Abstract

Background: Latitude affects both the quantity and quality of solar UVB reaching the earth’s surface and effective formation of previtamin D3 in the skin. Low 25-hydroxy vitamin D (25OHD) levels are associated with skeletal muscle strength. We studied the effect of latitude on 25OHD levels and muscle weight in three different latitude areas.
Methods: A total of 79 healthy adults age ≥65 years were included in the study, from among adult day- care center clients in Uji city (n= 23, Kyoto, 34.53 degrees N), Eiheiji-cho (n= 30, Fukui, 36.06 degree N) and Nanao city (n=26, Ishikawa, 37.02 degree N).The 25OHD level in these subjects was classified as either deficient (<20) or insufficient (≥20 to 29.9).Characteristics of 25OHD deficiency in three areas were analyzed using a Chi-square test. Limb and trunk muscle weight and body composition were measured using direct segmental multi-frequency bioelectrical impedance analysis. Correlations between the prevalence of 25OHD deficiency and latitude, and skeletal muscle mass and 25OHD levels in 25OHD insufficient subjects were assessed via Pearson correlation coefficients. C2C12 myoblast atrophy was induced with 50 µM dexamethasone (DEX) with and without various concentrations of 25OHD and intracellular ATP level and protein were analyzed.
Results: The 25OHD insufficient or sufficient ratio was significantly associated with latitude (χ2 = 7.919, p= 0.019, φ= 2). A positive association between degree of latitude and the prevalence of 25OHD deficiency in three areas was observed (ɤ= 0.981). 25OHD was weakly correlated with limb and trunk skeletal muscles. DEX treatment alone decreased myotube ATP significantly. 25OHD induced an increase in the cellular ATP concentrations in the presence of DEX in a dose-response manner.
Conclusion: These facts indicate the need to adopt active sunbathing in day-care services, especially in winter or at institutions located at higher latitudes, to prevent sarcopenia.