Coffee contains the strongest concentration of caffeine per cup. Other sources of caffeine include chocolate, tea and energy drinks. Caffeine is a central nervous system (CNS) stimulant. It is the world's most widely consumed psychoactive substance. .
Current UK clinical guidelines are max 400mg (about 4-5 coffees). Some people can tolerate different amounts - the amount you can tolerate is determined in your DNA. Too much caffeine can cause feelings of anxiety, nervousness, sleep disturbance and hyper-activity. Caffeine also has a short-term diuretic effect. .
Even if you feel you can 'handle' more, increased caffeine intake (over 9 cups a day) as been seen to be detrimental to your bone mineral density. Some studies have shown caffeine can slow down age-related cognitive decline, Alzheimer's, and Parkinson's.