For the sleep deprived, alcohol is a fickle mistress. A glass of wine may help you go down for the night, but a few too many can send your sleep cycle into a tailspin. But until very recently, what no one knew was that for women, this is particularly true. It's just one more way in which scientists say alcohol affects women differently than men.
The study, published in the journal Alcoholism: Clinical & Experimental Research indicates that women's sleep is more easily disrupted by alcohol than men's. Ninety-three subjects were given either a placebo or enough alcohol so that their BAL was .11 (most states consider .08 to be legally impaired), then monitored as they slept. Women reported feeling more tired before they went to bed than men did, and woke up more often during the night and stayed awake for more minutes, says Damaris J. Rohsenow, Ph.D., one of the study's authors. Interestingly, the women did not report feeling sleepier than the men did after their night of tossing and turning. "They had worse sleep quality, but didn't notice," says Rohsenow, an associate director at the Center for Alcohol and Addiction Studies at Brown University. (The mechanism for why women had more disrupted sleep than men did was not explained.)
Until 15 years ago, very little research had been done on women's response to alcohol, says Elizabeth Epstein, Ph.D. a research professor for the Center of Alcohol Studies at Rutgers. Prior to that, our understanding of how humans processed alcohol—and how we dealt with any subsequent addiction issues—was based on research in men. That was the case for most medical inquiries, which often limited their studies to male subjects both out of centuries-long habit and because women, with their pesky hormones, were viewed as liable to skew study results. At some point, however, the medical community started to realize that the response of half their patients might not be skewed, but significant, and integral to understanding successful treatment options.
When scientists did eventually begin to delve into the differences between men and women when it comes to drinking, they found some interesting differences. First, even when a man and a woman weigh exactly the same amount, a woman only needs 90 percent of what a man consumes to achieve the same blood alcohol level. (How drunk the woman will feel compared to the man depends on her individual tolerance.) The exact reason why this happens is unknown, but it may be because women have less body water. Women also have significantly fewer stomach enzymes that facilitate the breakdown of alcohol than men, which means that "more unmetabolized pure ethanol is going into the organs," says Epstein. "For women, since there's less being metabolized, more alcohol is directly affecting the liver, heart, brain, and intestines." Female alcoholics often start drinking later in life than men, but because of this phenomenon, known as the "telescoping effect," these women often show comparable organ damage to male alcoholics who have been drinking much longer.
Even when a man and a woman weigh exactly the same amount, a woman only needs 90 percent of what a man consumes to achieve the same blood alcohol level.
Coincidentally, a second study released this week in the European Journal of Clinical Nutrition found that alcohol consumption later in life can have a protective effect on bone density—but what type of alcohol was beneficial depended on one's gender. This is particularly compelling news for women, who lose bone density faster than men do. The researchers followed 862 subjects, all over 50, for two years. They found that in men, drinking red wine correlated with less bone loss, and frequent liquor and spirits consumption was connected with more. Women, however, showed none of these effects. But what women did see was a positive correlation between drinking and bone density if they consumed low-alcohol beer. In this study, quantity may have played a role: red wine is associated with moderate drinking, while liquor and spirits are correlated with heavier drinking.
When it comes to the psychology of drinking and gender, there is much more research. In those cases, however, it's difficult to parse how much of the findings are based on the physiology and brain chemistry versus how many are rooted in external cues. For instance, one study found that after experiencing a stressful or upsetting event, men were more likely to crave alcohol, while women were more likely to report feeling depressed or anxious. "There are certain neural circuitry that are associated with stress and neural circuitry associated with reward…and they might be more closely linked in men," says study author Tara Chaplin Ph.D., an assistant professor of psychiatry at the Yale school of medicine. On the other hand, "It could also be connected to social pressures that girls and women feel—it's more acceptable to cry or feel anxious about things. Men might be pressured to minimize, so perhaps they turn to drinking."
In her studies of problem drinkers, however, Epstein found that too much depression and anxiety can lead women to alcoholism, while men were triggered by specific stressful incidents, like the loss of a job. She also found that while women respond better to single-sex group therapy and team treatment approaches then men do, women are much less likely to seek help. "They have barriers to treatment that men don't have—childcare, fear of losing their children, and women on the whole are less likely to have medical insurance," she says.
There's still a lot scientists don't understand about alcohol (though Rohsenow and her colleagues found that there's no difference in drunkenness between dark and light liquors, no matter what your mother told you). And there's even less that they understand about how booze breaks down in men vs. women. But the one tried and true rule of drinking was further confirmed by the participants in the sleep study, and it didn't matter whether they were male or female—every subject who'd been given the alcohol reported feeling lousy the next day.
Kate Dailey is a senior articles editor at Newsweek, where she covers health, lifestyle, society and culture.