Risk of obesity in male shift workers: A chronophysiological approach

ABSTRACT

Aims: Why are some healthy male shift workers (SWers) overweight [body mass index (BMI) >25 and <30] if not obese (BMI >30)? Seven risk factors potentially causing overweight and obesity were evaluated, namely (1) age, (2) physical/sports activity, (3) length of exposure to shift work (SW), (4) speed of shift rotation, (5) tolerance to SW, (6) internal desynchronization of circadian rhythms and (8) night eating (nocturnal nibbling). “New” as well as “old” data, acquired from longitudinal and individual time series of 5–56 days recording span, were reanalyzed. The data were analyzed from a set of field studies of 67 SWers and 53 non-shift workers (non-SWers). To estimate the respective weight of these factors, a multiple regression analysis (MRA) was used among other statistical tools. A similar age-related increase in BMI was validated (with p < 0.001) in both SWers and non-SWers. However, in SWers, desynchronization of rhythms increases the effect of age on BMI. Length of exposure to SW, tolerance to SW and speed of rotation do not seem to play a role as risk factors. Major effects are likely to relate to a sedentary lifestyle (lack of regular physical or sport activities) (MRA with p < 0.01), as well as, presumably, to a nocturnal nibbling of carbohydrates, which mimics the night eating syndrome.

KEYWORDS:

• age
• body mass index
• body temperature
• circadian rhythms
• desynchronization
• eating behavior
• shift work
• sport exercise/activities

Acknowledgments

Credit and acknowledgment must be given to former coworkers with whom the included field studies and related data acquisition were performed: Pierre Andlauer, Medecin Inspecteur du Travail de la Région Rhône-Alpes, Norbert Vieux and Philippe Bourdeleau, Médecins du Travail de Shell France.

We thank the shift workers who volunteered with enthusiasm for the studies. We also thank the PSA Peugeot-Citroen direction in Cormelles-le-Royal, Normandy, France, as well as the Shell Oil Company, Le Petit Couronne, Normandy, France. Special thanks are due to Michael Smolensky for pertinent comments and advice regarding the present study.

The present review paper is dedicated by the authors to Erhard Haus, as the paper was almost ready for submission when Erhard unexpectedly passed away on June 14, 2013. Erhard was an outstanding researcher in chronobiology, as stated in the obituary that was published in this journal. His knowledge in biological rhythms was incredibly deep and broad, extending from basic mechanisms to chronobiology applied to clinical medicine. More specifically, Erhard was a world expert in the domain of chronobiology and nutrition. As such, he was regularly asked to lecture on this topic, in the USA as well as Europe. Despite his most indulgent smile when providing evidence, it was difficult for him to understand why many nutritionists still underestimate the experimental evidence showing that the amount of calories delivered by a nutrient varies according to a 24-h rhythm, and, as an illustrative example, that the energy that provides a given amount of carbohydrates to a diurnally active human, is largely burned with a morning intake and partly stored with an evening one. We want to acknowledge Erhard’s extensive contribution to the preparation and the writing of this challenging overview.

Declaration of interest

This study was partly supported by the Thérèse Tremel-Pontremoli donation for Research in Chronobiology at the Fondation A. de Rothschild, Paris – France. The content of this article represents the collective contributions of the listed authors. None of the authors have commercial interests of any kind to declare that are of relevance to the contents of the article.