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Cardiovascular refers to the heart and circulation in the body, the health of the cardiovascular system can be affected by different diseases or conditions. Cardiovascular disease (CVD) is one of the primary causes of mortality in the western world. CVD refers to any disease which affects the circulation and heart and is also known as heart disease and circularity disease. This means that many conditions such as stoke and coronary heart disease (angina and heart attacks) fall under the title CVD.
There are many risks which can lead to CVD some which can be modified and others which cannot. The main modifiable risks are smoking or exposure to tobacco smoke (second hand smoking), obesity, diabetes, hypertension (high blood pressure), high cholesterol, physical inactivity and alcohol intake- high alcohol intake has a negative effect on cardiovascular health. Non modifiable risks include, family history- if members of family have suffered with heart disease then it increases the risk, the sex of the person- males are more likely to sufferer from CVD than females, age- risk of CVD increases with age, people who are 50 years of age or older are more likely to suffer. Another non modifiable risk is ethnic group- for example south Asian people who live in the UK are more likely to suffer from CVD than other people who live in the UK. (BHF, (2008))
These factors make CVD a complex disorder, it is multifactorial as both genes and the environment around us can have an effect on the increasing risk. People who eat unhealthily and consume a lot of fat within their diet are more at risk of suffering from a heart attack. As we get older arteries in the body develop hyperlipidemea, this is where the blood fats increase and some fats and cholesterol get deposited in the arterial wall. This can lead to atherosclerotic plaque which reduces the size of the lumen of the arteries and thus reduces the blood flow to the heart. This plaque can become a problem if it ruptures as it leads to the blood in the lumen coming into contact with clotting factors which ultimately blocks the lumen of the artery preventing oxygen from reaching the heart, potentially resulting in a myocardial infarction (MI) - heart attack. This is represented in Figure 1. below, the arteries start off with a clear lumen so blood can easily flow through and gradually the arteries become blocked as fat from the diet is deposited causing less blood and oxygen to be able to flow through to the heart. (Talmud, (2008)).
Figure 1: The multifactorial nature of CAD. Talmud, (2008).
Cholesterol is a large factor in cardiovascular health as it can be both beneficial and harmful to the body. Cholesterol is a lipid and is a vital component of cell walls. As a lipid it means that it does not mix with water and therefore has to be carried around the body by lipoproteins in the blood stream. Cholesterol is a vital structural component of cell walls. There are two types of cholesterol, the first being low-density lipoprotein (LDL) which carries cholesterol from the liver to the cells that need it, it is essential for growth and repair of cells. However too much of this cholesterol in the cells (more than the cell needs) can be very harmful to us and. A high level in our blood can cause cholesterol to build up in our arteries which can potentially lead to the blocking of them. This is why LDL is known as 'bad cholesterol' and lower levels are better in the body. The other type of cholesterol is high-density lipoprotein (HDL), which carries cholesterol away from the cells and back to the liver where it is either broken down or passed from the body as a waste product. This can be know as a 'biological hover' as it sweeps up LDL and takes it back to the liver so that it cannot cause harm within our bodies. For this reason HDL is also known as 'good cholesterol' and higher levels are better for us. The total level of both LDL and HDL cholesterol in the body is known as serum cholesterol. A high cholesterol level in the body is known as hypercholesterolemia and can lead to various heart defects such as stroke, angina, heart attack and atherosclerosis. High cholesterol levels can be a result of a diet high in saturated fat and cholesterol, a lack of exercise, a family history of high cholesterol, being overweight, drinking more that the recommended daily amount and age and gender- cholesterol generally increases with age and men are more likely to be affected than woman. People who have diabetes and who have a high blood pressure are also likely to be more at risk of high cholesterol. The main way of testing if somebody is suffering from hypercholesterolemia is to carry out a simple blood test. Cholesterol levels should be 5mmol/L, however, 2 out of 3 adults in the UK have a cholesterol level of 5mmol/L or above. Treatment for hypercholesterolemia mainly involves having a healthier life style for example having a lower fat diet, eating healthy balanced meals and reducing portion sizes of meals. Physical activity should be increased and quitting smoking can also help to reduce hypercholesterolemia. (NHS, (2009))
Therefore the diet we eat can greatly lower risks of CVD, hypercholesterolemia and other related heart disorders, studies and research have been carried out to see how polyphenols can help to lower the risk of suffering from CVD.
