflavones may contribute to prevent disorders such as osteoporosis ( 3 ), atherosclerosis ( 4 ), and menopausal syndrome ( 5 ) that are associated with a reduced secretion of estrogens in postmenopausal women. Numerous epidemiological studies on the mortality of hormonedependent cancers such as breast cancer ( 6 ) and prostate cancer ( 7 ) have found a negative correlation between intake of soybean, especially soy isoflavones, and the incidence of these cancers.Furthermore, soy isoflavones are considered to have beneficial effects on the skin via mechanisms such as prevention of lipid oxidation of the skin tissue ( 8 ), stimulation of fibroblast proliferation ( 9 ), reduction of collagen degradation ( 10 ), and inhibition of 5 ␣ -reductase ( 11 ), and have been widely used as ingredients of cosmetics ( 12 ). Moreover, cosmetics containing isoflavones are reported to retard skin aging ( 13 ). Soy isoflavones are chemically comprised of aglycone and glycosides, and all the beneficial effects on the human skin mentioned above have been confirmed to derive from aglycone ( 12 , 14 , 15 ). An isoflavone intake...

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