Sunday, August 18, 2013

Feel the Heat

Heatwaves and IBD

A recent study posted in the American Journal of Gastroenterology looked at the correlation between heat waves and the hospitalizations due to both inflammatory bowel disease (IBD) and infectious gastroenteritis (IG).  The study found:

The presence of a heat wave increased the risk of IBD flares by 4.6% (95% confidence interval (CI): 1.6–7.4%, P=0.0035) and of IG flares by 4.7% (95% CI: 1.8–7.4%, P=0.0020) for every additional day within a heat wave period. In the control group there was no significant effect (95% CI: −6.2–2.9%, P=0.53). Screening of alternative forms for the effect of heat waves suggested that for IG the effect is strongest when lagged by 7 days (risk increase per day: 7.2%, 95% CI: 4.6–9.7%, P<0.0001), whereas for IBD no such transformation was required. (1)

The study looked at Zurich-based hospital admission on 738 IBD and 768 IG patients and 506 other chronic, non-infectious intestinal inflammations as a control group.  In press releases, the authors were quoted as saying:

The evidence of patients with IBD having a significant increase risk of flare ups compared to the control group shows a cause and effect between the climate and the disease," said lead author Christine N. Manser, MD. "This study ties heat stress to digestive symptoms supporting the observed seasonal variation in the clinical course of inflammatory bowel disease and suggests that microbial infections of the gut might be additionally influenced by climate changes.(2)

Before jumping to wild conclusions about stress and bacterial growth due to heat, there are a few issues to consider.  First, the study is retrospective and not prospective (I’m hoping the PR piece about showing cause and effect is the reporter or press person misquoting the author – this was a retrospective study).  Second, the control group’s p value is not very encouraging for drawing the baseline against which the study group was measured.

The most obvious mechanism isn’t given much press in the reporting – simple dehydration.   Those with IBD are already at a higher risk for dehydration-related issues, owing to poor absorption and chronic diarrhea.  Additionally, other studies have shown that everything from renal disease admissions (3) to general admissions increase during a heat wave.(4) 

Keeping hydrated (and keeping the electrolyte balance in check) is very important for anyone, and especially so for those with IBD.  Additional studies quantifying the risk (especially the aggregate risk the paper seems to show of multiple days of heat) due to exposure and the related preventative measures and their impact can help activity planning for Ulcerative Colitis and Crohn’s patients.  This study was a good initial study and will hopefully encourage additional work, but linking increased IBD admissions to climate change (which is a long term effect, not due to a few days of heat) is too far reaching, and the correlational data in the paper above is interesting, but may have been overplayed in the press. 

Bottom Line

·         Dehydration and electrolyte imbalance can affect those with inflammatory bowel disease, especially with prolonged exposure to hot weather.
·         Keeping cool and ensuring the intake of a proper volume and type of fluid are important.


1.     Manser, Christine N., Michaela Paul, Gerhard Rogler, Leonhard Held, and Thomas Frei. "Heat Waves, Incidence of Infectious Gastroenteritis, and Relapse Rates of Inflammatory Bowel Disease: A Retrospective Controlled Observational Study." The American Journal of Gastroenterology (2013).
3.      Hansen, Alana L., Peng Bi, Philip Ryan, Monika Nitschke, Dino Pisaniello, and Graeme Tucker. "The effect of heat waves on hospital admissions for renal disease in a temperate city of Australia." International journal of epidemiology37, no. 6 (2008): 1359-1365.

4.      Knowlton, Kim, Miriam Rotkin-Ellman, Galatea King, Helene G. Margolis, Daniel Smith, Gina Solomon, Roger Trent, and Paul English. "The 2006 California heat wave: impacts on hospitalizations and emergency department visits." Environmental health perspectives 117, no. 1 (2009): 61.

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