Background. In conditions of low insolation, which is typical for the northern regions of the Russian Federation, manifestations of low vitamin D availability often occur latently and for a long time unrecognized. This problem is especially relevant in young people, due to the failure to reach peak bone mass, which later determines the bone mineral density. Aims - to determine the prevalence of deficiency and insufficient supply of 25(OH)D in blood serum in the spring, their impact on the indicators of physical development and bone mineral density among cadets of a military higher educational institutions. Methods. We examined 198 cadets, studying in the first and fourth years of military higher educational institutions in St. Petersburg at the age of 17-25 years. As part of the study, a study of 25(OH)D in blood serum was performed, bone mineral density, muscle strength, anthropometric data, and body composition were additionally determined. The study was conducted in March-May 2023. Results. The optimal content of 25(OH)D was found only in 22 (11.1%) cadets, while the most pronounced deficiency was registered in boys of fourth of study. It was established that the 25(OH)D level of first year cadets, who arrived from the southern regions of the Russian Federation (21.6 (18.1; 26.3) ng/ml), was significantly different from the content of 25(OH)D in cadets who arrived from the middle zone (Me 18.7 (16.4; 21.4) ng/ml) (p = 0.017) and northern regions of the Russian Federation (Me 15.2 (13.6; 19.3) ng/ml) (p = 0.022). A decrease in the Z-criterion ≤ -2.0 SD was noted among cadets, mainly in the first year. It was revealed that muscle and fat mass were higher in fourth year boys, however, their muscle strength was not statistically significantly different from that of first year and muscle strength indicators did not depend on the availability of 25(OH)D. Increasing BMI was associated with higher muscle mass (p = 0.0004) and fat mass (p = 0.0006), with muscle strength (p = 0.026) and physical fitness performance (p = 0.012) among cadets with increasing BMI were significantly better compared to cadets who had an optimal BMI. Conclusions. The results obtained indicate that cadets of a military higher educational institutions of St. Petersburg experience 25(OH)D deficiency and insufficiency, against the background of increased physical activity and prolonged stay in conditions of reduced insolation. This fact indicates the need to correct vitamin D hypovitaminosis in order to prevent osteopenic syndrome and improve physical performance.