Coffee’s Effects on Health: A Mixed Bag

January 28th, 2010 | Sources: Wall Street Journal

More than half of American adults, 54%, drink coffee regularly. They consume nearly 400 million cups of it each day making its active ingredient, caffeine, by far the most widely consumed drug in the country.

whyarethesegirlslaughing?So you’d think we’d have reached some general agreement on how the stuff affects our health by this time, no?

Alas, that’s not the case.

Recent studies of the matter  suggest that coffee has beneficial effects on health. Last month for example, scientists reported that people who consumed 3-4 cups of Joe per day developed Type 2 diabetes 25% less frequently than those who had less than 2 cups per day.

Another group recently reported that men who drank at least six cups per day developed advanced prostate cancer 60% less often than abstainers.

Earlier studies had, in addition, linked coffee consumption to a reduced risk of colon cancer, head and neck cancer, endometrial cancer, cavities, gallstones, Parkinson’s disease, cirrhosis of the liver and Alzheimer’s disease.

On the other hand, many studies show that coffee, and caffeine in particular, raises heart rate and blood pressure as well as homocysteine levels in the blood. The latter is an amino acid that has been associated with stroke and heart disease.  Other studies have linked caffeine to bone loss in elderly women and shown that pregnant women who consume 2 or more cups per day have higher rates of miscarriages and low birth-weight babies.

What explains the confusion? It’s certainly possible that coffee has protean effects on the human body, and a mixed bag of health outcomes. After all, many drugs fall into that category. Another possible reason is that most studies of coffee’s health effects (including the 2 recent ones mentioned above) feature an observational trial design, in which scientists troll large data sets for associations between behavior and health outcomes, without a particular hypothesis in mind at the onset.
Observational studies are rarely able to control for obscure reasons that drive an apparent association between coffee and health. For example, older studies that linked coffee intake to cancer have subsequently been shown to be driven by higher rates of cigarette smoking in the coffee drinkers. Once this was controlled for, the negative association disappeared.

In conclusion, there isn’t enough evidence about positive health benefits to encourage non-coffee drinkers to begin doing so. Conversely, people who drink it probably needn’t worry that they are harming their health, unless they have high blood pressure or are pregnant or can’t sleep. When in doubt, ask your doctor!


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