Caffeine

Caffeine is a bitter substance found in coffee, tea, soft drinks, chocolate, some nuts and certain medicines. It has many effects on the body's metabolism, including stimulating the central nervous system. This can make you more alert and give you a boost of energy.Teens usually get most of their caffeine from soft drinks and energy drinks. (In addition to caffeine, these also can have added sugar and artificial flavors.) Caffeine is not stored in the body, but you may feel its effects for up to 6 hours.

Many people feel that caffeine increases their mental alertness. Higher doses of caffeine can cause anxiety, dizziness, headaches, and the jitters. Caffeine can also interfere with normal sleep.

Some people are more sensitive to the effects of caffeine than others. They should limit their use of caffeine. So should pregnant and nursing women. Certain drugs and supplements may interact with caffeine. If you have questions about whether caffeine is safe for you, talk with your health care provider.Though moderate caffeine intake isn't likely to cause harm, too much can noticeably affect your health. Heavy daily caffeine use — more than 500 to 600 mg a day, or about four to seven cups of coffee — can cause:

* Insomnia
* Nervousness
* Restlessness
* Irritability
* Nausea or other gastrointestinal problems
* Fast or irregular heartbeat
* Muscle tremors
* Headaches
* Anxiety

Most adults need seven to eight hours of sleep each night. But caffeine can interfere with this much-needed sleep. Chronically losing sleep — whether it's from work, travel, stress or too much caffeine — results in sleep deprivation. Sleep loss is cumulative, and even small nightly decreases can add up and disturb your daytime alertness and performance.