What are polyphenols?
Polyphenols are chemical substances which are made up of one or more phenol units. Polyphenols are frequently present in our food diets as they are found in plants, mainly in fruits and vegetables. The main sources of polyphenols are tea, grapes, wine, berries and cocoa. They have become increasingly popular for scientific research as they are said to have many health benefits including reducing the risk of CVD and other heart related disorders. Polyphenols can be divided into hydrolysable tannins e.g. gallic acid and phenylpropanoids e.g. flavonoids, condensed tannins and liginins.
Vassallo (2008. p3) states that 'Flavonoids are polyphenolic compounds derived from the secondary metabolism of plants.' There are several subclasses of flavonoids such as catechins, proanthocyanidins, anthocyanidins, and flavones, isoflavones, flavonols, flavanols, flavanones, chalcones and dyhydroflavonols. This group of polyphenols are one of the most important in the diet and are abundantly found in various plants. Flavonols and catechins are the most common flavonoids found in food with quercetin being most frequently found flavonol in our diets.
Quercetin make up around 60- 75% of total flavonols an is one of the most biologically active. It is usually found in onions, apples, cider, grapes, wine, teas and broccoli although small quantities are found in all plant products.
Catechins are rich in tea leaves, can give up to 30% of the dry leaf weight and are widely distributed within plants. Anthocyanidins give bright colours of flower petals for example orange, pink red and blue. Proanthocyanidins are also known as condensed tannins and are polyflavonoid in nature. They have flavan-03-ol units and are found in many foods including grapes, apples, strawberries and plums. Flavones, isoflavones, flavonols and their glycosides are found in large quantities within plants. 1g of these compounds is said to be taken in each day when a high fruit and vegetable diet is consumed. (Ho et al., (1992)).
Chun et al. (2007) calculated the mean daily intake of flavonoids to be 190mg per day with flavanols being the most abundant in the diet followed by flavonols and flavones.
Figure 2: Structures of the flavonoids, flavone, flavanone, and isoflavone. Cao et al., (1998).
Figure 2 above is the basic structure of the three flavonoids, flavones, flavanone and isoflavone. The heterocyclic C ring is affected by a series of transformations to form other flavonoids including anthocyanins found in wine and catechin found in tea.
There are two major types of tannins, these are known as condensed and hydrolysable. Condensed tannins are also known as proanthocyanidins as when they are heated in acidic conditions they realise anthocyanidins. They are widely distributed within plants and have been receiving and increased interest due to their natural antioxidant properties and health promoting agents. They are made up of chains of flavanol units linked by C-4-C-6 bonds and are produced via polymerization of flavonoids. Hydrolysable tannins are formed by the reaction of gallic acid with hexose molecules. (Packer, (2001)).
Flavonoids are the main polyphenols found in various types of tea and also in wine and beer.
Polyphenols in beverages
Tea is an ancient drink which dates back many years, it is very popular and is the second most consumed drink in the world after water. There are many different types of tea which are made from the leaves of camellia sinensis. The drinking of tea is related to many health benefits, including reducing the risk of CVD. Many epidemiological studies have shown this to mainly be due to the presence of polyphenols in the form of flavanoids.
Although green tea is most popular in Asia and originated from china, the consumption of green tea in Europe has started to increase due to various health benefits. Catechins are the polyphenols which are found in green tea, these are also found in other foods and beverages such as wine, chocolate and grapes. The catechin group are known as flavan-3-ols and approximately 70% of the polyphenols found in green tea are made up of these. Catechins can give up to 30% of the dry leaf weight and are widely distributed within plants. The green colour of the tea results from inactivation of polyphenol oxidase which prevents black, red and brown pigments being formed as a result of polymerization. This is done by treating the fresh tea leaves with hot steam and air (Koo, S and Noh, S. (2007)). The catechins present in green tea are said to be what makes the tea have these health benefits. The catechins which are most commonly found in tea are (−)-epigallocatechin gallate (EGCG), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC), and (−)-epicatechin (EC). Figure 3 below show the structure of the main green tea catechins.
