Re: Free full text access: polyphenols

[Guest guest]

Al: could you list the ref. cite for this article in addition to the link?

That way I can access it via pub med. Thanks.

Hi All,

Are polyphenols beneficial for health?

Read the latest thinking on this subject in the current issue of the Journal of the

Science of Food and Agriculture

Free full text access!

http://www3.interscience.wiley.com.qe2a-proxy.mun.ca/cgi-bin/fulltext/110493052/HTMLSTART

Al Pater, PhD; email: old542000@...

__________________________________

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[Guest guest]

--- albaughg@... wrote:

> Al: could you list the ref. cite for this article in addition to the link?

That

> way I can access it via pub med. Thanks.

>

> > From: Al Pater <old542000@...>

---------------------------------

Hi All,

Are polyphenols beneficial for health?

Read the latest thinking on this subject in the current issue of the Journal of

the

Science of Food and Agriculture

Free full text access!

http://www3.interscience.wiley.com.qe2a-proxy.mun.ca/cgi-bin/fulltext/110493052/\

HTMLSTART

Hi All,

Since the article is apparently not available without an e-journal access, the

article is below. The first two references are pdf-available.

Journal of the Science of Food and Agriculture

Volume 85, Issue 8, Pages 1239-1240

Published Online: 11 May 2005

Perspective

Polyphenols: dietary components with established benefits to health?

Kroon, on

No Abstract.

Article Text

The polyphenols are beneficial for health message appears to have considerable

momentum at present. Considering that real scientific interest in the role of

dietary polyphenols in maintaining human health only started about 10 years ago,

there has been a remarkable rate of progress. A decade ago, virtually nothing

was

known concerning the bioavailability, metabolism and fate of polyphenols in

humans.

Data concerned with dietary intakes were just appearing in the literature, and

studies concerned with how polyphenols might affect human health were limited

largely to an interest in their properties as antioxidants. Today there is

strong

evidence supporting a role for polyphenols in prevention of age-related diseases

including cardiovascular disease and cancer. In this respect it is noteworthy

that

the nutrition community has recognised the importance of dietary polyphenols as

health-promoting agents. This is demonstrated by an increasing number of human

intervention studies being undertaken by nutrition departments and the reporting

of

these studies in top nutrition journals. What is particularly striking is the

dichotomy that has formed between the consistent successes of polyphenols and

polyphenol-rich foods to elicit beneficial responses in human intervention

trials on

the one hand and the rather consistent failure of antioxidant vitamins (eg A, C,

E)

on the other.

The interest in health effects of polyphenols is exemplified by recent and

planned

conferences on this subject. In November 2003, the 1st International Conference

on

Polyphenols and Health was held at the magnificent Conference Hall-Opera at the

spa

resort of Vichy in central France, sparked by the completion of a big European

Research Project on polyphenols and health (called Polybind). The organisers,

with

special credit to Dr Augustin Scalbert at INRA, Clermont-Ferrand, France, were

in

the fortunate position of coping with double the number of expected attendees.

Following this success, it has been announced that the 2nd meeting will be in

,

California, USA on 3-7 October 2005. The papers from the 1st meeting have just

been

published in the top nutrition journal, The American Journal of Clinical

Nutrition.

Review papers in this January 2005 supplement[1] remind readers of two important

points: (1) there are now about a hundred studies on humans in the literature

which

demonstrate a convincing effect of polyphenols on some aspects of health; (2)

there

has been a substantial improvement in understanding of the uptake and absorption

of

polyphenols into the body, and there are about a hundred studies in humans on

this

topic too.

Nutrients are required for a cell to grow and divide. Strictly, polyphenols are

not

required for these basic biological processes, although it was proposed more

than 70

years ago to call polyphenols vitamin P. Even now some supplement manufacturers

on

the Internet, but not in the scientific literature, refer to polyphenols as

vitamin

P. The action of polyphenols on health is to help protect against environmental

stresses. If we were never exposed to oxygen, smoke, exercise, carcinogens,

toxins,

UV light or sunlight, then there would be no need for polyphenols. However,

since

this ideal situation does not exist, polyphenols are an essential part of any

balanced diet in the real world.

Polyphenols are well-known antioxidants and are particularly potent in this

respect,

but this appears to be only part of the health story. They have multiple

functions,

and recent research has highlighted several important mechanisms of polyphenols

which are not only related to their direct antioxidant activity but also to

their

ability to bind to proteins. These include binding to cellular receptors and

transporters and influencing gene expression, cell signalling and cell adhesion.

For

non-polyphenolic antioxidants there have also been some negative studies. The

fact

that they are negative often generates excessive publicity, while the positive

studies (good news) do not always receive such extensive press coverage and

comment.

