What to expect after a year in space: Space is the final frontier for understanding how extreme environments affect human physiology. Following twin astronauts, one of which spent a year-long mission on the International Space Station, Garrett-Bakelman et al. examined molecular and physiological traits that may be affected by time in space (see the Perspective by Löbrich and Jeggo). Sequencing the components of whole blood revealed that the length of telomeres, which is important to maintain in dividing cells and may be related to human aging, changed substantially during space flight and again upon return to Earth. Coupled with changes in DNA methylation in immune cells and cardiovascular and cognitive effects, this study provides a basis to assess the hazards of long-term space habitation. Science , this issue p. eaau8650 ; see also p. 127

Studies of body weight regulation have focused almost entirely on caloric intake and energy expenditure. However, a number of recent studies in animals linking energy regulation and the circadian clock at the molecular, physiological, and behavioral levels raise the possibility that the timing of food intake itself may play a significant role in weight gain. The present study focused on the role of the circadian phase of food consumption in weight gain. We provide evidence that nocturnal mice fed a high‐fat diet only during the 12‐h light phase gain significantly more weight than mice fed only during the 12‐h dark phase. A better understanding of the role of the circadian system for weight gain could have important implications for developing new therapeutic strategies for combating the obesity epidemic facing the human population today.

Disturbances of sleep and wake are among the most common and disabling nonmotor manifestations of Parkinson disease (PD), affecting as many as 90% of patients.^1,2 Disrupted sleep-wake cycles contribute to poor quality of life and increased risk for accidents, leading to increased morbidity and mortality in the PD population.^3-5 Current treatment options for disturbed sleep and alertness in PD are very limited and are associated with undesirable adverse effects. Therefore, the need to understand the mechanisms leading to sleep-wake dysfunction in PD and to develop innovative treatment modalities is great. The exact pathophysiological features of sleep-wake disturbances in PD remain largely unknown, but the cause is likely to be multifactorial, including the effect of motor symptoms on sleep, primary sleep disorders (sleep apnea and Rapid Eye Movement Sleep Behavior Disorder), adverse effects of medications, and neurodegeneration of central sleep-wake regulatory systems.^6-9

Kristen L Knutson, PhD, Fred W Turek, PhD; The U-Shaped Association Between Sleep and Health: The 2 Peaks Do Not Mean the Same Thing, Sleep, Volume 29, Issue 7