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NEW YORK (Reuters Health) - Women who down a lot of caffeinated drinks each day may have a slightly increased risk of developing 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 U.S. 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 percent more likely to develop frequent problems with bladder control (at least once a week).
The study found no increased risk among women consuming 299 milligrams of caffeine - the equivalent of about three cups of coffee - or less per day.
In the most highly caffeinated group that downed 450 mg or more per day, however, caffeine was particularly related to urge incontinence, or urgency, a type of incontinence where leakage happens after a sudden, strong urge to urinate.
The findings, reported 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, told Reuters Health in an email.
"We found no increase in risk among women with lower caffeine intakes," said 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 (see Reuters Health story of April 6, 2011). 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, 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 U.S. nurses who were between the ages of 37 and 79 at the outset. Of 65,176 women who were initially incontinence-free, half fell into the lowest caffeine intake group -- less than 150 mg of caffeine a day. That's roughly equivalent to less than a cup of coffee per day.
Another 9 percent reported downing more than 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 percent developed frequent urinary incontinence each year over the next 4 years. That compared with 1.9 percent in the lowest-intake group.
The researchers then factored in a number of other variables -- like women's age, weight and smoking habits. They found that a very high caffeine intake, itself, was tied to a 19 percent increase in the risk of frequent incontinence.
According to Townsend, caffeine might promote incontinence because it is a diuretic - it promotes flushing of water from the body -- and 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.
Urinary incontinence is about twice as common in women than men, and its likelihood rises with age. One large U.S. study found that almost one-quarter of women in their 60s and 70s said they had urine leakage at least once a month; the rate rose to one-third among women in their 80s.
Risk factors for urinary incontinence include obesity and past pregnancies with vaginal births.
SOURCE: bit.ly/gKhAVP Journal of Urology, online March 18, 2011.