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NutrInsight • Do we need dietary polyphenols for health?
Intervention studies
Many trials have looked at the effect of polyphenols on endothelial dysfunction, a prognostically relevant key event in atherosclerosis. Endothelial dysfunction is characterized by a decreased bioactivity of nitric oxide (NO) and impaired flow mediated dilatation (FMD), which is a measure of the compliance of the forearm artery in response to sheer stress (caused by blood flow). FMD evaluates the ability of the arteries to dilate in response to an increase in the demand for blood, oxygen and nutrients and is reduced if endothelial function is impaired in any way. Several intervention studies have therefore tested the effect of polyphenols on FMD. There are also a large number of studies that have measured changes in blood pressure, and plasma lipid profiles (particularly the levels of low density lipoproteins (LDL) and high density lipoproteins (HDL) and triglycerides) in response to a flavonoid-rich food or diet.
Several hundred human intervention trials have been conducted with polyphenols – a few with isolated polyphenols but more with polyphenol-rich foods. Although the former can pinpoint the beneficial effect of a sub class of polyphenols, the latter represents the real life situation and can be considered more relevant, even if less informative.
• Flavanols and isoflavone and CVD
Plasma lipids
Several trials have been done to evaluate the effect of flavanols on CVD endpoints. However the duration of the trials has usually been fairly short and the maximum duration is 18 weeks. To determine longer term effects, Curtis et al [Curtis et al., 2012] have recently reported a one year combined flavan-3-ol and isoflavone intervention in 118 postmenopausal women (93 completed the study) with type 2 diabetes who were on lipid lowering medication. They consumed two portions of 13.5 g chocolate which contained 850 mg flavan-3-ols (including 90 mg epicatechin) and 100 mg isoflavones as aglycone equivalents per day. They were able to demonstrate improved lipoprotein profiles in patients, even though they were already on lipid lowering therapy (including statins). LDL-cholesterol decreased in flavonoid enriched-chocolate group by 5% whereas it slightly increased in the placebo group (Figure 6).
0.20 0.15 0.10 0.05 0.00
-0.05 -0.10 -0.15 -0.20
*
Flavonoid
HDL-C
Placebo
0.15 0.10 0.05 0.00
-0.05 -0.10 -0.15 -0.20 -0.25
* p < 0.05 *
Cholesterol (CHOL)
LDL-C
CHOL: HDL-C
No effect on Triglyceride
Figure 6: Improvement in lipoprotein profiles with flavonoids intake
Source: Adapted from Curtis et al., 2012
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Change in mmoI/L (0 to 12M)
Change in total cholesterol: HDL-C (0 to 12M)