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Excerpt from Healthy Women, Healthy Lives

by Susan E. Hankinson, R.N., Sc.D., Graham A. Colditz, M.D., JoAnn E. Manson, M.D., and Frank E. Speizer, M.D.

Chapter 20: Alcohol

BACKGROUND

Alcohol has been used by humans for at least 4,000 years and occupies a unique place in most societies. It is often a sacred part of religious ceremony and is a focal point of many social celebrations and everyday interactions. Yet it is an addictive drug that, when abused, has potentially severe short-term and long-term health consequences. These consequences depend largely on how much a person drinks-and on how much he/she can tolerate physiologically.

Alcohol tends to be less well tolerated by women's bodies than men's, and thus the effects can be more dramatic among women. A central nervous system depressant, alcohol acts like a sedative or tranquilizer, slowing down motor coordination and reaction time. It also impairs judgment, memory, reasoning, and self-control. Drink for drink, women accumulate more alcohol in their bloodstream than men and so experience these effects much more rapidly. This is due to several physiologic differences between men and women. First, in order for alcohol to be moved out of the bloodstream, it must be neutralized by a certain enzyme in the stomach. Women inherently have lower levels of this enzyme than men. Second, women tend to have a higher proportion of body fat than men, and body fat does not absorb alcohol; it allows alcohol to accumulate in the bloodstream. Finally, despite having more body fat, women tend to have smaller bodies than men. As a result, they have less blood circulating in their bodies, so that the ratio of alcohol to blood rises much more rapidly than it does in men.

The other factor obviously influencing the health consequences of alcohol is how much is consumed. A committee of the Institute of Medicine has defined three levels of alcohol intake based on their health consequences: low, moderate, and heavy. For women, low alcohol intake means drinking less than half a drink a day, with a drink defined as a 12-ounce bottle of beer, a 5-ounce glass of wine, or a 1.5-ounce shot of 80-proof liquor. This is about what the average American woman drinks (that is, two to three drinks a week) and is still considered a relatively safe amount. Moderate drinking is the next step up and involves having up to two drinks a day. Though considered safe in the short term, moderate drinking comes with both risks and benefits in the long term. Heavy drinking, on the other hand, has no benefits. It can lead to cirrhosis, alcoholism, accidents, violence, and a number of different cancers. In this chapter, we examine the risks and benefits of moderate drinking, where, unlike low and heavy intake, the line is not always clear in terms of safe versus unsafe.

The Benefits of Moderate Alcohol Consumption

Lower Risk of Coronary Heart Disease

Thanks to extensive media coverage, most women now recognize that moderate alcohol consumption can lower the risk of coronary heart disease. Although red wine was initially thought to be the most beneficial type of alcohol, it is now apparent that beer, white wine, and liquor also offer protection. In the Nurses' Health Study, we found that drinking one drink a day-be it a glass of wine, bottle of beer, or shot of liquor-cut women's risk of coronary heart disease by about half (see Figure 20-1). Similar results have been reported in numerous other studies.

One of the questions that remains about this relationship is whether women can receive the same benefit by drinking two drinks on three days of the week as by drinking one drink on each day of the week. Few studies have looked at this, but those that have have suggested that the answer is no. In one large study, researchers looked at the number of drinks women consumed per day and the number of days they drank per week. The lowest risk was seen among women who drank one to two drinks per day on five to six days per week. Those who averaged the same number of drinks per week but consumed them on fewer days had either less benefit or none at all.

The reason for this is that the effects of alcohol on the cardiovascular system are thought to be only temporary. For example, alcohol may increase the level of "good cholesterol" in the blood and lower the level of a blood-clotting substance, but only for about twenty-four hours. By drinking a small amount of alcohol each day, a woman may keep these substances in the blood at the optimal level for protection against heart disease.

Lower Risk of Ischemic Stroke

Given that ischemic stroke is similar in nature to coronary heart disease (both being caused by clogged blood vessels), it is not surprising that alcohol has the same effect on ischemic stroke that it does on heart disease. When consumed in moderate amounts, alcohol can substantially reduce the risk of both conditions. In the Nurses' Health Study, we found that the risk of ischemic stroke was about 50 percent lower among women who drank one drink a day compared to those who did not drink at all (see Figure 20-2). These results have been replicated in many other large studies.

The Risks of Moderate Alcohol Consumption

Increased Risk of Breast Cancer

Alcohol is one of the most consistent dietary factors related to the risk of breast cancer. More than twenty-five studies have shown that it increases risk, most likely by raising the level of estrogen in the bloodstream or making the breast more vulnerable to carcinogens.

