Optimal Serum 25-Hydroxyvitamin D3 Level Associated with Functional Capacity and Physical Function among Frail Elderly People Living in Rural Area / 日本農村医学会雑誌

ABSTRACT

The purpose of this study was to investigate an optimal 25-hydroxyvitamin D3 [25(OH)D] level for Japanese frail elderly people aged 65 and above from the standpoint of quality of life, functional capacity, and physical function. A longitudinal study was conducted in two towns (latitude 36 degrees north) from 2006 to 2008. The subjects were 125 frail elderly individuals living in a rural setting and attending a 3-month exercise class for prevention of age-related diseases in order that they could do without receiving nursing care. An interview was conducted based on a questionnaire, and blood data, and physical fitness tests were administered to them at baseline and at the end of the 3-month exercise class. Functional capacity and physical fitness were compared on the basis of 25(OH)D≥50 nmol/L as a usual cut-off point, and 25(OH)D≥75 nmol/L as a severer cut-off point. A comparison of changes in physical fitness between before and after exercise class was done. The mean 25(OH)D level (±SD) was 58.9±13.6 nmol/L at baseline. The ratios of 25(OH)D level less than 50.0 nmol/L and less than 75.0 nmol/L were 23.9%, and 87.2%, respectively. The rates of house-bound subjects and those with worse scores of QOL were significantly higher in the group with 25(OH)D<50.0 nmol/L compared with the group with 25(OH)D≥50 nmol/L. The rate of those with superior functional capacity was significantly higher in the group with 25(OH)D≥75 nmol/L than the group with 25(OH)D<75 nmol/L. At the end of the 3-month exercise, Timed Up & Go indicating walking ability improved significantly in the group with 25(OH)D≥50 nmol/L, and an alternate step test indicating lower extremity strength significantly improved in the group with 25(OH)D≥75 nmol/L. From these findings, it was suggested that 25(OH)D level more than 50 nmol/L would be needed to maintain walking ability of the Japanese frail elderly and that 25(OH)D level more than 75 nmol/L would be needed to maintain lower extremity strength or functional capacity.