Vitamin D and muscle function: is there a threshold in the relation?

First, to determine the association between serum 25 hydroxyvitamin D (25OHD) concentration and muscle mass, strength, and performance. Second, to explore if there is a threshold in the association.

Cross-sectional, single-center study.

The central part of the Netherlands (52° Northern latitude).

A total of 802 independently living men and postmenopausal women 40 to 80 years of age.

Health-related and lifestyle factors, including physical activity, 25OHD concentration, lean mass, handgrip strength, knee extension strength, and physical performance were determined.

Overall, higher 25OHD level was significantly associated with higher lean mass (22.6 g per nmol/L, 95% CI 7.3-37.9), handgrip strength (0.020 kg per nmol/L, 95% CI 0.001-0.038), and physical performance (0.006 points per nmol/L, 95% CI 0.001-0.012), after adjustment for various confounders. This association was most pronounced below a 25OHD level of 60 nmol/L, with lean mass increase 79.6 g per nmol/L (95% CI 40.8-118.4, P < .01), handgrip strength 0.09 kg per nmol/L (95% CI 0.045-0.141, P < .01), and physical performance 0.02 points per nmol/L (95% CI 0.005-0.032, P < .01), and these significant associations attenuated to null above this threshold.

In middle-aged men and (postmenopausal) women, a higher 25OHD level was significantly associated with higher lean mass, muscle strength, and performance. These associations were most pronounced below 60 nmol/L and absent above 60 nmol/L, indicating a ceiling effect.