Vitamin D status, postural sway, and the incidence of falls in elderly community-dwelling Japanese women

INTRODUCTION: There is little evidence of a preventive effect of vitamin D on falling in Japanese populations. The purpose of this study was to evaluate the effect of vitamin D status on postural sway, muscle strength, and the incidence of falls in elderly community-dwelling Japanese women. This study utilized a cross-sectional design for postural sway and muscle strength as outcomes and a prospective design for the 1-year incidence of falls. METHODS: Subjects included 633 ambulant elderly women 69 years of age and older who participated in the baseline examinations of the Muramatsu Study. Measurements of serum 25-hydroxyvitamin D (25[OH]D) and 1,25-dihydroxyvitamin D (1,25[OH](2)D) concentrations, intact parathyroid hormone (PTH), locus length (cm/s) of gravity-center sway, grip strength, body height, body weight, body mass index (BMI), and physical activity levels were recorded. Falls that occurred between May 2003 and early July 2004 were documented. RESULTS: The average age and serum 25(OH)D concentration of the subjects was 74.3 years (SD 4.4) and 60.0 nmol/l (SD 17.9), respectively. The 1-year cumulative incidence of falls was 73/609 (12.0%). Multiple linear regression analysis showed that log-transformed locus length of the center of gravity was associated with age (R(2)=0.069, P<0.0001) and BMI (R(2)=0.025, P<0.0001) and that grip strength was associated with age (R(2)=0.141, P<0.0001) and height (R(2)=0.100, P<0.0001). A subgroup analysis revealed that log-transformed locus length was significantly associated with serum 25(OH)D concentrations (R(2)=0.075, P=0.0189) in 75 subjects who had vitamin D insufficiency [serum 25(OH)D <40 nmol/l]. CONCLUSIONS: The 1-year incidence of falls was associated with locus length of gravity-center sway. The present study failed to find associations between vitamin D status and gravity-center sway, grip strength, or the incidence of falls. This may be due to relatively high serum 25(OH)D level differences in this population. However, a significant association between vitamin D status and postural sway was found in the vitamin-D-insufficient subgroup, suggesting supplementation of vitamin D should be considered for those with vitamin D insufficiency.