Berry-derived anthocyanins reverse impaired glucose tolerance in adults with prediabetes. Digest
Prediabetes affects hundreds of millions of people worldwide, and growing evidence suggests that its different subtypes do not respond uniformly to the same interventions. In a new study, researchers focused on impaired glucose tolerance, a common form of prediabetes marked by high blood sugar after meals, and tested whether a supplement rich in anthocyanins (polyphenols found in berries and other deeply colored fruits) could help the body handle sugar more effectively.
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A total of 68 Chinese adults aged 30 to 60 with isolated impaired glucose tolerance took part in this randomized, double-blind, placebo-controlled trial for 12 weeks. Participants received standard lifestyle guidance and were randomly assigned to take either anthocyanin capsules (160 mg per day) or a placebo. The researchers measured how well participants processed glucose using an oral glucose tolerance test (OGTT), which tracks blood sugar and insulin levels after a glucose drink. They examined insulin sensitivity, meaning how effectively the body responds to insulin, and beta-cell function, which reflects how well the pancreas releases insulin.
- More than half of participants taking anthocyanins returned to normal glucose tolerance, compared with less than one-third of those taking placebo.
- Insulin sensitivity improved more in the anthocyanin group, measured by the Matsuda index, a calculation that reflects how well the body uses insulin during the OGTT.
- Insulin levels one and two hours after the glucose drink dropped more in the anthocyanin group, suggesting the body needed less insulin to manage blood sugar.
- The study's main beta-cell function measure, the oral disposition index, did not clearly differ between groups.
- Overall blood sugar exposure after the glucose drink declined with anthocyanins but changed little with placebo.
- Levels of advanced glycation end products (AGEs) in the skin fell in the anthocyanin group. These compounds form when sugars bind to proteins and are considered markers of long-term metabolic stress.
The findings indicate that improved insulin sensitivity, rather than increased insulin secretion, explains the remission of impaired glucose tolerance. A central mechanistic signal was the reduction in skin AGEs, which correlated modestly with improvements in overall glycemic exposure and insulin sensitivity, supporting a biologically meaningful link. This is consistent with evidence that AGEs can impair insulin's effectiveness by chemically binding to insulin itself and to insulin receptors. Anthocyanins may reduce AGE burden by neutralizing reactive sugar byproducts and limiting AGE-driven inflammation.
Although larger and longer trials are needed, these findings suggest that anthocyanin supplementation may represent a targeted, nutrition-based strategy for managing impaired glucose tolerance. In Q&A #61, I discussed strategies for diagnosing prediabetes and managing it through lifestyle changes.