National Coffee Day highlights health effects of popular brew

(CBS) National Coffee Day has java junkies looking to score a free cup of joe - and they may be in luck. At least a couple of fast food chains are offering free coffee to mark the day, which occurs every Sept. 29. 7-Eleven is offering free coffee from 7 a.m. to 11 a.m., and Krispy Kreme is handing out free cups of its house blend.

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But while freebies can be good for your financial health, what about coffee's effects on your physical well-being?

Researchers have served up a complicated brew of findings on coffee's health effects.

For a landmark 2008 study, Harvard researchers tracked 130,000 men and women for up to 24 years and found no evidence linking coffee consumption to increased mortality, according to a university website. Even people who drank up to six cups of coffee a day were at no higher risk of death.

In light of the evidence, Harvard researcher Dr. Rob van Dam, an assistant professor in the department of nutrition at the university's School of Public Health, concluded: "For the general population, the evidence suggest that coffee drinking doesn't have any serious detrimental health effects."

But that doesn't mean the hot stuff has no effect on health. As CBS News reported recently, research has tied consumption of caffeinated coffee to a reduced risk of depression in women. Other research suggests that coffee drinkers are less likely to develop type 2 diabetes, Parkinson's disease, dementia, heart rhythm problems, stroke, and certain forms of cancer, according to WebMD.

Sweet.

On the other hand, caffeine can contribute to anxiety, and heavy coffee drinkers - especially those who go for lots of sugar and cream - may be more likely to overload on calories, fat, and sugar. And according to the Harvard School of Public Health website, there's some evidence suggesting that drinking lots of coffee during pregnancy can lead to miscarriage and stillbirth.

One thing's for certain: coffee certainly is a popular beverage. According to the Harvard site, 54 percent of Americans over the age of 18 drink coffee every day.