Working Long Hours Increases Risk of Hypothyroidism

Rates of hypothyroidism are double in those working the longest hours

With Young Ki Lee MD and Elena Christofides MD

Hypothyroidism was more prevalent among those with longer working hours—3.5% for those working 53-83 hours, as compared to 1.4% for those working 36-42.

Working long hours may boost the risk of hypothyroidism, according to a new study. The association between long work hours and hypothyroidism was consistent in different subgroups, stratified by gender and socioeconomic status, says Young Ki Lee, MD, a specialist at the National Cancer Center of Korea.

"The results of this study should be further validated," Dr. Lee says, as it is believed the first research to show the link.

His study was accepted for presentation at ENDO 2020, the Endocrine Society annual meeting that was held virtually due to concerns over the COVID-19 pandemic. The research appears in the journal Thyroid, and is scheduled to be published in a special supplemental section of the Journal of the Endocrine Society.

Study details

Lee's team conducted a cross-sectional study, based on data obtained from the Korea National Health and Nutrition Examination Survey conducted from 2013 to 2015. They looked at 2,160 adults who worked from 36 to 83 hours weekly. The researchers evaluated thyroid function based on population thyroid-stimulated hormone (TSH) reference ranging. They excluded those with positive results for thyroid peroxidase antibodies.

After multinomial logistic regression, they confirmed the association between long working hours and hypothyroidism. It was more prevalent among those with longer working hours—3.5% for those working 53-83 hours, but 1.4% for those working 36-42. Those who worked longer hours had increased odds for hypothyroidism (OR 1.46, 95% CI 1.12-1.90, per 10-hour increase in working hours per week).

The association held after adjusting for age, sex, body mass index, urine iodine concentration, smoking status, work schedule, and socioeconomic status. The link was consistent in various subgroups stratified by sex or socioeconomic status.

Study origins

"Some of my patients with thyroid dysfunction asked me if their thyroid dysfunction was due to overwork," Dr. Lee says. "I was interested in these questions and the possibility of the relationship."

"The adverse health impact of long working hours has been well established regarding cardiovascular diseases. In addition, there is increasing epidemiologic evidence that long working hours are also associated with adverse metabolic and mental health outcomes such as diabetes mellitus, obesity, metabolic syndrome, fatigue, and depressive symptoms. Hypothyroidism is associated with many other diseases including atherosclerotic cardiovascular disease, congestive heart failure, diabetes mellitus, obesity, metabolic syndrome, fatigue, and depression, which have large overlaps with overwork-related health outcomes."

"Furthermore, a recent study showed that shift work, another occupational environmental factor that adversely affects health, increased the risk of hypothyroidism," Dr. Lee says.

In a recent review, published in February 2020, researchers conducting a systematic analysis found that night shiftwork was linked with increased TSH levels. Evidence was inconclusive from the studies on thyroid diseases and shift work.

Dr. Lee says, "These pieces of evidence suggest that long working hours may be associated with hypothyroidism." He speculated that the association observed cannot serve as proof of a causal relationship and that more research is needed.

His research relied on public data, and funding for expenses such as manuscript preparation came from internal institutional funding used for several studies on thyroid, Dr. Lee says.

Korean workers have long hours

South Korea is known as a country whose residents work long hours. In 2018, the National Assembly passed a bill aimed at shortening the working hours. It called for decreasing the maximum statutory work hours to 52, down from 68.

That legislation, which revised the Labor Standards Act, calls for phasing in the new maximums, beginning July 1, 2018, for companies with 300 or more workers. Next, those with 50 to 299 had to meet the new maximums by Jan. 1, 2020, and finally those employing 5 to 49 by July 1, 2021.

The number of business types exempted was curtailed to five, including those in healthcare and transportation services.

Expert analysis

"It's not unexpected that additional endocrine disruptions are identified in association with long working hours,'' says Elena Christofides, MD, FACE, a member of the editorial board of Endocrine Web and CEO of Endocrinology Associates in Columbus, OH. She reviewed the new research but was not involved in it.

She would have liked to have seen if there was a proportional relationship. "They mentioned that there were increased risks with every 10 hours of additional work,'' she says, but she would like more details. "For example, is 61 hours versus 59 hours proportionally worse than 59 hours versus 57 hours?"

Another factor to look at, in her opinion, are the different occupations, taking into account those with an increased time burden, such as healthcare workers, and those with a lower work/time burden.

Clinical takeaways

So, should physicians be asking patients, especially those at risk of thyroid issues, about their work hours?  "The results of this study should be further validated," Dr. Lee says. "However, if the association is reproduced in future studies, it may be helpful to consider the possibility of hypothyroidism while assessing the health of individuals working long hours. Additionally, if the association of long work hours and hypothyroidism is confirmed to be a causal relationship in future longitudinal studies, it could be the basis for recommending reduction in work hours to improve thyroid function among overworked workers with hypothyroidism."

While it's clear that longer working hours is associated with more endocrine disruption, it's important to factor in the quality of work, Dr. Christofides suggests. For instance, a person working long hours who is dedicated to her field may be a different case than someone working long hours at a job he loathes and putting in the time for income alone.

Continue Reading:
Telemedicine and COVID-19: One Year Later
close X