Drinking coffee appears to hamper efforts by people with type 2 diabetes to control their blood sugar levels, and can exaggerate the blood sugar rise which occurs after each meal, according to new research.

By continuously monitoring the blood sugar levels of 10 patients with the disease, researchers found that the stimulant amplified the increase in glucose levels after mealtimes. If blood sugar levels are not controlled, people with type 2 diabetes often go on to develop complications such as heart disease.

The 10 volunteers had a small glucose monitor embedded under the skin in their abdomen. To control the amount of caffeine the participants received, the team gave them pills containing caffeine equivalent to around four cups of coffee in one day or similar looking placebos.

When the volunteers consumed caffeine their average daily sugar levels went up by 8%. "We're not sure what it is about caffeine that drives glucose levels up," said Dr James Lane, at Duke University in North Carolina, who led the study, published in Diabetes Care.

There are currently no guidelines to diabetics to avoid caffeine. "It could be that caffeine interferes with the process that moves glucose from the blood and into muscle and other cells in the body where it is used for fuel."

Lane's research appears to contradict a Finnish study in 2004 which found that people who drink more coffee are less likely to develop type 2 diabetes.

Risk of miscarriage?

Women are being advised to cut out caffeine during the first three months of pregnancy, to help reduce their risk of having a miscarriage.

The warning follows a study that found pregnant women who consumed two or more mugs of coffee a day were twice as likely to miscarry than those who abstained from caffeine completely.

The study of 1,063 pregnant women showed that those who had at least 200mg of caffeine each day had a 25% risk of miscarriage compared with a 12% risk for women who avoided all caffeine, including in tea, soft drinks and chocolate.

The advice, from doctors at one of America's largest private health organisations, goes further than guidelines introduced by British government health officials in 2001.

These recommend that pregnant women limit their daily intake to 300mg. The government advice was based on a Food Standards Agency review of the scientific literature, which found an increased risk where caffeine intake was higher than 300mg a day - or three cups of instant coffee - in the first 15 weeks. Fresh coffee is typically stronger than instant, and a cup of tea has around 40mg. "It appears that 200mg a day is already a high enough dose to increase the risk of miscarriage," said Dr De-Kun Li, a perinatal epidemiologist who led the study at Kaiser Permanente, a California-based non-profit health foundation that runs 32 hospitals. He advised women to consider not consuming caffeine or at least limiting their intake to less than 200mg during the first 12 weeks of pregnancy.

The women were asked what they had eaten and drunk until the 20th week of gestation: 635 had up to 200mg a day; 164 women had 200mg or more daily; and 264 had none. The doctors accounted for other factors known to affect miscarriage rates, including age, income, a history of miscarriages, smoking and alcohol consumption.

Overall, 172 women miscarried, 95% within the first 15 weeks of pregnancy. The results suggested that even moderate amounts of caffeine increased the risk.


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