We all have coworkers who can down six cups of coffee in a given day without flinching, and friends who can indulge in an after-dinner cappuccino and be sleeping like a baby within the hour. Yet a single cup leaves many of us feeling jittery, anxious and restless. What gives?
To be sure, coffee is safe. According to the U.S. Food and Drug Administration, the average American consumes 300 milligrams of caffeine each day, and the Mayo Clinic says it is safe for adults to consume upward of 400 milligrams daily -- the equivalent of four cups of coffee. It is our most popular...
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