Effects of Prolonged Light Exposure on the Concentration of Some Hormones, Mineral Metabolic Exchange and Immunity Parameters in Students
Authors:   Kharkiv National Medical University. 4, Nauky Avenue, Kharkiv 61022, Ukraine, Gorbach T. V. , Balak O. K. , Martynova S. N. , Vlasenko O. V. 
Published: February 2021

In this work, we studied the influence of artificially prolonged daylight on the concentration of some hormones, the state of mineral metabolism, and immunity in students. Material and methods. The study involved 50 second-year students (44 girls and 6 boys) of Kharkiv National Medical University with different chronotypes. All students were on a proper diet, did not play sports, did not have any chronic diseases, and were healthy during the study period. Students were divided into 2 groups: 1) waking period from 5:00 to 23:00 (25 people), 2) waking period from 8:00 to 3:00 (25 people). Saliva was collected after careful oral hygiene at 8 a.m., 12 a.m., 4 p.m., and 12 p.m. Results and discussion. Our study showed that the artificial prolongation of daylight reduces the concentration of melatonin, especially at night (at the peak of secretion). It is established that at the artificial prolongation of the light day there is an inversion of a rhythm of thyroid's hormones secretion, decrease in their maximum concentration which probably is connected with the adaptation of an organism to an active mental activity at night. The obtained results showed that in students with the evening chronotype, the concentration of cortisol reduced both during the day and at 24 hours, which was probably associated with a decrease in melatonin secretion and its regulatory effect on the adrenal glands. Decreased concentrations of melatonin, cortisol, and thyroid hormones led to the impaired functional activity of the immune system, as evidenced by a decrease in secretory immunoglobulin and lysozyme in the saliva of students with evening chronotype, compared with students with morning chronotype of activity. Changing circadian rhythms of thyroid hormone secretion, reducing their concentration and cortisol content led to the development of metabolic disorders. We noted that dysfunction of mineral metabolism in students with evening chronotype caused a decrease in the concentration of calcium, magnesium, zinc in the saliva of students. The identified characteristics indicate that prolonged daylight reduced the ability to maintain the daily balance of the studied nutrients, which may be a manifestation of desynchrony. The concentration of immunoglobulin A in the saliva of students in the second group in the morning and the evening was significantly lower than in students of group 1, which indicated an absolute deficiency of immunoglobulin and, accordingly, a decrease in immunity with prolonged daylight. Students of group 2 also had a decrease in the content of lysozyme in saliva, which indicated a decrease in the degree of antibacterial protection. The peculiarities in the content of immunoglobulin A and lysozyme are most likely associated with a decrease in the concentration of melatonin. Conclusion. The artificial prolongation of daylight decreased the melatonin concentration in saliva and cortisol concentration. It also caused an inversion of secretion rhythm of thyroid hormones. The students with evening chronotype had a decrease in immunoglobulin A concentration, decrease in lysozyme in saliva and disturbance in a mineral metabolism