From the Children’s Hospital of Philadelphia Something that I consider to be more than a stretch, and possibly conflated junk science, especially since I’ve suffered kidney stones myself and live in a place with summer temperatures that average well over 50°F. See my comments and citations of other papers at the end.
CHOP-led research finds link between hotter days, kidney stones in US adults and children
As daily temperatures increase, so does the number of patients seeking treatment for kidney stones. In a study that may both reflect and foretell a warming planet’s impact on human health, a research team found a link between hot days and kidney stones in 60,000 patients in several U.S. cities with varying climates.
“We found that as daily temperatures rise, there is a rapid increase in the probability of patients presenting over the next 20 days with kidney stones,” said study leader Gregory E. Tasian, M.D., M.Sc., M.S.C.E., a pediatric urologist and epidemiologist at The Children’s Hospital of Philadelphia (CHOP), who is on the staff of the Hospital’s Kidney Stone Center as well as the Hospital’s Center for Pediatric Clinical Effectiveness (CPCE).
Tasian, senior author Ron Keren, M.D., MPH, also of CHOP and CPCE, and colleagues from other centers published their results today in Environmental Health Perspectives, the journal of the National Institute of Environmental Health Sciences. The Urologic Diseases in America Project, supported by the National Institute of Diabetes and Digestive and Kidney Diseases, sponsored the study.
The study team analyzed medical records of more than 60,000 adults and children with kidney stones between 2005 and 2011 in Atlanta, Chicago, Dallas, Los Angeles and Philadelphia, in connection with weather data. Tasian and colleagues described the risk of stone presentation for the full range of temperatures in each city. As mean daily temperatures rose above 50 F (10 C), the risk of kidney stone presentation increased in all the cities except Los Angeles. The delay between high daily temperatures and kidney stone presentation was short, peaking within three days of exposure to hot days.
“These findings point to potential public health effects associated with global climate change,” said Tasian. “However,” cautions Tasian, “although 11 percent of the U.S. population has had kidney stones, most people have not. It is likely that higher temperatures increase the risk of kidney stones in those people predisposed to stone formation.” Higher temperatures contribute to dehydration, which leads to a higher concentration of calcium and other minerals in the urine that promote the growth of kidney stones.
A painful condition that brings half a million patients a year to U.S. emergency rooms, kidney stones have increased markedly over the world in the past three decades. While stones remain more common in adults, the numbers of children developing kidney stones have climbed at a dramatically high rate over the last 25 years. The factors causing the increase in kidney stones are currently unknown, but may be influenced by changes in diet and fluid intake. When stones do not pass on their own, surgery may be necessary.
The study team also found that very low outdoor temperatures increased the risk of kidney stones in three cities: Atlanta, Chicago and Philadelphia. The authors suggest that as frigid weather keeps people indoors more, higher indoor temperatures, changes in diet and decreased physical activity may raise their risk of kidney stones.
The researchers argue that the number of hot days in a given year may better predict kidney stone risk than the mean annual temperature. Atlanta and Los Angeles share the same annual temperature (63 F, or 17 C), but Atlanta has far more hot days than Los Angeles, along with nearly twice the prevalence of kidney stones.
Tasian added that while the five U.S. cities have climates representative of those found throughout the world, future studies should explore how generalizable the current findings are. Other studies should analyze how risk patterns vary in different populations, including among children, represented by a small sample size in the current study.
The study’s broader context is in patterns of global warming. The authors note that other scientists have reported that overall global temperatures between 2000 and 2009 were higher than 82 percent of temperatures over the past 11,300 years. Furthermore, increases in greenhouse gas emissions are projected to raise earth’s average temperatures by 2 to 8 F (1 to 4.5 C) by 2100. “Kidney stone prevalence has already been on the rise over the last 30 years, and we can expect this trend to continue, both in greater numbers and over a broader geographic area, as daily temperatures increase,” concluded Tasian. “With some experts predicting that extreme temperatures will become the norm in 30 years, children will bear the brunt of climate change.”
