National survey data reveal distinct food choices and sleep patterns among Japanese shift workers, with notable differences emerging between men and women.
Study: The eating habits and lifestyle habits of shift workers: findings from the 2018 National Health and Nutrition Survey, Japan. Image Credit: KANGWANS / Shutterstock
A recent study in the journal Industrial Health compared the eating habits and lifestyle characteristics of male and female shift and daytime workers in Japan, focusing on behaviors relevant to long-term health.
Global Prevalence and Health Impacts of Shift Work
Shift work is common worldwide and remains important to the functioning of modern industries and businesses. The study cites estimates indicating that 18.6% of workers in Japan, 28.7% in the United States, and 17.0% in the European Union work shift work, including night shifts.
Shift work generally refers to work scheduled permanently or frequently outside normal daytime working hours. Daytime work, by contrast, typically follows conventional daytime schedules, which help stabilize daily routines. Numerous epidemiological studies have linked shift work to a greater risk of adverse health outcomes. For example, shift workers have been reported to have higher risks of cardiovascular disease, cancer, obesity, and diabetes.
One proposed factor underlying these health risks is disruption of circadian rhythms, the body’s internal clock that regulates sleep, wakefulness, and metabolism. Shift work often leads to irregular work and eating patterns, which can desynchronize biological processes. Over the long term, this circadian misalignment is believed to contribute to the development of chronic conditions such as obesity, type 2 diabetes, cardiovascular disease, and metabolic syndrome.
Previous studies have produced differing findings across regions and populations, and many have focused on specific occupational groups, such as nurses or airline personnel. Research from East Asia has also identified less favorable dietary behaviors among shift workers, including lower consumption of some traditional foods and greater reliance on convenient foods. Notably, important gaps remain concerning differences in real-world dietary choices, nutrient intake, and eating patterns associated with shift work across different occupations and populations.
Comparing Nutrition and Lifestyle Patterns among Shift and Daytime Workers in Japan
This cross-sectional analysis used national survey data from the 2018 Japan National Health and Nutrition Survey (NHNS), administered annually by the Ministry of Health, Labor and Welfare and covering all 47 prefectures.
For this study, the analytic sample included working adults aged 20 to 64 years. Individuals who were out of work, pregnant or lactating, worked fewer than four days or 24 hours per week, or had missing key BMI or work-schedule information were excluded from the analysis. The final sample comprised 1,814 workers, including 1,081 men and 733 women.
Participants were categorized into two primary groups based on self-reported work schedules: those reporting “daytime work” were classified as daytime workers, while those reporting either “night shift work” or “shift work” were combined as shift workers. Specific working hours, shift patterns, and shift durations were not recorded.
Daily food and nutrient intake were evaluated using a 1-day semi-weighed household dietary record. Specific food groups (e.g., fish and shellfish, milk and dairy products) and overall daily energy intake were calculated from the record, with food-group intake expressed relative to energy intake as grams per 1,000 kcal. Self-administered questionnaires assessed key criteria for daily food selection, such as price, preference, nutritional value, convenience, and seasonal availability. They also provided data on sleep duration and general lifestyle habits.
To compare outcomes between shift and daytime workers, analyses were stratified by sex. Dietary intakes, food selection behaviors, body mass index (BMI), and sleep duration were examined. Adjusted food and nutrient intakes were analyzed while accounting for age, BMI, working days, and working hours, while categorical outcomes were compared using chi-square tests. Because the study was exploratory, the researchers did not adjust for multiple statistical comparisons.
Sex-Specific Dietary and Lifestyle Patterns Among Shift and Daytime Workers
Demographic and occupational characteristics varied across groups. Mean age did not differ significantly between daytime and shift workers in either sex. However, among men, daytime workers had a significantly higher BMI than shift workers, although the proportions classified as underweight, normal weight, or overweight/obese did not differ significantly.
Job types and work patterns also displayed clear gender differences. Male shift workers were more likely than male daytime workers to be employed in security, transportation, and machine operation, and less likely to work in administrative or clerical roles. In contrast, female shift workers were more likely to work in professional, technical, or service occupations and less likely to work in clerical roles. Notably, female shift workers also reported working more days per week than female daytime workers, whereas men did not show this difference in work schedule.
Dietary intake differed significantly by work schedule. Although several differences were statistically significant, most dietary effect sizes were small. Male shift workers had lower adjusted intake of fish and shellfish overall, including raw fish and shellfish. Among women, shift workers had significantly lower adjusted intake specifically of raw fish and shellfish, while the adjusted difference in total fish and shellfish intake was not statistically significant. This reduction may have implications for the intake of the long-chain omega-3 fatty acids EPA and DHA, which are abundant in fish. However, total omega-3 polyunsaturated fatty acid intake did not significantly differ between the groups, and EPA and DHA were not measured separately.
Among female participants, shift workers also had a significantly lower daily intake of milk and dairy products compared to female daytime workers. Because dairy foods provide bioavailable calcium, vitamin D, protein, and other nutrients, this finding could have implications for bone health. However, calcium intake itself did not differ significantly, and the study did not assess osteoporosis, nutrient deficiencies, or other clinical bone outcomes.
Despite these dietary disparities, total daily energy intake did not differ significantly between shift and daytime workers in either sex. BMI was modestly higher among male daytime workers than among male shift workers, while no significant BMI difference was observed among women. However, food selection behavior differed. Male shift workers were significantly more likely to report food preference and convenience as factors influencing their dietary choices. They were not significantly less likely to consider nutritional value or seasonality. In contrast, female shift workers were less likely than their daytime counterparts to choose foods based on seasonal availability.
Sleep duration further distinguished the two groups. Male shift workers were more likely than daytime workers to report sleeping fewer than 5 hours per night, although this applied to a minority rather than the majority of shift workers. Female shift workers were less likely than daytime workers to report sleeping between seven and eight hours per night. Overall, sleep duration patterns differed between shift and daytime workers in both sexes, with the association between shift work and sleeping fewer than 6 hours particularly evident among men. These findings highlight how non-traditional work schedules may be associated with shorter sleep duration.
Conclusions
Shift work in Japan was associated with differences in sleep and dietary patterns, particularly lower raw seafood intake in both sexes, lower overall fish and shellfish intake among men, and lower dairy intake among women. Total energy intake was similar between work groups, while male shift workers were also more likely to cite preference and convenience when choosing foods.
Looking ahead, workplace and public health initiatives could consider practical, targeted strategies, such as making nutrient-dense foods more accessible and supporting better sleep environments. Future research is needed to develop and evaluate multifaceted programs that combine dietary guidance, workplace adjustments, and integrative health policies and to determine whether these approaches can improve long-term health outcomes among shift workers. Because the study was cross-sectional, it cannot establish that shift work caused the observed dietary and lifestyle differences or that these differences subsequently caused chronic disease.
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