Like most people, I enjoy a coffee. Meeting friends for a coffee when I'm out is such a handy way to catch up especially when I'm pressed for time. That wonderful aroma, the adrenaline hit and energy boost are also big draw cards for me.

However it's easy to fall into the caffeine trap. One morning, you start out sipping a short black or flat white, then before you realize it, you need four of them to get through your day (or 8 instant coffees), as one of my friends discovered.

Or maybe you rely on an energy drink to stay up late when you go out partying at night - a dangerous practice according to the Australian Medical Association (AMA) who warn against mixing caffeine-rich energy drinks with alcohol. The AMA says the combination can lead people to excessive consumption of alcohol and has the potential to be lethal.

How much caffeine is too much?

Surprisingly, some people never notice any side effects. They can even sip a coffee before bed and still sleep peacefully. Wish I could!

Other people, however, get warning signs from caffeine habituation, which is what the experts call the addictive quality of caffeine.

If you've got any of the following symptoms and you know you're a big coffee drinker, you can be fairly sure it means your caffeine intake is too high:

• insomnia
• upset stomach
• heartburn
• too-rapid heart rate (palpitations or feeling your heart race)
• mind always in overdrive
• irritability
• over-anxious ('coffee jitters')
• frequent urination

For me, two coffees in a row is enough caffeine to get my heart pumping strangely and make my stomach unhappy. I don't go there anymore.

Signs of caffeine withdrawal

For those people who say they never suffer any ill-effects, I have a simple test for you. Just give up the coffee or cola drinks or energy drinks or tea for three days and see how you fare. I suspect many have built up a tolerance to caffeine over time, so they are able to ingest large amounts without noticing problems.

Sometimes withdrawal is forced on you - say if you go camping or have to fast for a blood test. But otherwise you may choose to give it up and see if you notice anything.

This is what caffeine withdrawal feels like: when you say "No" to caffeine, you'll notice a massive never-goes-away headache and an incredible tiredness. This fatigue/lethargy lasts for a couple of days but it's bad enough to send you screaming back for a coffee fix remedy (which does work remarkably quickly and effectively). That's why caffeine is so hard to give up. And that's why you don't want to eliminate it all at once.

What amount is safe?

Most of us can handle around 300mg of caffeine a day without problems. This translates to 4 or 5 cups of instant coffee or 3 shots of espresso (a latte, short black or cappuccino all start with a shot). Although there's a great deal of variation in caffeine figures as you can see below.

How much caffeine is in my coffee?

Caffeine is naturally present in around 60 plants, including coffee beans, cocoa beans (which is made into chocolate), tea leaf, yerba maté, kola nuts and guarana.

Below is a list of coffees, teas, cola soft drinks, chocolate and their caffeine content in mg per serve. Keep in mind that figures like these give average values only.

• The caffeine content of coffee varies depending on the type of beans, how it is made and how strong it is. Espresso coffee is usually stronger than instant coffee.
• For tea, caffeine depends on the type of tea leaves and how long it was brewed for – the stronger and darker the tea, the more caffeine.
• Most herbal tisanes do not contain caffeine.
• Decaffeinated coffee and tea are available at supermarkets and are helpful but tend to lack the flavour and 'vigour' of the regular brew.
• These days it's not just coffee and tea you need to watch out for. Caffeine turns up in some surprising places such as 'energy' drinks like Red Bull or V as well as chocolate bars with guarana (whose chief ingredient is caffeine, even though it's often marketed as 'natural caffeine' and supposedly safe) and even corn chips!
• Don't forget there's caffeine in certain over-the-counter medications such as some cold and flu tablets, detox supplements, diuretics, stimulants aimed at helping you stay awake, and some weight loss tablets.

Caffeine in pregnancy

If you're pregnant, it's probably wise to limit caffeine to 150–200 milligrams a day or none at all. Earlier reports of caffeine causing birth defects or low-birth-weight or miscarriage have not been supported at moderate levels, but may occur at higher intakes.

You don't need to give up your morning coffee completely, but try to limit yourself to one or maybe two cups of coffee, or 4 cups of tea a day. Try substituting decaffeinated coffee for your regular cups or see my list of lower and caffeine-free options.

One of the problems with caffeine studies is that it's hard to isolate caffeine from other problem-causing habits. Studies repeatedly find that heavy coffee drinkers are also those who are heavy smokers, drink more-than-moderate alcohol and have high levels of stress. Not to mention the temptation to have a sweet treat with your coffee. Many cafés these days have specials on coffee and cake or coffee and fruit breads for little more than the price of the coffee. Hard to resist!

Caffeine and breastfeeding

During breastfeeding, again it's best to keep your caffeine intake to 150- 200 mg per day. Caffeine passes to the baby through breast milk (at a rate of about one per cent of what the woman consumes). If the mother drinks a lot of caffeine while breastfeeding, the baby can become irritable, cry more and sleep less. Not a good scene.

Caffeine's downsides

From time to time, caffeine has been singled out as the cause of various health problems ranging from heart troubles to high blood pressure and ulcers. Should you worry?

Heart problems and arrhythmia

Anyone with a pre-existing heart condition should be very cautious about consuming too much caffeine. In 1999, a 25-year-old women died from caffeine-induced cardiac arrythmia after consuming a 'natural energy' guarana health drink containing a high concentration of caffeine. This seems to happen with energy drinks rather than coffee.

High blood pressure

According to the Mayo Clinic, caffeine can cause a short, but dramatic increase in your blood pressure, even if you don't have high blood pressure. Why it does this no-one knows for sure. So cutting back is important especially if you're over 70, are overweight or already have high blood pressure.

Brittle bones

High intakes of caffeine promote the loss of calcium by 'dragging' calcium out of the body via the urine. If you continually overdo caffeine, your bones may eventually suffer, which may predispose you to osteoporosis in later life. The results of several studies reveal, however, that this applies only when calcium intake is already low. Coffee posed no increased threat to women who consumed at least a glass of milk a day. Ordering a milky coffee e.g. flat white or cappuccino can kill two birds with one stone.

Stomach or peptic ulcer

Caffeine increases the amount of acid produced by the stomach, which can irritate the stomach lining or worsen an existing ulcer. Cutting back is a good idea here.

Any positives?

On the positive side, there are promising reports that coffee consumption may help slow Parkinson's disease in older men and possibly decrease the risk of type 2 diabetes. A space to watch over the next few years.

Written by guest contributor, dietitian-nutritionist Catherine Saxelby, and reproduced here with permission from www.foodwatch.com.au.