Introduction. With age, there is a growing risk of vitamin D deficiency and cognitive impairment. Maintaining the older people’s health is socially relevant to health systems in the light of the population ageing trend. The study was aimed at identifying the relationship of vitamin D levels and symptoms of moderate cognitive impairment in older people. Methods. The authors conducted a cross-sectional screening of vitamin D status and cognitive impairment using the memory impairment screen (MIS) questionnaire, as well as the clinical, placebo-controlled study of vitamin D intake at a dose of 2,000 IU/day for 6 months. Results. The frequency of vitamin D deficiency in older patients with signs of cognitive impairment totaled 90.91 %, which was significantly more frequently compared with the group without cognitive impairment, where vitamin D deficiency was found only in 11.36 % of cases. In the dynamics on the background of the vitamin D intake for 6 months, the concentration in the intervention group amounted to 52.34 ± 2.43 ng/ml vs 14.71 ± 1.54 ng/ ml in the placebo group. The results of the study of cognitive impairment using MIS for the treatment group were 3.63 ± 0.01 points, which was significantly higher compared with the placebo group – 1.78 ± 0.22 points. A correlation analysis of vitamin D levels and MIS points showed a strong positive relationship, with a correlation coefficient of 0.92. Conclusion. The study identified a positive relationship of increasing vitamin D levels and reducing the symptoms of mild cognitive impairment in older people. Achieving vitamin D levels of over 40 ng/ ml greatly reduces the symptoms of cognitive impairment identified by the MIS questionnaire, however, the issue of treatment of impaired cognitive functions with vitamin D remains debatable.