Despite this bias, the negative studies have, of course, to be taken seriously.

On

closer examination the negative studies in the literature have all been on

vitamin

antioxidants (vitamin E, vitamin C, -carotene) given in supplements at very high

doses. The recent study on slightly increased risk of GI tract cancers was an

example of a negative effect of antioxidants.[2] However, for polyphenols, none

of

the intervention studies reported to date have shown a negative effect, although

a

significant proportion have shown no effect. In fact, for the cocoa

proanthocyanidins (the main polyphenol class in cocoa), administration of a

mega-dose of 2 g kg-1 body weight of grape seed proanthocyanidin extract in a

toxicological study showed no observable toxicity of any kind.[3] This is

equivalent

to 100 g of pure proanthocyanidin (contained in about 500-1000 apples!) for the

average person. For the record it is estimated that we eat 1 g day-1 of

polyphenols.

The main dietary sources of polyphenols are fruits, beverages (fruit juice,

wine,

tea, coffee, chocolate and beer) and, to a lesser extent, vegetables, dry

legumes

and cereals. There are several different classes of polyphenols, each with

different

biological effects, and so the situation is complex. The classes of polyphenols

(also called flavonoids) include flavonols, flavanones, flavones,

pro(antho)cyanidins, catechins, anthocyani(di)ns, isoflavones (phytoestrogens)

and

tannins. The USDA now has food composition databases for many of the classes of

polyphenols: http://www.nal.usda.gov/fnic/foodcomp/Data/Flav/flav.html

http://www.nal.usda.gov/fnic/foodcomp/Data/PA/PA.html

RDA (Recommended Daily Intake) values already exist for most micronutrients such

as

vitamins and minerals. It is possible that there could be a value for

polyphenols in

the future. One of the issues to be resolved would be how to provide a single

understandable RDA for the multiple classes of polyphenols.

There have been several attempts, some recent, to rank fruits and vegetables in

terms of their antioxidant power using in vitro chemical assays. The only merit

to

these types of test on foods is that they are approximately equivalent to the

contents of polyphenols (as these dominate in these assays). Apart from this,

they

do not necessarily reflect any anticipated health benefits. The biological

activities of polyphenols are much more complicated and complex than a simple in

vitro cell-free chemical test could ever demonstrate.

So will the food industry take the opportunity to include polyphenols in

products to

give a health benefit coupled with a healthy image? This depends on the reaction

of

consumers, who are in turn educated by the press, the Internet and the

supermarkets.

There are already a substantial and growing range of supplements on the market,

especially in the USA, containing polyphenols. Supplements could be especially

important for the polyphenols that have been shown to have health benefits but

are

found in foods that are not highly consumed in the Western diet, such as green

tea

polyphenols and isoflavones from soya. In fruits and vegetables there is a large

variation in the content of polyphenols owing to different geographical regions,

variety and strain differences, harvesting treatments and processing and storage

conditions. Foods and supplements containing guaranteed or standardised amounts

of

polyphenols can overcome these normal variations and uncertainties but need to

have

proven efficacy in time-consuming and expensive human intervention trials.

However,

for the credibility of the product, and of polyphenols, these types of study are

essential.

To conclude, although there is some way to go before everything is known about

the

health effects of polyphenols, the advances in the last 5 years on polyphenols,

especially in human intervention and bioavailability studies, appear to have

established this class of phytonutrients as a serious player on the nutrition

and

health scene.

References

1 Scalbert A, IT, Saltmarsh M.

Polyphenols: antioxidants and beyond.

Am J Clin Nutr. 2005 Jan;81(1 Suppl):215S-217S. Review.

PMID: 15640483

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=pubmed & dopt=Abstra\

ct & list_uids=15640483 & query_hl=51

http://tinyurl.com/8qlfu

2 Bjelakovic G, Nikolova D, Simonetti RG, Gluud C.

Antioxidant supplements for prevention of gastrointestinal cancers: a systematic

review and meta-analysis.

Lancet. 2004 Oct 2;364(9441):1219-28. Review.

PMID: 15464182

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=pubmed & dopt=Abstra\

ct & list_uids=15464182 & query_hl=53

http://tinyurl.com/87gjz

3 Ray S, Bagchi D, Lim PM, Bagchi M, Gross SM, Kothari SC, Preuss HG and Stohs

SJ,

Acute and long-term safety evaluation of a novel IH636 grape seed

proanthocyanidin

extract.

Res Commun Mol Pathol Pharmacol 109: 165-197 (2001).

Al Pater, PhD; email: old542000@...

__________________________________

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