Effect of vitamin D nutritional status on muscle function and strength in healthy women aged over sixty-five years

BACKGROUND: Vitamin D insufficiency is common in elderly adults, and leads to secondary hyperparathyroidism, bone loss, muscle weakness, and osteoporotic fractures. OBJECTIVE: To evaluate the relation between vitamin D nutritional status and muscle function and muscle strength in women aged over 65 years. METHODS: Fifty-four postmenopausal women from Buenos Aires (latitude 34° S), average age (X±DS) 71±4, were included in the study. Determinations of serum calcium, phosphate, 25 hydroxyvitamin D (25OHD), intact parathormone (iPTH) and calciuria / creatininuria ratio in 24-hour urine samples were performed. Muscle function was assessed by means of walking-speed test, standing balance, and sit-to-stand tests. Lower extremity muscle strength was determined using a manual dynamometer. RESULTS: 25OHD levels ≥20 ng/ml were found to be associated with better lower extremity muscle function and strength. Forty- six % of participants had 25OHD levels ≥20 ng/ml. Women with 25OHD levels ≥20 ng/ml scored higher on the muscle function tests (11.2±0.9 vs.10.0±2.1; p<0.003) and had stronger knee extensor (13.4±2.7 vs.11.6±2.5 Kg.; p<0.03) and hip abductor (8.3±2.7 vs. 7.3±3.1 Kg; p<0.04) muscles; strength of their hip flexors tended to be higher but did not reach significantly different values (17.0±3.3 vs. 15.4±2.8 Kg.; 0.1>p>0.05). Negative correlation was observed between iPTH and muscle function (r= -0.436; p<0.02). CONCLUSION: 25OHD levels ≥20 ng/ml are needed for a better muscle function and strength. Assessing vitamin D nutritional status in adults aged ≥ 65 years would allow correcting hypovitaminosis D and improve muscle function and strength.