Oxidative stress increases with advancing age and is a mediator of several diseases including cancer, cardiovascular disease, and diabetes. Moreover, postmenopausal women have a lower estrogen concentration, which is associated with elevated oxidative stress. However, there is no definitive evidence regarding the relationship between daily physical activity and oxidative stress status in older adults, including postmenopausal women. Twenty-nine adults (age, 70.1 ± 1.0 years, mean ± SE; 12 women and 17 men) were examined in this cross-sectional study. Prior to blood collection, the participants were asked to wear a uniaxial accelerometer for 4 consecutive weeks to determine their level of physical activity. After a 48-h period of physical activity avoidance and a 10-h overnight fast, venous blood samples were obtained from each participant. Fasting plasma derivatives of reactive oxygen metabolites (d-ROMs) and malondialdehyde (MDA) concentrations of oxidative stress markers were negatively correlated with the amount of physical activity in women (d-ROMs; r = -0.708, p = 0.002) (MDA; r = -0.549, p = 0. 028), but not in men. Fasting plasma biological antioxidant potential of antioxidant capacity marker was positively correlated with the amount of physical activity in women (BAP; r = 0.657, p = 0.006) (GSH; r = 0.549, p = 0.028), but not in men. Moreover, superoxide dismutase activity of antioxidant capacity marker was positively correlated with the amount of physical activity in men (r = 0.627, p = 0.039), but not in women. There were no associations between physical activity and other oxidative stress markers (reduced and oxidized glutathione, glutathione peroxidise, thioredoxin). These findings suggest that regular physical activity may have a protective effect against oxidative stress by increasing total antioxidant capacity, especially in postmenopausal women.

• It is important to consider daily physical activity status when evaluating antioxidant capacity.

• Sex differences affect the alteration of oxidative stress markers induced by daily physical activity.

• Regular physical activity may have a protective effect against oxidative stress by increasing total antioxidant capacity, especially in postmenopausal women.