Sedentary lifestyles increase all causes of mortality, double the risk of cardiovascular diseases, diabetes, and obesity, and increase the risks of colon cancer, high blood pressure, osteoporosis, lipid disorders, depression and anxiety. According to WHO, 60 to 85% of people in the world—from both developed and developing countries—lead sedentary lifestyles, making it one of the more serious public health problems of our time. It is estimated that nearly two-thirds of children are also insufficiently active, with serious implications for their future health.
Recent evidence is also showing that a lifestyle of inactivity can also have negative effects on our brain, both in terms of physical changes as well as cognitive changes.
Dementia, which is an umbrella term for conditions characterized by cognitive decline, is a growing global health issue. Combined projections from a meta-analysis predict that global dementia prevalence will double every 20 years. Dementia prevalence also represents a huge global economic cost, estimated to be US $604 billion in 2010. Strategies that can delay or prevent dementia are urgently needed given the burden it places on individuals, families, and the wider community. It has been estimated that if interventions could delay by 1 year the onset of Alzheimer's disease, the main cause of dementia worldwide, compared with no change in onset, there would be 11.8 million fewer cases of the disease by 2050.
Numerous studies have looked at the relationship between a sedentary lifestyle and cognitive levels:
- UCLA researchers recruited 35 people ages 45 to 75 — 25 women and 10 men — and asked about their physical activity levels and the average number of hours per day they spent sitting over the previous week. Each person had a high-resolution MRI scan, which provides a detailed look at the medial temporal lobe, a brain region involved in the formation of new memories.
The researchers found that sedentary behavior is a significant predictor of thinning of the medial temporal lobe and that physical activity, even at high levels, is insufficient to offset the harmful effects of sitting for extended periods. Medial temporal lobe thinning can be a precursor to cognitive decline and dementia in middle-aged and older adults.
- The California study examined 3,247 adults who were 18 to 30 years old when they enrolled in the Coronary Artery Risk Development in Young Adults Study. The study evaluated exercise and television-watching habits and their impact on cognitive function. Study subjects reported on their television viewing and exercise habits on three questionnaires completed over the course of 25 years.
The study indicated a relatively sedentary person who engaged in minimal exercise and watched a high amount of television was two times more likely than an active peer to perform poorly on cognitive tests in midlife. Those results suggest a sedentary lifestyle in young adulthood may have an impact on the risk of developing dementia in later life.
- A 2015 study published in the Journal of Aging and Physical Activityfound that adults aged 60 and older spend approximately 9.4 hours a day sedentary, which is equivalent to about 65-80 percent of their waking day.
For their study, Heisz and colleagues set out to investigate the association between physical activity and dementia risk among older adults with and without the APOE e4 gene.
The researchers came to their findings by analyzing the physical activity and dementia development of 1,646 older adults who were part of the Canadian Study of Health and Aging. All participants were free of dementia at study baseline and followed up for around 5 years.
Among adults who did not carry the APOE e4 gene, the researchers found that those who did not exercise were more likely to develop dementia than those who exercised. For APOE e4 gene carriers, however, there was no significant difference in dementia risk between those who exercised and those who did not.
According to the researchers, these findings indicate that a lack of exercise may be just as risky for dementia development than carrying the APOE e4 gene.
In addition, a meta-analysis conducted in 2020 of 18 cohort studies involving 250,063 participants and 2269 patients confirmed the positive association between sedentary behavior and the risk of dementia. Compared with individuals who had not been exposed to sedentary behavior, individuals who were exposed to sedentary behavior had a 30% higher risk of experiencing dementia. Sedentary behavior was associated with several chronic diseases that were also associated with cognitive impairment and risk of dementia. Previous data suggested that prolonged sedentary time could impair glucose and lipid metabolism, which were recognized as the risk factors for cognitive decline and all-cause dementia. In addition, inflammation was also identified as a potential risk factor for dementia. Meanwhile, sedentary behavior might conversely induce or aggravate individual inflammation. Finally, exercise was considered a protective factor for dementia. However, physical activity declines with age, while sedentary behavior increases with age. Increases in sedentary behavior and sedentary time were significantly observed in individuals who were about to retire and were continuously observed in adults after the age of 60 years, and individuals aged over 80 years are often involved in sedentary behavior, with an average sedentary time of 9 h per day, eliminating the benefits of physical exercises on individual’s cognitive health.
The bottom line is that a sedentary lifestyle, which seems to be increasing with the increase in technology, has led up to an increased 30% risk of cognitive decline through direct and indirect methods.
Wheeler, Michael J et al. Sedentary behavior as a risk factor for cognitive decline? A focus on the influence of glycemic control in brain health. Alzheimer’s & Dementia: Translational Research and Clinical Interventions. Volume 3, Issue 3, September 2017, Pages 291-300.
Yan, S., Fu, W., Wang, C. et al. Association between sedentary behavior and the risk of dementia: a systematic review and meta-analysis. Transl Psychiatry 10, 112 (2020).