People who work at night and sleep during the day often experience disruption of their circadian rhythm and misalignment between the natural biological clock and their patterns of sleeping and eating. Being awake when the circadian drive for alertness is low, and asleep when it is high leads to sleep disruptions and poor health outcomes in the long term. And yet our society is dependent on night-shift workers in fields such as manufacturing, energy production, transportation, healthcare, law enforcement, and the military, among other essential services.
Shift workers account for up to 20 percent of the workforce in industrial societies and these workers – when assigned night shifts, early morning shifts or rotating shifts – must modify their sleep and eating schedules. This places millions of people in the U.S. alone, in positions of sleep disruption and forced wakefulness. The short- and long-term health consequences of this can be significant and can include the development of metabolic and gastrointestinal problems, cancer and cardiovascular issues. Importantly, shift workers also have a 25 to 40 percent higher risk of experiencing depression and anxiety.
In a new research study, investigators from Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system, have tested whether the timing of eating meals has an impact on the vulnerability of shift workers to depressed mood levels. They designed a study that simulated the timing of night work and then tested the effects of daytime and nighttime eating on depression-like and anxiety-like mood levels among the participants.
To conduct the investigation, the researchers enrolled 19 participants (12 men and 7 women) for a randomized controlled study. The individuals underwent a Forced Desynchrony protocol in dim light for four 28-hour “days,” such that by the fourth “day” their behavioral cycles were inverted by 12 hours, simulating the conditions of night work and causing circadian misalignment.
The participants were also randomly assigned to one of two meal timing groups: the Daytime and Nighttime Meal Control Group, which had meals according to a 28-hour cycle (resulting in eating meals both during the night and day, which is typical among night-shift workers), and the Daytime-Only Meal Intervention Group, which had meals on a 24-hour cycle (resulting in eating only during the daytime). The team assessed the depression- and anxiety-like mood levels of the participants every hour.
The findings, published in the Proceedings of the National Academy of Sciences, showed that meal timing significantly affected the participants’ mood levels. During the simulated night shift (day 4), those in the Daytime and Nighttime Meal Control Group had increased depression-like mood levels and anxiety-like mood levels, compared to baseline (day 1). By contrast, there were no changes in mood in the Daytime Meal Intervention Group during the simulated night shift. Participants with a greater degree of circadian misalignment experienced more depression- and anxiety-like mood.
“Our findings provide evidence for the timing of food intake as a novel strategy to potentially minimize mood vulnerability in individuals experiencing circadian misalignment, such as people engaged in shift work, experiencing jet lag, or suffering from circadian rhythm disorders,” said study co-author Dr. Frank A. J. L. Scheer.
“Shift workers – as well as individuals experiencing circadian disruption, including jet lag – may benefit from our meal timing intervention,” said study co-author Dr. Sarah L. Chellappa. “Our findings open the door for a novel sleep/circadian behavioral strategy that might also benefit individuals experiencing mental health disorders. Our study adds to a growing body of evidence finding that strategies that optimize sleep and circadian rhythms may help promote mental health.”
Shift workers do not only experience disruption of their sleeping and eating patterns when working at night. Since they commonly need to sleep as soon as they return home from work, they forgo other activities such as exercise, personal care and socializing with others in order to catch up on sleep. This makes it difficult for them to live healthy lifestyles. In addition, they may be tempted to opt for fast meals (fast food) because there are fewer healthy eating options at night, or because shopping for and preparing healthy meals is time-consuming. All these aspects of shift work can have negative outcomes on health, both physical and mental.
“Meal timing is emerging as an important aspect of nutrition that may influence physical health,” said Dr. Chellappa. “But the causal role of the timing of food intake on mental health remains to be tested. Future studies are required to establish if changes in meal timing can help individuals experiencing depressive and anxiety/anxiety-related disorders.”
“Future studies in shift workers and clinical populations are required to firmly establish if changes in meal timing can prevent their increased mood vulnerability,” said Dr. Sheer. “Until then, our study brings a new ‘player’ to the table: the timing of food intake matters for our mood.”