Unlike vitamins, minerals and other nutrients, there is no set limit for a maximum daily dose of caffeine. Depending on your own sensitivity to caffeine, you could max out with a single cup of coffee, which generally contains up to 100 mg of the stimulating drug. The maximum limit is any amount that changes caffeine's pleasant side effects into unpleasant ones.
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Amount and Sources
Most adults can consume 200 mg to 300 mg of caffeine per day, which translates to two to four cups of coffee, without any health concerns or negative side effects. Once you start drinking four or more cups of coffee, or otherwise consuming 500 mg to 600 mg of caffeine daily, you are more likely to experience the ill effects of caffeine. Coffee is one of the most abundant sources of caffeine, although other consumable items contain the drug. These include cola, root beer, orange sodas, energy drinks and other beverages, cocoa and chocolate products, tea, coffee-flavored ice cream and yogurt, pain-relief medications and over-the-counter stimulants.
Too much caffeine can leave you jittery, nervous and even nauseous. Restlessness, irritability and a rapid heartbeat are other negative side effects, as are muscle tremors and insomnia. Caffeine intoxication is a possibility, a condition that can result in muscle weakness, vomiting, diarrhea and weight loss, as was the case of one British teenager who was drinking about two gallons of soda every day for two years, according to Encyclopedia.com. Her daily caffeine consumption for the two-year period topped out at about 1 g, or 1,000 mg, per day.
Although you can live a fulfilling, healthy life without ever consuming caffeine, it does have its benefits. Caffeine can be useful in treating pain and tension-type headaches and, in certain cases, during athletic training. Coffee, specifically, may have additional benefits such as helping to protect against liver cancer, type 2 diabetes and Parkinson's disease.
Other factors that contribute to your maximum limit for caffeine include your gender, body size, age, medication use, health conditions and tolerance. If you are used to drinking copious amounts of caffeine, you will not be as immediately and severely affected by its consumption as someone who rarely takes a sip of tea. Men are generally more sensitive to caffeine than women, and certain medications and health conditions, such as anxiety disorders, can also play a part on its effect. Caffeine also takes a few hours to leave your system, according the American Council on Exercise. Its half-life is about four hours, which means half the amount you consumed remains in your system four hours after your consumption. Even after 12 hours, your body still retains about one-eighth of the amount of caffeine you originally consumed.