No abstract

Many people in our modern civilized society sleep later on free days compared to work days. This discrepancy in sleep timing will lead to so-called 'social jetlag' on work days with negative consequences for performance and health. Light therapy in the morning is often proposed as the most effective method to advance the circadian rhythm and sleep phase. However, most studies focus on direct effects on the circadian system and not on posttreatment effects on sleep phase and sleep integrity. In this placebo-controlled home study we investigated if blue light, rather than amber light therapy, can phase shift the sleep phase along with the circadian rhythm with preservation of sleep integrity and performance. We selected 42 participants who suffered from 'social jetlag' on workdays. Participants were randomly assigned to either high-intensity blue light exposure or amber light exposure (placebo) with similar photopic illuminance. The protocol consisted of 14 baseline days without sleep restrictions, 9 treatment days with either 30-min blue light pulses or 30-min amber light pulses in the morning along with a sleep advancing scheme and 7 posttreatment days without sleep restrictions. Melatonin samples were taken at days 1, 7, 14 (baseline), day 23 (effect treatment), and day 30 (posttreatment). Light exposure was recorded continuously. Sleep was monitored through actigraphy. Performance was measured with a reaction time task. As expected, the phase advance of the melatonin rhythm from day 14 to day 23 was significantly larger in the blue light exposure group, compared to the amber light group (84 min ± 51 (SD) and 48 min ± 47 (SD) respectively; t36 = 2.23, p < 0.05). Wake-up time during the posttreatment days was slightly earlier compared to baseline in the blue light group compared to slightly later in the amber light group (-21 min ± 33 (SD) and +12 min ± 33 (SD) respectively; F1,35 = 9.20, p < 0.01). The number of sleep bouts was significantly higher in the amber light group compared to the blue light group during sleep in the treatment period (F1,32 = 4.40, p < 0.05). Performance was significantly worse compared to baseline at all times during (F1,13 = 10.1, p < 0.01) and after amber light treatment (F1,13 = 17.1, p < 0.01), while only in the morning during posttreatment in the blue light condition (F1,10 = 9.8, p < 0.05). The data support the conclusion that blue light was able to compensate for the sleep integrity reduction and to a large extent for the performance decrement that was observed in the amber light condition, both probably as a consequence of the advancing sleep schedule. This study shows that blue light therapy in the morning, applied in a home setting, supports a sleep advancing protocol by phase advancing the circadian rhythm as well as sleep timing.

Behaviour may contribute to changes in fitness prospects with age, for example through effects of age-dependent social dominance on resource access. Older individuals often have higher dominance rank, which may reflect a longer lifespan of dominants and/or an increase in social dominance with age. In the latter case, increasing dominance could mitigate physiological senescence. We studied the social careers of free-living jackdaws over a 12 year period, and found that: (i) larger males attained higher ranks, (ii) social rank increased with age within individuals, and (iii) high-ranked individuals had shorter lifespan suggesting that maintaining or achieving high rank and associated benefits comes at a cost. Lastly, (iv) social rank declined substantially in the last year an individual was observed in the colony, and through its effect on resource access this may accelerate senescence. We suggest that behaviour affecting the ability to secure resources is integral to the senescence process via resource effects on somatic state, where behaviour may include not only social dominance, but also learning, memory, perception and (sexual) signalling. Studying behavioural effects on senescence via somatic state may be most effective in the wild, where there is competition for resources, which is usually avoided in laboratory conditions.

It is known that light in the morning is able to induce phase advances of the endogenous clock, however most studies have tested the phase advances in highly controlled laboratory conditions. At home the environmental lighting is more variable. In theory, a high intensity short morning-light pulse in the short-wavelengths-range (blue light) should be capable of inducing phase advances. If this is also true in a home setting, this could be a firm basis supporting light treatment in late chronotypes who suffer from a late sleep phase. In a study carried out in summer, 11 normal to relatively late (habitual midsleep 4:15-6:09 hours) chronotypes (age range 23-27 years, 4f/7m) participated in two conditions: (1) 1 baseline day followed by 3 consecutive days of 30 min. blue morning-light pulses, (2) 1 baseline day followed by 3 consecutive days of 60 min. blue light pulses. Blue light was applied by use of the Philips GoLite BLU (HF3320, blue leds, intensity at the cornea 2306 melanopic-lux, 300 lux, 3.65 W/m 2 ). During all four evenings, subjects were asked to protect themselves from light exposure (<10 lux). The response of the melatonin rhythm, calculated as a shift in dim light melatonin onset (DLMO), to a single 30 min. light pulse varied between subjects and resulted in a non-significant phase advance of 15 (±48) min. (t10 = 1.04; P = 0.33), and a significant advance of 30 (±41) min. to a single 60 min. light pulse. (t10 = 2.40; P < 0.05). After 3 days of light exposure both in the 30-and in the 60 min. light pulses condition significant phase advances of DLMO were observed; 49 (±58) min. (t10 = 2.80; P < 0.05) and 59 (±29) min. (t10 = 6.9; P < 0.001) respectively. No significant differences were found in the DLMO shifts between conditions. In addition there was a trend for a lower sleepiness score directly after waking up after using light for 3 days in both conditions (t10 = 3.38; P = 0.096, 60 min. and (t10 = 4.10; P = 0.070, 30 min.). A prelimin.ary analysis of actimetry data indicated some support for an effect on sleep timin.g. The data support the conclusion that light pulses of 30 min. in the morning on three consecutive days, in a home setting, in combination with dim light during the evenings, can be part of an efficient phase advancing chronotherapy protocol.