Association between Vitamin D with Walking Speed and Muscle Strength: NHANES 2001-2002

Background: Vitamin D is an essential nutrient and a precursor hormone that plays an important role in many biochemical functions, such as bone renewal, cell growth, blood cell formation, hormone balance, and glucose metabolism. Deficiencies in vitamin D have been associated with a wide range of adverse health effects including cognitive decline, depression, cancer, diabetes, heart disease, osteoporosis, lower immune function and obesity. In recent literature, neuromuscular symptoms including muscle weakness and gait variability have been shown to be related to low serum 25-hydroxyvitamin D (25OHD) concentrations. The objective of this study was to assess the relationship between vitamin D with walking speed and muscle strength, markers that has been shown to predict falls and survival.

Methods: We used linear regression to examine the cross-sectional association between vitamin D and motor functions on those age 50 years and older using the National Health and Nutrition Examination Survey (NHANES), 2001-2002. There were 2260 study participants, 1115 men and 1145 women. Walking speed was derived from observed time to walk 20-feet and 8-feet. Muscle strength was measured by knee extensor (quadriceps) power. Thresholds of serum 25-hydroxyvitamin D (25OHD) were used: insufficient < 10 ng/mL, moderate 10-30 ng/mL and normal > 30 ng/mL. Potential confounders considered were age, education level, ethnicity, height, waist circumference, alcohol consumption, smoking, physical exercise, general health status, and medical comorbidities.

Results: Among women, 52.3% (n=599) had 25OHD insufficiency, 40.4% moderate, and 7.3% (n=84) normal concentrations. Among men, a total of 51.5% (n=574) of subjects had 25OHD insufficiency, 42.1% (n=470) moderate, and 6.4% (n=71) normal concentrations. In the fully adjusted walking speed models, both women and men with insufficient 25OHD concentrations had slower walking speed of 0.18 (p<0.01) and 0.12 feet/second (p=0.04), respectively, compared with normal or moderate 25OHD. 25OHD insufficiency was also associated with decreased knee extensor power: 3.20 Watts (p=0.13) less in women and 11.8 Watts (p<0.01) less in men compared with those with normal 25OHD.

Conclusions: Insufficient serum 25OHD concentrations were associated with decreases in walking speed and muscle strength. Our results support the hypothesis that vitamin D insufficiency may contribute to frailty in the elderly through disturbances of the neuromuscular system and loss of muscle mass.