Ingestion of hyaluronans (molecular weights 800 k and 300 k) improves dry skin conditions: a randomized, double blind, controlled study.

Hyaluronan (HA) has been increasingly used as a dietary supplement to improve the skin. However, the effect of ingested HA may depend on its molecular weight (MW) because its physiological activities in the body vary with its MW. In this study, we examined the effects of ingested HA with varying MW on the skin. In this randomized, double blind, placebo controlled study, 61 subjects with dry skin received oral HA (120 mg/day), of MWs 800 k and 300 k or placebo, for 6 weeks. The skin moisture contents of the first two groups increased more than those of the placebo group during the ingestion period. In addition, group HA 300 k exhibited significant improvements in skin moisture content 2 weeks after ingestion ended compared with the placebo group. A questionnaire survey about subjective facial aging symptoms showed that the HA treated groups exhibited significantly improved the skin condition compared with the placebo treated group. Furthermore, dermatologists objectively evaluated the clinical symptoms of the facial and whole body skin, showing that no adverse events were related to daily ingestion of HA. This study shows that both of ingesting HAs (MWs 800 k and 300 k) improved the skin condition by increasing the moisture content.

Dietary hyaluronic acid migrates into the skin of rats.

Hyaluronic acid is a constituent of the skin and helps to maintain hydration. The oral intake of hyaluronic acid increases water in the horny layer as demonstrated by human trials, but in vivo kinetics has not been shown. This study confirmed the absorption, migration, and excretion of (14)C-labeled hyaluronic acid ((14)C-hyaluronic acid). (14)C-hyaluronic acid was orally or intravenously administered to male SD rats aged 7 to 8 weeks. Plasma radioactivity after oral administration showed the highest level 8 hours after administration, and orally administered (14)C-hyaluronic acid was found in the blood. Approximately 90% of (14)C-hyaluronic acid was absorbed from the digestive tract and used as an energy source or a structural constituent of tissues based on tests of the urine, feces, expired air, and cadaver up to 168 hours (one week) after administration. The autoradiographic results suggested that radioactivity was distributed systematically and then reduced over time. The radioactivity was higher in the skin than in the blood at 24 and 96 hours after administration. The results show the possibility that orally administered hyaluronic acid migrated into the skin. No excessive accumulation was observed and more than 90% of the hyaluronic acid was excreted in expired air or urine.

Ingested hyaluronan moisturizes dry skin.

Hyaluronan (HA) is present in many tissues of the body and is essential to maintain moistness in the skin tissues, which contain approximately half the body's HA mass. Due to its viscosity and moisturizing effect, HA is widely distributed as a medicine, cosmetic, food, and, recently marketed in Japan as a popular dietary supplement to promote skin moisture. In a randomized, double-blind, placebo-controlled clinical study it was found that ingested HA increased skin moisture and improved treatment outcomes for patients with dry skin. HA is also reported to be absorbed by the body distributed, in part, to the skin. Ingested HA contributes to the increased synthesis of HA and promotes cell proliferation in fibroblasts. These effects show that ingestion of HA moisturizes the skin and is expected to improve the quality of life for people who suffer from dry skin. This review examines the moisturizing effects of dry skin by ingested HA and summarizes the series of mechanisms from absorption to pharmacological action.