Here are questions and my answers from an interview on caffeine that I did in 2006. See also a similar interview I did about Vitamins and Athletes.
Please outline the positive and negative effects of our daily caffeine (coffee/tea) consumption. Caffeine is a central nervous stimulant and can have some positive effects on the human body. Caffeine in low doses is thought to be associated with an improvement in sporting performance, increased alertness and reduction in fatigue potentially lifting a person's mood. Coffee and tea also contain some antioxidants which have positive effects on heart health. However, increased amounts of caffeine lead to dependency due to increased tolerance and hence the need for greater amounts to gain the same stimulatory benefits. Heavy users who have to go without can experience withdrawal symptoms such as headaches and fatigue. Too much caffeine can produce restlessness, nausea, sleep difficulties, upset stomach, increased urine production causing dehydration, and cardiac arrhythmias (irregular heartbeats). It has also been associated with elevated blood pressure in sensitive persons.
What is the "right" amount of coffee/tea to consume every day? The recommendation for safe drinking levels is 500mg per day, less for those with heart conditions, elevated blood pressure, and pregnant women (The last one may not interest your readers of course!). The average cup of instant coffee contains between 80 and 100mg/cup. The stronger the coffee the more caffeine it contains. Tea usually has less caffeine than this, except if it is very strongly brewed.
Do the above answers differ as we grow older ie; males 20-30, males: 40-50? There is no evidence that the effect of caffeine changes with age, except that the older you are, the more likely you will be to have high blood pressure and heart problems.
There is no conclusive evidence to implicate caffeine consumption as being significantly harmful to health, but there still is controversy with this. Having some caffeine daily is ok, but using the above food and exercise strategies can certainly help in reducing fatigue and avoiding caffeine addiction.