Singapore - Can coffee really keep the doctor away?

He was a healthy 35-year-old man who had no known medical problems but was seen in my clinic for fast, irregular heart rate after drinking several cups of coffee to keep himself awake during a symposium. His question was 'Is coffee harmful to my heart?'

While the answer may have seemed obvious a decade ago, more recent studies have shown rather surprising data.

Not all coffees are the same

The universe of research data on coffee is dotted with contradictions on outcomes. Other than methodology and size of studies, some of these differences may be due to the different ways in which coffee is prepared.

Unfiltered coffee contains chemicals called diterpenes such as kahweol and cafestol, which are associated with an increase in 'bad' cholesterol and hence an increase in risk of heart disease. Some studies suggest that drinking unfiltered boiled coffee can increase cholesterol by as much as 10 per cent.

These chemicals can be removed with a paper filter.

The most well-known chemical in coffee is caffeine. On the average, one cup of brewed or one shot of espresso has about 100mg of caffeine. Decaffeinated coffee contains a few mg in each cup. The equivalent of a lethal dose of caffeine will be akin to drinking 100 cups of coffee in a day.

Will my heart skip a beat?

It is a common perception that drinking coffee can cause your heart to skip a beat. Perception appears to be different from reality. A Canadian study published in the Annals of Internal Medicine in January 1991 reviewed five studies of people with abnormal heart rhythms and found that drinking up to five cups of coffee a day did not worsen the heart rhythm.

Interestingly, a study of about 130,000 Kaiser Permanente health insurance members showed that those who were drinking up to three cups of coffee a day were 20 per cent less likely to be hospitalised for abnormal heart rhythms than non-drinkers.

While the Harvard study on 45,000 healthy men in the Health Professionals Follow-Up Study published in the New England Journal of Medicine in 1990, found that coffee drinking had no effect on the risk of heart attack or stroke, studies in the last few years have put a positive spin on coffee.

A more recent study of more than 81,000 men and women in Japan published in the Journal of Epidemiology and Community Health showed that drinking one or two cups of coffee a day was associated with up to a 23 per cent risk reduction of death from heart disease. Another large 2008 Spanish study in the Annals of Internal Medicine that tracked 129,000 men and women over two decades found that women who drank four to five cups per day were 34 per cent less likely to die of heart disease, while men who had more than five cups a day were 44 per cent less likely to die.

Is coffee good for my brain?

It appears that the benefits on the heart seen in recent large trials appear to extend to the brain as well. A 2009 Harvard study of 83,000 women published in the journal Circulation showed those who drank two to four cups of coffee a day had a 19 to 20 per cent lower risk of stroke than women who drank less than one cup a month.

The data was supported by a 2011 Swedish study of 34,670 women published in Stroke journal that found women who drank more than a cup of coffee each day had a 22 to 25 per cent lower risk of stroke than women who drank less coffee.

This benefit is not gender-specific and a 2008 Finnish study of more than 26,000 male smokers found that the men who drank eight or more cups of coffee a day had a 23 per cent lower risk of stroke than the men who drank little or no coffee.

Coffee and other health benefits

Possible benefits that appear to be associated with regular coffee drinking include lower risk of developing diabetes mellitus, gallstones, liver damage, dementia, Parkinson's disease and colon cancer.

In addition, it also appears to be associated with improved cognitive function and performance in physical endurance activities.

Should I start drinking coffee?

Before you start recommending coffee to your friends as a health drink, you will need to answer this question: Can coffee be harmful to health?

Most of the purported benefits of regular coffee consumption are statistical associations and researchers have yet to be able to produce definite evidence that coffee has a direct causative effect for these benefits.

There are more than 1,000 chemicals reported in roasted coffee of which many of those which have been tested have been shown to have cancer-causing effects in animal experiments when given in high doses.

One of these carcinogenic chemicals, acrylamide, is higher in instant coffee than brewed coffee. Acrylamide also causes nerve damage in people exposed to very high levels at work.

Caffeinated coffee may not be suitable for some. Elderly individuals who are unable to metabolise caffeine effectively do not tolerate coffee well. In some, it may aggravate pre-existing heartburn, migraine, abnormal heart rhythms and insomnia.

Therefore, while regular coffee lovers can continue enjoying their espresso, there is as yet insufficient evidence to start recommending it to non-drinkers.

There are better ways to reduce heart disease and strokes, such as cessation of smoking, dietary reduction of cholesterol and exercise. As for the young man, he was advised to avoid heavy coffee consumption - he did not have a subsequent recurrence of abnormal heart rhythm.

Dr Michael Lim

Dr Lim is medical director at the Singapore Heart, Stroke & Cancer Centre. He is also editor-in-chief, Heart Asia; British Medical Journals Publishing Group, chairman; Scientific Advisory Board, Asia Pacific Heart Association honorary professor and senior medical adviser, Peking University Heart Centre.

The Business Times