Figure 3: Structures of major green tea catechins. Koo, S and Noh, S. (2007).
Vassallo (2008) sated that reactive oxygen species bring about molecular alterations in cellular components which leads to various changes in cell structure, function and also viability e.g. side chain oxidation and DNA lesions. Increase oxidative stress can damage endothelial function and is thought to mediate vascular diseases. As a result of this, the beneficial effects of the polyphenols in green tea which are associated with cardiovascular health are due mainly to antioxidant properties. Green tea polyphenols are excellent electron donors and efficient scavengers of free radicals e.g. nitric oxide and siglet oxygen. This is due to the number and arrangement of phenolic hydroxyl groups.
Suzuki et al., (2009) looked into the effects of green tea catechins on inflammatory cardiovascular diseases as this area has not been well investigated. They stated that catechins have a biological function of being anti- inflammatory by inhibiting a number of inflammatory factors. These include nuclear factor- kappa B (NF-kB) - a protein complex that controls the transcription of DNA, a multipotential promoter of matrix metalloproteinases (MMPs) - zinc dependent endopeptidases, cytokines and adhesion molecules. They noted that myocardial ischemia and ventricular remodeling cause a lot of damage which can lead to severe heart failure. Ischemia of myocardium can be enhanced by NF-kB related inflammation, the activated NFkB induces MMPs. The inhibition of MMPs is a benefit for treatment of myocardial reperfusion injury as they are key components in the positive feedback loop of the heart remodeling. Suzuki et al., (2009 p.2) state that 'It is also well known that catechins suppress several inflammatory factors including MMPs induced by NF-kB.' As a result of this information they wanted to make the role of catechins on the ischemic hearts clear. They did this by making a rat myocardial ischemia model and divided them into two groups, a non-treated ischemia group and a non-treated sham-operated group. The non-treated ischemia group had a significant decline in blood pressure when compared to the non-treated sham-operated group. The catechin treated hearts showed significantly less left ventricular circumference, less infarct size and length and a smaller ventricular inner diameter than the hearts in the non-treated ischemia group. They found that there was increased gelatinase (MMP-2 and MMP-9) activity in the non-treated ischemia hearts however catechin administration decreased this activity showing that catechins can prevent ventricular remodeling after ischemic injury as MMPs as inflammatory factors are suppressed.
Maron, D.J et al., (2003) conducted a study on the impact of theaflavin-enriched green tea extract on lipids and lipoproteins of subjects with mild to moderate hypercholesterolemia. The study involved 240 male and female participants who were ages 18 years or older. The participants had to be on a low fat diet and they were randomly assigned to receive daily capsules containing theaflavin-enriched green tea extract (375mg) or placebo capsules for a period of 12 weeks. After the 12 week period the mean changes from baseline in total cholesterol were -11.3%, in LDL- cholesterol -16.4%, in HDL- cholesterol 2.3% and in triglyceride 2.6%. The mean levels of the placebo group did not significantly change. This shows that green tea polyphenols in addition to a low saturated fat diet can reduce LDL- cholesterol in hypercholesterolemic adults.
