We really are a world of coffee achievers. The U.S. Food and Drug Administration (FDA) says about 90 percent of the world population ingests caffeine, and in the U.S. about 80 percent of us consume some every day. This doesn't mean that caffeine, especially when gulped down in large quantities, is a risk-free way to stay alert.

Ironically, a health professional who has downed too much coffee to survive long hospital shifts could be at greater risk of having a life-threatening health problem than the patient she's treating.

Measuring the risks

"What the nurse pounding down black coffee from the beginning of her shift until the end may not realize is that just 600 milligrams of caffeine a day is considered too much by the FDA."

Side effects from overdoing it range from the nuisance of jittery nerves and an upset stomach to an irregular heartbeat and trouble breathing. Though rare, a caffeine overdose can result in hallucinations, confusion and even death.

A hazardous habit

What the nurse pounding down black coffee from the beginning of her shift until the end may not realize is that just 600 milligrams of caffeine a day is considered too much by the FDA – and that's the amount found in just four to seven cups of coffee. That's also assuming the cup she's drinking from is just eight ounces – and if she's refilling a travel mug several times a day, there's a good chance she's drinking more coffee than she realizes.

There are short-term and long-term side effects from consuming too much caffeine. For people who have anxiety disorders or trouble sleeping, consuming coffee can make those problems worse. Because caffeine increases stomach acid, it can cause heartburn and, in large quantities, diarrhea, increased urination and excessive thirst.

While caffeine doesn't have long-term effects on blood pressure in most people, it can briefly elevate blood pressure – making the heart work harder. People with high blood pressure and other heart-related problems should ask their doctors if caffeine is safe for them.\

Curbing the habit

Conversely, abruptly stopping coffee intake can result in withdrawal symptoms, such as headaches, anxiety, irritability, drowsiness and tremors. Nausea, achy muscles and vomiting are other possible problems. Over the long term, too much caffeine can interfere with the absorption of calcium, contributing to osteoporosis.

For pregnant women, it can slow fetal growth and increase miscarriage risk. For nurses and doctors, kicking the coffee habit may be their own recommended prescription for better health.