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Research Christmas 2017: Natural Phenomena

Individual differences in normal body temperature: longitudinal big data analysis of patient records

BMJ 2017; 359 doi: (Published 13 December 2017) Cite this as: BMJ 2017;359:j5468
  1. Ziad Obermeyer, assistant professor1 2,
  2. Jasmeet K Samra, research analyst1,
  3. Sendhil Mullainathan, professor3
  1. 1Department of Emergency Medicine, Brigham and Women’s Hospital, Boston, MA, USA
  2. 2Department of Emergency Medicine and Health Care Policy, Harvard Medical School, Boston, MA, USA
  3. 3Department of Economics, Harvard University, Boston, MA, USA
  1. Correspondence to: Z Obermeyer zobermeyer{at}
  • Accepted 23 November 2017


Objective To estimate individual level body temperature and to correlate it with other measures of physiology and health.

Design Observational cohort study.

Setting Outpatient clinics of a large academic hospital, 2009-14.

Participants 35 488 patients who neither received a diagnosis for infections nor were prescribed antibiotics, in whom temperature was expected to be within normal limits.

Main outcome measures Baseline temperatures at individual level, estimated using random effects regression and controlling for ambient conditions at the time of measurement, body site, and time factors. Baseline temperatures were correlated with demographics, medical comorbidities, vital signs, and subsequent one year mortality.

Results In a diverse cohort of 35 488 patients (mean age 52.9 years, 64% women, 41% non-white race) with 243 506 temperature measurements, mean temperature was 36.6°C (95% range 35.7-37.3°C, 99% range 35.3-37.7°C). Several demographic factors were linked to individual level temperature, with older people the coolest (–0.021°C for every decade, P<0.001) and African-American women the hottest (versus white men: 0.052°C, P<0.001). Several comorbidities were linked to lower temperature (eg, hypothyroidism: –0.013°C, P=0.01) or higher temperature (eg, cancer: 0.020, P<0.001), as were physiological measurements (eg, body mass index: 0.002 per m/kg2, P<0.001). Overall, measured factors collectively explained only 8.2% of individual temperature variation. Despite this, unexplained temperature variation was a significant predictor of subsequent mortality: controlling for all measured factors, an increase of 0.149°C (1 SD of individual temperature in the data) was linked to 8.4% higher one year mortality (P=0.014).

Conclusions Individuals’ baseline temperatures showed meaningful variation that was not due solely to measurement error or environmental factors. Baseline temperatures correlated with demographics, comorbid conditions, and physiology, but these factors explained only a small part of individual temperature variation. Unexplained variation in baseline temperature, however, strongly predicted mortality.


  • Contributors: ZO and SM designed the study and wrote the manuscript. ZO obtained funding. JKS and ZO analyzed the data. All authors had full access to all of the data (including statistical reports and tables) in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis. ZO acts as guarantor.

  • Funding: This study was supported by a grant from the office of the director of the National Institutes of Health (DP5 OD012161) to ZO. This research was independent from funders. The funder had no role in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the article for publication.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare: no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: This study was approved by the institutional review boards of Partners HealthCare, the parent organization of the hospital where the research was conducted.

  • Data sharing: No additional data available.

  • Transparency: The lead author (ZO) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained.

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