Three studies carried out by Sato et al., (1989), Nakachi, K et al., (2000) and Iwai et al., (2002) looked into the association between green tea consumption and CVD mortality. Sato et al., (1989) looked into the possible contribution of green tea drinking habits to the prevention of stroke. 5910 non-drinking and non smoking woman were used to conduct this experiment based in Japan. They concluded that medical history of stroke was less frequently observed among those who consumed more green tea in daily life, incidence of stoke and cerebral haemorrhage during the four year follow up was twice as high in participants who drank less than 5 cups of tea per day than those who drank more than 5 a day. No correlation was seen between tea drinking and hypertension history. Nakachi, K et al., (2000) looked into the significance of drinking green tea in the prevention of CVD and cancer. 8552 participants were used in this study and were all general residents in Saitama Prefecture, Japan. The study showed a decreased relative risk of death from CVD in men of 0.58 and 0.82 for woman, the risk was lowered to 0.72 for members of both sexes consuming over 10 cups/day of tea. Iwai et al., (2002) carried out a cohort study to investigate the effects of coffee and green tea consumption on all-cause mortality in Japan. 2855 men and woman were used in the study and the Cox regression model was used to adjust for potential confounding factors. The results showed a multivariate hazard ratio of mortality of 0.43 for men who consumed two or more cups of tea or coffee per day compared with those who consumed less than half a cup per day.
As none of these three studies regarded the association between consumption of green tea and CVD incidence Kuriyama et al., (2006) decided to examine the relation between green tea consumption and mortality from CVD, cancer and all causes, using a large sample size so that the study would be more generalisable. 40, 530 participants were used where as the other studies used fewer, 2855 to 8552. All the participants were national health insurance beneficianes aged 40- 79 years. A questionnaire was given to the participants where they had to record their dietary intake. The findings from the study showed that as the consumption of green tea increased the rate of mortality due to CVD and all causes decreased. Those who consumed five or more cups of tea per day had a 16% lower rate of mortality than those who consumed less than one cup per day during the 11 year follow up.
Serafini et al., (1996) was another study that found health benefits from the consumption of green tea. They evaluated in vitro antioxidant activity of green and black tea, the in vivo effect on plasma antioxidant and the effect of milk addition to the tea. Green tea was found to be sixfold more effective than black tea but both teas inhibited the in vitro peroxidation in a dose- dependent manner. These results show that tea has strong antioxidant properties in vitro which are said to be exerted by the polyphenols present. They stated that the results also provide convincing evidence that tea also has effective activity in vivo in man. Due to the fast in vivo response Serafini et al., (1996) suggested that the absorption of the bioactive components of tea take place in the upper part of the gastrointestinal system. They found that the addition of milk to tea inhibited these processes. Similarly to this study was the research carried out by Leenen et al., (2000) which looked into the effect of black and green tea consumption, with and without milk, on the plasma antioxidant activity in humans. They concluded that the consumption of green and black tea promotes a significant rise in plasma antioxidant activity. The addition of milk in this study had no effect on this increase.
Princen et al., (1998) found conflicting results from their study into the effect of consumption of black tea, green tea and of the intake of isolated green tea polyphenols (3.6g approx. 18 cups per day) on LDL oxidation ex vivo. They also looked at how this would affect plasma levels of antioxidants and lipids. They concluded that although intake of green tea polyphenols significantly decreased (-11%) the plasma vitamin E when compared to the control, had no effect on LDL oxidation ex vivo. The consumption of six cups of tea per day also had no effect on plasma lipids and no sparing effect on plasma antioxidant vitamins. All the authors above concluded positive effect of green tea consumption on health, Hodgson et al., (2002) showed conflicting results. This study researched whether regular ingestion of tea could inhibit in vivo lipid peroxidation by measurement of urinary F-2-isoprostane (Isoprostanes derived from the free radical oxidation of arachidonic acid) excretion. Similarly to Princen et al., (1998) they found that F, isoprostane excretion was not altered due to ingestion of green tea when compared to the participants dinking only hot water. The results didn't show any support that the polyphenolic antioxidants found in tea inhibit in vivo lipid peroxidation.
