Scientists identify 'physically demanding' jobs that increase dementia risk by a fifth

Jobs that involve strenuous physical activity and heavy lifting such as building and scaffolding could increase the risk of dementia, a major study has warned. In contrast, exercise done in leisure time - such as running, swimming and cycling - can protect against the memory-robbing condition. The research - published in the journal The Lancet Public Health - is the first to examine whether the so-called 'physical activity paradox' applies to dementia. The paradox describes the observation that doing exercise as part of a job is linked with an increased risk of chronic disease - despite the well-established benefits of physical activity.Scientists from the University of Southern California analysed data from 74 studies involving more than 4.2 million participants aged 45 to 93-years-old, followed for around a decade. Researchers tracked diagnoses of dementia, including Alzheimer's disease and vascular dementia - caused by reduced blood flow to the brain. Those who engaged in higher levels of leisure time physical activity had a 24 per cent lower risk of dementia than those who were least active. By contrast, physical activity performed as part of a job was associated with a 20 per cent higher dementia risk. Work requiring long periods of standing, heavy lifting and strenuous physical activity could increase the risk of dementia The researchers also observed a modest increase in dementia risk among people who actively commuted, although this finding was based on only two studies and the evidence remains uncertain. Physical exercise has long been shown to reduce the risk of Alzheimer's - the most common type of dementia - with sedentary lifestyles a known driver of ill health in later life. Dementia is a leading cause of disability, with 14 modifiable risk factors, including physical inactivity, accounting for 45 per cent of cases. But these findings challenge the common assumption that 'every move counts for brain health,' Professor Natan Feter, the study's first author, explained. Physical activity, the researchers said, often combines exercise, manual labour, housework and commuting into a single measure. But these different forms of activity occur under very different circumstances and may have distinct effects on long-term health. Leisure time exercise is usually self-directed and is often accompanied by social interaction and a reduction in stress levels. Physically demanding jobs tend to involve repetitive tasks, long periods of standing, heavy lifting, limited recovery time and exposure to workplace hazards. Everyone experiences dementia differently. Use this checklist to help you make a note of your symptoms before you talk to your GP.However, the researchers stressed, the apparent harms associated with workplace activity are unlikely to be caused by the movement itself. Rather, they may reflect the broader social and environmental conditions that often accompany physically demanding work. Manual occupations are more likely to involve psychosocial stress and greater exposure to air and noise pollution, all factors that have independently been linked to dementia risk. Workers in these jobs may also work longer, unsociable hours and have fewer opportunities for recreational exercise. 'In other words, when it comes to protecting the brain, the context of physical activity may matter just as much as movement itself,' Professor David Raichlen, an expert in biological sciences, and study co-author said. 'Improving access to safe parks, walking trails and recreational facilities, ensuring people have adequate leisure time for exercise, and reducing harmful workplace exposures may ultimately prove as important as promoting physical activity itself.' It comes following a study published earlier this year that found that sitting down for more than eight hours a day can increase the risk of dementia by almost a third. Researchers at York University in Canada analysed data from millions of adults aged over 35 to see how physical activity, time spent sitting, and sleep affect brain health. They found that regular exercise and sufficient sleep could help protect against the disease while spending the entire working day sitting down increases the risk by 27 per cent. Research led by Prof Raichlen last month and published in the journal Alzheimer’s & Dementia similarly found that sedentary behaviour may have an impact on brain structure. In that study, physically sedentary but mentally stimulating behaviours, such as working while seated at a desk, were associated with higher volume in regions of the brain’s cortex, including areas responsible for executive function, when compared to passive sedentary activity such as watching TV. The researchers concluded the findings highlight the importance of activity context and carry implications for public health.Rather than simply encouraging people to move more, dementia prevention efforts should recognise that not all physical activity occurs under the same circumstances and that leisure time activity should be encouraged where possible.