Most of us consume it every day, but how much do we really know about caffeine? The naturally-occurring substance with a bitter taste stimulates the central nervous system, making you feel more alert. In moderate doses, it can actually offer health benefits, including boosts to memory, concentration, and mental health. And coffee in particular, a major source of caffeine for Americans, has been associated with a host of body perks, including a possible decreased risk of Alzheimer's disease and certain cancers. But in excess amounts, caffeine overuse can trigger a fast heart rate, insomnia, anxiety, and restlessness, among other side effects. Abruptly stopping use can lead to symptoms of withdrawal, including headaches and irritability. According to the American Academy of Sleep Medicine, it takes about 30 to 60 minutes for caffeine to reach its peak level in the blood (one study found increased alertness can begin in as few as 10 minutes). The body typically eliminates half of the drug in three to five hours, and the remainder can linger for eight to 14 hours. Some people, particularly those who don't regularly consume caffeine, are more sensitive to the effects than others. Sleep experts often recommend abstaining from caffeine at least eight hours before bedtime to avoid wakefulness at night. The body might process caffeine differently based on gender, race, and even birth control use. New York magazine previously reported: "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." 

http://www.shape.com/healthy-eating/healthy-drinks/10-surprising facts-about-caffeine/ em 26/08/2014.

O consumo de café, que é uma fonte de cafeína está associado a um possível