A large amount of research has been carried out to see if the polyphenols presents in tea do actually have cardiovascular health benefits. The majority of authors above have shown that catechins have a positive effect on health as they can raise plasma antioxidant activity, reduce CVD related mortality, reduce serum cholesterol and help to prevent ventricular remodeling. However there are still studies which show no beneficial health effects due to the consumption of green tea for example Hodgson et al., (2002) and Princen et al., (1998). Kuriyama (2008, p1552) conducted a literature search into green tea and prevention of CVD or CVD risks and found that out of 30 studies 17 showed beneficial effects of green tea consumption. He stated that 'The equivocal findings may be explained by the variety of study designs, participant populations, green tea products tested, and study outcomes'. Further studies need to be conducted using larger samples and within different countries in order for results to be more generalisable. Sato et al., (1989), Nakachi, K et al., (2000), Iwai et al., (2002) and Kuriyama et al., (2006) all conducted their studies using participants from Japan. Green tea is a regularly consumed as it is an important component of the Japanese diet. This could have lead to these studies reporting beneficial effects of green tea on cardiovascular health when compared to studies where participants had only consumed green tea for a number of weeks.
Black tea similarly to green tea is rich is flavonoids with 30% of the dry content of the tea being from the flavonoids present. Although both green tea and black tea are rich in flavonoids, black tea contains theaflavins (TFs) which are not present in green tea, this is because oxidative polymerization of the polyphenols occurs during fermentation. These theaflavins include theaflavin, theaflavin-3-gallate, theaflavin-3, 3'-digallate and theaflavin-3'-gallate. Black tea also includes 6-12% of thearubigins- these are products of catechins after polymerisation. (Trautwein et al., (2009)).
Figure 4: Structures of theaflavin and the gallate esters. Miller, N et al., (1996). P.41.
Figure 4 above shows the structures of the theaflavins found in black tea and the gallate esters. Theaflavins are formed from flavon-3-ols during enzymic oxidation.
Trautwein et al., (2010) conducted a study to see how the consumption of purified TFs, TFs/ catechins or placebo controlled capsules could lower serum total cholesterol, in particular LDL, in 224 participants who have mild to moderate raised cholesterol levels. In the capsules containing TFs/catechins the ratio of the two flavonoids were very similar to what is found in freshly brewed black tea, the TFs capsule contained four of the typical TFs in black tea. Although the black tea was said to be beneficial to cardiovascular health by helping to lower LDL cholesterol in the blood, the results of this study showed differently. Trautwein et al., (2007) found that an 11 week daily intake of either 77mg of TFs or 75mg of TFs with 150mg of catechin compared to the placebo did not significantly lower LDL cholesterol or serum total cholesterol.
The study conducted Bingham et al., (1997) showed similar results to those from Trautwein et al., (2009). The study was carried out to see if black tea consumption had any effect on blood lipids, blood pressure and aspects of bowel habit. The study involved 31 male and 34 female participants who were asked to drink a minimum of 6 cups of tea per day (twice the national average). The tea bag had to stay in the boiling water for a minute and be prodded 6 times and squeezed before taken out of the water to ensure that there was maximum polyphenols content in the water. The diets of the participants were also recorded and they all had a fat intake typical of the UK (37% of total energy) when compare with the national samples. The level of total serum cholesterol, LDL-cholesterol, HDL- cholesterol and the blood pressure of these participants after the 10 week experiment were assessed to see the potential effect of the consumption of black tea in reducing the risk factors of CVD. These results were compared to the results for the placebo group who were matched to milk, water, caffeine and sugar intake, 1.5 litres of water had to be consumed daily and the only other drink that was allowed was coffee. The results showed no significant difference in total serum cholesterol, LDL- cholesterol, HDL- cholesterol and blood pressure between the placebo group who were free from the polyphenols associated with black tea and the tea drinking group. There was a slight decrease in both HDL- and LDL- cholesterol however this was only a difference on average of 0.07mmol (1%) so was therefore not significant at p<0.05.
