Variation by Season and Demographic (IMAGE) University of California - San Diego Caption The effect on sleep of warmer than usual nights is most acute during the summer and among lower-income respondents and the elderly. Credit Courtesy N. Obradovich. Usage Restrictions With reporting on this research only. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.