Book 1 Reading and Speaking (1108795), страница 18
Текст из файла (страница 18)
Millions whoremember Prohibition, when all alcoholic beverages were illegal, now witness a constant stream of advertisementsfrom producers of alcoholic beverages encouraging people to drink. Despite alcohol’s popularity today, however,many still consider abstinence a virtue. Certainly, heavy drinking and alcoholism deserve deep concern for theterrible toll they take on alcohol abusers and society in general. But worry about the dangers of abuse often leadsto emotional denials that alcohol could have any medical benefits. Such denials ignore a growing body of evidenceindicating that moderate alcohol intake wards off certain cardiovascular conditions, most notably heart attacks andischemic strokes (those caused by blocked blood vessels). A few studies even show protection against dementia,which can be related to cardiovascular problems.The Alcohol EffectA discussion of moderate drinking requires a working definition of “moderate.” Simple definitions of light,moderate or heavy are somewhat arbitrary, but a consensus in the medical literature puts the upper limit formoderate drinking at two standard-size drinks a day.
Studies show that drinking above that level can be harmful tooverall health, although sex, age and other factors lower and raise the boundary for individuals.The main medical benefit of reasonable alcohol use seems to be a lowering of the risk for coronary heartdisease (CHD), which results from the buildup of atherosclerosis (fatty plaque) in the arteries.
Atherosclerosisrestricts blood flow to the heart and can promote the formation of vessel-blocking clots. It can thereby cause angina(chest discomfort resulting from low oxygen levels in the heart muscles), heart attack (the death of heart tissue thatoccurs when a blood clot or narrowing of the arteries prevents blood from reaching the heart) and death, oftenwithout warning. The condition usually starts at a young age but takes decades to blossom into overt CHD. Themost common form of heart disease in developed countries, CHD causes about 60 percent of deaths fromcardiovascular ills and about 25 percent of all deaths in those nations.Pathologists uncovered the first clues to the value of alcohol in the early 1900s, noting that the large arteriesof people who died of alcoholic liver cirrhosis seemed remarkably “clean”—that is, free of atherosclerosis.
Oneexplanatory hypothesis assumed that alcohol was a nebulous solvent, essentially dissolving the buildup in thearteries; another explanation held that heavier drinkers died before their atherosclerosis had a chance to develop.Neither idea truly explained drinkers’ unblocked arteries, however.43A more telling hint emerged in the late 1960s, when Gary D. Friedman of the Kaiser Permanente MedicalCenter in Oakland, Calif., came up with a novel idea: use computers to unearth unknown predictors of heartattacks.
The power of computing could first identify healthy people who had risk factors similar to heart attackvictims. Such factors include cigarette smoking, high blood pressure, diabetes, elevated levels of low-densitylipoprotein (LDL, or “bad”) cholesterol, low levels of high-density-lipoprotein (HDL, or “good”) cholesterol, malegender, and a family history of CHD. Friedman then searched for predictors of heart attacks by comparing thepatients and the newly found controls in hundreds of ways—for example, their exercise and dietary habits and theirrespective levels of various blood compounds.
The computers spit out a surprising discovery: abstinence fromalcohol was associated with a higher risk of heart attack.Since then, dozens of investigations in men and women of several racial groups in various countries havecorrelated previous alcohol use with current health.
These studies have firmly established that nondrinkers developboth fatal and nonfatal CHD more often than do light to moderate drinkers. In addition, in 2000 Giovanni Corrao ofthe University of Milan-Bicocca in Italy, Kari Poikolainen of the Järvenpää Addiction Hospital in Finland and theircolleagues combined the results of 28 previously published investigations on the relation between alcohol intakeand CHD. In this meta-analysis, they found that the risk of developing CHD went down as the amount of alcoholconsumed daily went up from zero to 25 grams.
