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ScienceWeek
MEDICAL BIOLOGY: ALCOHOL AND COGNITIVE FUNCTION IN WOMEN
The following points are made by M.J. Stampfer et al (New Engl. J. Med. 2005 352:245):
1) Habitual excess alcohol intake impairs the brain,[1] but the effect of moderate consumption is unclear. A cognitive benefit from moderate alcohol intake is plausible, given the strong link between moderate alcohol intake and the decreased risk of cardiovascular disease[2,3]. Cognitive impairment and cardiovascular disease share common risk factors.[4] In addition, Ruitenberg et al[5] reported that moderate alcohol consumption was related to a decreased risk of both vascular and nonvascular dementia and proposed that moderate alcohol consumption may increase the release of brain acetylcholine. Most studies, but not all, have tended to show that moderate drinkers do better on cognitive tests than nondrinkers. However, few studies have had samples that were large enough to yield statistically significant results or to assess long-term stable patterns of alcohol intake and very early signs of cognitive decline. Also, many studies have been limited by inadequate control for confounding, and none have examined specific alcoholic beverages.
2) The Nurses' Health Study began in 1976, when 121,700 female registered nurses, 30 to 55 years of age, completed a mailed questionnaire about their lifestyle and health. Every two years, the authors mailed follow-up questionnaires, and in 1980 they added a food-frequency questionnaire. Starting in 1995, the authors identified participants in the Nurses' Health Study who were 70 years of age or older for a study of cognitive function. Eligible women were community-dwelling participants without a diagnosis of stroke. Of the 21,202 women contacted, 93 percent completed the telephone cognitive interview, with response rates varying by no more than 2 percent across categories of alcohol intake. With the exclusion of the 3 percent of women who died after the baseline cognitive assessment, the authors repeated the telephone assessments of cognitive function after an average of 1.8 years (range, 1.3 to 5.5) in 93 percent of the women; 7 percent declined or were lost to follow-up. All aspects of the study were approved by the human research committee at Brigham and Women's Hospital. For the questionnaire information, the return of the completed questionnaire was considered to imply informed consent. For the telephone interview, the authors obtained oral consent. For the genetic substudy, the authors obtained written informed consent.
3) The authors report that older women who consumed up to one drink per day had consistently better cognitive performance than nondrinkers. Overall, as compared with nondrinkers, women who drank 1.0 to 14.9 g of alcohol per day had a decrease in the risk of cognitive impairment of approximately 20 percent. Moreover, moderate drinkers were less likely to have a substantial decline in cognitive function over a two-year period. The authors found similar inverse associations for all types of alcoholic beverages.
4) The authors point out their study had several limitations. They could not assess the effect of high levels of alcohol intake, since there were few heavy drinkers in their cohort. Also, cognitive decline was assessed only over a two-year interval; thus, the association between alcohol consumption and longer-term cognitive decline could not be evaluated. Information on alcohol consumption was self-reported, perhaps leading to some misclassification. However, the assessment of alcohol intake was validated on the basis of dietary records and levels of biochemical markers and has been used to predict several disease outcomes in this cohort.
5) The authors conclude their data suggest that in women up to one drink per day does not impair cognitive function and may actually decrease the risk of cognitive decline.
References (abridged):
1. Chick JD, Smith MA, Engleman HM, et al. Magnetic resonance imaging of the brain in alcoholics: cerebral atrophy, lifetime alcohol consumption, and cognitive deficits. Alcohol Clin Exp Res 1989;13:512-518
2. Rimm EB, Stampfer MJ. Alcohol abstinence: a risk factor for coronary heart disease. Heart Disease Updates 2000;2:1-9
3. Rimm EB, Williams P, Fosher K, Criqui M, Stampfer MJ. Moderate alcohol intake and lower risk of coronary heart disease: meta-analysis of effects on lipids and haemostatic factors. BMJ 1999;319:1523-1528
4. Breteler MM, van Swieten JC, Bots ML, et al. Cerebral white matter lesions, vascular risk factors, and cognitive function in a population-based study: the Rotterdam Study. Neurology 1994;44:1246-1252
5. Ruitenberg A, van Swieten JC, Witteman JC, et al. Alcohol consumption and risk of dementia: the Rotterdam Study. Lancet 2002;359:281-286
New Engl. J. Med. http://www.nejm.org
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Related Material:
ALCOHOL AND BREAST CANCER
The following points are made by K.W. Singletary and S.M. Gapstur (J. Am. Med. Assoc. 2001 286:2143):
1) The association of alcohol consumption with increased risk for breast cancer has been a consistent finding in a majority of epidemiologic studies during the past two decades. The authors summarize information on this association from human and animal investigations, with particular reference to epidemiologic data published since 1995.
