Deeper Dive: Melatonin mysteries — can supplementation decrease circadian misalignment and body weight in night shift workers?

Light exposure is one of the primary cues that synchronize our circadian rhythm: an internal clock that constantly calibrates to the 24-hour solar day. It establishes cyclic physiology^[1] that allows humans to anticipate environmental changes (e.g., radiation, temperature, food availability, sleep, etc.), and helps to regulate various aspects of metabolic, immune, and cardiovascular health. While there was a clear contrast between light and darkness during the pre-industrial age, modern lifestyle involves mostly indoor living throughout the day accompanied by artificial electrical lighting at night that can adversely^[2] affect our circadian rhythm. And as shown in Figure 1, lifestyle choices such as patterns of activity and eating^[3] can affect peripheral clocks that indirectly influence the primarily light-driven central clock.

Figure 1: Misalignment of central and peripheral clocks

Circadian misalignment^[4] is the off-set between sleep/wake cycles and circadian regulated physiology that often occurs in night shift workers and is associated with various chronic diseases and disorders (e.g., cardiovascular disease, diabetes, depression, bipolar disorder). Generally, a larger difference between an individual’s chronotype (the time of day someone generally sleeps) and sleep timing of a particular day, will lead to greater dysregulation^[4] of metabolism (e.g., feeding behavior, appetite stimulating hormones, etc.) and mood.

Melatonin^[5] is a signaling molecule that is produced and secreted in the absence of light, primarily by the pineal gland. It is suppressed upon light exposure and is thought to synchronize circadian clocks throughout the body. Melatonin also appears to be involved in energy metabolism and balance.

Human trials have demonstrated potential^[6] for supplemental melatonin to time-shift sleep/wake cycles, improve sleep disorders, and reduce circadian misalignment, but its effects on body weight and other anthropometrics are less clear. In a recent meta-analysis^[7], only three of seven human clinical trials that investigated supplemented melatonin demonstrated a decrease in body weight. The authors of the study under review aimed to evaluate the effects of supplemental melatonin on circadian misalignment and body weight in overweight night shift workers.

The modern lifestyle has increased the prevalence of circadian misalignment and associated adverse health effects due to the changes in light exposure and activity throughout a 24-hour solar day. Melatonin has been shown to synchronize sleep/wake cycles and is involved in metabolic health. This study was designed to determine whether supplemental melatonin can reduce circadian misalignment and decrease body weight.