Anyone who has passed a kidney stone has people – including doctors – tell them “you need to drink more water.” While sometimes it may be that simple, often there are multiple factors at work. I know many people who obsessively drink water every day and still form stones. On the flip side, I know people who seem to survive on soda and fast food and yet they never form stones. Regardless, the more patients understand about stone disease the better it can be prevented.
Recently the American Urologic Association reviewed the epidemiology of stone disease. Epidemiology is the branch of medicine that deals with the incidence, distribution and possible control of diseases and other factors relating to health. There were some intriguing findings. In the U.S. the overall prevalence of kidney stones has increased from 3.2% of the population in 1976 to 8.4% in 2010. In other words, within just over 30 years the prevalence of stones in the U.S. population has nearly tripled and now affects nearly 1 in 11 people. This is especially impressive when you factor in that more research has been done regarding prevention of kidney stones during this period.
As we all know, Las Vegas has a relatively hot climate. There is research confirming a geographic variation in stone prevalence. Studies show that between 1988-1994 the Southeastern United States had the highest prevalence compared to other regions in the country. This is thought to be due to the heat, humidity and associated risk of dehydration. However, the Southeast also has the highest prevalence of obesity and this may also be a risk factor. Stones tend to exhibit peak incidence in warmer months and outside workers in hot environments tend to have a higher prevalence of stones.
Kidney stones can happen in all ages with the peak incidence being from 40-59 years old. The rate of stone disease seems to be increasing for all age demographics over time, including pediatric patients. It used to be felt that kidney stones were predominately a male disease, but women are increasingly likely to have stones. Currently in the U.S. the overall prevalence of stones in males is 10.6 percent versus 7.1 percent in females. In the U.S. today stones are most common in Caucasians (10.3 percent) followed by Hispanics (6.4 percent) and least common in African Americans (4.3 percent). Reasons for differences in the prevalence of stones related to race or ethnicity remain unclear.
When other family members have a history of stone disease the risk of kidney stones in a related individual is more than twice as high – much research is currently being done in this field.
A number of studies have identified associations between kidney stone risk and health issues such as diabetes and obesity. Individual risk for stones increases with weight gain, body mass index (BMI) and increase in waist circumference. The association likely involves changes in urinary composition, perhaps stimulated by increasing levels of insulin.
Many patients have no other associated diseases or symptoms so this can only be diagnosed through testing. It is recommended that all patients with a history of recurrent stones or large stones go through a metabolic evaluation. This includes blood lab testing as well as specialized 24-hour urine tests and actual stone analysis from passed stones or stones that are removed surgically. A urologist or a nephrologist can perform these tests. Often these tests can give clues as to why certain individuals are more prone to stone formation. As a result many patients can modify their lifestyle or diet in a certain way or even start a medication that may prevent future stones. Research has shown that despite more knowledge about risk factors and preventative medication, the rate of patients actually having metabolic evaluations and potentially starting preventative medication is relatively low.
The American diet is likely contributing to a lot of the increased prevalence of stones. To truly understand what dietary changes may be beneficial to a specific patient, metabolic testing should be used. In general though, it is felt that along with increasing water intake, decreasing sodium intake and decreasing intake of animal meat/protein may be beneficial.
People need to realize that not all fluid intake is the same. Some beverages may increase risk of stones, especially beverages that act as a diuretic such as coffee, alcohol, and caffeinated sodas (a diuretic is any substance that promotes the production of urine). These beverages can dehydrate the kidneys, increasing the risk of stone formation. Some research has shown that increasing citrate in your diet – such as adding lemon juice to your water – can help prevent stones because of the way it alters your urinary pH.
Patients often ask how much water should they drink. My answer is “as much as you can.” It has to become a habit. Research has shown improvement in stone risk with drinking 8 glasses of water a day, or about one liter. I often tell people to use the “eyeball test,” which means just looking at your urine. In general, if it appears dark then you probably should be drinking more water. If it appears clear than you are probably doing all right.
Despite advances in minimally and non-invasive treatments to remove stones and a significant decrease in mortality from stone disease, the prevalence of stone disease continues to rise remarkably. It is obvious that in many patients increasing water intake alone is not sufficient. I think it is important to understand that not all the stones are the same and not all patients with stones are the same. Hopefully as we better understand risk factors and better use metabolic evaluations we can do a better job at preventing future stones.
In the meantime, make sure you are drinking more water!