Effects of infrared radiation on the diurnal rhythms of melatonin, rectal temperature and heart rate

Article type: Research Article

Authors: Griefahn, Barbara^{; *} | Künemund, Christa | Blaszkewicz, Meinolf

Affiliations: Institute for Occupational Physiology at Dortmund University, Ardeystrasse 67, D-44139 Dortmund, Germany

Correspondence: [*] Corresponding author. Tel.: +49 231 1084 221 (222); Fax: +49 231 1084 400; E-mail: griefahn@ifado.de

Abstract: Infrared radiation presented in the early night was expected to delay the circadian rhythm via suppression of melatonin synthesis. Seven healthy men (16–22 yrs) had completed a constant routine (24-h bedrest, <30 lux, 18°C) and 2 experimental sessions where bright light (BL, 1 500 lux) or infrared radiation (IR, 65°C) was applied from 1700 to 0100 h. Salivary melatonin levels were determined hourly, rectal temperature and heart rate continuously. Melatonin synthesis was suppressed by BL; the onset and the maximum of the melatonin profile and the minima of rectal temperature and heart rate were then delayed thus indicating a circadian effect. IR did not affect melatonin concentration whereas the minima of rectal temperature and heart rate were delayed indicating a dissociation due to the heat-induced elevation of both the latter variables rather than a chronobiologic effect. This study does not indicate that infrared radiation affects the circadian rhythm in night shift workers.

Keywords: Bright light, infrared radiation, melatonin, rectal temperature, heart rate, circadian rhythm

DOI: 10.3233/OER-2006-6105

Journal: Occupational Ergonomics, vol. 6, no. 1, pp. 47-53, 2006