Page 18 - Nutrinsight-3

NutrInsight • Do we need dietary polyphenols for health?
2.2 Effectofpolyphenolsondiabetes
Coffee and diabetes: epidemiological evidence
Van Dam [van Dam, 2008] has considered the relationship between coffee and diabetes by reviewing 17 studies (from diverse populations across the US, Europe and Japan) published since 2002. Fourteen of them showed an inverse relationship. A dose-response relationship was shown with 4 cups/day or more being associated with substantially lower risk of type 2 diabetes, whereas results were more variable for lower levels of consumption. High coffee consumption was associated with lower post-prandial glucose in non-diabetics (several cross-sectional studies) and decreased incidence of impaired glucose tolerance (two prospective studies). Coffee is a rich source of phenolics, particularly chlorogenic acid, but contains caffeine which is also bioactive. Furthermore, all of the five published studies reporting increased consumption of decaffeinated coffee also showed reduced risk of diabetes which should tend to show that the polyphenols play a protective role in the development of diabetes.
Flavanols, isoflavones and diabetes: an intervention study
The one year intervention trial reported by Curtis et al. [Curtis et al., 2012] in 116 postmenopausal women
with type 2 diabetes (see page 15) also showed that insulin sensitivity was improved with flavanols and
Insuline sensitivity and resistance
isoflavones in chocolate. In this intervention, the consumption of 2 portions of 27 g flavonoid-enriched chocolate containing 850 mg flavan-3-ols during 1 year lead to an improvement in insulin sensitivity (net difference in insulin secretion between the test and the control groups was -1.36 mU/L; p=0.02) and a decrease of insulin resistance measured as HOMA-IR (net difference in HOMA-IR index was -0.78 between the intervention and the control group; p=0.004) (Figure 8).
Flavonoid
*
Placebo
* p < 0.05 0.80
0.60 0.40 0.20 0.00
-0.20 -0.40 -0.60
** p < 0.01 **
1.20 1.00 0.80 0.60 0.40 0.20 0.00
-0.20 -0.40 -0.60 -0.80 -1.00 -1.20
Glucose, mmol/L (0 to 12M)
HOMA-IR (0 to 12M)
Insulin, mU/L (0 to 12M)
Figure 8: The improvement in insulin sensitivity by flavonoids intake
Source: Adapted from Curtis et al., 2012
Conclusion on polyphenols and diabetes development
Epidemiological studies tend to show a positive effect of polyphenols, particularly flavonoids, on the prevention of diabetes. This effect should be induced by a reduced insulin resistance and an improvement in insulin sensitivity. Additional studies are also needed to better understand the mechanism of actions and the dose required to have an effect.
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HOMA-IR score