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The effects of polyphenols on heart health

Linda Main
BSc SD
Dietetic Adviser
HEART UK - The Cholesterol Charity

Can carefully chosen beverages really make a difference to your patients' heart health? What advice would you give to ageing patients or the postmenopausal woman whose NHS health check puts them at greater than 20% risk of a cardiovascular event in the next 10 years?

Cardiovascular disease (CVD) is the primary cause of death in the Western world. The links between CVD and the way we live our lives are among the most well researched areas of patient health. It is estimated that as much as 80% of premature CVD could be prevented by changes to diet and lifestyle.1

Best practice dietary advice calls for a diet that is rich in plant-based foods, such as whole grains, fruit, vegetables, beans, peas, pulses and nuts, as well as fish (particularly oily fish), and one that is low in saturated fat and salt. This pattern of eating is rich in vitamins, minerals, trace elements and fibre, all of which are essential for good health. This diet also contains a range of non-nutritive food components that possess biological activity and are becoming increasingly associated with a healthy cardiovascular system.

While there is a wealth of patient advice available about maintaining cardiovascular health, information about drinking is confined to whether or not to drink alcoholic beverages, and if so what amount is acceptable. However, many beverages are a rich source of polyphenols, a diverse range of antioxidant compounds found in plant foods. The role of various beverages in heart health is set out below.

Alcohol
Data from the Low Income Diet and Nutrition Survey underline health professionals' concerns about alcohol consumption.2 Of those surveyed who consume alcohol, 16% of men and 9% of women consumed more than 60 g of alcohol daily, providing an average intake of more than 540 kcals each day. In fact, 2.5% of the men and women surveyed (who consumed alcohol) were consuming more than one third of their energy as alcohol.

While this level of alcohol consumption is of considerable concern because of its association with increased mortality, hypertension, cardiomyopathy, cancer and cerebrovascular events, a high alcohol intake will also displace better sources of energy and beneficial nutrients in the diet. Regular high consumption of alcohol can cause deficiencies in a number of vitamins, minerals and other food components, ultimately resulting in effects on long-term health. 

So should people drink at all? If so, how much should they drink? And who should be doing the drinking? The current recommendations are for women to limit their intake to no more than 2-3 units a day (14 units per week) and men to drink no more than 3-4 units a day (21 units per week). This upper level of consumption provides 1,000 kcals a week for women and 1,500 for men and represents 8.5% and 7% of the guideline daily amount (GDA) for energy for men and women respectively. A standard alcohol unit in the UK provides 8 g alcohol, and each gram of alcohol provides 9 kcals.

There is little doubt that modest alcohol consumption confers some reduction in cardiovascular risk and this is regardless of the source of alcohol (beer, wine or spirits). However, according to the meta analysis of 34 prospective studies by Di Castelnuovo and associates, the maximum reduction in mortality can be attained from a very low consumption of alcohol - just 6 g per day, which is less than one unit of alcohol in the UK.3

Red wine and grape juice
For some time, there has been speculation that red wine might have a beneficial effect on cardiovascular risk in addition to that of alcohol. Red wine contains significant levels of polyphenols, including resveratrol and proanthocyanidins thought to be responsible for this effect.

However, are the benefits of consuming alcohol in women diminished by the increased risk of developing breast cancer? What advice should we give to the woman living with, or at greater risk of, breast cancer?

The World Cancer Research Fund estimate that in the UK, 41% of mouth, pharynx and larynx cancers, 51% of oesophageal cancers and 22% of breast cancers could be prevented if everyone stopped drinking. Its public recommendation (for those who choose to drink) is to limit consumption to no more than one drink a day in women and no more than two drinks a day in men (one drink being defined as no more than 10-15 g alcohol). Gronbaek has suggested that red wine consumption might confer some benefit against cancer, compared to consumption of alcohol from other sources.4 He
postulated that other constituents in red wine not found in other forms of alcohol (eg, resveratrol from red grapes) may be contributing to this protection against cancer. This finding is also supported by Jang and colleagues, who noted that resveratrol from red grapes inhibits initiation, promotion and progression of cancer.5

So how practical is it to consume alcoholic drinks, particularly wine, within the recommended limits? Perhaps not that easy, as 10 million people regularly exceed the daily guidelines.2 Most wines are now 11-14% alcohol by volume, meaning that a very modest 125 ml of wine provides 1.4 to 1.75 units of alcohol and a 250 ml glass can contain as much as 2.8 to 3.5 units. Just 50-65 ml of red wine per day can confer the optimum benefit attributed to alcohol but, unfortunately, only provides a modest polyphenol intake.

Grape juice, essentially red wine without the alcohol, provides an alternative for women at increased risk of breast cancer and for those who abstain from alcohol but wish to benefit from greater intakes of polyphenols. Purple grape juice, made from Concord grapes, is particularly rich in resveratrol and potent proanthocyanidins; the combination of which appears to bestow health benefits to red wine.6

[[Tab 1 heart]]

Non-alcoholic beverages
Tea contains a rich source of flavonols and, for regular tea drinkers, provides a significant contribution to total polyphenol intake. Two meta-analyses have indicated that tea may have a beneficial effect on heart health; the first concluding that drinking three or more cups a day is associated with a reduced risk of myocardial infarction (MI) of 11%, and the second pointing to a 20% reduction in CVD death from the equivalent of drinking just two cups a day.7

Coffee contains chlorogenic acid and other phenolic compounds, which can contribute significantly to overall polyphenol intake. Some concern does remain over two diterpenes - cafestol and kahweol - which are found in coffee beans and have cholesterol-raising properties. They are released by the boiling of coffee and removed through filtering.
Fortunately, the vast majority of coffee consumed in the UK is instant or filtered and, therefore, is not affected. The best advice to patients would be to allow the kettle to go off the boil before making coffee; to filter boiled coffee (such as Turkish coffee) before drinking; and not to reheat coffee in the microwave.

