By Robert Bazell Chief science and health correspondent
NBC News
updated 10/23/2007 11:39:32 AM ET 2007-10-23T15:39:32
Commentary

Many women were surprised by a recent study linking consumption of alcoholic beverages to an increased risk of breast cancer.

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I was shocked, not by the results of the study, but by how many people — even colleagues in the news business — had never heard of the association before.

Scientific studies showing an increased risk of breast cancer for female drinkers have appeared hundreds of times over the past 20 years. I personally have often reported this conclusion. A quick search of newspaper and magazines articles, as well as news broadcasts, finds at least 11,000 stories mentioning this subject over the same 20-year period.

How could people be so ignorant of the warnings? The numerous reports were overlooked because, when it comes to health news, we tend to hear what want and manage to miss the rest.

Some of the earliest research connecting alcohol and breast cancer came from the Nurses' Health Study, one of the major sources of our knowledge about women's health. Beginning in 1980, researchers from the Harvard School of Public Health asked almost 90,000 female nurses to fill out questionnaires about what they ate, drank and other lifestyle factors. The researchers have regularly checked the women's health since then.

By 1987, an article in the New England Journal of Medicine based on the Nurses' Health Study concluded that women who consumed three to nine drinks a week had about a 30 percent increased risk of getting breast cancer. The more that women drank, the greater the risk.

Video: All alcohol linked to breast cancer Other studies soon came to the same conclusion. In 1998, the Harvard scientists published a paper in the Journal of the American Medical Association pooling the results of six studies from around the world that included more than 320,000 woman. The paper concluded that one drink a day led to a 10 percent increase in breast cancer risk and two to five drinks a day caused a 40 percent increase.

Risk from all alcohol
Despite those risks, 60 percent of readers responding to an MSNBC.com poll said they wouldn't quit or cut back their drinking.

And nothing makes some people happier than hearing a health justification for drinking. In recent years, several studies have found that moderate alcohol consumption — particularly of red wine — in both women and men reduces the risk of heart disease. In no time at all, countless red wine corks were popped in the pursuit of healthier hearts.

What seemed to upset many about last week's study was the risk from all types of alcohol, including red wine. After years of being praised for its antioxidant and antibacterial benefits, red wine was suddenly being lumped with hard liquor in the risky category. In reality, the ingredients in red wine that protect against heart disease and other illnesses are tiny compared to the overall effects of the alcohol.

Helpful and harmful
Indeed, wine, beer and spirits can cause both the increase in breast cancer risk and the reduction in heart disease risk. In lab studies alcohol increases the amount of the female hormone estrogen, which could account for its effects on both heart disease and breast cancer.

Drinking carries many risks and benefits that have nothing to do with breast cancer or heart disease. It is a major source of addiction, traffic accidents and family violence, as well as being a popular social lubricant and agent for relaxation.

Beyond the latest breast cancer study, there are a few tips for weighing the credibility of health news.

  • Observational studies like the Nurse's Health Study — where scientists follow people over time — do not produce evidence as powerful as placebo-controlled trials where half the group gets a treatment and the other half get a dummy pill. But no one is going to tell thousands of woman to have a daily drink and instruct thousands more to abstain and then watch them for years. Besides, there could be no placebo; when you have a drink you know it. That's why we have to rely on observational studies for certain types of research.
  • Be skeptical about the first time you hear anything. Studies of human beings can have many variables. Any first report, including the oft-cited Nurse's Health Study, could have been analyzed incorrectly. Unfortunately, the first report usually gets the most attention, which is why health studies can seem frustratingly contradictory.
  • When repeated studies come to the same conclusion, it is time to believe them.

Many people cried foul over last week's news, confused that alcohol can be both beneficial and harmful. You have to make your own decisions. But if you want truly to be informed, you cannot just hear what you want.

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