CARDIOPROTECTIVE EFFECTS OF LIGHT–MODERATE CONSUMPTION OF ALCOHOL: A REVIEW OF PUTATIVE MECHANISMS
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Abstract
— There is abundant epidemiological and clinical evidence showing that light–moderate drinking is associated with a reduced risk of coronary heart disease (CHD), total and ischaemic stroke and total mortality in middle-aged and elderly men and women. The epidemiological evidence suggests a J- or U-shaped relationship between alcohol and CHD. However, the apparent benefits of moderate drinking on CHD mortality are offset at higher drinking levels by increasing risk of death from other types of heart diseases (cardiomyopathy, arrhythmia etc.), neurological disorders, cancer, liver cirrhosis, and traffic accidents. The plausible mechanisms for the putative cardioprotective effects include increased levels of high-density lipoprotein cholesterol, decreased levels of low-density lipoprotein cholesterol, prevention of clot formation, reduction in platelet aggregation, and lowering of plasma apolipoprotein(a) concentration. Thus, alcohol reduces the risk of coronary vascular diseases both by inhibiting the formation of atheroma and decreasing the rate of blood coagulation.
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INTRODUCTION
Drinking excessive amounts of alcohol regularly for years is toxic to almost every tissue of the body. Many of the toxic effects of alcohol are due to disturbances of a wide variety of metabolic functions and organ damage. Long-term alcohol use increases the risk of liver disease, heart disease, peptic ulcers, certain types of cancers, complicated pregnancies, birth defects, and brain damage (Agarwal and Seitz, 2001). Heavy or binge drinking may even result in respiratory depression and death. Alcohol use can also cause mood changes and loss of inhibitions as well as violent or self-destructive behaviour.
On the other hand, epidemiological and clinical evidence shows that light–moderate drinking is associated with a reduced risk of coronary heart disease (CHD), total and ischaemic stroke and total mortality in middle-aged and elderly men and women (Doll, 1997; Grobbee et al., 1999; Rimm et al., 1999; Klatsky, 2001; Rotondo et al., 2001; van Tol and Hendriks, 2001). The evidence suggests a J- or U-shaped relationship between alcohol and CHD. This article reviews the epidemiological evidence for alcohol’s putative cardioprotective effects and discusses the plausible underlying biological mechanisms.
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ALCOHOL AND CHD MORBIDITY AND MORTALITY
Risk of death from all causes has been found to be significantly lower among men who drink moderately, compared to abstainers. Several epidemiological investigations have shown that a low to moderate level of alcohol intake has a definitive protective role against CHD and stroke. Such conclusions have been based upon epidemiological studies on the risks for heart disease, coronary artery disease and death in individuals with low or moderate alcohol intake, when compared with the corresponding risks in persons who do not consume alcohol at all (Rimm et al., 1999; Corrao et al., 2000; Meister et al., 2000; Agarwal and Srivastava, 2001). The dose–response curve usually is found to be J- or U-shaped, i.e. the risk is higher when alcohol consumption is high, lower when alcohol consumption is low or moderate, and tends to go up again in individuals not consuming any alcohol (Andreasson, 1998; San Jose et al., 1999). Level of alcohol consumption that has been associated with lower risk for CHD ranges as widely as from 1 drink daily to ∼3 drinks per day (Rimm et al., 1999; Gronbaek et al., 1999). When all cohort data of the above-mentioned studies are combined, there appears to be a decline in the risk for myocardial infarction at doses up to 1 drink per day, with little further change in risk associated with increased alcohol intake (Rimm et al., 1999). Berger et al. (1999) found that light–moderate alcohol consumption reduced the overall risk of stroke and risk of ischaemic stroke in men. The benefit was apparent with as little as 1 drink per week. Greater consumption up to 1 drink per day did not increase the observed benefit. In a Finnish study, Makela et al. (1997) observed that, among men aged 30–69 years, the beneficial effects of light– moderate alcohol consumption ‘prevented’ some 400 CHD deaths each year, which corresponds to 12–14% of the observed CHD deaths. Rimm et al. (1999) in their meta-analysis concluded that alcohol intake (30 g of alcohol per day) is causally related to 24.7% reduction in risk of CHD through changes in lipids, lipoproteins and fibrinogen.
ALCOHOL DRINKING PATTERN AND THE RISK OF CHD
The strongest inverse correlation between moderate drinking and CHD has been shown among both men and women who consumed 1–2 drinks per day on 5–6 days per week (McElduff and Dobson, 1997). Rimm et al. (1999) observed that men who reported drinking, on average, on 3–4 days per week had a relative risk of 0.66, compared with men who drank less than 1 day a week. Alcohol drinking pattern may also have a profound influence on the blood pressure effects of alcohol. Intervention studies in men have shown acute increases in blood pressure in men who drink predominantly at weekends, compared to longer-term pressor effects in regular daily drinkers (Marques-Vidal et al., 2001). The binge-drinking pattern observed among Northern Irish drinkers leads to physiologically disadvantageous consequences regarding blood pressure levels, whereas no such fluctuations in blood pressure levels were found for regular consumption noted among French drinkers (Puddey et al., 1999). Hence, exploration of any protective association of alcohol against CHD needs to consider carefully the implications of pattern of drinking for the relationship.
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ALCOHOL AND THE FRENCH PARADOX
The low CHD mortality rate observed in Mediterranean populations in association with red wine consumption and a high saturated fat intake has given rise to what is now popularly termed the ‘French paradox’. This phenomenon refers to people residing in certain parts of France and other Mediterranean countries where red wine is customarily consumed during meals. These populations show a low CHD mortality, despite living a lifestyle considered to have comparably high CHD risks, like those in the USA and many other developed countries (Criqi, 2001). This relationship has been observed in both men and women and in different age groups. Many investigators have claimed that wine is the significant factor explaining the French paradox (see below).