Academic journal article Scandinavian Journal of Work, Environment & Health

Gender-Specific Association between Night-Work Exposure and Type-2 Diabetes: Results from Longitudinal Study of Adult Health, ELSA-Brasil

Academic journal article Scandinavian Journal of Work, Environment & Health

Gender-Specific Association between Night-Work Exposure and Type-2 Diabetes: Results from Longitudinal Study of Adult Health, ELSA-Brasil

Article excerpt

Diabetes is a chronic, multifactorial disease of increasing prevalence globally. The International Diabetes Federation estimated a global prevalence among adults of 8.3% in 2013 and 11.1% in 2033 (1). Although a genetic component is present in the etiology of type-2 diabetes (DM2), obesity-related aging and environmental factors - notably low physical activity and low quality diet - are also strongly at play (2).

Additional aspects of modern life have also been investigated as a possible risk factor for DM2, including night work (3). The biological mechanisms that make this a plausible association are generally associated with circadian rhythm mismatches, which may lead to metabolic problems such as increased postprandial glucose, insulin and blood pressure levels, reduced leptin action and sleep efficiency, and complete inversion of the cortisol profile. Abnormally high levels of cortisol at the end of waking and the beginning of sleeping times can contribute to hyperglycemia and insulin resistance (4). In addition, reduced leptin action stimulates appetite and lowers energy expenditure, which may lead to obesity. The combination of these effects resulting from circadian disruption, may favor increased risk of obesity, hypertension, and DM2 among shift and night workers (4, 5).

The discussion of the putative connection between night work and diabetes can benefit from an analysis of alterations in glycemic levels preceding the diagnosis of diabetes. Although relevant studies are scarce, a significant association between shift work and impaired glucose tolerance (IGT) has been observed in both longitudinal (6) and cross-sectional studies (7).

A recent meta-analysis suggests that shift work is associated with significantly increased risk of DM2, especially among men (8). According to Shiri (9), the gender differences found in this meta-analysis could be explained by confounders, selection bias, and the types of shift schedule (9).

Given the discussion of the association between work schedule and glucose metabolism (3, 10) and the need for population studies to explore gender differences (8), the aim of this study was to investigate gender-specific associations between years of exposure to night work and the presence of DM2 and IGT, using baseline data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

Methods

Study population

ELSA-Brasil is a prospective cohort study designed to identify risk factors for diabetes and cardiovascular diseases. The cohort comprises 15 105 civil servants (current and retired workers), aged 35-74 years at baseline (2008-2010), who were sampled from universities or research institutions in six of Brazil's state capitals. The Research and Ethics Committees of the institutions involved approved the study: São Paulo University, Oswaldo Cruz Foundation, Bahia Federal University, Minas Gerais Federal University, Espírito Santo Federal University and Rio Grande do Sul Federal University. All participants in the study provided written informed consent (11).

To minimize inclusion of type 1 diabetes cases in the DM2 definition, those who were diagnosed at age ≤30 years and used insulin as their first medication (N=12) were excluded (12) as were 3 participants lacking diabetes laboratory data for classification and 663 participants with missing information related to work and/or covariates.

Variables

A comprehensive set of questionnaires was applied, providing detailed information about socioeconomic conditions, habits and lifestyle, work aspects, and health. In addition, clinical measurements and laboratory tests were carried out.

A blood sample was drawn by venepuncture soon after arrival at the clinic following an overnight fast and a 75 g oral glucose tolerance test (OGTT) was then carried out with participants without known diabetes (N=14 507). Glucose was measured by the hexokinase method (ADVIA Chemistry; Siemens, Deerfield, IL, USA). …

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