Cardio-autonomic control and wellbeing due to oscillating color light exposure Vincent Grote a, b , Christina Kelz a, b , Nandu Goswami b, ⁎, Harald Stossier c , Erwin Tafeit d , Maximilian Moser a, b a HUMAN RESEARCH INSTITUTE for Health Technology and Prevention Research, Weiz, Austria b Institute of Physiology, Medical University of Graz, Austria c VIVA-Centre for Modern Mayr Medicine, Maria Woerth, Austria d Institute of Physiological Chemistry, Medical University of Graz, Austria HIGHLIGHTS • Cardio-autonomic and psychological effects of colored light cycling investigated. • Vigilance improved over the two weeks of light therapy. • Repeated light exposure sessions are required to produce psychological effects. • Oscillating visual inputs activate processes connected to physiological regulation. abstract article info Article history: Received 24 January 2012 Received in revised form 28 November 2012 Accepted 6 March 2013 Available online 16 March 2013 Keywords: Cardiovascular Heart rate variability Vigilance Human health Circadian rhythms Wellbeing Ultradian Light exposure Autonomic control We investigated the cardio-autonomic and psychological effects of colored light cycling with the wavelength of ultradian rhythms. In two consecutive experiments, an explorative, longitudinal test followed by a randomized crossover design, 20 healthy subjects each were exposed to oscillating red, green and blue light. Heart rate, heart rate variability (HRV) and subjective wellbeing were measured. Significant effects of the oscillating color light exposure were observed for heart rate and cardio-autonomic control rhythms, derived from HRV (p ≤ .001). These effects on HRV were replicated in the second experiment in comparison to a similar white light exposure protocol (p ≤ .05). Vigilance showed improvement over the two weeks (p ≤ .001) in the longitudinal study. External color light cycling at the wavelength of blood pressure oscilla- tions appears to amplify the endogenous autonomic oscillations. This leads to an optimization of cardio-autonomic control; an effect that was reflected shortly after the onset of the light exposure sessions by the increase of heart rate variability. From the results, we conclude that it takes repeated light exposure session to foster the positive effects on the psychological aspects, as we observed an increase of subjectively perceived mood only in the longitudinal study, not for the crossover design study. The results of our study imply some possible health effects of a color light exposure that is adjusted to 10 s and 1 min oscillations of humans' ultradian rhythms. These novel results show possible applications of oscillating visual inputs to the activation of processes connected to physiological regulation. © 2013 Elsevier Inc. All rights reserved. 1. Introduction Over the course of a day, human beings are exposed to sunlight of changing spectral composition and color temperature [1]. There are dif- ferent pathways, via which light can affect the humans: non-visual – e.g. via skin – to light and visual/optical. Both of these can affect neuroendocrine and physiological responses and influence endogenous rhythms, wellbeing and behavior. 1.1. Non-visual Skin exposed to the ultraviolet components of sun light supports the production of serotonin [2] and vitamin D by conversion of pro- vitamin 7-dehydrocholesterol to vitamin D3 [3] which can improve health [4] and subjective well-being [5]. Serotonin, additional to its own anti-depressive action, is a progenitor substance for the production of melatonin, which is secreted by the pineal gland and is itself depen- dent on light as well as the circadian rhythm [6]. 1.2. Visual Recently discovered photoreceptors are located in both the inner and outer layers of the retina [7]. Light falling on the retina is Physiology & Behavior 114–115 (2013) 55–64 ⁎ Corresponding author at: Institute of Physiology, Medical University Graz, Harrachgasse 21, A-8010 Graz, Austria. Tel.: +43 316 380 4278; fax: +43 316 380 9630. E-mail address: nandu.goswami@medunigraz.at (N. Goswami). 0031-9384/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.physbeh.2013.03.007 Contents lists available at SciVerse ScienceDirect Physiology & Behavior journal homepage: www.elsevier.com/locate/phb