Although both of these studies showed that black tea had no beneficial effects on reducing the risk of CVD by lowering LDL- cholesterol, the study by Davies et al., (2003) showed conflicting evidence. This study was carried out to assess the effects that black tea consumption has on lipid and LDL- cholesterol concentrations in slightly hypercholesterolemia participants. 15 participants were used for this study, 8 females and 7 males, who were all over the age of 35 and had no major health problems such as diabetes, heart disease or cancer. The woman who participated also had to be post menopausal and not undergoing any hormone replacement therapy. A set diet was given to all the participants who followed a national cholesterol education programme where 58% of total energy was from carbohydrates, 26% from fat and 16% from protein. The tea drinking group had to consume 5 cups of black tea per day and the total cholesterol levels, levels of LDL- cholesterol and lipoprotein were compared after the experiment to a placebo group who consumed no tea or added caffeine. After the experiment another group was then added which was a placebo group where participants receive placebo with caffeine at a concentration equivalent to that in tea. The results showed that total cholesterol in the tea drinking group was lowered by 6.5%, LDL- cholesterol by 11.1%, apolipoprotein B by 5% and lipoprotein (a) by 16.4% when compared to the placebo with added caffeine. When compared to the placebo group without added caffeine, total cholesterol decreased by 3.8% and LDL- cholesterol by 7.5%. HDL- cholesterol, lipoprotein (a) and apolipoprotein B remained unchanged. Davies et al., (2003) thought that the possible mechanism for the effect of tea on cholesterol may be due to the tea limiting cholesterol absorption in the intestine.
Another study with similar findings to those of Davies et al., (2003) was a study carried out by Stensvold et al., (1992). This study was carried out on 9857 men and 10233 men living in Oppland. The study was restricted to people who had no history of CVD, diabetes, angina pectoris or atherosclerosis obliterans. The participants attended examination which included taking a blood sample from the participants which was analysed for total cholesterol, triglycerides and glucose. A questionnaire was also handed out on dietary habits including tea consumption. The participants were split into five different groups who all had to consume varying amounts of tea each day. The groups were <1, 1-2, 3-4, 5-6 and 7 cups/day. The results showed a linear trend; mean serum cholesterol decreased as tea consumption increased. In the male participants a difference of 0.24mmol/litre was seen between drinkers of less than one cup of tea a day and those who drank five or more cups a day. In woman the difference was slightly lower at 0.15mmol/litre. There was also a decrease in systolic blood pressure as tea consumption increase, with a difference between the same teas groups of 2.1mm in men and 3.5 mm in woman.
There are similarities in the studies carried out by Stensvold et al., (1992) and Davies et al., (2003), who both found that the consumption of black tea did help to lower total and LDL- cholesterol, when compared to the studies by Trautwein et al., (2010) and Bingham et al., (1997), who both found that black tea didn't have any effect on lowering cholesterol levels, even though the findings were different. All four studies used varying amounts of participants, although the study by Davies et al., (2003) only used 15 participants the study carried out by Stensvold et al., (1992) found similar results and used a similar experiment and this study used over 19000 people so the amount of participants used in the study isn't really a real reason for the contrasting results. The study by Trautwein et al., (2010) gave their participants theaflavins in a capsule form rather than fresh tea so this could have lead to the negative results of the study as only 77 mg of four of the major theaflavins were in this capsule, so the fresh black tea used in the studies by Stensvold et al., (1992) and Davies et al., (2003), could have contained more theaflavins and a larger quantity thus having positive consequences by lowering cholesterol. Even though consuming the flavonoids in the tea could be more beneficial than consuming them in a capsule, the amount of tea used in all three of the studies was at least double the daily intake of three cups per day. This shows the studies lack generalisability as the results will not be able to be applied to many people as a lot of people don't consume at least 6 cups of tea per day. The main difference between these four studies was that those carried out by Stensvold et al., (1992) and Davies et al., (2003) involved the participants eating a healthy diet with lower fat levels than in the other two studies, also the participants had to be free from any health problems such as diabetes, CVD and angina and even if they didn't have any of these problems they still couldn't take part if they had a family history of any of these. This means that the lowering of cholesterol in these two studies could have been due to the healthier, lower fat diet rather than positive effects of the consumption of black tea. Polyphenols are also present in many fruits and vegetables (Paganga et al., 1990) so if a diet rich in fruit and vegetables were consumed by the participants then there is no evidence that it wasn't the polyphenols present in these that was leading to lower cholesterol levels.
