With Texas Ranger Josh Hamilton’s recent diagnosis of ocular keratitis due to excessive caffeine, coffee’s most famous chemical compound has come into the spotlight yet once again. With study after study being published about the health effects of caffeine — and the new attention in relation to vision issues — when all is said and done, is coffee your friend or foe?

Coffee’s reputation took a severe beating in the 1980s when it was connected to pancreatic cancer, yet more recent studies have not found the same link, according to the American Cancer Society.

But for many, coffee retains an aura of unhealthiness. It's a vice, something that people seem to be constantly trying to “give up.” But is it really bad for us?

The answer varies. According to the Mayo Clinic, moderate coffee intake isn't likely to cause harm, but too much — more than 500 to 600 milligrams a day — may cause insomnia, nervousness, restlessness, irritability, stomach upset, fast heartbeat and muscle tremors. Individual sensitivity to caffeine varies from person to person. And for some people, it just isn't a good fit.

But that said, coffee continues to surprise with the array of health benefits it can deliver. Here’s what the studies say:

  • Although there are higher specific antioxidant levels in fruits and vegetables, a 2005 study found that Americans get more antioxidants from coffee than anywhere else.
  • Scientists at Harvard University examined data from 67,470 middle-aged women who were followed for about 26 years. When compared to women who drank little or no coffee, the ones who drank four or more cups per day had a 25 percent lower risk of developing endometrial cancer. Those who drank two or three cups per day had a 7 percent lower risk.
  • According to a 2009 meta-analysis, at least fourteen out of eighteen cohort studies revealed a substantially lower risk of type 2 diabetes mellitus with frequent coffee intake, and that the risk of type 2 diabetes goes down with each cup of coffee consumed daily.
  • Studies have demonstrated that those who use caffeine are less likely to develop Parkinson's disease. The latest study examining the connection found that caffeine can also help with movement symptoms for people who already have the disease.
  • The New England Journal of Medicine published a study that found that increased coffee consumption is linked to longer a longer life. Coffee drinkers didn't die as early from heart or respiratory disease, stroke, diabetes, injuries, accidents or infections, and in fact, they decreased their risk of death from these factors by 10 to 16 percent.
  • According to a meta-analysis published in the American Heart Association's journal Circulation: Heart Failure, coffee drinkers who consume two 8-ounce cups a day appear to have an 11 percent lower risk of developing heart failure compared to those who don’t drink coffee at all.
  • Researchers looking at data from the Nurses' Health Study (Harvard’s broad and long-running study on women’s health) found that a lower risk of developing basal cell carcinoma was linked to consumption of caffeinated coffee (in addition to caffeine from tea, cola and chocolate). Decaffeinated coffee did not prove to have the same effect.
  • A 2007 meta-analysis of nine studies found that an increase in consumption of 2 cups of coffee per day was associated with a 43 percent reduced risk of liver cancer.
  • The Harvard School of Public Health conducted a study which concluded that women who drank two to three cups of caffeinated coffee a day were 15 percent less likely to develop depression over a 10-year period compared to those who drank one cup of coffee or less per week.
  • A study from the Karolinska Institute in Sweden found that women who drink five or more cups of coffee a day are 57 percent less likely to develop estrogen receptor-negative breast cancer than women who drink less than a cup of coffee a day.
  • At high levels (more than 744 milligrams/day), caffeine may increase calcium and magnesium loss in urine. But recent studies suggest it does not increase your risk for bone loss, especially if you get enough calcium.

And what about that ocular keratitis? Most studies and medical literature don't list caffeine as a common cause, so it's probably not much to worry about.

If you are very sensitive to caffeine or are prone to anxiety or panic attacks, limiting your caffeine intake may be prudent.

But above all, just be careful about how you consume your caffeine. Coffee may have a great array of health benefits, but it often comes packaged in horrendously unhealthy concoctions. For example, Cold Stone Creamery's Caramel Latte comes with a whopping 1,790 calories and 90 grams of fat — clearly not a friend to good health.

More coffee stories on MNN:

MNN tease photo of coffee: Shutterstock

Coffee: Friend or foe?
With all of the conflicting studies about caffeine's effect on the body, should you shun the pick-me-up or have a second cup? According to the Mayo Clinic, mode