The familiar sensations we all experience from drinking coffee are due to the physiological effects of caffeine on our bodies. Caffeine stimulates the central nervous system by blocking the receptors for adenosine, a neurotransmitter that normally functions to slow the body down. By stimulating brain activity, caffeine counteracts fatigue, increases alertness, improves motor skills, and speeds up thought processes. These effects are usually produced by the amount of caffeine in one or two cups of coffee, and are accompanied by other physiological reactions including increased heart rate and digestion. Over-consumption of coffee can cause a person to be restless, irritable, nervous and generally uncomfortable. The effects of caffeine are, however, influenced by factors such as age, sex, environment, and physical condition, creating a wide range of physiological reactions to coffee. Your individual sensitivity to coffee's stimulating effects will determine how much coffee is right for you.

Growing interest in health issues has spurred some concern that the physiological effects of coffee may be harmful to our minds and bodies. Clinical reports and studies have attempted to implicate caffeine in heart disease, stroke, high blood pressure, cancer, and birth defects. To date, the results of these studies have been largely inconclusive and, in some cases, contradictory. In addition, no studies have assessed the health implications of stale coffee. While it is true that some people are adversely affected by caffeine, recent evidence suggests there are also beneficial effects on our health from drinking coffee. We present some of the findings here so that you may draw your own conclusions about the pros and cons of drinking coffee.

The Pros of Coffee

1. Coffee May Help You Fight Cancer

A professor of environmental toxicology at the University of California at Davis says freshly brewed coffee may contain cancer-fighting anti-oxidants. Anti-oxidants appear to protect the body against the oxygen-induced damage to tissues that occurs as a result of normal metabolism. Because such damage is associated with increased cancer risk, anti-oxidant nutrients are thought to protect against cancer. According to this study, coffee consumed within 10 minutes of brewing may contain the same amount of anti-oxidants as 3 oranges.

2. Coffee May Prevent Gallstones

Gallstones are lumps composed of cholesterol caused by fatty diets. An epidemiologist at Harvard University of Public Health in Boston found that drinking at least two cups of coffee a day lowers a man's risk of developing gallstones by 40 percent. Drinking four or more cups a day offered a 45 percent lower risk. This benefit only comes from caffeinated coffee; not from tea, soda, or decaf coffee. Caffeine may help prevent formation of the lumps by preventing cholesterol from crystallizing and cutting fat storage through increased energy expenditure.

3. Coffee May Improve Athletic Performance

In addition to increasing alertness and concentration, caffeine can improve endurance. According to a study published in the Journal of Sports Medicine, two cups of coffee two hours before exercise can aid marathon and cycling trial times. The competitive edge offered to athletes by caffeine has led the International Olympic Committee to impose limits on its use. According to international standards, an athlete can have no more than 12 mcg of caffeine in a millimeter of urine (the equivalent to drinking about six to eight cups of coffee in an hour or two). Researchers warn that drinking excessive amounts of coffee can lead to dehydration during exercise, so combine your morning coffee with a glass of water.

4. Coffee May Improve Your Mental Skills and Keep You Awake

As most coffee drinkers already know, caffeine helps you stay awake. A study published in the journal Physiology & Behaviour found that drinking caffeine helps you fight fatigue and process new information. Researchers have also found that caffeine increases alertness and motor skills in sleep deprived people. Caffeine stimulates the central nervous system, thus increasing neuronal activity and brain function.

The Cons of Coffee

1. Coffee May Weaken Your Bones

According to the National Institute of Health, heavy caffeine intake (the equivalent of more than five cups a day) may interfere with calcium absorption. Caffeine decreases the amount of calcium that is absorbed during digestion and increases the amount that is excreted in your urine. Fortunately, the effects of one cup of coffee on calcium absorption can be offset with a tablespoon or two of milk, or about the amount found in a typical latte.

2. Unfiltered Coffee May Increase Cholesterol Levels

According to a study at Johns Hopkins University School of Medicine, drinking unfiltered coffee may increase your cholesterol level. Cafestol, a compound found in coffee, may affect the liver's metabolism of cholesterol. A single cup of unfiltered coffee contains three to four milligrams of cafestol, enough to significantly raise bloodstream cholesterol levels. The healthiest solution is to pass coffee through a paper filter to remove the cafestol before drinking your morning brew.

3. Coffee May Complicate Pregnancy

Heavy coffee consumption has been linked to infertility, miscarriage, and birth defects, however most results are controversial. A study published in the New England Journal of Medicine suggests that pregnant women who drink 6 cups of coffee a day have an increased risk of miscarriage. Researchers say that caffeine can pass through the placenta affecting the fetal nervous system. Another study by the Georgetown University Medical Center found that women who drank three cups of coffee a day had no increased risk for spontaneous abortion. To be on the safe side, researchers propose that women should limit their caffeine intake to one or two cups of coffee a day while pregnant or breastfeeding.

4. Caffeine May Keep You Awake

Caffeine will help you fight fatigue by giving you a morning boost, but it may also keep you awake if consumed late in the evening. A study published in the journal Neuropsychobiology found that coffee can delay the time you fall asleep and interrupt REM sleep. Researchers recommend avoiding caffeine six hours before bedtime if you have trouble falling asleep at night.