In the Nurses' Health Study, we found that the type of alcohol consumed was not as important as the amount consumed. Women who drank half a drink a day-be it beer, wine, or liquor-had a slightly elevated risk of breast cancer, while those who drank a whole drink a day had an even higher risk. When researchers combined our data with those from other large studies, they found similar results: a woman's risk of breast cancer rose by about 10 percent for every additional drink she consumed per day. In other words, a woman who averaged two drinks a day had a 10 percent greater chance of developing breast cancer than a woman who averaged one drink a day. This was true regardless of the type of alcohol consumed.

Because breast tissue may be particularly vulnerable during adolescence and early adulthood, researchers have speculated that drinking alcohol during these time periods might be more harmful than drinking alcohol later in life. To date, studies on this topic have been inconsistent.

Increased Risk of Hip Fracture

Hip fractures become increasingly common as women age. Prior to menopause, the body produces enough estrogen to keep bones healthy and strong. However, after menopause, estrogen levels drop, and bones can become brittle and vulnerable to fracture. About 90 percent of all hip fractures occur in those over the age of sixty-five, and most are the result of a bad fall.

Although alcohol increases estrogen levels in postmenopausal women, and moderate alcohol consumption has been linked to higher bone mass, it is more likely that alcohol actually leads to fractures. Drinking alcohol, even in moderate amounts, can make a person less steady and increase the likelihood that they will fall and injure themselves. In the Nurses' Health Study, we found that women who consumed about a drink a day were twice as likely to fracture their hips as women who did not drink at all. Similar results have been reported in several other studies, including the Framingham Study.

Probable Increased Risk of Colon Cancer

Only a handful of long-term studies have examined the relationship between moderate alcohol consumption and the risk of colon cancer. To date, results have been inconsistent. Several studies have shown that alcohol does not alter colon cancer risk, while others have demonstrated a modest increase in risk. Overall, the epidemiologic evidence suggests that alcohol probably does increase the risk of colon cancer. This may be because alcohol lowers the level of folate in the body, which may in turn influence the risk of colon cancer.

Probable Increased Risk of Hemorrhagic Stroke

Hemorrhagic stroke is much less common than ischemic stroke but tends to be more severe. It occurs when a small blood vessel in the brain ruptures, causing bleeding (hemorrhaging) into or around the brain. Although every stroke is serious, brain hemorrhages are often devastating because they can affect younger people and are more likely to cause death.

It has been suggested but not confirmed that moderate alcohol consumption might increase the risk of hemorrhagic stroke. In the Nurses' Health Study, we found a doubling of risk among women who drank even small amounts of alcohol each day. However, few studies have confirmed these results.

If alcohol does in fact have an effect on the risk of hemorrhagic stroke, it is most likely indirect. Alcohol can raise a woman's blood pressure, enhance blood flow to her brain, and increase the chance of having irregular heartbeats, all of which make it more likely that a blood vessel in the brain will burst and bleed. In addition, high levels of alcohol intake have been shown to increase the tendency for bleeding.

How Alcohol Use Affects Length of Life

Drinking in moderation can decrease a woman's risk of dying from some diseases, but increase her risk of dying from others. The best evidence of this to date comes from the American Cancer Society Cancer Prevention Study II. In that study, women who drank in moderation were about 20 percent less likely to die during the nine-year study period than women who did not drink at all. When researchers looked at specific causes of death, they found that moderate drinkers were much less likely than nondrinkers to die of coronary heart disease and stroke. However, moderate drinkers were also more likely to die of breast cancer. Results in the Nurses' Health Study were similar. Overall, these findings suggest that while moderate drinking does confer an overall mortality benefit-and a great benefit in terms of heart disease-women must still consider the increased risk of breast cancer and possibly other cancers.

WHAT IT ALL MEANS

Alcohol can have a wide range of effects on your health, depending on how much you consume. If you drink heavily (two or more drinks a day), you are at increased risk of cancer, heart disease, alcoholism, cirrhosis, and fatal accidents. This type of drinking has no benefits and is not recommended for women at any age. Moderate drinking, on the other hand, does have some benefits, although it too has risks. If you drink one drink a day, you receive some protection against heart disease and ischemic stroke. However, you are also at increased risk of breast cancer, hip fracture, and probably colon cancer and hemorrhagic stroke. These risks and benefits are the same whether you drink beer, wine, or liquor.