Impact of a single, short morning bright light exposure on tryptophan pathways and visuo- and sensorimotor performance: a crossover study

Abstract

BackgroundBright light (BL) has been shown to be effective in enhancing both cognitive and physical performances. Alterations in nighttime melatonin levels have also been observed. However, evaluations of light-induced changes in the preceding biochemical processes are absent. Therefore, the impact of a single morning BL exposure on sensorimotor and visuomotor performance, as well as tryptophan (trp) and trp metabolites, was evaluated in this study.MethodsIn a crossover design, 33 healthy volunteers were randomly exposed to 30 min of < 150 lx at eye level (office light, OL) and 5000 lx at eye level (bright light, BL) of 6500 K in the morning hours. Trp, sulfatoxymelatonin (aMT6s), and kynurenine (kyn) courses over the morning hours were analyzed, and changes in sensori- and visuomotor measures were examined.ResultsMotoric performance increased in both setups, independent of light intensity. aMT6s and kyn decreased equally under both lighting conditions. Trp levels decreased from a mean (95% confidence interval) of 82.0 (77.2–86.9) to 66.5 (62.5–70.1) in the OL setup only.ConclusionThese data suggest that BL in the morning hours has a limited effect on visuo- and sensorimotor performance. Nevertheless, trp degradation pathways in the morning show diverse courses after OL and BL exposure. This suggests that trp courses can potentially be altered by BL exposure.

A review of the studies on nonvisual lighting effects in the field of physiological anthropology

“…The vast majority of these papers inspected influences on the circadian rhythm [33–44]. A smaller number of papers have also addressed the influences of light intensity, when exposure occurs during a relatively short period, on the central nervous system (CNS) [45–47], the ANS as assessed by measurements such as HRV [46], PLR, nocturnal melatonin suppression [48], body temperature regulation [49], and serum tryptophan concentration and visuomotor and sensorimotor performance [50]. Two studies have specifically addressed effects on thermal regulation as measured by assessments of dressing behavior during cold exposure [51, 52].…”

“…They found CIZ in summer to be higher than that observed during winter in both light exposure conditions. The effect of the morning bright light (07:40–08:10, 5000 lx) exposure on sensorimotor and visuomotor performance and serum tryptophan and its metabolites was evaluated [50]. These data suggest that morning bright light exposure has a limited effect on visuomotor and sensorimotor performance, but can potentially alter serum tryptophan concentration.…”