A study by the University of Otago has found that, contrary to popular belief, the timing of evening screen use, rather than the activity itself, has a negative impact on adolescents’ sleep. Current sleep guidelines recommend no screen use in the hour or two before bedtime. However, the researchers found that screen use in the two hours before bedtime had little effect on adolescents’ sleep, while screen use after bedtime caused problems. The lead author of the study, Dr. Bradley Brosnan of the Edgar Diabetes and Obesity Research Centre, explains that screen use is an integral part of adolescents’ sleep patterns and that sleep guidelines need to be re-evaluated to better suit modern life.

Screen Use After Bedtime is Crucial

In the study published in the journal JAMA Pediatrics, 85 adolescents aged 11 to 14 wore a body camera on their chest for one week, three hours before bedtime until they went to bed. In addition to the body camera, which recorded when, what and how they used their screens, a second infrared camera was placed in their bedrooms to record their screen time in bed. They also wore an actigraph, a watch-sized device that measures sleep.

According to Brosnan, it quickly became clear that the teenagers spend a large proportion of their screen time in bed. The researchers found that 99 percent of participants used screens in the two hours before bedtime, more than half used screens once they were in bed, and a third used them after they had first tried to fall asleep. The most interesting findings were that this screen time before bedtime had little effect on sleep during the night. However, screen use after bedtime did affect sleep – it kept teens from falling asleep for about half an hour, and reduced sleep duration at night.

This was especially true for interactive screen activities such as gaming and multitasking, i.e. using multiple devices at the same time, e.g. watching a movie on Netflix on a laptop and playing Xbox on a gaming device. “Each additional 10 minutes of screen activity of this type reduced sleep duration at night by almost the same amount.

The results suggest that the impact of screen time on sleep is primarily through a temporal shift that delays sleep onset, rather than direct effects of blue light or interactive engagement, as we found no associations with sleep latency and wakefulness during the sleep period. Dr. Brosnan says that a “simple” sleep guideline – in theory, but not necessarily in reality – would be to keep devices out of the bedroom and allow teens to use their devices before bed, but not in bed.

Cell Phones and Cardiovascular Disease

Other research goes even further, suggesting that regular cell phone use causes health problems, such as increasing the risk of cardiovascular disease, especially in smokers and diabetics. In addition, this link has been partially associated with poor sleep, psychological stress and neuroticism. The article in the Canadian Journal of Cardiology, published by Elsevier, describes the results of this large-scale prospective cohort study.

Dr. Yanjun Zhang, Department of Nephrology, Nanfang Hospital, Southern Medical University, Guangzhou, China, explains: “Mobile phone use is a ubiquitous exposure in modern society, so studying its effects on health is of great value to public health. Radiofrequency electromagnetic fields (RF-EMFs) emitted from cell phones lead to dysregulation of the hypothalamic-pituitary-adrenal axis, inflammatory responses and oxidative stress, and can therefore be expected to affect a number of organs such as the heart and blood vessels. However, it is still uncertain whether cell phone use is associated with the risk of cardiovascular disease. The researchers’ aim was to assess the prospective association between regular cell phone use and the incidence of cardiovascular disease, and to investigate the mediating effects of sleep and mental health. The researchers found that regular cell phone users had a significantly higher risk of cardiovascular disease compared to irregular users.

The researchers found that sleep behavior, psychological distress and neuroticism could be potential mechanisms for the association between cell phone use and cardiovascular disease. Poor sleep behavior and mental health may adversely affect the development of cardiovascular disease through disrupted circadian rhythms, hormonal and metabolic disturbances, and increased inflammation. In addition, chronic exposure to RF-EMF radiation emitted by cell phones could lead to oxidative stress and inflammatory responses. Therefore, RF-EMF radiation exposure from cell phones in combination with smoking and diabetes could have a synergistic effect that increases the risk of cardiovascular disease.

An accompanying editorial contextualizes the results of the study. Given that the recruitment window of this study (2006-2010) predates the widespread use of modern smartphones, which are now more commonly used for other activities (e.g. entertainment, text messaging/email, social networking, etc.), the generalizability and current relevance of these findings need to be carefully considered.

Nicholas Grubic, MSc, Dalla Lana School of Public Health, University of Toronto, ON, Canada, is co-author of the editorial . According to Grubic, while the current study suggests that cell phone use may moderately increase the risk of cardiovascular disease, more conclusive evidence with valid measures of cell phone use is needed before this association becomes of concern to the general public. Responsible cell phone use should be an important part of a comprehensive approach to promoting cardiovascular health.