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Health Effects of Alcohol Consumption: Review
Dr Dee Blackhurst and Professor David Marais
The full version of this review appears in the September 2005 edition of the South African Medical Journal.
South African drinkers are among the heaviest consumers of alcoholic beverages in the world, with a consumption of approximately 50 ml ethanol per day per drinker (1), leading to alcohol abuse being one of South Africa's top ten health and social problems. Alcohol abuse is associated with many adverse health effects, for example fetal alcohol syndrome (FAS). The highest incidence of FAS in the world occurs in the Western Cape.
It is generally accepted that moderate, responsible consumption of alcoholic beverages is not harmful, and there is evidence that it may have certain health benefits. Moderate drinking is now generally accepted as the consumption of 10 - 20 g alcohol per day for women and 10 - 35 g for men. Evidence for the possible beneficial effects of alcohol consumption may be derived from both epidemiological and experimental research. In the absence of a controlled interventional study, there should be strong evidence from both types of investigation, and the benefits should exceed the harm, before public health claims can be made for including moderate consumption of alcoholic beverages in daily living. This review provides some background information on alcoholic beverages and describes the potential health benefits of the consumption of alcoholic beverages, with an emphasis on wine.
Studies examining the impact of alcoholic beverages on health report the intake either as units or grammes of alcohol, representing almost pure ethanol, per day. A 'unit' is defined as approximately 10 g ethanol, which is equivalent to 1 drink (100 ml wine, 200 ml beer, 50 ml fortified wine and 25 ml spirits). Sherry and port are 'fortified' by additional alcohol.
Wine essentially consists of water, ethanol, organic acids, aldehydes, ketones, esters as well as many different phenolic compounds. Red wines contain approximately five- to tenfold more phenols than white wines. Approximately half of the total extractable phenols in grapes enter red wine.
The bio-availability of the different phenolic compounds varies widely. After the consumption of 10 - 100 mg of a single phenolic compound, the maximum plasma concentration is more than a thousand times dilute, and urinary excretion varies from 0.3 - 43% of the particular phenol taken. Wine polyphenols may broadly be divided into non-flavonoids and flavonoids, with the latter making up the larger group. Two of the individual chemical structures are depicted in figure 1. Flavonoids may be classified into several major classes which include flavanols and flavonols. Flavanols form the largest class and include catechins. Quercetin is a flavonol.
In 1926, the first finding of a U-shaped association between all-cause deaths and the consumption of alcoholic beverages was reported by Raymond Pearl in a book titled Alcohol and Longevity. Since then, a large number of epidemiological studies have also demonstrated this U- or J-shaped association, indicating that moderate daily alcohol consumption results in a significant reduction in mortality compared with abstinence or excessive consumption. The vast majority of epidemiological studies show benefits with regard to vascular disease, in particular coronary heart disease (CHD). Two large studies showed that the apparent cardioprotective effect seems to be affected by age and that the effect is strongest among the elderly and those with risk factors for cardiovascular disease (CVD) (2,3). Reports indicate a reduction of 30 - 50% in vascular deaths. The 'French Paradox', a sometimes controversial phenomenon described in 1992 by Renaud and de Lorgeril, found a lower rate of mortality from CHD among the French compared with other developed countries, despite similar dietary intakes in these countries. It was suggested that the greater consumption of red wine by the French protected them against heart disease. It has also been suggested however, that the paradox may be due to differences in data collection.
Compared with abstention, moderate consumption of alcohol, particularly wine, is associated with better mental function and memory in subjects greater than 65 years, and higher bone mineral density amongst postmenopausal women. Interestingly, moderate consumption of alcohol has been reported to diminish the incidence of type 2 diabetes mellitus and to reduce cardiovascular disease in established diabetic men and women. Various studies have reported a reduction in the risk for total and ischaemic strokes, but an increased risk of haemorrhagic stroke in regular consumers of alcoholic beverages relative to abstainers or occasional drinkers. The cumulative epidemiological evidence, summarised in Figure 2, shows paradoxical results: heavy drinkers suffer predominantly harmful results while abstainers may fare less well than regular moderate drinkers in the risk for CHD, strokes and total mortality.
