Few things in life are as unpleasant as kidney stones, the hard, solid particles of mineral and acid salts that form in the urinary tract and sometimes get stuck there and cause extreme pain.
There's plenty to go around these days. Americans are developing kidney stones at almost twice the rate as 20 years ago, wreaking particular havoc on middle-age adults. According to UCLA research, kidney stones now affect 1 in 11 Americans, more than diabetes, heart disease or stroke. The rate was 1 in 20 as recently as 1994. Men are affected by kidney stones more often, but the number of women impacted is rising as well.
Many stones are as small as a grain of sand and pass through us without incident. But the pain caused by larger particles drive 500,000 people to emergency rooms nationwide each year, according to the National Institutes of Health. At that point, stones can be broken up with sound waves, removed with the help of a stent inserted through the urethra or addressed through surgery.
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"The risk for developing kidney stones is greatest in middle age," says Dr. Charles Scales, Jr., a urologic surgeon at the David Geffen School of Medicine at UCLA and a co-author of the study. "The risk increases for men in their 40s and continues to rise until age 70. For women, the risk peaks in their 50s."
The rise in kidney stones can be blamed on the same cause as many other conditions: obesity. "Our findings suggest the increase in kidney stones is due, in large part, to the increase in obesity, metabolic syndrome and diabetes among Americans," Scales says. The nation's obesity rate has risen from 23 percent in 1994 to more than 35 percent today.
How to Avoid Kidney Stones
Researchers exploring the prevalence of kidney stones argue that adults who want to avoid the condition need to do more to prevent it. The main approach to kidney stones has always been to treat them when people are already suffering, but primary-care physicians should make it clear to their patients that stones are a likely byproduct of poor diet and health and then urge them to take preventive action.
"Imagine that we only treated people with heart disease when they had chest pain or heart attacks and did not help manage risk factors like smoking, high cholesterol or high blood pressure," Scales said in a statement accompanying the UCLA study. "This is how we currently treat people with kidney stones. We know the risk factors, but treatment is directed toward patients with stones that cause pain, infection or blockage of a kidney rather than helping them to prevent kidney stones in the first place."
Researchers have learned more about the impact of other strategies for reducing our risk of developing kidney stones, besides weight loss. Now we just need to follow their advice.
Exercise An encouraging new study has found that women between 50 and 80 who engaged in moderate exercise reduced their likelihood of developing kidney stones by as much as 31 percent. "Even small amounts of exercise reduced the risk and the intensity of exercise didn't matter," says Dr. Matthew Sorensen, a urologist at the University of Washington School of Medicine and lead author of the study. "Women do not need to run marathons — just practice consistent, regular exercise."
To reap maximum benefits, Sorensen says women should strive for 10 "metabolic equivalents," or METs per week. That works out to 3 hours of light walking, 4 hours of light gardening or 1 hour of moderate jogging.
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Hydrate, the right way Hydration encourages flushing of the urinary tract, a key to avoiding kidney stones. "I advise all my patients to increase their fluid intake since, on average, stone formers drink less fluid and make about 500cc less urine daily than non–stone formers," Sorensen says. "Patients need to drink enough fluid to make one-and-a-half to two liters of urine daily or enough so that the urine never gets darker than a light yellow color."
Drinking sugar-sweetened soda, however, can undermine those efforts. A study published in May by the Clinical Journal of the American Society of Nephrology found that daily consumption of soda and other sugary drinks like fruit punch was associated with a higher risk of developing kidney stones. Coffee, tea and wine appeared to help lower the odds. Data on artificially sweetened diet sodas was inconclusive.
Reconsider supplements Postmenopausal women often take calcium and vitamin D supplements to prevent osteoporosis and bone fracture, but there is evidence that these supplements also increase the risk of developing kidney stones. In February, the U.S. Preventive Services Task Force advised that otherwise healthy women over 50 need not take these supplements to prevent fractures because the low-to-moderate daily doses of vitamin D (up to 400 IU) and calcium (up to 1,000 mg) many take were ineffective.
Echoing the task force's advice, Sorensen says women with osteoporosis or vitamin D deficiency should continue taking the supplements "even if they are a stone former. But if they have normal bone density and are a recurrent kidney stone former, then I suggest they get calcium from their diet rather than supplements."
Eat to avoid kidney stones When it comes to diet, Sorensen says, there are four primary things you can do to reduce your risk: Increase your fluid intake, especially of water; reduce your salt consumption; limit your portions of animal protein, maybe by substituting legumes for meat; and maintain an adequate intake of calcium through your diet. (Unlike calcium supplements, calcium-rich foods do not spur the production of kidney stones.)
Some people who are prone to stones — less than 15 percent of sufferers overall — have excess oxalate excretion in their urine. If you're part of this group, you'll need to restrict consumption of oxalate-rich foods like spinach, soy, dark chocolate, okra, Swiss chard, sweet potatoes, rhubarb, beets, nuts and tea. "Periodic intake is okay," Sorensen says, "but weekly intake is too much — and when oxalates are consumed they should be taken with a glass of milk or other dairy product."