Soya milk
Evidence has been accumulating for some time to support the role of soya in heart health. Approved health claims for soya and its link with cholesterol-lowering have been granted in several countries, including the UK and USA. Systematic reviews indicated that consuming 25 g of soya protein per day can lower LDL cholesterol levels by 5%.8,9 One of the easiest ways to contribute to soya protein intake is through the consumption of soya milk, which provides 10 g of soya protein per 500 ml.

Although concerns have been raised that soya isoflavones, because of their weak oestrogenic properties that are thousands of times weaker than mammalian oestrogen, may stimulate the growth of oestrogen-sensitive breast cancers, this is largely theoretical. On the contrary, considerable data indicate that soya may, in fact, protect against breast cancer. Patients can, therefore, be reassured that drinking soya milk (or eating soya-based foods) as part of an overall healthy diet, at levels consistent with a traditional Asian diet, is safe.    

Fruit juices, vegetable juices and smoothies
Fruit and vegetables have, for many years, been the focus of a healthy diet. Much of the credit has been centred on the antioxidant activity of these foods, but other mechanisms are currently being investigated. They provide a rich source of vitamins, antioxidants, fibre, potassium and polyphenols. A systematic review in 2006 reported that pure fruit and vegetable juices offer comparable health benefits to whole fruits and vegetables, the most likely explanation being the similarities in antioxidant and polyphenol contents.10 

Fruit smoothies are made from fruit juice combined with the juice and flesh from whole fruits and provide the added benefits of soluble fibre. The Department of Health has recently confirmed that smoothies made from at least 150 ml fruit or vegetable juice combined with 80 g of fruit or vegetable pulp can count for as many as two of your "five-a-day".

[[Fig 1 heart]]

Mechanisms of action
Mounting evidence from epidemiological studies, lab research and limited human studies suggests that polyphenols afford some protection against CVD. Oxidative stress, vascular inflammation and endothelial dysfunction are central to the development of CVD. The actions of polyphenols have not been completely elucidated, but it is likely they are working in a variety of ways, including:

  • Lowering LDL cholesterol.
  • Raising HDL cholesterol.
  • Improving endothelial function.
  • Improving blood flow.
  • Inhibiting platelet aggregation.
  • Reducing oxidative stress via direct and indirect antioxidant activity.  

Summary

  • There is mounting evidence that the non-nutritive components of fruits and vegetables afford some protection against CVD.
  • Polyphenols may be acting in a variety of ways to help reduce CVD risk, only one of which is directly though their antioxidant activity.
  • Beverages can provide a significant contribution to overall polyphenol intake.
  • Patients should be encouraged to drink a range of healthy beverages which complement the range of fruits and vegetables eaten as foods and so provide a broad range of different types of polyphenols.
  • Purple grape juice is particularly rich in the polyphenols found in red wine and can provide a source of proanthocyanidins, which may otherwise be lacking during the early part of the year. 

References
1. World Health Organization (WHO). Preventing chronic diseases: a vital investment. Geneva: WHO; 2005.
2. Nelson M, Erens B, Bates B, Church S, Boshier T. Low income diet and nutrition survey. Vol 2: Food consumption, nutrient intake. London: Food Standards Agency; 2007.
3. Di Castelnuovo A, Constanto S, Bagnardi V et al. Alcohol dosing and total mortality in men and women: an updated meta-analysis of 34 prospective studies. Arch Intern Med 2006;166:2437-45.
4. Gronbaek M, Becker U, Johansen D et al. Type of alcohol consumed and mortality from all causes, coronary heart disease and cancer. Ann Intern Med 2000;133:411-19. 
5. Jang M, Cai L, Udeani GO et al. Cancer chemopreventive activity of resveratrol, a natural product derived from grapes. Science 1997;275:218-20.
6. Mullen, W Marks SC, Crozier A. Evaluation of phenolic compounds in commercial fruit juices and fruit drinks. J Agric Food Chem 2007;55(8):3148-57.
7. Ruxton CHS. Black tea and health. Nutrition Bulletin 2008;33:91-101.
8. Joint Health Claims Initiative. Generic health claims for soy protein and blood cholesterol. Available from: www.jhci.org.uk/approv/schol2.htm
9. Harland JI, Haffner TA. Systematic review, meta analysis and regression of randomised controlled trials reporting an association between an intake of circa 25g soya protein per day and blood cholesterol. Athersclerosis 2008;200:13-27.
10. Ruxton CH, Gardner EJ, Walker D. Can pure fruit and vegetable juices protect against cancer and cardiovascular disease too? A review of the evidence. Int J Food Sci Nutr 2006;57:249-72.