UCLA Fielding-led research finds connections between work, diet, and chronic illnesses, including diabetes and heart disease

Two related and recently published studies by international teams - including researchers with the UCLA Fielding School of Public Health - have studied how chronic illnesses, including diabetes and heart disease, can stem from the combination of working conditions and lifestyle factors.

“Cardiovascular disease remains the leading cause of death in the United States, with rising healthcare expenses and a growing prevalence, even among the younger working-age population,” said co-author Dr. Onyebuchi Arah, a physician and professor in UCLA Fielding’s Department of Epidemiology. “In the U.S., 14.7% of the adults of working age have diabetes, and the prevalence has been continuously increasing – these studies make clear that long work hours, poor eating habits, and poor diet lead to obesity, which has a very real impact on health, and together they can interact to make a bad situation even worse.”

The research suggests that long working hours - 55 hours or more per week – combined with a poor diet can lead to a 61% higher rate of obesity, a 33% higher rate of diabetes, and a 73% higher chance of death due to cardiovascular disease. Similarly, independent of diet, consistently eating more, and more often, was associated with a 51% higher rate of diabetes among workers aged 45 years or younger.

The peer-reviewed research examined connections between working conditions (e.g., long work hours or shift work) and lifestyle factors (e.g., poor diet or poor eating habits). The studies, with authors affiliated with UCLA Fielding School of Public Health, UCLA’s Wen School of Nursing, and/or Aarhus University (Denmark), and Heinrich Heine University (Germany), are:

• “Eating duration and shift work are associated with diabetes: a cross-sectional study among US workers,” British Journal of Nutrition, published by the Cambridge University Press (Cambridge, U.K.); and
• “The associations of long working hours and unhealthy diet with cardiometabolic outcomes and mortality in US workers,” Journal of Preventive Medicine, published by Elsevier Press (Amsterdam, Netherlands)

In the study published in the British Journal of Nutrition, researchers examined whether work shifts and meal duration were associated with diabetes in a cross-sectional study of a nationally representative sample of U.S. workers, and whether workers’ age affected this association. In the Journal of Preventive Medicine study, the researchers analyzed whether longer working hours were associated with obesity and cardiovascular disease, and how a poor diet contributed to such associations.

“We found that working hours and diet scores were jointly associated with obesity and cardiovascular mortality,” said senior author Dr. Liwei Chen, a physician and professor in UCLA Fielding’s Department of Epidemiology. “Long work hours and unhealthy diet are independent risk factors, but they appear to interact to make adverse health outcomes even worse.”

Researchers found the following:

• Working 55 hours per week or more was associated with higher odds of obesity in U.S. workers.
• Long working hours increased cardiovascular mortality in workers at high risk.
• Shift work was associated with higher odds of diabetes, particularly among workers aged 45 or younger.
• Unhealthy diet increased the risks of obesity, diabetes, and cardiovascular mortality.
• Long working hours and poor diet jointly worsened obesity and heart disease risk.
• A healthy diet may mitigate cardiometabolic risks linked to long working hours.

“Workers who reported weekly working hours longer than 55 hours were more likely to have obesity than those working standard hours,” said co-author Dr. Jian Li, a physician and professor in UCLA Fielding’s Departments of Environmental Health Sciences and Epidemiology. “Among workers who already had a higher risk of cardiovascular disease at the start of the study, long working hours were also linked to a greater risk of dying from heart-related causes.”

The researchers said the findings suggest ways individuals and their employers can try to reduce these health risks.

“In light of our findings, a comprehensive approach addressing both working conditions and personal behaviors could be critical for preventing diabetes in the workplace,” said co-author Dr. Adrian Loerbroks, a professor of occupational health at Heinrich Heine University in Düsseldorf, Germany. “At the organizational level, employers may consider mitigating the adverse effects by providing adequate work-time arrangement and more flexible meal breaks, while at the individual level, workers, especially younger people, should adopt healthier eating habits.”

Research methodology

The British Journal of Nutrition study used data from the U.S. National Health and Nutrition Examination Survey (NHANES), a national representative sample collected from 2005 to 2020, before the COVID-19 pandemic, and when work schedules were available. The Journal of Preventive Medicine study also used NHANES data from the 1999–2020 March cycles (pre-pandemic). In both cases, standardized analyses were used to quantify the associations of work conditions and diet with disease and health outcomes. Survey design and sampling were accounted for according to NHANES analytic guidelines.

Research support and funding

Both studies were supported by the authors’ respective institutions. They were funded by UCLA and the Southern California National Institute for Occupational Safety and Health (NIOSH) Education and Research Center (SCERC), including funding from the U.S. Centers for Disease Control and Prevention (CDC)/National Institute for Occupational Safety and Health (NIOSH) (Grant Agreement No. T42 OH008412). In both cases, the sponsors had no role in the design and conduct of the study; the collection, management, analysis, and interpretation of the data; the preparation, review, or approval of the article; or the decision to submit the article for publication.