More from Rodale News: What Junk Food Is Doing to Your Kidneys
The most likely suspect in the increase of kidney stones: our ever-growing obesity rates, says lead study author Khurshid R. Ghani, MD, MS, FRCS, clinical assistant professor in the department of urology at the University of Michigan's Ann Arbor VA Healthcare System. But more specifically, he says, "There is a condition called metabolic syndrome, which is used to describe the condition when hypertension, obesity, and diabetes are preset in the same patient. This by far, in my opinion, is the major risk factor."
Kidney stones form when you have high concentrations of minerals and acid salts in your system that aren't getting diluted by urine, as they normally would. Those minerals and salts stick together to form painful stones that pass through the urethra. Diabetics have high uric acid concentrations in general, Dr. Ghani says, putting them at high risk for stones, and too much salt in the diet—which is typical of people suffering from hypertension—just compounds that.
Adding to all that, people who are obese don't exercise and lead sedentary lifestyles, he says, and that leads to crystallization of minerals in urine, as well.
But even if you aren't suffering from metabolic syndrome, obesity, or diabetes, there are some other environmental causes of kidney stones that researchers are paying closer attention to. Some of these factors are more established scientifically than others, Dr. Ghani points out, but they're worth noting if you suffer from kidney stones that weight and other factors can't explain away:
#1. You live in the "Stone Belt."
Heat is a major contributor to stone formation, and in his study, Dr. Ghani's data showed that kidney stone visits peaked in the summer. Why? "In one word: dehydration," says Dr. Ghani. "Hot weather and poor fluid intake lead to urine formation that is 'supersaturated' with crystals," he says. And those living in warmer parts of the country suffer more. The Southern U.S., all of Texas, Southern California, and parts of Arizona and New Mexico make up what's known as the "Stone Belt," a region that sees higher diagnoses for kidney stones than any other area of the country. Climate change is likely to make that worse. One study in the journal Kidney International predicted that kidney stone diagnoses are likely to increase another 10 percent by midcentury as global temperatures rise and we experience the subsequent heat waves they produce. (Here's one of our favorite product picks to prevent dehydration.)
#2. You eat too much animal protein.
Animal proteins increase the excretion of calcium from your system, which can lead to high concentrations of the mineral in your kidneys, where stones form. They also reduce the levels of calcium-dissolving citrate in your urine, according to the National Institute of Diabetes and Digestive and Kidney Diseases. (Swap out servings of meat for these 9 Super-Healthy Sources of Vegetarian Protein.) An added benefit: Vegetarian proteins, such as whole grains, beans, and seeds, along with dark leafy vegetables, are foods that are high in magnesium, and a study in Urology found that magnesium can decrease urinary levels of oxalate, which also contributes to stone formation.
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#3. You're seriously stressed.
A 2012 study from the University of Minnesota found that loss of a loved one, unemployment, or another major stressful event were strong predictors, particularly among women, of suffering from at least two kidney stones in one year. The theory is that extremely stressful life events increase levels of a hormone called vasopressin, which decreases the volume of urine and can lead to a concentration of the minerals and salts that form stones. The links between everyday stress and kidney stones are less clear, says Dr. Ghani, and have more of a knock-on effect: Stressful days can lead to a bad diet and lack of motivation to exercise, he adds, both of which can create kidney stones.
#4. You aren't eating organic.
A number of studies have investigated the link between the heavy metal cadmium and kidney stones, primarily in workers exposed to the metal every day. But one study of the general public found that high urinary cadmium levels were associated with a 40 percent higher chance of developing kidney stones. Your biggest exposure to cadmium is through food, present as a contaminant from the phosphates used in synthetic fertilizers. Some cadmium also exists naturally in soil. You can avoid the cadmium-fertilizer issue by going organic, since organic farmers are prohibited from using synthetic fertilizers on their crops. Also, stop smoking! Tobacco is particularly effective at absorbing cadmium from soil, and smokers have abnormally high levels of the metal in their system, according to the Centers for Disease Control and Prevention.