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·kg−1·d−1), and activity durations (min·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.
1Graduate School of Comprehensive Human Sciences, Doctoral Program of Sports Medicine, Tsukuba University, Ibaraki, JAPAN; 2Institute for Biomedical Engineering Consolidated Research Institute for Advanced Science and Medical Care, Waseda University, Tokyo, JAPAN; and 3Faculty of Sport Sciences, Waseda University, Saitama, JAPAN
Address for correspondence: Ichiro Kono, M.D., Ph.D., Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8574, Japan; E-mail: email@example.com.
Submitted for publication September 2006.
Accepted for publication December 2006.