A major study involving more than 14,000 people in Finland, which has the highest rate of coffee consumption in the world, has revealed that those who drink most have the lowest incidence of adult-onset or type 2 diabetes.

When people drank three to four cups of coffee a day, their risk of developing diabetes fell by 29 per cent for women and 27 per cent for men.

“Coffeeholics” who drank very large amounts of coffee — ten or more cups a day — were even less likely to suffer from the disease: such high consumption reduced the risk by 79 per cent for women and 55 per cent for men.

In the study, a team at the Finnish National Public Health Institute in Helsinki combined the results of three surveys conducted in 1982, 1987 and 1992, involving a total of 6,974 Finnish men and 7,655 women.

The subjects, who were all aged between 35 and 64 and had no history of stroke, coronary heart disease or diabetes, were asked to record their coffee consumption and were then followed up by doctors to assess their health.

Jaakko Tuomilehto, who led the research, said it suggested that coffee drinking offered some protection against adult-onset diabetes, particularly in women.

“This study revealed un- equivocal evidence for an inverse and graded association between coffee consumption and type 2 diabetes mellitus, independent of other risk factors for type 2 diabetes mellitus,” he said.

“Because the Finnish population drinks more coffee than other populations, we had power to determine the risk of diabetes mellitus at high levels of coffee consumption”.

The research, details of which are published today in the Journal of the American Medical Association, does not indicate why coffee appears to protect against diabetes. Scientists believe caffeine is a likely candidate, though minerals such as potassium and magnesium and the vitamin niacin have also been suggested.

Dr Tuomilehto said more research was needed to determine this. “The mechanisms or process by which coffee contents may exert their beneficial effects . . . are nevertheless unclear,” he said, The results add to a growing body of evidence. Previous studies at the Harvard School of Public Health in the US, and the Dutch National Institute for Public Health and the Environment, have made similar findings.

The benefits, however, seem to be greatest at much higher levels of coffee consumption than are recommended for general health. The Dutch study, for example, found that men who drank seven cups a day were 50 per cent less likely to develop diabetes than those who drank just two cups daily.

Excessive coffee drinking has been linked to a range of health problems, including miscarriage, insomnia, anxiety, diarrhoea and an irregular heartbeat. Most nutritionists advise against drinking more than four cups a day, particularly during pregnancy.

Type 2 diabetes, which usually develops in middle age and is often linked to obesity, has become a worldwide epidemic. While it can be controlled by diet and drugs, it can have long-term consequences such as heart disease and blindness.

The condition develops when the body becomes insensitive to insulin. Coffee reduces insulin sensitivity but other components in it, such as magnesium or chlorogenic acid, may have beneficial effects.

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