BACKGROUND: The subject of discussion is the issue of the separation point, which determines sufficient levels of vitamin D for bone health. When determining the adequate reference range of vitamin D, researchers are mainly guided by the results of research, where the level of 25(OH)D is determined, at which the PTH level decreases and reaches a plateau. AIM: To establish the cut-off point of vitamin D by suppressing excessive secretion of PTH. MATERIALS AND METHODS: Observational, single-site, single-stage, selective, uncontrolled study of the search for vitamin D levels by the effect on PTH secretion in residents of Tyumen region was conducted (n = 176). All selected study participants determined the level of 25(OH)D and PTH in serum. The calculation of the cut-off point was carried out using the method of searching for changes in the correlation dependence of PTH on the level of vitamin D, followed by verification of the data obtained using ROC analysis. RESULTS: A mathematical analysis of the dependence of 25(OH)D and PTH showed the cut-off point of vitamin D, equal to 23.6 ng/ml. CONCLUSION: The cut-off point of 23.6 ng/ml is optimal for suppressing excessive PTH secretion. The data obtained may be an incentive for further working out the cut-off point of vitamin D for the Russian population and can be used to clarify the classification of deficiency, insufficiency and optimal levels of vitamin D for the population of the Russian Federation.