Thirty minutes after a good, strong cup of coffee, your resting metabolic rate increases by as much as 10%, your blood pressure climbs, your heart rate accelerates and your breathing speeds up. You will feel more awake, more energised.

The hike in blood pressure and heart rate led scientists to believe that the caffeine in coffee could pose a heart risk. But a recent study by Harvard researchers found no significant increase in the risk of heart disease or stroke among men who drank up to four cups of coffee per day. Results in women were more or less the same.

The benefits of coffee
While the jury is still out on the real health risks of caffeine, there is good evidence that drinking up to three cups of coffee a day shouldn't pose any health risk. In fact, a good cuppa might actually be good for you, according to findings presented to the American Dietetic Association.

Some of the well-documented benefits of caffeine include improved concentration, faster reaction time, better short-term memory and less fatigue.

There's even more good news. Recently, scientists discovered that coffee is also an important source of flavonoids. These potent antioxidants could help to reduce the coffee drinker's risk of heart disease and cancer.

Interestingly enough, coffee might one day also be a way to put the sizzle back into your sex life.

A study with rats showed that a moderate dose of caffeine before mating increased the rodents' libido. The caffeine shortened the amount of time it took the females to return to the males for another round of mating.

Caffeine seems to stimulate the part of the brain that regulates arousal. However, more research needs to be done to determine whether the effect is the same in humans.

When you should cut back
Some people should rather cut back on caffeine or even delete it from their menus. You are one of them if you:

Are prone to migraines and headaches. Caffeine may trigger a migraine.

Suffer from PMS. It may worsen the symptoms.

Are taking antibiotics, bronchodilating theophylline or another stimulant such as ephedra in some dietary supplements. Caffeine may cause drug interactions and severe anxiety when combined with any other stimulant.

Are trying to conceive. A few studies have linked caffeine to infertility.

Suffer from sleep disturbances. With coffee's effect lasting a few hours, it's best to have your last cup of the day before 4 p.m. if you are serious about a good night's sleep.

Suffer from anxiety or depression. Caffeine can worsen symptoms.

Do serious exercise training. The amount of caffeine in just two cups of coffee limits the body's ability to increase blood flow to the heart during exercise. Stop drinking coffee at least two hours before your training session.