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High-stress jobs were tied to incident Parkinson's disease in men, a study of 2.5 million people in Sweden found.

While the findings are not conclusive, they show possible links between occupational stress and increased risk for Parkinson's, especially among men with a high level of education, reported Karin Wirdefeldt, MD, PhD, of Karolinska Institutet in Stockholm, and colleagues in .

High-stress job demands did not affect Parkinson's risk in women, however. And, surprisingly, high-control jobs also were tied to increased Parkinson's risk, but only among people with low education levels, especially women.

Earlier studies have tied stress to neurodegeneration and . "Psychological stress is known to reduce levels of neurotrophic factors as well as increase oxidative stress, activity of the hypothalamic-pituitary-adrenal axis, and neuro-inflammation, all of which contribute to neurodegeneration," said Amie Miller, MD, of Oregon Health & Science University in Portland, who was not involved in the study.

"Animal studies have shown a negative effect of psychological stress specifically on dopaminergic cells, known to be particularly affected in Parkinson's disease," she told 口袋女优.

In the Swedish study, the researchers used the , a way to assess work-related stress that has been used to predict the risk of stroke, cardiovascular disease, and other disorders. The model has two dimensions: job demands and job control. The demand component measures time pressure and psychological and cognitive demands. The control component refers to a combination of decision-making authority (influence over time and work planning) and skill discretion (having a variety of tasks and the possibility of learning new things).

Wirdefeldt and co-authors studied 2,544,748 Swedes born from 1920 to 1950 who had an occupation reported in the 1980 (or if missing, the 1970) census, linking that data to Swedish national health registers from 1987 to 2010.

Over a mean follow-up time of 21.3 years, the team identified 21,544 incident cases of Parkinson's disease. Among men, jobs with high demands were associated with increased Parkinson's risk, which was most evident in men with high education. Jobs with high amounts of control, which often are associated with less stress, also were linked to increased Parkinson's risk among people with low education, an effect that was more pronounced in women.

"Job control has generally been considered beneficial, but the relationship between job control and health may be more complex," the authors said. Job control may be more stressful for some people, leading to longer work hours, more interpersonal conflicts, and more interference with home life: "It is possible that women may not derive the same benefits of positions of authority as men."

The researchers noted that the associations found in this analysis might be explained by reverse causation, that people in prodromal phases of Parkinson's might change from stressful or physically demanding jobs due to impaired stress coping or job performance. And personality traits that predispose people both to choose specific types of jobs and to have increased Parkinson's risk may confound the results. In addition, work conditions may differ within job titles and the individual variation in how people perceive and react to the same type of stress.

"These types of studies are difficult because exposure to stressors and stress response are not interchangeable," Miller observed. And while the results are not conclusive, they "lend support for further investigation of the stress response in and the effects of stress reduction on persons with Parkinson's disease."