Running On Empty Bottles

 For others, it might be a matter of blowing off stress. Which may be why some women offset their tension with a boot-camp class, or by getting loaded, or both. "Exercising stimulates the release of serotonin, which is your natural antidepressant, as well as dopamine, which is the primary neurotransmitter in your brain's reward center. It makes us feel good," says brain chemistry researcher J. David Glass, Ph.D., a professor at Kent State University. Alcohol has a similar effect—hence, the buzz you get soothes your worries (if only temporarily).

More: 4 Tips to Run the Stress Off

The Pleasure Principle

The downside of constantly activating these reward pathways is this: Your brain gets used to it and wants more, says Brian R. Christie, Ph.D., neuroscience program director at the University of British Columbia Division of Medical Sciences. So it's not shocking that someone who craves a 10K or a blistering CrossFit session will also readily down a couple of vodka sodas.

Animal studies bear out this effect. In a 2010 study, University of Houston scientists took a group of alcohol-loving rats and gave half of them running wheels while the other half stayed sedentary for three weeks. Then they took away the wheels and granted half the rodents in each group an open bar, suspecting that the fit rats would drink less than the lazy ones. Wrong. They drank more.

More: 4 Ways to Reward Yourself After a Run

Associate professor of psychology and study author J. Leigh Leasure, Ph.D., was surprised—until she saw the epidemiological research, such as the aforementioned landmark human study. She began to look at what was going on in the brain. "We found that rats that exercised before drinking alcohol needed to consume more than sedentary rats to show the same signs of intoxication," she says.

In short, the rats needed more booze to get buzzed, which could explain some things about human behavior. "Since alcohol enhances the activity of the brain's opioid system, it's possible that exercise could cause cross-tolerance to alcohol—meaning, it may make alcohol less rewarding, so people would therefore drink more of it in order to get its feel-good effects," says Leasure.

Interestingly, Glass's research found that, in moderation, exercise and alcohol may replace one another as a means to the feel-good end, allowing people to swap a natural, healthy high (exercise) for a potentially harmful one (alcohol). But that goes out the window when you start bingeing, which you might do when the usual drink or two doesn't budge your reward meter after a sweat session.

Your Health, on the Rocks

Theoretically, there's a perk to the exercise-drinking connection: Excessive swilling can lead to apoptosis, or cell death in the brain. Sweat sessions, on the other hand, dramatically increase neurotrophin production so you can make new brain cells, says Christie. One exercise by-product: super-fertilizer for the brain that doubles and triples neurons and leads to better cognitive functioning.

That said, don't be fooled into thinking your daily trip to the gym gives you a free pass at the bar. Being fit can make you feel impervious to the ill effects of drinking, such as liver disease, diabetes, and certain cancers, and even trick you into thinking that you could never turn into an alcoholic. But as it turns out, that same Columbia University survey found that more women are becoming alcoholics. And as a woman, you're particularly vulnerable to the very real (and physical) risks of overdoing it.

More: Can Beer Improve Your Run Time?

For one, women have proportionately more body fat and less water, so they don't absorb or dilute alcohol as well as men do. They also have a lower concentration of dehydrogenase, the primary enzyme that breaks down alcohol in the body. Women's fluctuating hormones make matters worse, since estrogen affects alcohol metabolism. That's why one drink might give you a slight buzz one night and slam you a few weeks later.

Women also fall victim to alcohol-related illnesses more easily. They're more likely to develop liver disorders and are more prone than men to alcohol-related brain and heart damage. Alcohol also increases their chance of getting breast cancer. And excessive alcohol consumption can lead to all of these no matter how much you exercise, says Tavis Piattoly, R.D., a sports dietitian for Tulane University athletics.

On a less dire note, too much booze is also just plain bad for your exercise performance.

Drinking five or more drinks on any one occasion affects the brain and body for several days. Even lesser amounts, especially in women, can hurt your fitness on nearly every level.

How Much Is Too Much?

Nobody is saying to turn off the tap completely. Moderate alcohol consumption (two drinks a day for guys, one for women) is linked to longevity. Some experts tended to lean a little more liberally, though. "I tell my clients, 'Have a plan and limit yourself,'" says Piattoly. "For women, I'd say don't have more than three—and in between every drink, have water, which keeps you hydrated and slows down the alcohol intake."

The warning signs that you (or a friend) are in trouble are the same whether the problem behavior is extreme exercise or consumption, says Abrantes. "If you're spending a lot of time doing either and not fulfilling work and personal responsibilities; if you need to do more of the behavior to get the same effect; if you feel very irritable when you can't engage in the behavior, there's a problem," she says. In a nutshell: If you have to ask, there's probably a problem.

When you do go on a bender, follow it with a few dry days to give your body a rest. "If you only occasionally go overboard, then taking a few days off is a good way to let your stomach lining heal, so you can absorb all the nutrients you need from food as well as restore a healthy sleep pattern and generally help your body recover," says Christie. You may also want to try yoga. Research shows that practicing it may help raise your brain's GABA levels, which also helps lift depression and reduce anxiety—without the hangover. Says Christie: "It might be an effective way to reduce the cravings for less-healthy stress relievers."

More: The Benefits and Risks of Alcohol

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