Background: Oxidative stress plays an essential role in the pathogenesis of type 2 diabetes. Anthocyanin, a natural antioxidant, has been reported to reduce oxidative stress and to attenuate insulin resistance and diabetes in animal models; however, the translation of these observations to humans has not been fully tested.
Objective: This study was designed to investigate the effects of purified anthocyanins on dyslipidemia, oxidative status, and insulin sensitivity in patients with type 2 diabetes.
Methods: A total of 58 diabetic patients were given 160 mg of anthocyanins twice daily or placebo (n = 29/group) for 24 wk in a randomized, placebo-controlled, double-blind trial. Participants and investigators were masked to treatment allocation.
Results: Anthocyanin supplementation significantly decreased serum LDL cholesterol (by 7.9%; P < 0.05), triglycerides (by 23.0%; P < 0.01), apolipoprotein (apo) B-48 (by 16.5%; P < 0.05), and apo C-III (by 11.0%; P < 0.01) and increased HDL cholesterol (by 19.4%; P < 0.05) compared with placebo after the 24-wk intervention. In addition, patients in the anthocyanin group showed higher total radical-trapping antioxidant parameter and ferric ion reducing antioxidant power values than did patients in the placebo group (both P < 0.05). Serum concentrations of 8-iso-prostaglandin F2α, 13-hydroxyoctadecadienoic acid, and carbonylated proteins in patients in the anthocyanin group were significantly less than in patients in the placebo group (23.4%, 25.8%; P < 0.01 and 20%; P = 0.022, respectively). Furthermore, supplementation with anthocyanin lowered fasting plasma glucose (by 8.5%; P < 0.05) and homeostasis model assessment for insulin resistance index (by 13%; P < 0.05), and elevated serum adiponectin (by 23.4%; P< 0.01) and β-hydroxybutyrate (by 42.4%; P = 0.01) concentrations compared with placebo supplementation.
Conclusion: These findings demonstrate that anthocyanin supplementation exerts beneficial metabolic effects in subjects with type-2 diabetes by improving dyslipidemia, enhancing antioxidant capacity, and preventing insulin resistance.
Alex’s Notes: About two weeks ago I wrote about a study of Amazonian hunter gatherer diets that provided strong evidence in favor of a diverse food supply and plentiful phytochemicals for the promotion of visual health. Near the end of the study I further supported the conclusion with a reference to a randomized clinical trial showing improved visual acuity in persons suffering from myopia with the consumption of a phytochemical-rich bilberry extract. As it turns out, the majority of those bilberry phytochemicals are anthocyanins, which give plants a characteristic purple hue.
Other well-known food sources include purple cabbage, blueberries, raspberries, purple sweet potato, and cherries. A greater consumption of these anthocyanin-rich foods has been associated with a reduced risk of developing type-2 diabetes (T2D), and animal models of T2D have demonstrated anthocyanin to regulate glucose metabolism, improve insulin sensitivity, and improve β-cell function. But no study to date has yet tested these effects in humans, which led Li et al to conduct the study at hand and hopefully extend the promising animal research to humans with T2D.
Overall, 58 men and women with T2D completed this double-blind, randomized, clinical trial. They were on the elderly side, averaging 58 years, but they were free from other chronic diseases except for T2D. Moreover, the average BMI was 24, indicating that these people were not overly fat. Over a 24-week period, all participants were asked to maintain their diet, lifestyle, and medications (if taking any), except that they were randomized into the anthocyanin group (160 mg twice daily with breakfast and dinner) or a maltodextrin placebo. The total amount of anthocyanins consumed daily (320 mg) was equal to about 100g of a mixture of fresh blueberries and blackcurrants. Before and after the intervention, dietary assessments and blood-borne markers were collected for analysis.
Elderly men and women with T2D (but otherwise healthy) consumed 320 mg of anthocyanins (~100g fresh blueberries) daily or a placebo.
And I must admit that the results are quite impressive. After 24-weeks, the anthocyanin group significantly increased their HDL-c (19.4%), and reduced their total cholesterol (4%), LDL-c (7.9%), triglycerides (23%), apoB-48 (16.5%), and apoC-III (11%). This translates into 7-10 mg/dL changes in cholesterol values and an 18 mg/dL change in triglycerides. And before you think that this is low, remember that the only change in diet was eating the equivalent of 100g of blueberries. To illustrate this point, a meta-analysis of randomized lipid medication trials reported that the rate of cardiovascular disease is reduced by nearly 1% for each 1% reduction in LDL cholesterol and by ~1% for each 1% increase in HDL cholesterol. Therefore, the 7.9% decrease in LDL-c and the 19.4% increase in HDL-c observed in the present study would result in a nearly 27.3% reduction in cardiovascular disease risk.
Pretty damn impressive.
In addition to blood lipids, the anthocyanin group demonstrated significantly increased levels of TRAP and FRAP, and significantly reduced levels of 8-iso-PGF2a and 13-HODE. The first two are markers of antioxidant capacity, while the latter two are markers for oxidative stress. Thus, the results clearly demonstrate and improved antioxidant profile with supplementation of anthocyanin. This may be the cause of the two final important findings: reduced inflammatory cytokines (IL-6 and TNF-α) and reduced insulin resistance.
What can we do with this information?
Unfortunately, generalization to other populations warrants caution as the study population was elderly individuals with well-controlled T2D. That said, this was a very well conducted trial that clearly demonstrates benefits of supplementing anthocyanins, and this can probably be extended to anthocyanin-rich foods as well. The dose used was equal to about 100g of blueberries, so that would be a good starting point.