JoAnn E. Manson, MD, DrPH, of Harvard Medical School

 JoAnn E. Manson, MD, DrPH, of Harvard Medical School writes at Bottom Line Health that if you worry that coffee could harm your health? Relax.

Studies suggest that, when consumed in moderation — meaning two to four eight-ounce servings daily — coffee may in fact be good for you.

It is not clear whether the benefits come from coffee itself or its caffeine. Even decaffeinated coffee may have some caffeine, and there is limited research on other caffeinated beverages, such as tea. Per cup, coffee has about 100 mg of caffeine… black tea has about half as much.

Studies show that coffee may… Reduce risk for some cancers. An analysis of nine studies found that drinking two cups of coffee daily lowered liver cancer risk by 43%. Coffee also may protect against colorectal cancer.

Help prevent diabetes. Among 200,000 study participants, those who drank four to six cups of regular or decaffeinated coffee daily were 28% less likely to develop type 2 diabetes than people who drank two cups or less daily.

Possible reason: Chlorogenic acid, an antioxidant in coffee, slows sugar’s release into the bloodstream. 

 Protect memory. In a study of 7,000 seniors, women who drank more than three cups of caffeinated coffee or six cups of caffeinated tea daily had less memory loss than women who drank two cups or less.

 Prevent gallstones. In a study of 80,000 female nurses, drinking two or more cups of caffeinated coffee daily cut gallstone risk by about 20%.

Why: Caffeine may aid the digestive fluid bile, reducing formation of cholesterol crystals that become stones… and stimulate gallbladder contractions, flushing away crystals.

 Lower Parkinson’s disease risk. In the nurses’ study, women who drank one to three cups of caffeinated coffee daily were 40% less likely than nondrinkers to develop Parkinson’s, a movement disorder caused by loss of brain cells. 

 Improve physical performance. The amount of caffeine in two to five cups of coffee boosts endurance… helps the body burn fat instead of carbohydrates… and eases muscle soreness.

Reassuring: Coffee drinkers are no more likely to have heart attacks or chronic high blood pressure than nondrinkers. Coffee oils can raise cholesterol, but paper filters remove these oils. Coffee doesn’t appear to increase risk for ovarian or breast cancer. Some women say coffee worsens premenstrual syndrome and fibrocystic breast disease (benign breast lumps), but research does not support this.

Cautions: Both regular and decaf coffee can cause digestive upset. Caffeine can trigger migraine or cause insomnia. Animal studies suggest that at high doses, caffeine may weaken bones by blocking calcium absorption. Moderate amounts of caffeine do not impair fertility or cause birth defects, but consuming more than 200 mg daily may double miscarriage risk — so limit caffeine to 100 mg per day while pregnant.