May 17, 2011 -- Those of us who feel guilty reaching for a second cup of coffee during the day may admit that we have a love-hate relationship with the drink. Some of us may need it to stay awake, and some of us, try as we might, just can't quit.
Conflicting research on the health benefits and risks of drinking coffee only add to the confusion over whether we should be cutting back. This time, a new study found that men who drank six or more cups of coffee per day over nearly two decades were 60 percent less likely to develop more aggressive forms of prostate cancer.
Men who drank 1 to 3 cups per day lowered their risk of prostate cancer by 13 percent, according to the study which was published Tuesday in the Journal of the National Cancer Institute.
The findings were the same in both caffeinated and decaffeinated coffee drinkers, said Lorelei Mucci, associate professor of epidemiology at the Harvard School of Public Health and co-author of the study.
"We're not sure exactly what helps the association," said Mucci. "Coffee is one of the strongest antioxidants."
Coffee also helps with insulin and glucose metabolism, and may help regulate sex hormone levels, which all play a role in prostate cancer, she said.
Beyond Mucci's research, other recent studies have tipped the health scale in favor of coffee.
Just one week ago, a Swedish study showed women who drink five or more cups of coffee a day had a much lower risk of developing an aggressive form of breast cancer.
"Coffee now has been associated with a lower risk of diabetes, a lower risk of Parkinson's disease, a lower risk of cirrhosis and liver disease," said Mucci.
But many experts, including Mucci, admit that these studies don't necessarily estabish a cause-and-effect link between coffee and certain disease. And, they're not willing to say that drinking many cups of coffee is healthy.
"This study is in isolation," said Howard Soule, chief science officer at the Prostate Cancer Foundation.
"Their finding does not impinge on pancreatic cancer, or other health effects that coffee may or may not be related to."
While studies are conflicted about the risk and benefits of coffee for some types of cancer, it is clear that drinking excessive amounts of coffee can lead to jitters, heart palpitations and insomnia.
"All the epidemiological studies on risks and benefits of coffee look promising," said Soule. "But then we're seeing the findings didn't hold up in prospective studies."
Still, Soule said the factors hypothesized in the study suggesting that coffee may contribute to the decreased risk of prostate cancer could hold some weight. But without a stronger form of studies looking at coffee's relationship to any given disease, it's hard to definitively say what the true risks and benefits could be.
"The disclaimer is that it requires a prospective randomized trial over 20 years, which likely will never be done," he said.