Coffee tastes good - but is it good for you? More than half of Americans are java junkies, yet the average joe doesn't know beans about the health effects of our daily brew. In fact, scientists say there are grounds to claim that coffee has many effects on health - some good, some bad.
Keep clicking as we filter coffee truth from coffee fallacy - and be prepared for some jolts...
Moderate coffee drinking -- less than five cups per day -- has been linked to a decreased risk of death from chronic illnesses like heart disease, type 2 diabetes and neurological diseases. The study from the Harvard T.H. Chan School of Public Health found protective effects in both regular and decaf coffee, suggesting that it's not just caffeine that comes with health benefits, but possibly the naturally occurring chemical compounds in the coffee beans.
About three cups of coffee each day might stave off Alzheimer's for older adults experiencing memory declines. A small study found coffee consumption helped slow the progression of mild cognitive impairment, a condition that often leads to Alzheimer's.
Coffee may lower the risk for the most serious type of skin cancer, malignant melanoma. A 2015 study found that frequent coffee drinkers -- those who consumed four cups or more per day -- had a 20 percent lower risk for developing malignant melanoma. Prior research has also shown coffee may help prevent other types of non-melanoma skin cancers. Decaf did not seem to offer the same protection.
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Coffee & calories
Coffee contains almost no calories - as long as you drink it black. But fancy sweetened drinks sold by specialty coffee retailers are often loaded with sugar and fat - and hundreds of calories that can contribute to weight gain. A venti white chocolate mocha from Starbucks delivers 510 calories - roughly 25 percent of an adult's normal daily calorie intake.
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Caffeine can increase blood pressure - but apparently mostly transiently. Long-term studies have found no link between regular coffee consumption and high blood pressure, a.k.a. hypertension.
"Still, for persons with hypertension it may be worthwhile to see if switching to decaf improves control of blood pressure," said coffee researcher Dr. Rob van Dam, an adjunct assistant professor of nutrition at Harvard School of Public Health and associate professor at Yong Loo Lin School of Medicine in Singapore.
Coffee beans contain a potent cholesterol-raising compound called cafestol. If you drink instant coffee or coffee that's passed through a paper filter, your brew will contain only a negligible amount of cafestol.
But traditional Turkish, Greek, Scandinavian coffee and coffee that's prepared via the French press method can contain high levels of cafestol. Studies have shown that drinking lots of these kinds of coffee can raise cholesterol levels. However, a large body of research suggests that regular consumption of filtered coffee does not increase risk for heart disease or stroke.
Preliminary studies have shown that habitual consumption of coffee is linked to lower risk for depression, at least among women.
Coffee during pregnancy
Heavy coffee consumption during pregnancy has been linked to miscarriage and low birth weight. A developing fetus isn't good at metabolizing caffeine, and research has shown that the stimulant easily crosses the placenta. To limit the risk, doctors often urge women to have no more than one cup of coffee a day during pregnancy (or two cups of tea).
Studies have shown that men who drink lots of coffee have a below-average risk for Parkinson's, a neurological condition marked by tremors and difficulty to coordinate movements. Animal studies suggest that caffeine prevents the death of nerve cells that produce the neurotransmitter dopamine, which is a core problem in Parkinson's.
In women, the relationship between caffeine intake and Parkinson's may be a bit more complicated. Recent research suggests that caffeine has a beneficial effect on women not using estrogen-replacement therapy, but not in those who do take hormones.
Coffee and the liver
Recent evidence suggests that coffee lowers the risk for both liver cirrhosis and liver cancer, though there's no clear explanation of the apparent protective effect.
A study from the University of Texas Health Science Center at Houston found that men who drink two to three cups of caffeinated coffee each day have a lower risk of erectile dysfunction. Caffeinated tea, soda and sports drinks had a similar effect.
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People who drink coffee on a regular basis actually seem to have a lower-than-average risk for type 2 diabetes. The reduced risk has been seen with both caffeinated and decaf, which suggests that it's something other than caffeine that explains the effect. A compound known as chlorogenic acid is one possibility, as are other compounds like trigonelline and ligans.
Recent studies have linked high consumption of both caffeinated and decaffeinated coffee to reduce risk of gout, a painful condition in which crystals of uric acid accumulate in the joints. In addition to reducing levels of uric acid in the bloodstream, coffee may reduce the risk of insulin resistance. That's a condition that precedes diabetes and is considered a risk factor for gout.
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Coffee and cancer risk
The World Health Organization used to classify coffee as a "possible carcinogen," but in June 2016 it reversed course, stating that there is not enough proof to establish any link to cancer.
"I'm not really sure why coffee was in a higher category in the first place," Owen Yang, an epidemiologist at Oxford University, told the Associated Press. "The best evidence available suggests that coffee does not raise the cancer risk."
The WHO's International Agency for Research on Cancer, or IARC, advises that drinking "very hot" beverages of any kind could potentially raise the risk of cancer, although the evidence is limited.