Caffeine's half life of about 5 hours varies in individuals depending on weight, metabolism, and other factors. But, what doesn't vary is that when caffeine is consumed even in the early evening, significant amounts are still present in the system at bedtime.

Some people claim that caffeine does not have any effect on their sleep. It is possible that these people are carrying such a load of sleep debt that they don't notice the effect. They may have been consuming enough caffeine that they have become desensitized to it's effects. Or perhaps they are young, or are under great stress.

Here is an experiment to try: Go for one week without caffeine. Beware, it is found in caffee, tea, colas, energy drinks, diet pills, and other places. Check the labels of foods you eat..... Then after one week without caffeine, try consuming your normal amount of coffee, soda, and other caffeinated foods. You might be surprised at how much of an effect caffeine has after you give your body a chance to regain it's normal sensitivity.... After this experiment, resolve to drink non-caffeinated beverages in the afternoon and at night.

One of our readers wrote us with his story of the link between caffeine and headaches.