Background: A sedentary lifestyle, that is, physical inactivity and vitamin D deficiency is becoming more common in adults as well as in the younger world population. Both physical inactivity and vitamin D deficiency can have serious effects on the human body both physically and psychologically. Among other things, it is believed that the consequences of vitamin D deficiency and physical inactivity are disorders of general psychological state (anxiety-depressive disorder) and the appearance of fatigue. Aim: The aim of this research paper was to investigate the relationships and possible correlation between physical activity, that is, inactivity, and the level of vitamin D in the blood with the fatigue and anxiety-depressive symptoms. Subjects and Methods: Twenty subjects were included in this study, of which 15 were female and 5 were male. The middle age of the respondents was 21 years. Subjects were drawn to measure their blood levels of Vitamin D and completed the following questionnaires: PedsQL, CORE-OM, and a lifestyle survey. Results: A statistically significant (p = 0.02) negative mean strong association (r = - 0.50) was found between the level of vitamin D in the blood and the general psychological state measured by the CORE-OM questionnaire, although statistically significant differences related to the general psychological state between the vitamin D deficiency group and the optimal vitamin D blood group. With higher levels of Vitamin D in the blood, the sum of PedsQL levels increases and fatigue decreases. Furthermore, a higher level of vitamin D in the blood lowers the total CORE-OM value, and by reducing fatigue it reduces distress and improves one's psychological well-being. Also, with more time spent on cardio exercise, fatigue, distress, and general psychological well-being are reduced. Similarly, subjects with lower levels of vitamin D feel more tired and more sleepy. No statistically significant difference in cognitive and general fatigue was observed between the mentioned groups, as well as no statistically significant difference in the amount of walking, sun exercise, cardio exercise and strength training between subjects with low and normal levels of vitamin D in the blood. Conclusion: This research provides a good basis for further exploration of this growing problem.