Caffeinated or decaf - either way, coffee's not good for you

It's tough being a coffee drinker. New research has shown that even small levels of caffeine can decrease insulin sensitivity in healthy humans, but cutting out the caffeine altogether can have other effects. A separate study shows that more than three cups of decaf a day can increase the risk of rheumatoid arthritis.

Writing in the February issue of Diabetes Care, Dr Paul Smits and colleagues from the University Medical Centre in the Dutch town of Nijmegen said they had carried out a randomised, double-blind, crossover study in 12 healthy subjects.

The subjects were told to abstain from caffeine intake for 72 hours and were then given 3 mg/kg of caffeine or a placebo. The researchers then used hyperinsulemic-euglycemic glucose clamps to assess insulin sensitivity.

"Insulin sensitivity was calculated as whole-body glucose uptake corrected for the insulin concentration,"​ the researchers said in the journal. "Caffeine decreased insulin sensitivity by 15 per cent compared to the placebo."​

The researchers found that after caffeine administration, plasma free fatty acids increased and remained higher than the levels found in the placebo group. In addition, there was a fivefold increase in plasma epinephrine (adrenaline), while smaller increases were observed in plasma norepinephrine and blood pressure. Both epinephrine and norepinephrine are secreted by the adrenal gland and lead to increased heart rate and blood rate.

Dr Smits pointed out that the findings of the research were not sufficient to warn against caffeine consumption, especially as patients who consume a lot of caffeine could become tolerant to its effects.

Meanwhile, a separate study in the US showed that drinking decaffeinated coffee was no more safe, at least among older women. Researchers taking part in the Iowa Women's Health Study found that drinking more than three cups of decaffeinated coffee per day could increase the risk of developing rheumatoid arthritis.

Ironically, perhaps, drinking caffeinated coffee seems to have no effect, while drinking tea can actually reduce the risk, according to a report in the January issue of Arthritis and Rheumatism.

More than 30,000 women aged 53 to 69 were questioned in 1986 regarding average intake of the beverages over the previous year as part of the study. Between 1986 and 1997, there were 158 cases of rheumatoid arthritis within the group.

Dr Kenneth Saag of the University of Alabama at Birmingham and his team of researchers have estimated the relative risks for rheumatoid arthritis after adjusting for age, marital status, smoking history, alcohol use, age at menopause and use of hormone replacement therapy.

The relative risk associated with regular coffee intake of at least four cups per day was 0.98 compared with those drinking none, while for the highest category of caffeine intake, those drinking more than 376.5 mg/day, the relative risk was 0.94.

For the same amount of decaffeinated coffee consumption, the relative risk was 2.44. However, there did not appear to be a dose response, because the relative risk associated with less coffee was no more than 1.11, the researchers said.

For more than three cups of tea per day, the relative risk was 0.35. However, this finding was not statistically significant because only five women reported this amount of tea consumption.

Dr Saag suggested that the link with decaffeinated coffee may be related to the direct application of industrial solvents to coffee beans, the method used to extract caffeine prior to the mid-1970s. Tea's apparent protective effect could be due to its anti-inflammatory and antioxidant properties.