Association of the interaction between physical activity and sitting time with mortality in older Japanese adults

To examine how physical activity (PA) and sitting time (ST) are associated with mortality in older Japanese adults.

We used the data of 10 233 older Japanese adults aged ≥65 years who provided valid responses to the International Physical Activity Questionnaire-Short Form (IPAQ-SF) by a mail survey. Both PA and ST were assessed using the IPAQ-SF. The results were classified into high or low categories using ≥3.0 metabolic equivalent PA (150 min/week) and ST (300 min/day) into the following four groups: High PA (HPA)/Low ST (LST), HPA/High ST (HST), Low PA (LPA)/LST, and LPA/HST. Mortality data were collected from July 30, 2011, to November 30, 2016. We assessed the interaction of PA and ST status with the risk of all-cause mortality using the multivariable Cox proportional-hazards model.

A total of 1014 people were recorded to have died during a median follow-up period of 5.3 years (51 553 person-years). After adjustment for confounders, the risk of mortality was higher in the LPA/HST group than in all other groups (HPA/LST: reference; HPA/HST group: hazard ratio [HR] 0.86 (95% confidence interval [CI]: 0.66 to 1.12); LPA/LST group: HR 1.09 (95% CI: 0.88 to 1.35); LPA/HST group: HR 1.36 (95% CI: 1.10 to 1.67); and multiplicative interaction: HR 1.44 (95% CI: 1.07 to 1.94)).

The risk of mortality associated with LPA/HST depends on the level of PA, duration of ST, and their interaction with each other. Our results may be useful in ameliorating the adverse effects leading to mortality in individuals with lower PA, by reducing ST.