. Sedentary Behavior and Incident Dementia Among Older Adults. JAMA. 2023 Sep 12;330(10):934-940. PubMed.

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  1. The U.K. Biobank study findings are stronger than what the Women's Health Initiative Memory Study/Objective Physical Activity and Cardiovascular Health in Older Women, aka WHIMS/OPACH, study showed. In OPACH, higher total sitting time and longer mean sitting bout durations were not associated with higher dementia risk. Differences in study findings between the U.K. Biobank and the WHIMS/OPACH could be due to differences in study population characteristics, what particular activity monitor was used, and where it was worn on the body, and how dementia was classified.

    In OPACH, the mean age was 81.8 + 6.2 years, whereas in the U.K. Biobank the median age for those with incident dementia was 71 (IQR=68-74) and 67 (IQR=64-70) for those without incident dementia, so the U.K. Biobank study population was not yet old enough to observe higher dementia rates.  Additionally, OPACH women wore the well-known research grade ActiGraph GT3X+ , which is worn around the hip, as opposed to a wrist-worn device, and sedentary behavior was classified using a novel and validated machine-learned algorithm that captures postural transitions more accurately than traditional accelerometer data-processing methods. Importantly, dementia diagnosis in the WHIMS/OPACH involved careful annual cognitive assessments over time and adjudication using several sources of neurocognitive data and a panel of experts, as opposed to clinical diagnoses in the medical record.

    Physical functioning was not accounted for in analyses, which could distort the relationship between sedentary behavior and dementia. Individuals with lower physical functioning might accumulate more sedentary behavior, have less physical activity, and could have health conditions not captured in the other study variables, or be at higher risk of developing health conditions, resulting in higher dementia risk.

    Nonetheless, the findings from this rigorous and thorough U.K. Biobank study are plausible and relevant, as higher sedentary behavior is associated with higher risk of cardiovascular disease, which in turn is associated with higher dementia risk. The results are also consistent with current evidence-based guidelines recommending that individuals reduce their sedentary time.

    The take-home is that given there are few if any risks of adverse outcomes with reducing sedentary behavior, it seems prudent to encourage individuals to sit less and move more.

  2. This paper can be used to better counsel patients on how lifestyle choices and dementia risk are related. In my opinion, the main strength of this study is a very large sample size, which enables the authors to control for many co-variates at once, e.g., age, sex, education, ApoE, Townsend score, chronic conditions, etc. Having this sort of statistical power and ability to account for covariates is rare, and lends credence to the conclusions they draw.

    The lack of significantly increased risk in Quartile 3 (9.27h to 10.44 h/d) suggests that there may be substantial improvement in risk conferred by modestly decreasing the amount of one’s sedentary behavior, i.e., moving from Q4 to 3.

    I would have liked more discussion of device-measured sleep in the paper. While the overall n is high, at 49,841, the number of incident dementia cases was fairly low, at 414 incident dementia cases, <1 percent. ... Perhaps that’s due to the relatively young age? This might impact the generalizability of the results.

  3. In this retrospective study, more sedentary behaviours were associated with an increased risk of dementia. The size of the study, the main length of follow up (6.72 years), and the careful statistical analyses covarying for usual demographic factors, exercise, diet, sleep, chronic health conditions, smoking, alcohol use, body mass index, APOE E4 make the findings plausible.

    Further, the possibility of reverse causality was lessened by the authors’ use of landmark analysis, whereby people who developed a dementia diagnosis within four years of accelerometer recording were excluded. There was a dose effect, although at the very high end of sedentary behaviour, numbers were small and confidence intervals wide.

    The mechanism for the association is not clear. Chronic health conditions, which were controlled for, were based on physician diagnosis of vascular or heart disease including myocardial infarct, angina, stroke or current high blood pressure, diabetes, or cancer. There were many limitations to the study, which require caution in interpreting the results.

  4. To me these findings are not surprising at all. Sitting all day long deteriorates pretty much all biological system in the body, including the brain. It is likely that most of these cases are related to vascular dementia, hence the observed effects with inactivity. The main take-home message is that one should break sitting time and replace it with some active time to counteract the negative effects of too much sitting.

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