Daily Mean Temperature and Clinical Kidney Stone Presentation in Five U.S. Metropolitan Areas: A Time-Series Analysis
Background: High ambient temperatures are a risk factor for nephrolithiasis, but the precise relationship between temperature and kidney stone presentation is unknown.
Objectives: Our objective was to estimate associations between mean daily temperature and kidney stone presentation according to lag time and temperatures.
Methods: Using a time series design and distributed lag non-linear models, we estimated the relative risk (RR) of kidney stone presentation associated with mean daily temperatures, including cumulative RR for a 20-day period, and RR for individual daily lags through 20 days. Our analysis used MarketScan data for 60,433 patients who presented for evaluation or treatment of kidney stones from 2005–2011 in Atlanta, Chicago, Dallas, Los Angeles, and Philadelphia.
Results: Associations between mean daily temperature and kidney stone presentation were not monotonic, and there was variation in the exposure-response curve shapes and the strength of associations at different temperatures. However, in most cases RRs increased for temperatures above the reference value of 10°C. The cumulative RR for a daily mean temperature of 30°C versus 10°C was 1.38 in Atlanta (95% CI: 1.07, 1.79), 1.37 in Chicago (95% CI: 1.07, 1.76), 1.36 in Dallas (95% CI: 1.10, 1.69), 1.11 in Los Angeles (95% CI: 0.73, 1.68), and 1.47 in Philadelphia (95% CI: 1.00, 2.17). Kidney stone presentations also were positively associated with temperatures < 2°C in Atlanta, and < 10°C in Chicago and Philadelphia. In 4 cities, the strongest association between kidney stone presentation and a daily mean temperature of 30 versus 10°C was estimated for lags ≤ 3 days.
Conclusions: In general, kidney stone presentations increased with higher daily mean temperatures, with the strongest associations estimated for lags of only a few days. These findings further support an adverse effect of high temperatures on nephrolithiasis.
First I’ll give them high marks for not putting it behind a paywall. The full paper is available here: http://ehp.niehs.nih.gov/1307703/
Figure S1 from the Supplemental Material immediately caught my eye:
What immediately struck me was what I dubbed the “Philly Cheesesteak effect”. Look at how sharp the curve is above 20°C for Philadelphia. Similarly, Chicago. Now what strikes me as odd is that both of these cities have average annual mean temperatures that are below the others.
From my perspective, regional diets and obesity might explain this. I have been to every one of these U.S. cities, and I think I have a pretty good handle on the tendencies of the local cuisines.
I back that up with this list. Philadelphia is of course on it. In fact Philadelphia appears on several lists of this kind. Here’s another:
Note that every city in the Tasian et al. study appears on that list, but not on this one:
Those lists are based on CDC data. One wonders if Tasian et al. ran the same study on sone of the most fit cities if the relationship they claim would hold. I’ll bet it wouldn’t. It is almost as if they pre-screened for use of the most obese cities.
So, to me, reading the paper, it seems that Tasian et al. didn’t control for diet, obesity, and other health factors. Further, by limiting it to 5 cities, all with high obesity rates, it seems guaranteed to produce a result, especially when you look at this study:
Obesity, Weight Gain, and the Risk of Kidney Stones
Taylor et al. Journal of American Medical Association, 2005.
Context Larger body size may result in increased urinary excretion of calcium, oxalate, and uric acid, thereby increasing the risk for calcium-containing kidney stones. It is unclear if obesity increases the risk of stone formation, and it is not known if weight gain influences risk.
Objective To determine if weight, weight gain, body mass index (BMI), and waist circumference are associated with kidney stone formation.
Design, Setting, and Participants A prospective study of 3 large cohorts: the Health Professionals Follow-up Study (N = 45 988 men; age range at baseline, 40-75 years), the Nurses’ Health Study I (N = 93 758 older women; age range at baseline, 34-59 years), and the Nurses’ Health Study II (N = 101 877 younger women; age range at baseline, 27-44 years).
Main Outcome Measures Incidence of symptomatic kidney stones.
