This week Maryam Naz, 19 Maryam asks: I heard coffee stunts your growth - is this true? Wynnie says: This myth was started decades ago, when it was believed that caffeine led to reduced bone mass, which could encourage osteoporosis or brittle bone disease in later life. A lot of early research looking at links between caffeinated drinks and osteoporosis covered people who had a low calcium intake. Caffeine is a diuretic and can cause calcium - the mineral needed for strong, healthy bones - to leach out of bones and pass out in the urine. But more recent scientific studies show that even if caffeine does compromise stored calcium, this can be offset by adding some milk to tea, coffee or other caffeinated beverages. There are currently no recommendations for daily caffeine consumption for teens. Canadian guidelines recommend that preschool children get no more than 45mg of caffeine a day. That's equivalent to the amount of caffeine in 355ml of cola. The American Dietetic Association states that 200-300mg of caffeine a day - that's two or three cups of coffee - are safe for adults. Caffeine is a stimulant, and too much - if you're drinking 10 cups of coffee a day, that's too much - can make you feel jittery and anxious, cause headaches and nausea, and make it difficult for you to fall and stay asleep. Although caffeine by itself is not harmful, it's not a bad idea to cut down on your intake. But it's best to do this slowly and gradually because abrupt cessation for people who regularly drink caffeinated beverages can produce withdrawal symptoms. A scientific review published in Psychopharmacology in 2004 listed the following reactions to caffeine withdrawal: headache, fatigue or drowsiness depressed, irritable mood difficulty concentrating flu-like symptoms of nausea and/or vomiting muscle pain or stiffness According to researchers, withdrawal symptoms usually start 12-24 hours after the last dose of caffeine, become more severe after one to two days and last for between two and nine days. They believe that these effects may be magnified in children and teens. You can kick the caffeine habit by following some of these suggestions from the American Dietetic Association: Mix decaffeinated coffee with regular coffee Drink a latte with more low-fat milk than coffee Brew tea for less time Drink juice, milk or water instead of cola or energy drinks And if you want a caffeine-free energy boost, try doing something physical to get you going in the mornings. Maryam's diary Breakfast: Toast or biscuits with milk tea Lunch: Juice, sandwich and a fruit Dinner: Soup, rice with various side dishes and vegetables Snack: Crisps and chocolate Exercise: Tennis or squash, once a week for two hours