Working Long Hours Doubles Chance of Hypothyroidism

Working long hours more than doubled an adult’s chance of having hypothyroidism, new findings to be presented at the Endocrine Society (ENDO) 2020 Annual Scientific Sessions, showed.

The findings suggested that appropriate monitoring and treatment of hypothyroidism—an underactive thyroid—were needed for individuals who work long hours.

Young Ki Lee, MD, and a team of Korea-based investigators obtained data from the Korea National Health and Nutrition Examination survey to assess long working hours as a risk factor for thyroid dysfunction. The investigators included 2160 adults who worked 36-83 hours per week.

Lee, from the National Cancer Center in Goyang-si, Korea, and the team defined thyroid function based on the population thyroid-stimulating hormone reference ranges after excluding those with positive results for thyroid peroxidase antibody. The team used multinomial logistic regression to confirm the association between working hours and thyroid function.

The investigators found that hypothyroidism was more than twice as prevalent in adults who worked longer hours: 3.5% vs 1.4% for 53-83 and 36-42 working hours per week, respectively. Adults who worked longer had increased odds for hypothyroidism (OR, 1.45; 95% CI, 1.12-1.9, per 10-hour increase in working hours per week) after the team adjusted for age; sex; body mass index; urine iodine concentration; smoking status; shift work; and socioeconomic characteristics.

The association was seen across various groups stratified by sex or socioeconomic characteristics, even though hypothyroidism more commonly affects women more than men.

“Overwork is a prevalent problem threatening the health and safety of workers worldwide,” Lee said in a statement. “To our knowledge, this study is the first to show that long working hours are associated with hypothyroidism.”

The findings could lead to a recommendation for a reduction in working hours to improve thyroid function among overworked adults with hypothyroidism. What’s more, screening for underactive thyroid could be integrated into workers’ health screening programs using laboratory tests.

In South Korea, a law was passed in 2018 to reduce the maximum number of hours in a week from 68 to 52.

“If long working hours really cause hypothyroidism, the prevalence of hypothyroidism in Korea might decrease slightly as the working hours decrease,” Lee said.

Hypothyroidism typically causes tiredness, depression, feeling cold, and weight gain, but most participants had a mild form of hypothyroidism that did not yet cause symptoms.

Additional research should be conducted to determine whether long hours cause hypothyroidism, a known factor for heart disease and diabetes.

The study, “Long Working Hours Are Associated with Hypothyroidism: A Cross-Sectional Study with Population-Representative Data,” will be presented at the Endocrine Society (ENDO) 2020 Annual Scientific Sessions.