2) Increased estrogen and androgen levels in women consuming alcohol appear to be important mechanisms underlying the association. Other plausible mechanisms include enhanced mammary gland susceptibility to carcinogenesis, increased mammary carcinogen DNA damage, and greater metastatic potential of breast cancer cells, processes for which the magnitude likely depends on the amount of alcohol consumed.
3) Susceptibility to the breast cancer-enhancing effect of alcohol may also be affected by other dietary factors (such as low folate intake), life-style habits (such as use of hormone replacement therapy), or biological characteristics (such as tumor hormone receptor status).
4) Additional progress in understanding the enhancing effect of alcohol on breast cancer will depend on a better understanding of the interactions between alcohol and other risk factors and on additional insights into the multiple biological mechanisms involved. There is apparently firm evidence that in general women who consume alcohol, even at the level of 1 drink per day, have higher blood levels of estrogen (estradiol) than women who do not drink. The authors recommend that in general women who do not drink should not start, and those who do drink should do so in moderation, which is generally recognized to be approximately 1 drink per day.
J. Am. Med. Assoc. http://www.jama.com
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Related Material:
ON ALCOHOL IN THE WESTERN WORLD
Notes by ScienceWeek:
The consumption of alcohol (ethanol) is recognized as a major and potentially preventable health problem. In general, a linear correlation exists between the intensity of alcohol abuse in terms of duration and dose and the development of a wide spectrum of pathologies, especially liver disease. As little as 200 ml wine or 60 ml whiskey in women, 1200 ml of 5% beer in men, when consumed on a daily basis over years, can produce liver injury. The mechanisms by which alcohol damages the liver are still unclear, but the damage is undisputed. Given all of the above, however, it is a fact that alcohol consumption has been an important aspect of Western civilization for thousands of years, and has probably existed for at least 10,000 years in various communities.
The following points are made by Bert L. Vallee (Scientific American 1998 June):
1) Ethanol (ethyl alcohol) is a multifaceted entity: it may be social lubricant, sophisticated dining companion, cardiovascular health benefactor, or agent of destruction.
2) For most of the past 10,000 years in the Western world, alcoholic beverages may have been the most popular and common daily drinks, indispensable sources of fluids and calories in a world of contaminated and dangerous water supplies.
3) The experience of the East differed greatly. For at least the past 2000 years, the practice of boiling water, usually for tea, has created a potable supply of non-alcoholic beverages. In addition, genetics plays an important role in making Asia avoid alcohol: approximately half of all Asian people metabolize alcohol differently than non-Asians, making the experience of drinking alcohol quite unpleasant [see background material below].
4) Beer and wine became staples in Western societies and remained there until the end of the last century. Indeed, throughout Western history, the normal state of mind may have been one of inebriation.
5) Although yeasts produce alcohol, they can tolerate concentrations of only about 16 percent, so that fermented beverages had a natural maximum proof. Distillation, introduced by the Arabs about 700 A.D., circumvented the fermentation limit by taking advantage of alcohol's boiling point being lower than water (78 vs. 100 degrees centigrade) to boil off and then condense the alcohol from fermented mixtures.
6) Presently, alcohol contributes to 100,000 deaths in the US each year, making it the 3rd leading cause of preventable mortality.
7) Each year, approximately 12,000 children of drinking mothers are born with the physical signs and intellectual deficits associated with full-blown fetal alcohol syndrome, and thousands more suffer lesser effects.
8) Alcoholism, in historical terms, has only just been understood and accepted as a disease, and we are still coping with the historically recent arrival of concentrated alcohol. The author concludes: "Alcohol today is a substance primarily of relaxation, celebration and, tragically, mass destruction. To consider it as having been a primary agent for the development of an entire culture [Western civilization] may be jolting, even offensive to some. Any good physician, however, takes a history before attempting a cure."
Scientific American http://www.sciam.com
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Notes by ScienceWeek:
Ethanol is readily absorbed from the gastrointestinal tract, and more than 90 percent is metabolized by the liver through oxidative mechanism involving mainly the enzyme alcohol dehydrogenase and certain other enzymes. Alcohol cannot be stored and all of it is metabolized. Alcohol dehydrogenase oxidizes alcohol to acetaldehyde. Apparently, approximately 85 percent of the Japanese population has an atypical alcohol dehydrogenase that operates about 5 times faster than the same enzyme does in non-Japanese. Other Asian groups may exhibit the same phenomenon. Consumption of alcohol by such persons leads to the accumulation of acetaldehyde, resulting in extensive vasodilation, facial flushing, and compensatory tachycardia (rapid heartbeat greater than 100 per minute).
ScienceWeek http://scienceweek.com
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