Results We documented 4827 incident kidney stones over a combined 46 years of follow-up. After adjusting for age, dietary factors, fluid intake, and thiazide use, the relative risk (RR) for stone formation in men weighing more than 220 lb (100.0 kg) vs men less than 150 lb (68.2 kg) was 1.44 (95% confidence interval [CI], 1.11-1.86; P = .002 for trend). In older and younger women, RRs for these weight categories were 1.89 (95% CI, 1.52-2.36; P<.001 for trend) and 1.92 (95% CI, 1.59-2.31; P<.001 for trend), respectively. The RR in men who gained more than 35 lb (15.9 kg) since age 21 years vs men whose weight did not change was 1.39 (95% CI, 1.14-1.70; P = .001 for trend). Corresponding RRs for the same categories of weight gain since age 18 years in older and younger women were 1.70 (95% CI, 1.40-2.05; P<.001 for trend) and 1.82 (95% CI, 1.50-2.21; P<.001 for trend). Body mass index was associated with the risk of kidney stone formation: the RR for men with a BMI of 30 or greater vs those with a BMI of 21 to 22.9 was 1.33 (95% CI, 1.08-1.63; P<.001 for trend). Corresponding RRs for the same categories of BMI in older and younger women were 1.90 (95% CI, 1.61-2.25; P<.001 for trend) and 2.09 (95% CI, 1.77-2.48; P<.001 for trend). Waist circumference was also positively associated with risk in men (P = .002 for trend) and in older and younger women (P<.001 for trend for both).
Conclusions Obesity and weight gain increase the risk of kidney stone formation. The magnitude of the increased risk may be greater in women than in men.
The Taylor et al. study from JAMA is not listed as a reference in the Tasian et al. study claiming that global warming is linked to kidney stones, but this horrid paper is:
Marcott SA, Shakun JD, Clark PU, Mix AC. 2013. A reconstruction of regional and global temperature for the past 11,300 years. Science 339:1198 -1201.
Further, this study:
Kidney Stones: A Global Picture of Prevalence, Incidence, and Associated Risk Factors, Romero et al. 2010, published in Reviews in Urology http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2931286/
In the United States, overall stone prevalence has doubled since the 1964–1972 time period, and appears to have stabilized since the early 1980s.1–3 Other countries with documented increases in prevalence include Germany, Spain, and Italy.4–7 Regional reports from Milan, Italy, also document an increased prevalence. 8 Only Scotland had a slight decrease in prevalence from 3.83% in 1977 to 3.5% in 19879,10 (Table 1 and Table 2).
They do cite Romero et al in the paper, but they seemed to have missed that part. Here is the portion of Table 1 covering the USA:
So if global warming was to blame, and since there are regular claims that we’ve seen most of the global warming since about that same time, what caused the stabilization of kidney stone prevalence since the early 1980s in the United States?
Maybe diet, especially greasy fast foods is the cause for the jump since the early 1960’s? There seems to be quite a jump since 1961.
Source article here, which adds:
The data comes from USDA figures; fast food expenditures were not tracked before 1929. There are a few things to note here:
- 93 percent of food was consumed at home in 1889, and most of that was homemade from scratch.
- In 2009, barely half (51%) of food was consumed at home, the rest was consumed in either full-service or fast food restaurants. Probably a high proportion of what was consumed at home was actually processed food.
- Fast food was not a significant expenditure before 1960, after which it rapidly gained in popularity. Today, fast food accounts for 18 percent of total food expenditures.
It would seem to me that obese people, who are already at risk from kidney stones might sweat more (hyperhidrosis) and thus consume more fluid to make up for the imbalance than non obese people during hot days, and that would increase the chances of flushing out a kidney stone or two, which could account for the increase in reported incidents that the Tasian et al. study uses as the basis for its claims.
I think Tasian and friends have their p-values all out of whack, and the Tasian et al. paper is nothing but junk science designed to produce a result due to the pre-selection of some of the most obese cities in America, creating a small biased sample set, with no control done on cities that aren’t part of that group.
Is there a doctor in the house that can write a challenge this paper?