The pursuit of healthier skin transcends the realm of cosmetics, delving into the interplay between nutrition and dermatology. Soy contains multiple compounds that enhance skin appearance -- particularly isoflavones. A growing body of research indicates that soy supplementation contributes to both skin health and appearance through a variety of mechanisms, favorably influencing various dermatologic parameters such as hydration, elasticity, collagen synthesis, skin barrier function, fine lines, and wrinkles.1

Isoflavones, which are nonsteroidal compounds found in uniquely high amounts in soybeans, are classified as phytoestrogens.2 The three isoflavones in soybeans are genistein, daidzein, and glycitein.3 By binding to estrogen receptors (ERα and ERβ), isoflavones may exert some of the same effects as the hormone estrogen, although they may also exert effects opposite to those of estrogen. In other cases, such compounds may have no effects on tissues affected by this hormone.4,5 Isoflavones are being studied for their anti-inflammatory, antioxidant, antimicrobial, and anti-cancer effects.6-9

Reducing the Effects of Skin Aging with Soy

As the body’s outermost layer of protection, the skin is subject to both extrinsic and intrinsic influences, which impact its structure and function as individuals age.10 Skin aging can be impacted by a multitude of factors, including genetics, environmental exposures, lifestyle behavior, and the aging process itself.11 As the skin ages, wrinkles, dryness, a diminished barrier integrity, and a reduction in the thickness of the epidermis may occur.10 The decline in estrogen levels among postmenopausal women lead to diminished synthesis of the protein collagen, which can be regarded as a key factor contributing to alterations in the skin.12 Evidence increasingly suggests soy isoflavones can help combat the effects of skin aging, potentially among both pre- and postmenopausal women.13

For example, a 2007 study evaluated the effects of soy isoflavones on skin health in premenopausal Japanese women. Twenty-six females were randomized to receive either a supplement of 40mg of soy isoflavones or a placebo daily for 12 weeks. Assessments of linear and fine wrinkles, particularly at the lateral angle of the eyes, were conducted throughout the duration of the study. The study found there were statistically significant improvements in fine wrinkles at week 12 and in skin elasticity at week eight when compared to the placebo group. Importantly, no adverse effects due to isoflavones were reported.14

One year earlier, a study in post-menopausal women examined the effects of isoflavones plus a cocktail of bioactives that included fish protein polysaccharides, white tea extracts, grape seed, tomato, vitamins C and E, zinc, and chamomile extract. Women were randomized to receive either the dietary supplement or a placebo twice daily for six months. Skin aging was assessed via clinical grading and photo evaluation of face, hands, and decolletage. At study termination, compared to the placebo group, women receiving the supplement experienced significant improvements in facial wrinkles, pigmentation, laxity, under eye dark circles, and overall appearance of the skin.15 Although the results were impressive, the experimental design of this study does not allow a determination of the extent to which isoflavones contributed to the results.

A 14-week, randomized, double-blind and placebo-controlled trial conducted in 2014 has the same limitations as the previously cited study. In this case, postmenopausal women received a placebo or a mixture of isoflavones along with lycopene, vitamins C and E, and fish oil. A total of 166 women were enrolled and randomly allocated to three groups: test group 1 (n=51), test group 2 (n=53), and placebo group (n=55). Test group 1 contained higher levels of the active ingredients compared to test group 2. At study end, there was a significant improvement in skin texture and a reduction in depth of facial wrinkles in groups 1 and 2 compared to the placebo group. Also, skin biopsy analysis revealed increased levels of collagen in subjects in test group 2 compared to those in the placebo group.16

The above findings plus results from other studies17 provided the justification for more specifically examining the influence of soy isoflavones on facial hydration, pigmentation, and wrinkles in postmenopausal women. In the last study, which was conducted by our research laboratory, women in the soy group (n=23) consumed 30g/d soy protein isolate that contained 50mg isoflavones, whereas the placebo group consumed 30g/d casein. Skin biophysical assessments and facial imaging were obtained at baseline, eight, 16, and 24 weeks. Women in the soy group exhibited a significant reduction in the average wrinkle severity: 5.9% at week 16 and 7.1% at week 24, compared to baseline and compared to the casein supplementation group. Imaging analysis also revealed a significant decrease in average facial pigment severity in the soy group of 2.4% at week 24 compared to baseline and the casein supplementation group. Additionally, the soy group experienced a significant increase in skin hydration in both cheeks at week 24, with the right cheek increasing by 68% and the left cheek by 39% when compared to baseline, whereas there were no significant changes in the casein supplementation group.18 These results provide the most direct support currently available for the efficacy of isoflavones.

Conclusion

Soy isoflavones have garnered an increasing amount of attention for a variety of proposed benefits. Accumulating clinical evidence indicates these naturally occurring soybean components exert a range of beneficial effects on the appearance of the skin. The dose of isoflavones shown to be efficacious in clinical studies ranges from about 40 to 60mg/d, an amount provided by approximately two servings of soy foods. Future research is needed to determine the long-term effects of isoflavones and to gain more insight into the dose needed for optimal benefit.

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