The Austrian researchers suggest it could be useful in the treatment of type 2 diabetes, affecting growing numbers of people around the world. The disease increased by one-third during the 1990s, due to the prevalence of obesity and an aging population and if nothing is done to slow the epidemic, the number will exceed 333 million by 2025, according to the International Diabetes Federation.
The new study, published in the Feburary issue of Diabetes Care (27(2):436-40) is the first to demonstrate long-term efficacy of the supplement on glucose control.
Caiapo is derived from the skin of a variety of white sweet potato of South American origin, ipomoea batatas, cultivated in a mountainous region in Kagawa Prefecture, Japan. It has been eaten raw for many years in the belief that it is effective for anaemia, hypertension and diabetes and is sold in Japan by Fuji-Sangyo.
Dr Bernhard Ludvik, from the University of Vienna Medical School in Austria, and colleagues examined the tolerability and efficacy of Caiapo on metabolic control in 61 patients with type 2 diabetes. The subjects were randomly assigned to receive 4 grams of Caiapo or a placebo, daily for 12 weeks.
The researchers report that levels of hemoglobin A-1c (HbA1c), used to measure excess blood sugar, decreased significantly from 7.21 per cent to 6.68 per cent after treatment with Caiapo. In the placebo group however, HbA1c remained unchanged.
Decreases in fasting blood sugar levels (from 143.7 to 128.5 milligram per deciliter) were observed in Caiapo-treated patients, while no significant change was observed in those who received placebo.
On glucose tolerance testing, patients in the Caiapo group also had significantly decreased 2-hour glucose levels compared with the placebo patients and mean cholesterol was also lower.
A decrease in body weight was observed in both groups, probably due to a better-controlled lifestyle, said the researchers, although they suggest that in the Caiapo group, body weight was related to the improvement in glucose control.
Caiapo was also well tolerated without significant adverse effects.
"This study confirms the beneficial effects of Caiapo on plasma glucose as well as cholesterol levels in patients with type 2 diabetes," said the researchers.