Optimal Levels of Daily Physical Activity to Maintain Immunological Function in Older Individuals: The Nakanojo Study

Abstract

The purpose of the present investigation was to examine the optimal levels and timings of daily physical activity to maintain immunological function in older individuals. Twenty older women, aged >65 yr., participated in the present investigation. All subjects were independently living, and were recruited from the NAKANOJO-study. In order to assess the number of steps and the time for moderate to vigorous intensity physical activity, all subjects wore a pedometer with one-axial accelerometer （Lifecorder, Kenz, Nagoya） continuously for 1 year. Furthermore, based on the intensity categories （0 to 9） determined every 2-min, we evaluated the hourly intensity and frequency of physical activity such as the hourly intensity of physical activity, the hourly time for moderate to vigorous intensity physical activity, and the time spent hourly distribution of moderate to vigorous intensity of physical activity. After the assessment of physical activity, as the index of the immunological function, we assessed the salivary secretory immunoglobulin A and the neutrophil phagocytosis function at the resting condition. As results, the neutrophil phagocytosis function significantly associated with the number of step counts （p<0.05）．The salivary secretory immunoglobulin A significantly associated with both the number of step counts and the time for moderate to vigorous intensity physical activity （p<0.05）．However, both indexes of the immunological functions did not correlated significantly with the hourly levels of physical activity （hourly intensity of physical activity, hourly time for moderate to vigorous intensity physical activity, the time spent hourly distribution of moderate to vigorous intensity of physical activity）．These results indicate that the habitual physical activity have important role to maintain the immunological functions in older individuals. The optimal timing for physical activity to maintain the immunological functions remains unclear.