Abstract
Research on whether sedentary behaviour (SB) is related to cognitive decline in older individuals is conflicting, potentially caused by methodological differences in previous studies. To inform public health policies, we analysed both the forward and reverse association across four-years between subjective TV time and objectively-measured SB and four cognitive outcome measures in older adults. The Irish Longitudinal Study on Ageing (TILDA) quantified time spent watching TV using a questionnaire and objective physical activity patterns with a GENEActiv accelerometer. Mixed model analysis examined whether these two measures of SB related to changes in cognitive function (immediate and delayed recall, MMSE, and animal naming task) during a four-year follow-up period. Furthermore, the reverse association between changes in cognition over the preceding four years and SB was investigated. We included 1,276 participants (67 ± 9 years). Longitudinally, every hour of objective SB per day was associated with a −0.01 (95%CI = −0.03;−0.00) lower MMSE score per year. Reversely, a worse decline in immediate and delayed recall over the preceding waves was related to slightly more objective SB (B = −0.24 (95%CI = −0.41;−0.07)) and TV time (B = −0.25 (95%CI = −0.48;−0.03)) at the end of those four years. To conclude, in healthy older individuals, higher levels of objective SB are related to cognitive decline across a four-year follow-up, although the magnitude and clinical relevance are questionable. As preceding cognitive decline is associated with more SB across follow-up, this suggests that a bidirectional association is plausible.
Highlights
Evidence suggests that physical activity (PA) promotes healthy brain ageing, making exercise a prominent focus of dementia prevention strategies (Brini et al, 2018)
Correlations were observed between both TV time and objective sedentary behaviour (SB) with higher age, higher systolic blood pressure, a higher cardiovascular morbidity count, worse sleep quality, and lower moderate-to-vigorous PA
Higher levels of SB were seen for people who were retired compared to people who were employed (8.5 vs 7.6 h of objective SB/day (p < 0.001) and 3.1 vs 2.2 vs hours of selfreported TV time/day (p < 0.001))
Summary
Evidence suggests that physical activity (PA) promotes healthy brain ageing, making exercise a prominent focus of dementia prevention strategies (Brini et al, 2018). Some evidence indicates that sedentary behaviour (SB; low-intensity activities with a Metabolic Equivalent of Task (MET) of < 1.5) (Gibbs et al, 2015), independent of physical ac tivity, might be negatively affecting cognitive health (Falck et al, 2017). Bakrania et al found associations between some specific subjective SBs and cognitive decline (Bakrania et al, 2018). Using subjective sedentary measures modest associations between SB and cognitive decline were identified in TILDA (Olanrewaju et al, 2020). Before SB can be identified as a potential target for dementia prevention, these con tradictory results need to be elucidated
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