Abstract
To clarify the preventive effect on diabetes of the hot water extract (GvEx) from leaves of Psidium guajava L. which has been currently used as a remedy for diabetes in Japan and subtropical zones, several administration experiments were done using mice or human volunteer subjects. In advance of these investigations, the inhibitory effect of the GvEx on the activities of sugar-degrading enzymes, maltase, sucrase, and α-amylase, was examined in vitro. The GvEx was found to inhibit the activities of these three enzymes and the inhibitory effect on the α-amylase activity was higher than that on the activities of the other two enzymes. In an administration experiment using mice, maltose, sucrose, or soluble starch was orally loaded to GvEx administered normal ICR mice. The results showed that the blood glucose level in mice was reduced by GvEx ingestion. In a separate experiment, GvEx was administered to genetically diabetic model mice (C57BL/KsJ, db/db) which develop wide spread pathologic abnormalities including a well defined nephropathy. In contrast to control mice without GvEx, the hemoglobin A1c% in blood and providing index of thickening of glomerular mesangial matrix significantly decreased in GvEx-fed mice. In oral administration of guava tea prepared from guava leaves to human subjects, the postprandial blood glucose level was measured. Increase of postprandial glucose level in blood was apparently suppressed in the guava tea administrated subjects, whose age and BMI index were over 40 and 22.0, respectively. All the results in these studies strongly suggest that the intake of guava tea by the humans prevents increases in the blood glucose level presumably by inhibiting digestion of sugars in gastrointestinal tract. Consequently, daily intake of guava tea might be useful to prevent the development of diabetes, which is frequently generated in human adults.
