Relationships of physical activity and sedentary behaviours with markers of oxidative stress in the older population.

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INTRODUCTION: The scientific evidence has stated sex differences in oxidative stress markers such as homocysteine and total antioxidantcapacity (TAC), establishing sex hormones as the possible mechanism. However, the evidence showed that these differences still occur inthe older population which could imply that other lifestyle factors, such as physical activity (PA) or sedentary behaviours have a relevantrole, due to increased susceptibility to oxidative stress associated with ageing. Therefore, the current aim was to compare the oxidativestress markers between sexes and their relationships with accelerometer-based PA and sedentary behaviours.METHODS: Sixty-three participants (36 women, 68.84±3.02 years) from a randomised control trial (NCT03923712) were included in theanalysis. The PA levels [light, moderate, vigorous, and moderate-to-vigorous(MV), min/day] and sedentary behaviours (min/day) weremeasured using hip-worn accelerometers for 7 consecutive days. Raw data from accelerometers were used with the open-source packageGGIR for analysis and transformed to euclidean norm minus one with negative values rounded to zero. Three 24 h dietary recalls wereobtained from each individual to evaluate the nutrient intake. Plasma TAC levels (μmol/L) were measured using the ferric reducing antioxidant power method with some modifications. Serum homocysteine levels (μmol/L) were obtained using standard enzymatic methods. Weconducted multiple regression models, with homocysteine and TAC as dependent variables and PA and sedentary behaviours as predictorsafter controlling sex.RESULTS: Men showed significantly higher levels of TAC (1063.31±158.22 vs 894.12±171.75 μmol/L, p<0.001) and homocysteine(15.18±2.91 vs 12.43±2.70 μmol/L, p<0.001) compared to women, which remained significant after adjusting for nutrient intake. No significant differences between sexes were found for any of the PA or sedentary behaviours variables. In the multiple regression models, onlyMVPA was positively associated with TAC (β=0.25, p=0.042) which remained significant after controlling for sex (β=0.24, p=0.033). Nosignificant associations were found between homocysteine and PA and sedentary behaviours.CONCLUSION: The findings of the present study showed that, in our sample, there are still sex differences in oxidative stress which areindependent of PA levels or sedentary behaviours. Additionally, even though it is well established that daily PA is beneficial for ageing, thisstudy suggests that only MVPA intensity may have a protective and beneficial effect, even though it can acutely increase oxidative markers,it is also able to induce an adaptive response increasing the antioxidant defence without chronically increasing oxidative markers amongolder adults, contributing to a better overall oxidative stress balance.