The majority of research carried out into alcohol and cardiovascular health relates to the benefits of red wine consumption. Although there have been studies carried out into the consumption of cider and beer or cardiovascular health, the results of these are very conflicting and generally have been shown to have no effect on the prevention of CVD and other heart defects. More research needs to be conducted into these areas for some more conclusive evidence.
Polyphenols and anthocyanins are of large importance in wine as they help to develop taste, appearance and flavour. Polyphenol tannins also help to give the wine body, backbone and longevity which mean that polyphenols are essential in wine making. Although polyphenols in the wine are beneficial it is possible for the wine to have too much. This occurs when the grapes are left in the summer heat which causes the skin to thicken so more pigment and polyphenols are present in the grapes (Chèze et al., (2001)). Red wine contains several phenolic compounds including tannins, resveratrol, catechin, quercetin and epilcatechin all found in grape skins. Red wine is said to be more beneficial to cardiovascular health than white wine and it's said that the non- alcoholic compounds may help prevent atherogenesis by reducing chemically mediated peroxidative reactions and also by down- regulating thrombotic tendencies. (Esturch, 2000). A large amount of research has been carried out on the polyphenols associated with wine as the consumption of wine is said to have various health benefits including increasing cardiovascular health. Up until about 30 years ago the research into the beneficial effects of wine consumption have been quite unreliable, however, more recent studies have proven to show many health benefits of wine for different reasons.
Wine has been consumed by people for many years and is also an important component of the Mediterranean diet. The World Health Organisation (WHO), (1990), revealed that the French have a lower risk of heart disease even though they are said to consumer a higher level of saturate fat and exercise less than North Americans. This was supported by research carried out by Renaud and de Lorgeril (1992) who noted that men from Toulouse in South France have a 57% lower mortality rate from heart disease before then age of 64 than men in Stanford, US. They also stated that men from Toulouse had a 79% lower mortality rate from heart disease than men in Belfast, Northern Ireland and Glasgow, Scotland this occurrence is now known as the 'French paradox' in which some of the regions in France have a 40% lower mortality rate from CHD than other Northern-European countries with similar CHD risk factors (Chèze et al., 2001). The level of support on this finding helps to prove that it is not due to unreliable statistics as many authors have reported the same thing. The 'French paradox' has also been supported by MONICA project which was set up by The WHO (1989).
Many authors have linked the 'French paradox' to red wine consumption and a number of studies have been carried out in order to see the effects of red wine or cardiovascular health. Renaud et al., (1988) conducted a study on 34,000 middle aged men, the mortality rates from CHD in those consuming two or more glasses of wine per day decreased by 30- 39% after the model was adjusted for six confounding factors. Another study showing similar results was carried out by Groenback et al., (1995) in Denmark using 6051 male and 7234 female participants aged between 30- 70 years. They carried out the study to examine the association between intake of different types of alcoholic drinks and mortality. The subjects were followed for 12 years after the study and the results showed the protective effects of wine as the risk of dying decreased steadily as wine consumption increase to 3-5 glasses per day. The relative risk lowered from 1.00- 0.51. Beer drinking was not associated with reduced risk and the risk of drinking spirits increased from 1.00 to 1.34 with 3-5 drinks per day compared to those having no drinks.
Parks and Booyse, (2007) researched into how alcoholic beverages result in a reduction in the risk factors associated with cardiovascular disease and also decreases in mortality rates. They stated that the atherothrombotic problems which result in MI and the pathogenesis of CHD involve cellular and molecular mechanisms that have been changed through interactions with various environmental and systemic factors. Wine and alcohol are systemic factors so therefore will help to reduce these complications and thus reduce the risk of CHD. They found there were many health benefits of drinking red wine in our diets including decreased platelet aggregation (the clumping together of platelets in the blood leading to a clot being formed), increased fibrinolysis (the process where a fibrin clot is broken down), inhibited ex vivo LDL oxidation and increased plasma levels of HDL cholesterol and apolipoprotein. In comparison they looked into the health benefits of drinking white wine with similar alcohol content to the red wine and pure alcohol, however found that they did not show any cardio protective effect. The main difference between red and white wines is that red wine contains approximately 20 times more polyphenols (mainly flavonoids) than white wines.
