National Institute on Alcohol Abuse and Alcoholism (NIAAA) program staff have completed an extensive review of current scientific knowledge regarding the health risks and potential benefits of moderate alcohol consumption. Their findings – with a focus on cardiovascular disease, breast cancer, obesity, birth defects, breastfeeding, and aging – will be published in the June issue of Alcoholism: Clinical & Experimental Research, and will also serve as the National Institutes of Health’s formal position paper on the issue.
"Our reviewers have found that the lowest total all-cause mortality occurs at the level of one to two drinks per day," said T.K. Li, NIAAA director. "The state of current science does not advocate drinking; these findings simply point out what the research says about the health-related effects of moderate drinking. In short, except for those individuals at identifiable risk, consuming two drinks per day for men and one drink per day for women is unlikely to cause problems."
Some of the key findings are:
- Moderate levels of alcohol consumption do not increase risk for heart failure/myocardial infarction or ischemic stroke and may, in fact, provide protective effects in terms of coronary heart disease (CHD) among older individuals and those otherwise at risk for heart disease.
However, cautioned Lorraine Gunzerath, NIAAA Branch Chief for Strategic Research Planning and corresponding author for the study, more research is needed on the lifetime accumulation of CHD benefits and/or risks.
"The effects of 20 to 30 years of moderate drinking begun at age 45 may not be comparable to the effects of 50 to 60 years of moderate drinking begun at age 22," she said. For example, the medical consequences of chronic alcoholism – such as cirrhosis and cardiac myopathy – appear to be related to lifetime consumption levels. Although these diseases are normally associated with excessive rather than moderate consumption, it remains unclear if the 25-year-old moderate drinker might lower his risk of heart disease by age 65, only to succumb to cirrhosis by that age instead."
- The average alcohol consumption of one drink per day appears to be associated with a 10-percent increase in the risk of breast cancer in the overall population; the risk may be higher among women with a family history of breast cancer as well as those on hormone replacement therapy.
"The controversy surrounding the issue of alcohol and breast cancer takes two forms," said Gunzerath. "First, there is the ‘absolute’ issue of whether alcohol increases the risk of breast cancer in women without a family history or other acknowledged risk factors for the disease. There are many behavioral, biological, and environmental factors that may contribute to the risk calculation, such as smoking, weight, nutrition and exercise, as well as factors that determine ‘lifetime’ levels of endogenous estrogen, such as age at menstruation and at menopause, number of pregnancies, and age at first pregnancy. However, there have been few, if any, studies that have managed to separate out the effects of alcohol from other risk factors. One exception is the finding of an increased risk of breast cancer when alcohol is combined with postmenopausal use of estrogen replacement (ER) – an increase not found in moderate-drinking women who do not use ER."
The second issue relates to what Gunzerath calls "offsetting" risks. For example, the risk of breast cancer by age 80 increases from approximately nine percent for nondrinkers to approximately 10 percent for those who regularly consume two drinks per day. When this increase is applied across 150 million American women, it means 1.5 million more may get the disease. But for any individual woman, the one-percent increase in risk is relatively small. "A women may want to weigh this lifetime increase in risk against a potential reduction of heart-disease risk over the same time span, especially as heart disease is the number one killer of women over age 45," she said.
- The relationship between moderate alcohol consumption and weight gain, body mass index, and/or obesity remains unclear; however, moderate consumption does appear to be associated with a reduced risk of diabetes and metabolic syndrome (which often co-exist with or develop from obesity).
"Some of the conflicting findings on the relationship between alcohol consumption and obesity may be due to studies that consider limited timeframes, such as a period of several weeks or months, rather than lifetime habits," said Gunzerath. "In addition, studies have not necessarily used comparable definitions of ‘moderate’ drinking or considered the same confounding factors such as food intake volume or composition, exercise, or medication use," she said.
Normally, when a person eats, insulin is released to process the food. Insulin helps sugar (or glucose) get out of the blood and into muscle cells that use it for energy. When an individual is "insulin resistant" or has poor insulin sensitivity, blood sugar levels become elevated, which can increase the risk for developing diabetes. "Our review has found that consuming moderate amounts of alcohol may help the body better utilize insulin," said Gunzerath.
