Stanford professor Dr. William C. Dement, author of The Promise of Sleep, identified sleep deprivation as the most common brain impairment and says “We are a sleep-sick society.” He regularly challenges his students to identify the optimum amount of sleep for their brains and to adopt a sleep-smart lifestyle. Guesstimate how much sleep you think your brain needs (e.g., seven or eight hours). Then get more sleep than that for several nights in a row. Eventually, your brain will begin to wake up spontaneously when it has had sufficient sleep. Make a note of the number of hours, which typically represent your brain’s optimum sleep needs. Then give your brain the quantity and quality of sleep it needs on a daily basis. Otherwise, you can accumulate a sleep debt that can be difficult if not impossible to pay back. Fewer than seven hours of sleep at night has been associated with a decrease in overall blood flow to the brain. Studies have shown a growing link between sleep duration and a variety of serious health problems, including diabetes, hypertension, depression, and obesity. More tomorrow.