| Objective To explore the serum level of 25 hydroxyvitamin D in the residents living in different altitudes in Qinghai plateau in winter and summer, and to analyze the relationship between the changes of plateau seasons and bone metabolism indexes as well as the related influencing factors. Methods The number of low temperature days in the research areas was counted. The basic data from the same healthy residents aged 21-45 in different altitude areas between November 2020 and July 2021 were collected. The data of 303 residents were collected in winter (November) and that of 253 residents were collected in summer (July). Serum levels of 25(OH)D, PTH, β-CTX, and PINP in those residents were measured. Vitamin D levels of residents at different altitudes and in different seasons were evaluated. The changes of bone metabolism indexes under different vitamin D levels as well as their correlations were analyzed. Results The number of low temperature days corresponding to the microthermal climate was 226. In the research areas at different altitudes, the residents with vitamin D deficiency in summer were accounted for 95.6% and those residents in winter were accounted for 99% of all the subject population, respectively. There was no significant difference in the levels of vitamin D and PTH among the populations at different altitudes (P>0.05). However, in the same group of people, there were significant differences in their levels of 25(OH)D and bone metabolism indexes between winter and summer (P<0.01). The levels of 25(OH)D and PTH were significantly different among different gender and age groups in different seasons (P<0.05). The average PTH level of people over 40 years old in winter was 71.01±23.26 pg/ml, accounting for 20% of the total population. In summer, the levels of 25(OH)D were negatively correlated with age and PTH (P<0.05), while those levels were negatively correlated with age, PTH, β-CTX, and PINP (P<0.05) in winter. There was a positive correlation between the levels of 25(OH)D and serum Ca levels both in winter and summer (P<0.01). Conclusion The vitamin D levels of the adult residents in Qinghai plateau is slightly affected by the altitudes. However, as an area with a long winter climate, the Qinghai plateau has a limited time of sunlight exposure, which leads to the vitamin D deficiency or insufficiency in the population all year around. The vitamin D levels in women are especially lower in this area. In winter, the population with 25(OH)D deficiency in the research areas has experienced the reduced serum calcium level and the hypermetabolism of the bone, while one third of people even have secondary hyperparathyroidism. |