RESUMEN
The purpose of the present investigation was to study the aftereffect of UV-B-irradiation applied during 10 or 20 sessions. The biological effect and aftereffect duration of UV-B-irradiation of the upper body of 9 healthy volunteers (residents of the city of Moscow and its suburbs) were evaluated in autumn and winter. During UV-irradiation in the range 220-280, 280-320, or 320-400 nm the flux density was 0.035, 1.75, or 0.65 W/m2, respectively. Group 1 subjects (5 men) were exposed to UV-B-irradiation 10 times (once with 0.5, 0.6, 0.75, 0.9, 1.1, 1.35, 1.65 MED and three times with 2.0 MED) and Group 2 subjects (4 men) were exposed to UV-B-irradiation 20 times (twice with 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 MED and eight times with 2 MED). The sessions were arranged every other day. The exposure produced a beneficial effect on the human body: skin sensitivity decreased, resistance of skin capillaries increased, Ca metabolism normalized, blood 25 (OH) D grew. The trend of responses was similar after 10 and 20 sessions; however, 20 sessions caused a longer-term aftereffect. In relation to space programs, it is concluded that UV-irradiation can be applied on the ground before short-term flights (less than 4 months) and in space during longer-term flights (greater than 4 months).