It is important for wine trials to be carried out as there are discrepancies as to whether the cardioprotective effect is due to the ethanol in the wine or the antioxidant content which is mainly polyphenols within red wine (Esturch, 2000). de Rijke et al., (1996) studied the effects of non alcoholic components of red wine by reducing the alcoholic content. The consumption of the dealcoholized red wine did not show any beneficial effects on LDL oxidation and the propensity of LDL to copper mediated oxygen was not affected. Fuhrman et al., (1995) concluded that the consumption of red wine, not white, reduced the susceptibility of LDL to undergo lipid peroxidation. They also stated that the anti oxidant effect of red wine on plasma lipid peroxidation could be related to increased polyphenols concentration in plasma LDL. Therefore some of the phenolic compounds that are present in red wine are absorbed and bind to plasma LDL and could be responsible for the antioxidant properties of red wine.
However although wine is said to help improve cardiovascular health there are discussions as to the level of alcohol which needs to be consumed in order for these health benefits to occur.
Parks and Booyse, (2007) also highlighted that the polyphenols in red wine can trigger .NO dependent cell signalling, including endothelial-dependent relaxation that is modulated both by 02 and SOD, a family of enzymes that catalyze the formation of hydrogen peroxide and molecular oxygen. They found that the quercetin, which is present in red wine but not in white, inhibited copper- catalyzed oxidation of low-density lipoprotein (LDL) as well as scavenging oxygen and lipid peroxy radicals.
Even though alcohol is said to have cardiovascular health benefits a heavy consumption of alcohol can actually have an opposing effect. High alcohol consumption has said to be related to vascular and myocardial complications. Light or moderate alcohol intake (1-2 drink/day for men and 1 drink/day for woman) for a long term period is related to reduce risks of coronary artery disease when compared with abstainers and heavy drinkers. As well as this it also decreases the mortality by nearly one third. The mortality curve is J-shaped or U-shaped, this represents the lowest risk being seen in moderate drinkers and the higher risk (top of the J or the U) being seen in heavy drinkers, many studies and books have been in agreement with this information for example Groenbaek M et al., (1995), Goldfinger and Facc (2003) and Chèze et al., (2003). The relationship between relative risk mortality and alcohol intake (J-shaped or U- shaped curve is shown in figure 5 below.
Figure 5: Relative risk mortality in relation to alcohol intake. Estruch, R. (2000).
The authors above have all shown how wine, when drank in moderation can have beneficial effects to cardiovascular health. It is clear from looking at these studies and the research carried out that red wine can help to reduce risk factors of CVD and mortality, related to heart disorders, when a light to moderate amount is consumed (1- 3 glasses per day). However this is not the same for white wine as it contains less polyphenols than red wine so doesn't have the same beneficial effect when consumed. All the research carried out by the authors above concluded positive effects of red wine and there is very little scientific evidence that a moderate intake of red wine has the opposing effect.
The purpose of this literature review was to find out how polyphenols present in beverages can affect cardiovascular health. The research into green tea, black tea and wine polyphenols is plentiful with many authors concluding beneficial effects on various aspects related to cardiovascular health. Research has concluded that green tea polyphenols have positive effect on cardiovascular health as they can raise plasma antioxidant activity, reduce CVD related mortality, reduce serum cholesterol and help to prevent ventricular remodeling. The theaflavins present in black tea were found to lower serum cholesterol and also LDL cholesterol thus reducing the risks of CVD. There was some research however that conflicted with these findings and found that there wasn't a significant difference between the polyphenols associated with tea and the reduced risk of CVD and other related disorders, showing that more research into this subject area needs to be carried out so that results are more conclusive. The polyphenols present in wine have shown to be the most beneficial with studies and research showing a positive effect of light to moderate red wine consumption on the prevention of CVD. Overall the majority of research have has show that polyphenols present in beverages have a positive effect on cardiovascular health.