Last week's column established how easy it is for teens and preteens to get more than a healthy amount of caffeine during the day, especially if they consume an energy drink. But the excess of caffeine creates more than a few hours of bouncing-off-the-walls hyperactivity.

It also reduces sleep time and makes any sleep less restorative.And according to research referenced on 16-year-old subjects, those sleeping six or fewer hours a night for any reasons were 20 percent more likely to become obese no, not just overweight! than the 16-year-old subjects who slept eight or more.In short, last week's column made a strong argument for parents to monitor the amount of caffeine consumed by kids. But monitoring caffeine consumption also helps most adults for a whole host of reasons.First of all, caffeine utilized properly can really enhance rather than detract from your health. For instance, if used infrequently and in relatively small amounts, it can supercharge workouts.Caffeine does so because it enhances the central nervous system, increasing alertness focus, and coordination. Concurrently, it stimulates the heart, dilates blood vessels, and relaxes the lungs, all of which give you the sense that you're not exercising as hard as you really are.But caffeine can make tasks other than physical ones seem easier to do, too. Multiple studies have found it to reduce mental fatigue and aid memory. Furthermore, research has linked caffeine ingestion via coffee with lowering the risk of type 2 diabetes, liver disease, liver cancer, prostate cancer, breast cancer, colorectal cancer, Parkinson's disease, and Alzheimer's disease.Moreover, in a 13-year study of 400,000 men and women performed by the National Cancer Institute, established a correlation between coffee consumption and reduced death risk. Compared to women who drank no coffee, those who averaged two to three cups per day experienced a 13 percent decrease in death risk. Men drinking the same amount experienced a 10 percent reduction in death risk when compared to non-drinkers.And as little as a half a cup of coffee has been found to elevate the rate at which calories burn by 4 to 5 percent, an elevation which can aid weight loss.With so many positives, why not just consume caffeine every single chance you get? Because it only takes four days of use for the body to develop a tolerance, which reduces the stimulant-like effect.Unless you increase the dosage.But increasing the dosage may cause heartburn, gastrointestinal distress, heart palpitations, irritability, and as mentioned at length in last week's article a reduction in sleep time as well as the quality of sleep.So if you want to use caffeine to enhance health, you need to walk a figurative tight rope. You need to consume enough of the stuff for all the positives to take place but not enough to keep you up at night.And the width of that tight rope is created by a number of physiological factors.Here's how an old article in New York magazine summarized them."Women generally metabolize caffeine faster than men. Smokers process it twice as quickly as nonsmokers do. Women taking birth-control pills metabolize it at perhaps one-third the rate that women not on the Pill do. Asians may do so more slowly than people of other races."In The World of Caffeine: The Science and Culture of the World's Most Popular Drug, authors Bennett Alan Weinberg and Bonnie K. Bealer hypothesize that a nonsmoking Japanese man drinking his coffee with an alcoholic beverage another slowing agent would likely feel caffeinated (about five times longer than an Englishwoman who smoked cigarettes but did not drink or use oral contraceptives.)"So it's easy to see how one person might enjoy a cup of green tea before bed while another would drink it only if she needed to keep working on something well past her normal bedtime.And here's one final thought to add to the equation: not all commercial coffees are brewed equally. In other words, the caffeine content of your take-out brew varies sometimes tremendously.Research performed by the Center for Science in the Public Interest found that the typical cup of coffee served at Starbucks contained more than 38 percent more caffeine per ounce than Dunkin' Donuts and 56 percent more per ounce than McDonald's.In other words, downing two, 16-ounce cups from McDonald's throughout the day keeps you within the Mayo Clinic's "considered safe" limit, but the same amount from Starbucks contains enough caffeine to make the Mayo Clinic warn that you may become nervous, restless, irritable, disturb your stomach, create muscle tremors, increase heart rate, and disturb sleep that night.