- Low-to-moderate drinking during pregnancy does not appear to be associated with an increased risk of fetal physical malformations, but may have behavioral or neurocognitive consequences. There is some evidence for a dose-response association but, so far, there is no "threshold" below which consumption may be safe. Heavy drinking during pregnancy is clearly unsafe.
"Heavy drinking during pregnancy can increase the chances of the child being born with the physical, mental, behavioral, and/or learning disabilities known as Fetal Alcohol Spectrum Disorders (FASD)," said Gunzerath. "The most severe of these, Fetal Alcohol Syndrome, includes a distinct pattern of facial abnormalities, growth deficiency, central nervous system dysfunction, and some level of mental retardation. Less severe manifestations include difficulties with memory, attention, judgment, learning, and behavior. Prenatal alcohol exposure – even at the highest levels – does not always result in FASD; however there is no ‘known’ safe level of consumption. Women who have consumed alcohol during pregnancy – for example, before realizing that they are pregnant – should discuss these issues with their health-care provider."
- Given that alcohol will dissipate from breast milk in time, the safest course is to allow sufficient time between drinking and nursing so that the mother can fully metabolize the alcohol. In addition, and contrary to folklore, alcohol does not aid lactation and may actually decrease it for several hours following consumption.
"A reduction in infant consumption, apparently due to a decrease in the mother’s milk yield, directly contradicts folklore/anecdotal claims of alcohol aiding in lactation," said Gunzerath. "Furthermore, the presumption that the effects of maternal alcohol consumption passed through breast milk may relax the infant and thus promote sleep has not been demonstrated. In fact, short-term alterations that are consistent with alcohol’s effects on adults have been found in infants’ sleep-wake patterning. However, deficits in both consumption and sleep are short-lived, in that the infant later ‘makes up the difference’ or compensates, provided that the mother’s alcohol consumption is not maintained."
Infants may be able to link memories with the sensory input experienced during nursing, which may include the flavor of alcohol in their mothers’ milk. "One study found that infants who had more exposure to alcohol behaved differently – that is, were more interested – in the presence of an alcohol-scented toy versus a neutral toy than did infants with less alcohol exposure," said Gunzerath.
- Although elderly drinkers reach higher blood alcohol concentrations at lower levels of consumption than younger drinkers, there is no evidence that moderate alcohol consumption causes cognitive impairment as one ages.
"The inconclusive nature of the relationship between moderate alcohol use and Alzheimer’s dementia is likely due in part to the role that genetics plays in Alzheimer’s occurrence," said Gunzerath. "About 25 percent of Alzheimer cases are hereditary; they are caused by mutated genes and tend to cluster in families. Although the remaining 75 percent are classified as sporadic, with no other blood relatives known to be affected, genetics may nonetheless play some role. We do not yet know if alcohol use may increase susceptibility for some genetic combinations and offer a protective effect in others."
Given the complex nature of both Alzheimer’s and macular degeneration (a reduced ability to see fine detail, and a leading cause of vision loss in older Americans), as well as the absence of further findings, Gunzerath suggested that elderly individuals refrain from altering moderate levels of alcohol consumption in an attempt to affect risk.
Gunzerath added that the review findings can be condensed into two key "take-away" messages.
"Drinking patterns are at least as important as total consumption in terms of alcohol’s harms and benefits," she noted. "Low per-occasion consumption occurring regularly – for example, one or two drinks per day, four days a week – generally confers greater benefits and poses less harm than the same total amount consumed all at once. Secondly, the relationship between moderate alcohol consumption and disease outcome is influenced by numerous individual differences – age, sex, genetic susceptibility, lifestyle factors, metabolic rate, etc. Protective and detrimental levels of alcohol consumption cannot be generalized across the population but instead should be determined by an individual in consultation with her or his health-care provider."
Funding for this Addiction Science Made Easy project is provided by the Addiction Technology Transfer Center National Office, under the cooperative agreement from the Center for Substance Abuse Treatment of SAMHSA.
Articles were written based on the following published research:
Gunzerath, L., Faden, V., Zakhari, S., & Warren, K. National institute on alcohol abuse and alcoholism report on moderate drinking. (June 2004). Alcoholism: Clinical & Experimental Research, 28(6) 829-847.