While epidemiological studies may associate alcoholic beverage consumption with better health, it is difficult to prove a causal relationship for several reasons. If a randomised interventional study is not undertaken, there may be a selection bias for subjects who drink alcoholic beverages or even a particular kind of alcoholic beverage. Because different diets are often associated with the consumption of different alcoholic beverages, it may be difficult to attribute the benefit to the beverage. Wine consumption, for example, tends to be associated with a higher intake of healthy food such as fruit, vegetables, fish and olive oil. Factors such as gender, age, diet, smoking, economic status, social class, ethnicity and education play a role in population health and may also be confounders in studies of the effects of alcoholic beverages on health. Epidemiological studies should ideally be carried out over a number of years, because diseases against which alcoholic beverages may confer protection, e.g. CVD, develop slowly. Similarly, harmful effects may only be evident in the long term.
Many reports support the proposal that wine has superior effects on health, relative to the other alcoholic beverages (4), but some studies have found benefits with all the alcoholic beverages on the risk of coronary heart disease and mortality, and other studies failed to demonstrate an effect. The interpretation of reported differences in health benefits of the different alcoholic beverages should be viewed with caution until confounding effects have been clearly ruled out or mechanistic differences are evident.
Data for the effects of moderate alcohol consumption on cancer are inconclusive, with some studies finding an increased risk of cancers of the liver and upper digestive tract, particularly after consumption of beer and spirits, and an increased risk of breast cancer. Other studies found no increased risk of breast, lung, bladder, prostate or ovarian cancers. A number of epidemiological studies indicated an association between alcohol consumption and increased blood pressure, with a threshold dose of 20 - 30 g ethanol per day, above which the pressure unequivocally increases. The acute and chronic effects of excessive consumption of alcohol on social and physical well-being are well-established.
The experimental evidence
Some studies have reported that it is the ethanol that is responsible for the beneficial health effects rather than the other characteristics of the beverage. This is contradicted by studies which demonstrate that the benefits of wine in particular are derived from the non-alcoholic fraction, suggesting that phenols and/or antioxidant activity confer(s) the benefits. Red wine is often reported as having greater antioxidant activity that can be attributed to its higher phenolic content. However, some white wines that have an increased extraction of grape skin polyphenols, have similar antioxidant characteristics to red wines (5). Ethanol-free red wine extracts have been shown to improve post-ischaemic ventricular function as well as to inhibit ex vivo low density lipoprotein (LDL) oxidation. Some studies suggest that both the polyphenols and the alcohol in red wine reduce the incidence of CHD, but by different mechanisms.
High density lipoprotein (HDL) concentrations are significantly and consistently increased in humans after consumption of alcoholic beverages, particularly red wine (6,7). Platelet aggregation promotes the development of atherosclerosis by the formation of blood clots in arteries. A number of studies demonstrate the anti-aggregating effect on platelets by alcohol, red wine and de-alcoholised red wine. Red wine has bactericidal effects against Helicobacter pylori (associated with gastric cancer) and Chlamydia pneumoniae (which is associated with the development of CHD). Consumption of beer and spirits, though not as effective, also has this effect (8).
Conclusions
Atherosclerosis is the dominant cause of morbidity and mortality in developed countries and is rapidly rising in developing countries (9). It is preferable to combat atherosclerosis by preventive strategies involving lifestyle, including a balanced diet, exercise, maintaining an ideal body weight, and abstaining from smoking. Epidemiological evidence suggests that moderate consumption (1 - 3 drinks per day) of alcoholic beverages, particularly red wine, is associated with an overall improvement in health, especially cardiovascular health. Although the epidemiological information is attractive, it is not adequately compelling for the deliberate inclusion of alcoholic beverages in the lifestyle of westernised subjects. Nevertheless, moderate consumption of affordable alcoholic beverages in otherwise healthy subjects will not increase the risk for disease, especially if it accompanies a healthy lifestyle. The consumption of larger amounts of alcohol is clearly ill-advised. The consumption of alcoholic beverages during pregnancy clearly places the fetus at risk for developmental abnormalities.
Although several lines of experimental evidence suggest mechanisms by which alcoholic beverages may reduce the risk of vascular disease, there is inadequate understanding of atherogenesis to know whether these mechanisms apply to any given individual at risk and whether the alcoholic beverage will be of direct benefit. Scientific research will hopefully elucidate these mechanisms for specific intervention. The research into the health benefits of alcoholic beverages may thus yield new avenues of treatment for atherosclerosis in the future.
Acknowledgement:
Further reading
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FIG 1: Chemical structures of a) (+)-catechin and b) quercetin.
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