Not All Exercise Is Beneficial: The Physical Activity Paradox Explained

ISLAMABAD, DEC 20 (ONLINE):In the pursuit of optimal health, regular physical activity (PA) is recommended to protect against dementia, cardiovascular disease (CVD), cancer, and other no communicable diseases. A significant body of research suggests the benefits of PA are positively correlated with higher frequency and intensity — with more often deemed better. This research has spawned a focus on increasing step counts and investing in standing desks and other interventions aimed at keeping people active.
But for many people, PA is a work requirement over which they have little control, and emerging evidence suggests that these workers not only do not reap the benefits associated with leisure-time PA, but they also actually experience an increased risk for the very conditions that PA is intended to prevent.

A study published recently in The Lancet Regional Health – Europe used registry data from more than 7000 adults in Norway, following them from age 33 to 65 years, to assess PA trajectories and risks for later-life mild cognitive impairment (MCI) and dementia at age 70 or older.

“Incorporating a life-course perspective gives a broader picture of how participants’ occupational histories relate to cognitive impairment later in life,” principal investigator Vegard Skirbekk, PhD, Columbia University Mailman School of Public Health, New York City, told Medscape Medical News. Other studies typically have assessed occupational PA at a single time point, often close to the end of an individual’s career, and largely relied on self-report, he said.

Study participants worked in more than 300 different occupations. General physical activities performed on the included jobs required “considerable” use of arms and legs and moving the whole body, such as climbing, lifting, balancing, walking, stooping, and handling of materials.

Skirbekk and colleagues grouped participants into four PA trajectories over the 44-year study period: stable low, increasing then decreasing, stable intermediate, and stable high.

A total of 902 individuals were diagnosed with dementia and 2407 with MCI at age 70 years or older. After adjustment, risks for MCI and dementia were 15.5% for those with higher occupational PA scores in the latter part of their working life and 9% for those with lower physical demands. The researchers conclude that “consistently working in an occupation with intermediate or high occupational PA was linked to an increased risk of cognitive impairment.”

The findings support those of the Copenhagen Male Study. Published in 2020, this longitudinal study compared leisure-time and occupational PA among more than 4000 men in Denmark aged 40-59 at baseline in 1970-1971 and followed them until they turned 60. After adjustment, participants with high occupational PA had a 55% greater risk of developing dementia compared with those doing sedentary work.

Good vs Bad PA
Kirsten Nabe-Nielsen, PhD, lead author of this study, is quoted as saying, “[T]he WHO [World Health Organization] guide to preventing dementia and disease on the whole mentions physical activity as an important factor. But our study suggests that it must be a ‘good’ form of physical activity, which hard physical work is not.”