Genes may play an important role in developing urinary incontinence, while lifestyle -- including diet - may be the biggest factor in overactive bladder, new research suggests.
In one study of more than 25,000 adult twins, Swedish researchers found that genes appeared to explain a large share of the risk of having urinary incontinence -- about half of it. However, genes seemed to play little role in overactive bladder, where lifestyle and environment appeared largely responsible for the risk.
Exactly what those lifestyle factors are was not clear from the study, which appears in the journal European Urology.
But in a separate study in the same journal, researchers found evidence that diet -- particularly vitamin C and calcium intake -- might be one.
Urinary incontinence refers to problems with urine leakage. Overactive bladder can cause urinary incontinence, but not necessarily. In general, a person with overactive bladder needs to make frequent trips to the bathroom -- at least eight times in 24 hours -- and often has a sudden, strong urge to urinate.
It has not been clear how important genetics on one hand, and environment on the other, might be in either bladder-control problem.
So for the Swedish study, researchers led by Dr. Ian Milsom of Sahlgrenska University in Gothenburg surveyed more than 25,000 identical and fraternal twins between the ages of 20 and 46.
Identical twins share all of their genes, while fraternal twins share about half of their genes. So twin studies allow researchers to estimate how much of a disease risk might be related to genes, to "shared" environment, or to "non-shared" environment, including adulthood lifestyle habits.
The study found that when it came to urinary incontinence -- reported by 7 percent of women and 1 percent of men -- genes appeared to explain 51 percent of the variation in women's risk. (There were too few men with bladder-control problems to do a similar estimate.)
With overactive bladder, however, genes explained very little of the variation in women's risk. Instead, shared environment explained about one-third, while individual environment accounted for the rest.
Shared environment, according to Milsom's team, could reflect lifestyle habits learned from parents -- including diet, exercise and smoking habits. Individual environment could reflect adulthood lifestyle choices, as well as factors like pregnancy.
Smoking and obesity have been linked to urinary incontinence and overactive bladder. And women who've given birth, particularly through vaginal delivery, have a higher long-term risk of bladder-control problems than other women.
Does vitamin C play a role?
In the second study, researchers surveyed just over 2,000 Boston-area women ages 30 to 79. They found that those with a high intake of vitamin C from food and supplements were more likely to report symptoms of overactive bladder.
Overall, 35 percent of the women reported such symptoms. Those odds were more than three-times greater among women who averaged more than 500 milligrams (mg) of vitamin C per day, versus those who consumed less than 50 mg.
The recommended vitamin C intake for women is 75 mg per day.
The connection does not prove that vitamin C is the reason for some women's overactive-bladder symptoms, according to lead researcher Nancy N. Maserejian, of New England Research Institutes in Watertown, Massachusetts.
"The findings from this study are new and need to be confirmed in future studies, so it's too early to make a recommendation for women based on these results," Maserejian told Reuters Health in an email.
"At most," she said, the findings suggest that women with overactive bladder who take high doses of vitamin C could try cutting down to see if their symptoms improve.
On the other hand, the study found, the more vitamin C women got from food, the less likely they were to have "voiding" problems. Those symptoms, reported by 8 percent of the study participants, include having a weak urinary stream or feeling like your bladder is still full after using the bathroom.
It's possible, according to Maserejian, that foods rich in vitamin C somehow protect against voiding symptoms -- either because of the vitamin or because of other nutrients in those foods. (Beta-cryptoxanthin, a nutrient often found in vitamin-C-rich foods, was also related to a lower risk of voiding problems.)
On the other hand, high doses of vitamin C can make the urine more acidic.
So, Maserejian said, "it is reasonable to wonder whether high doses of vitamin C from supplements irritate the bladder walls and therefore lead to problems with urinary urgency and frequency."
Foods high in vitamin C include fruits like oranges, grapefruit, strawberries, kiwi and cantaloupe; and vegetables like red and green peppers and broccoli.
The study also found a connection between calcium intake and overactive-bladder symptoms. Women who took more than 1,000 mg of supplemental calcium each day were twice as likely to have symptoms than women who took less.
The reason for that link is not clear, and Maserejian cautioned against making too much of it.
"Calcium supplements might have important health benefits," she said, "and women should not change their calcium intake based on these early findings."
Experts recommend that women younger than 51 get 1,000 mg of calcium a day, while older women should get 1,200 mg. The mineral is needed for bone health, and may help lower a woman's risk of developing the brittle-bone disease osteoporosis.
SOURCES: http://bit.ly/gj39hU and http://bit.ly/dHoJEN European Urology, online March 15, 2011.
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