SAN FRANCISCO — The risk for kidney stones can be affected by substances found in community drinking water, new research shows.
“We did identify some novel exposures that warrant further study,” said investigator William Brubaker, MD, from Stanford University in Palo Alto, California. Some substances, such as trichloropropane — an artificial solvent — are associated with an increased risk, whereas others, such as potassium, are associated with a decreased risk.
More investigation into these substances might help explain why the incidence of kidney stones has been climbing in recent years, he said here at the American Urological Association 2018 Annual Meeting. In the United States, the incidence is elevated in the Southeast and in places with softer water, higher temperatures, and more precipitation.
Although the correlation between water quality and the incidence of kidney stones has been known for some time, only a handful of studies have looked at the association between these two variables.
“That is what set off this research,” said senior investigator Simon Conti, MD, also from Stanford University.
The team identified 218,324 emergency department visits for kidney stones from 2010 to 2012, and 27,361 surgeries, using the California Office of Statewide Health Planning and Development. They then cross-referenced these events with ZIP codes to create a stone score.
Using water-quality reports issued by the California State Water Resources Control Board from 2009 to 2012, which cover 90% of the population supplied with municipal water, investigators found 273 variables — from 3,547,535 individual tests — that seemed to be clinically relevant and were tested frequently in the majority of the ZIP codes.
To control for socioeconomic status, the investigators used data from the 2011 American Community Survey on wealth, income, education, and occupation.
Table. Associations Between Water Constituents and Kidney Stones
| Water Constituent | Odds Ratio |
|---|---|
| Association | |
| 1,2,3-trichloropropane | 1.56 |
| Total organic carbon | 1.42 |
| Trichloroacetic acid | 1.40 |
| Zinc | 1.34 |
| Inverse association | |
| Bicarbonate alkalinity | 0.85 |
| Laboratory pH | 0.85 |
| Selenium | 0.84 |
| Barium | 0.83 |
| Alkalinity (as calcium carbonate) | 0.82 |
| Dibromochloromethane | 0.79 |
| Nitrate | 0.78 |
| Ethyl tert-butyl ether | 0.78 |
| Tert-amyl methyl ether | 0.78 |
| Magnesium | 0.76 |
| Natural-source fluoride | 0.74 |
| Dibromoacetic acid | 0.74 |
| Bromoform | 0.73 |
| Sodium | 0.72 |
| Potassium | 0.71 |
| Hardness (as calcium carbonate) | 0.70 |
| Calcium | 0.69 |
| Chloride | 0.67 |
| Sulfate | 0.66 |
| 2,3,7,8-tetrachlorodibenzo-p-dioxin | 0.61 |
Previous research has suggested that dietary calcium, magnesium, and potassium protect against kidney stones. But some of the other the associations came as a surprise.
“This is a pretty long list of associations,” Brubaker told Medscape Medical News. “Some of these compounds haven’t been studied within the realm of kidney stone development.”
“Carbon content was associated with more stone disease,” Conti reported. “That’s a measure of how clean the water is.” He said he is intrigued by the associations between kidney stones and sulfate and zinc.
The investigators plan to study the literature for relevant information about the substances they identified. And they are considering using data from the US Environmental Protection Agency to conduct a similar nationwide study.
They might also use a fruit fly model of kidney stones to test for links with these substances. Ultimately, they envision randomized controlled trials that, for example, compare bottled water with municipal water.
Currently, the only dietary intervention that has been shown in a randomized controlled trial to reduce the risk for kidney stones is adequate hydration, Conti said. However, cutting back on sodium and animal proteins and increasing vegetable consumption might help, depending on the type of stone.
Although a high intake of dietary calcium was once considered a risk factor, research has since indicated that inadequate dietary calcium might be a bigger problem.
There are several limitations to this study, Brubaker acknowledged. Water district connections change over time; water districts have overlapping ZIP codes; the period of exposure examined was short, whereas it can take years or decades for effects to emerge; and no very small water suppliers were included in the analysis, nor were private wells, filtered water, or bottled water.
And correlation does not prove causation, he cautioned.
However, this research could have implications for public health policy, said James Borin, MD, from NYU Langone in New York City, who moderated the press conference during which the results were presented.
“One of the important things about these studies is that clinicians saw a trend and they investigated. This is the way research is supposed to be done,” he added.
Brubaker, Conti, and Borin have disclosed no relevant financial relationships.
American Urological Association (AUA) 2018 Annual Meeting: Abstract MP13-02. Presented May 18, 2018.
Follow Medscape on Twitter @Medscape and Laird Harrison @LairdH
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