Caffeine Nation...When used wisely caffeine can be beneficial. A diet soda has about 40 mg and a cup of coffee can contain anywhere from 70 to 300 mg depending on what you get and where you get it. The 'energy drinks' can contain anywhere from 160 to 320 mg per can. Caffeine has been shown to improve both cognitive and athletic performance, but not when you chug a gallon of it. If you have a heart condition or high blood pressure, then be aware of how much you are consuming. Try to minimize it after 3-4pm to avoid any affect on your sleep. The old wive's tale (no offense to any old wives) that you will become dehydrated from drinking caffeinated beverages is actually not true. Drinking something is better than not drinking anything at all. So enjoy your morning cup of joe or tea after a good night of sleep, but not to replace it.