At 25 grams—the amount of alcohol in about two standarddrinks—an individual’s risk of a major CHD event, either heart attack or death—was 20 percent lower than it wasfor someone who did not drink at all. New data about alcohol protecting against death from CHD are even moreimpressive. At a meeting of the American Heart Association last November, it was announced that those who hadone or two alcoholic drinks a day had a 32 percent lower risk of dying from CHD than abstainers did.The possible mechanisms by which alcohol has such an apparently profound effect on cardiovascular healthprimarily involve cholesterol levels and blood clotting. Blood lipids play a central role in CHD. Numerous studiesshow that moderate drinkers have 10 to 20 percent higher levels of heart-protecting HDL cholesterol. And peoplewith higher HDL levels, also known to be increased by exercise and some medications, have a lower risk of CHD.That lower risk stems from HDL’s ability to usher LDL cholesterol back to the liver for recycling or elimination,among other effects.
Alcohol seems to have a greater influence on a different HDL subspecies (HDL3) than on thetype increased by exercise (HDL2), although both types are protective. (The biochemical pathways in the liver thatcould account for alcohol’s ability to raise HDL levels remain incompletely known; it is thought that alcohol probablyaffects liver enzymes involved in the production of HDL.) Three separate analyses aimed at determining specificcontributions of alcohol all suggest that the higher HDL levels of drinkers are responsible for about half of thelowered CHD risk.Alcohol may also disrupt the complex biochemical cascade behind blood clotting, which can cause heartattacks when it occurs inappropriately, such as over atherosclerotic regions in coronary arteries.
Blood platelets,cellular components of clots, may become less “sticky” in the presence of alcohol and therefore less prone toclumping, although data on this question remain ambiguous. Overall, alcohol’s anticlotting capacity is not as wellestablished as its HDL effect, and some effects, such as platelet clumping, may be reversed by heavy or bingedrinking. In addition, studies have shown a beneficial effect on CHD risk in people who have far fewer than twodrinks a day—say, three or four drinks a week. Anticlotting could be a major factor in the protection accorded byalcohol in these small amounts, which seem insufficient to affect HDL levels greatly.Before accepting alcohol’s benefits, an epidemiologist attempts to locate hidden factors possibly at work. Forinstance, could lifelong abstainers differ from drinkers in psychological traits, dietary habits, physical exercise habitsor other ways that might account for their higher CHD risk without the need to invoke the absence of alcohol? Weresuch traits to explain away alcohol’s apparent protection, they would need to be present in both sexes, variouscountries and several racial groups.
Considering that no such traits have been identified, the simpler and moreplausible explanation is that light to moderate alcohol drinking does indeed enhance cardiovascular health.In fact, the available evidence satisfies most standard epidemiological criteria for establishing a causalrelation. The numerous studies examining light and moderate alcohol intake and health reach consistentconclusions. The positives associated with alcohol can be attributed to biologically plausible mechanisms.
Alcoholoffers specific enhancement of cardiovascular health, not general protection against all illness. And alcohol’s effectcan be identified independent of known “confounders,” other alcohol related factors that could be responsible for asubject’s cardiovascular condition.Because heavy drinking is not more protective than lighter drinking, this absence of a clear dose-responserelation is also a weakness. Nevertheless, the collected data make a strong case for the cardiac benefits ofcontrolled drinking.To Drink or Not to DrinkMost people drink for reasons other than alcohol’s health benefits, and many of them are already usingalcohol in amounts that appear to promote cardiovascular health.
But the accumulated research on alcohol’spositive effects presents a challenge to physicians. On the one hand, mild to moderate drinking seems better forheart health than abstinence for select people. On the other hand, heavy drinking is clearly dangerous. It cancontribute to noncardiovascular conditions such as liver cirrhosis, pancreatitis, certain cancers and degenerativeneurological disorders, and it plays a part in great numbers of accidents, homicides and suicides, as well as in fetalalcohol syndrome. (No conclusive evidence links light to moderate drinking to any of these problems.)Heavy drinking also contributes to cardiovascular disorders.
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