Caffeine risk interview may be a storm in a teacup


I recently listened to an interview given on national radio by Jack James, professor of psychology at NUI Galway. Prof James described a study he was carrying out on the ill-health effects of consuming caffeine, specifically its possible links to heart attacks and stroke. Because of his concerns, the professor no longer drinks tea or coffee.

I was surprised as I was unaware of any significant hazards associated with sensible levels of caffeine consumption. If caffeine is dangerous this would have serious implications - we Irish are amongst the most prolific tea-drinkers in the world.

On an average day I drink three cups of tea and two cups of coffee, so this encouraged me to look at the scientific studies about a connection between caffeine and ill-health. I am no expert in this area but my brief investigation indicates that the moderate consumption of caffeine by the average person is not dangerous.

Caffeine is a natural chemical found in the leaves, seeds or fruits of more than 63 plant species worldwide. The most common sources are coffee, cocoa beans, cola nuts and tea leaves. An 8 oz cup of instant coffee contains about 75 milligrams (mg) of caffeine; an 8 oz cup of tea contains about 50 mg of caffeine; a can of cola contains about 50 mg of caffeine; 1 oz of milk chocolate has about 6 mg of caffeine.

The average adult ingests about 200 mg of caffeine daily. The average 5 to 18-year-old youngster ingests about 40 mg of caffeine daily.

Caffeine is a mild central nervous stimulant. It is only one of many substances in food which are pharmacologically active. Another example is capsaicin in hot peppers which induces a burning sensation and sometimes sweating.

The effects of caffeine are transient and pass off within a few hours. Caffeine doesn't accumulate in the body and is excreted within several hours. However, I understand that a small minority of people find that the general stimulatory effects of caffeine makes them feel "hyper" and find it best either to avoid the substance altogether, or to confine themselves to, for example, very weak tea.

Specific areas which have been investigated to determine if caffeine intake is a predisposing factor include: cancer; heart attack; stroke; female fertility; miscarriage and osteoporosis. Some studies show a weak correlation between caffeine intake and ill-effects but the majority of studies show no correlation.

My brief review of the scientific literature indicates that for the average person, few, if any ill-health effects are induced by average consumption of caffeine. However, a note of caution is in order in one area. Malignant hyperthermia (MH) is a genetic disease that afflicts about one person in 12,000.

MH can pose a major problem if the afflicted person undergoes a general anaesthetic under the commonly-used anaesthetics. This can trigger off a sharp rise in body temperature caused by muscle spasms which is usually fatal unless the antidote drug Dantrolene is administered immediately.

Prof Jim Heffron in the biochemistry department at UCC is an expert on MH. Several years ago in collaboration with Prof Tommie McCarthy, he identified the gene responsible for MH. He also, in collaboration with European co-workers, developed the now standard test for MH which involves testing muscle samples for their susceptibility to caffeine-induced contraction.

The muscles of those with MH are much more susceptible to this contraction than those without MH. The caffeine intake from average tea and coffee consumption would have no effect on normal muscles. However it would be wise for an MH sufferer to be very sparing in their intake of caffeine.

Caffeine stimulation can cause a transient increase of blood pressure and this is the focus of Prof James's research. Elevated blood pressure is an established factor that increases the risk of both heart attack and stroke.

Prof James argues that the small increases in blood pressure induced by average consumption of tea and coffee could be responsible for about 12 per cent of all heart disease and for 20 per cent of strokes. He summarises his argument in the medical journal, Lancet, Vol. 349, January 25th, 1997.

However, some studies have shown that any temporary rise in blood pressure due to caffeine consumption is less than the elevation in blood pressure produced by normal daily activities. Also, as far as I can judge, the majority of epidemiological studies in the area have failed to show any link between intake of caffeine and cardiovascular disease.

So where does all of this leave us? As in so many other things, the best advice as regards caffeine is moderation. If you are an average, healthy person you need not be concerned about drinking a few cups of tea every day. Of course if you have high blood pressure or a heart condition, or if you suffer from MH, then you would be wise to discuss caffeine intake with your GP.

Prof James does have a logical case to argue but perhaps the main value of his argument is to provide incentive to those "tea-holics" or "coffee-holics" amongst us to moderate our appetites.

Very many people are under the false impression that they must carefully monitor every mouthful of food they eat. The key to a healthy lifestyle for the average person is to eat a varied diet and to take aerobic exercise. You should eat a wide variety of foods in moderate amounts and, every second day, you should do at least 30 minutes of vigorous aerobic exercise - fast walking, jogging, cycling or swimming. This is enough exercise to make you break into a sweat. And if you succumb to the yen for "a nice cup of tea" a few times per day, well that's fine too.

(William Reville is a senior lecturer in biochemistry and director of microscopy at UCC.)