Women who consume a lot of caffeinated beverages may have a slightly increased risk of urinary incontinence, a new study suggests. The results add to conflicting evidence on whether caffeine worsens a common condition.
Researchers found that of more than 65,000 US women, those with the highest caffeine intake - roughly equivalent to four or more cups of coffee per day or 10 cans of soda - were more likely than the less-caffeinated to develop urinary incontinence over 4 years.
Compared with women who got the least caffeine, those with the highest intake were 19% more likely to develop frequent problems with bladder control (at least once a week).
The study found no increased risk among women consuming 299 mg of caffeine - the equivalent of about three cups of coffee - or less per day.
In the most highly caffeinated group that consumed 450 mg or more per day, however, caffeine was particularly related to urge incontinence.
The findings, reported online 18 March in the Journal of Urology, do not prove that caffeine caused the women's bladder-control problems. And if caffeine is to blame, it may only be at very high amounts.
"We only observed an increased risk of urinary incontinence among women with the highest intakes of caffeine - that is, women who consumed about four or more cups of coffee per day," Dr Mary K. Townsend, one of the researchers on the work said.
"We found no increase in risk among women with lower caffeine intakes," said Dr Townsend, of Harvard Medical School in Boston.
She said it is too early to give women specific advice on caffeine intake. More studies are needed to confirm the current results.
Another study published in March looked at 14,000 Swedish women and found no increased risk of incontinence among coffee drinkers when age was taken into account. That analysis did not factor in the amounts of caffeine individual women consumed, however.
Women who already have urinary incontinence are commonly told to limit their caffeine intake, Dr Townsend noted.
"Our study suggests that avoiding higher caffeine intake might also be useful advice for women who do not have urinary incontinence, but are concerned about developing (it)," she said.
The findings are based on data from two large long-term studies of 65,000 US nurses between the ages of 37 and 79. Half fell into the lowest caffeine intake group - less than 150 mg/day, roughly equivalent to less than a cup of coffee per day.
Another 9% consumed 450 mg of caffeine or more per day. That equates to about four or more cups of coffee each day, or 10 cups of tea or cans of caffeinated soda.
Of the women in that high-caffeine group, 2.7% developed frequent urinary incontinence each year over the next 4 years. That compared with 1.9% in the lowest-intake group.
On adjustment for variables such as age, weight and smoking habits, very high caffeine intake itself was tied to a 19% increase in the risk of frequent incontinence.
According to Dr Townsend, caffeine is a diuretic, and so people who already have an overactive bladder may be more susceptible to those effects.
There's also evidence, she said, that even low doses of caffeine can speed muscle contractions in the bladder. (Reuters Health/ April 2011)