Physical activity undertaken during leisure time, but not at work, is associated with a lower risk of dementia

The authors are quite clear about the limitations: most studies use self-reported physical activity data. There are few high-quality studies, long-term follow-ups are rare, and so on. Above all, however, there is a lack of randomised prospective studies that would allow causality to be established.

There is a great deal of evidence regarding the so-called ‘physical activity paradox’ and the conclusions drawn from the meta-analysis: the greater the total amount of exercise, the greater the protection against dementia; and the greater the physical activity during one’s working life, the lower the protection (perhaps due to less intellectual engagement; working life spans many years).

On this last point, we need to be more nuanced and not lump everyone together. The classification of the population according to occupational activity distinguishes between physical (or manual) and intellectual work. I believe that this is where the bias lies – in considering only physical or sedentary activity and failing to take into account cognitive reserve or a sense of purpose in life. The answer will be provided by studies that consider physical activity, occupation, cognitive reserve and work-related stress in conjunction. It is very important to study how all these aspects interrelate, rather than looking at each factor in isolation.

The study highlights the importance of disseminating knowledge so that people understand the significance of cognitive reserve if their work involves only physical and manual tasks. Conversely, it emphasises the importance of physical exercise for those in sedentary occupations. Most importantly, in both cases, we must learn to manage work-related stress and look after our brain health.