Effect of free-living daily physical activity on salivary secretory IgA in elderly.

PURPOSE: The aim of this work was to assess the relationship in elderly subjects between free-living daily physical activity and mucosal immunity, especially salivary secretory immunoglobulin A (SIgA).

METHODS: Elderly volunteers (114 men and 170 women) aged 71.3 +/- 0.3 yr (range: 65-86 yr) participated in this study. Resting saliva samples were collected in the morning. Saliva samples stimulated by chewing a sterile cotton ball at a frequency of 60/60 s were collected. The SIgA concentration was measured using enzyme-linked immunosorbent assay (ELISA), and the SIgA secretion rate was calculated. Free-living step count (steps per day), energy expenditure (kJ x kg(-1) x d(-1)), and activity durations (min x d(-1)) at specific intensity levels (inactive, light, moderate, and vigorous) were evaluated using an electric pedometer. The data obtained were stratified by pedometer-determined steps per day using quartiles (Q1-Q4) for distribution.

RESULTS: Elderly in quartiles showed step counts of 2962 +/- 94, 5118 +/- 62, 6832 +/- 59, and 9951 +/- 264 steps per day. Significant differences were found in the mean step count (P<0.0001), energy expenditure (P<0.0001), and activity duration (P<0.0001) with increasing pedometer-determined activity quartiles. Both SIgA concentration and SIgA-secretion rate were significantly higher for Q3 than for Q1 (P<0.05). Meanwhile, saliva flow rates showed no significant differences across quartiles.

CONCLUSION: These results suggest that a free-living daily physical activity level of approximately 7000 steps per day might be regarded as a moderate daily physical activity target for elderly people to improve mucosal immune function.