Page 19 - Nutrinsight-3

NutrInsight • Do we need dietary polyphenols for health?
2.3 Polyphenolsandcancer
There are also numerous reports of associations between polyphenol intake and various types of cancer. Although the data from such studies are overall equivocal, with some studies showing no effect, there is a definite tendency towards a protective effect of increased polyphenol consumption. The best indications arise from meta-analyses where the data from several studies investigating the same cancer sites are combined and reanalysed. As an example, a meta-analysis for flavonoids and lung cancer reported data from twelve studies, located in Finland (3), the US (4), Uruguay, Spain, and the Netherlands (3) [Tang et al., 2009]. There were 5073 cases and 237,981 non-cases. There was a relative risk of 0.76 (CI 0.63-0.92). An increase in 20 mg flavonoids per day was associated with a 10% reduction in risk. This will obviously be an exciting area of future research.
However, there are almost no reports of high quality dietary intervention studies demonstrating the effects of polyphenol consumption on cancer risk or disease progression. This is largely because of the lack of easily measurable and validated biomarkers for cancer, and the variability in the aetiology of cancers within the same and between different tissues.
2.4 Polyphenolsandbonehealth
A study conducted with 3000 women undergoing osteoporosis screening in Scotland [Hardcastle et al., 2011] demonstrated a significant positive association between energy-adjusted total flavonoid intakes and bone mineral density (BMD) at the femoral-neck and lumbar spine sites (p≤0.05). It was also reported that the annual percentage change in BMD was associated with intakes of procyanidins and catechins (p ≤ 0.05), and that flavanone consumption was negatively associated with bone-resorption markers (p ≤0 .001).
Previous research has shown that hesperidin (an orange flavanone) prevented bone loss in ovariectomised rodents [Horcajada et al., 2008; Habauzit et al., 2009]. However, when the effect of two years dietary hesperidin supplementation was investigated on bone metabolism in post-menopausal women, no effect on bone mineral density (BMD) was found at any site [Habauzit et al., 2011]. But, in this parallel, placebo-controlled double-blind trial in which 110 women were randomised to take either 500 mg hesperidin or placebo, a significant group x time effect on bone turnover index was shown. There is also a report showing that supplementation of rat diets with quercetin inhibited the rate of bone loss in a rodent model of osteopenia (a pre-osteoporosis condition) [Liang et al., 2011].
• Flavonoids are the polyphenols that have been the most studied for their health benefits.
• The strongest evidence supports the effect of polyphenols and especially of flavonoid classes on the risk of CVD and CHD. Cocoa polyphenols could potentially have an effect on CVD via several putative mechanisms: increased vascular reactivity, reduced blood pressure, improved blood lipid profile.
• There is also relevant evidence for their beneficial effect on diabetes development, osteoporosis and some cancers. But it is currently not possible to determine the specific role of polyphenols.
• Evidence for the benefits of polyphenol-rich foods is increasing. There is a need to focus future research on long-term intervention studies specifically designed to estimate the separate effects of polyphenols from the other compounds of the foods.
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Key Points