Factbox:

Health Canada recommends the following daily limits on caffeine intake for children:

• 45 mg for children aged 4-6.
• 62.5 mg for children aged 7-9.
• 85 mg for children aged 10-12.

Those recommended maximums are equivalent to about one to two 12-oz (355 ml) cans of cola a day — as long as that's the sole source of caffeine.

Trimethylxanthine — known in some circles as C8H10N4O2 — is the drug of choice for an overwhelming number of North Americans. Most of us refer to it as plain old caffeine.

As many as 80 per cent of us include it as part of our daily ritual. The rest of us probably have some caffeine at some point — often without realizing it.

It's estimated that every man, woman and child will consume 70 milligrams of caffeine every day — or about the amount in the average 200-millilitre cup of coffee.

But very few of us buy 200-ml cups of coffee. Order a large at your favourite coffee shop and you're getting about 500 ml and anywhere from 200 to 400 mg of caffeine. Have two servings of that size and you're more than likely taking in far more than Health Canada's maximum recommended daily dose of 400 to 450 mg of caffeine.

Caffeine is the addictive element that makes coffee so appealing — and provides the jolt to smooth the transition from sleep to facing another day at work or school.

But if your daily dose of caffeine is up around 600 mg, you may start to show symptoms of caffeine overdose. They will vary from individual to individual, but could include:

• Restlessness.
• Dizziness.
• Nausea.
• Headache.
• Tense muscles.
• Sleep disturbances.
• Irregular heartbeat.

Get up over 750 mg and the list could grow to include:

• A reaction similar to an anxiety attack, including delirium, drowsiness and ringing ears.
• Diarrhea.
• Vomiting.
• Light flashes.
• Breathing difficulties.
• Convulsions.

You can even suffer a fatal caffeine overdose — but you'd have to consume more than 5,000 mg over a very short period of time. That's the equivalent of 50 200-ml cups of strong coffee.

As Canadians we are taking in more caffeine than we used to. Statistics Canada reports that coffee consumption increased from 96 litres per person in 1990 to 101 litres per person in 2000. Consumption of tea — another popular drink that usually contains caffeine — increased even more, from 42 litres per person in 1990 to 70 litres per person in 2000.

Factbox:

Caffeine does not cancel out any effects of alcohol. Having a cup (or two) of coffee after drinking does not sober you up, nor does it allow you to safely operate a car.

It's not just coffee or tea that provide a caffeine jolt. You'll get it from some soft drinks, chocolate and cold medications. A 355-ml can of Coke has about 36 mg of caffeine. A 50-gram chocolate bar has about 20 mg.

Once caffeine enters your bloodstream, it takes about 15 minutes for you to start feeling its effects. Caffeine stimulates the brain in the same way that cocaine and heroin do:

• It blocks adenosine reception so you feel alert.
• It injects adrenaline into the system to give you a boost.
• It manipulates dopamine production to make you feel good.

For the short-term, your body loves caffeine. But it's the long-term effects that can be a problem. Once the adrenaline wears off, you face fatigue and depression. To turn that around, your body wants more caffeine.

The half-life of caffeine is about six hours. That means if you have a large cup containing 200 mg of caffeine at three in the afternoon, there will still be 100 mg of caffeine in your system six hours later, as bedtime approaches. You may fall asleep, but you might not get the deep sleep your body needs. You wake up tired. You need that caffeine blast. The circle begins again.

What's worrying health officials even more is the increase of caffeine intake among youth. Teens and young adults have been fuelling a surge in sales of energy drinks. In 2005, more than 500 new energy drinks were introduced worldwide.

Factbox:

Pure caffeine is odourless and tastes bitter. It is most commonly found in: some soda pop, coffee, tea, chocolate, some medications.

Red Bull hit the market first. It was introduced in Austria in 1987. Now it's the world's top selling energy drink, with sales of 2.5 billion cans a year in 130 countries. Each 250-ml can — at a cost of about $3 — contains 80 mg of caffeine.

Part of the concern is that Red Bull is an energy drink, but it doesn't replenish the body after physical exertion (like sports drinks such as Gatorade).

In fact, because Red Bull has so much caffeine — it can actually dehydrate the drinker. That means if you're physically exerting yourself and drink just a Red Bull, the lack of hydration could strain your heart.

And if you combine energy drinks with alcohol, your risk of dehydration rises.

Health Canada has received four reports of adverse reactions to energy drinks. Each case involved "improper use" of energy drinks, such as mixing them with alcohol or drinking too many of them in a day.

The agency recommends that if you do use energy drinks:

• Drink no more than two cans — or 500 ml — a day.
• Do not mix them with alcohol.
• Drink plenty of water if you have an energy drink before intense physical activity or exercise.

The actual caffeine content of energy drinks may be even higher than what's listed on the label. Some contain ingredients — like guarana — that are loaded with caffeine. But because caffeine was not added as a separate ingredient, the label may not have to say the drink contains caffeine.

But despite the health concerns, there are studies that suggest that coffee — and the caffeine it contains — can be good for you.

• In May 2006, a Canadian-led study found that caffeine may help premature babies get through their first days of life.
• A Harvard University study in 2001 found that moderate amounts of caffeine reduce the risk of Parkinson's Disease in men and women.
• In November 2005, Harvard researchers concluded that caffeine won't increase your risk of high blood pressure. But sugary soft drinks might.
• A study conducted for the American Diabetes Association found that drinking more coffee can dramatically decrease the risk of developing Type 2 diabetes. The researchers didn't know why — but said the findings warrant further study.

Most people have no trouble tolerating moderate doses of caffeine. But there are those who are extremely sensitive to even small doses of the drug. A single cup of coffee can leave them anxious, restless and irritable.

For those who make caffeine part of their daily lives, cutting caffeine will likely cause withdrawal symptoms such as headaches, fatigue, irritability and nervousness. The symptoms generally take a few days to clear up.

If you are looking at curbing your caffeine intake, the Mayo Clinic offers these tips:

• Read labels carefully. Caffeine added to drinks must be listed in product ingredient lists.
• Gradually reduce the amount of caffeine you consume. It will lessen the withdrawal symptoms when you go caffeine-free.
• Replace caffeinated beverages with decaffeinated counterparts.
• When making tea, reduce the time you leave the tea bag in the cup. It will cut the amount of caffeine in the tea. Or drink herbal tea.
• Check the caffeine content in over-the-counter medication you take. Many headache pills contain significant amounts of caffeine.