Study under review: Exogenous melatonin decreases circadian misalignment and body weight among early types
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 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 affect our circadian rhythm. And as shown in Figure 1, lifestyle choices such as patterns of activity and eating can affect peripheral clocks that indirectly influence the primarily light-driven central clock.
Circadian misalignment 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 of metabolism (e.g., feeding behavior, appetite stimulating hormones, etc.) and mood.
Melatonin 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 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, 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.
Other Articles in Issue #82 (August 2021)
Citrulline malate may help you pump out a few extra reps
According to this meta-analysis, taking six to eight grams before a resistance training session could help crank out a few more reps. There was some evidence of publication bias, though.
Does exercise affect fat mass differently than a caloric deficit?
This review suggests that exercise alone can help people lose proportionally more visceral fat compared to dieting or dieting plus exercise. However, some nuances in how the study was analyzed make it difficult to put much faith in this finding.
Nulls: May–June 2021
Here's a quick roundup of studies that looked for evidence of efficacy but came up empty-handed.
Deeper Dive: How do structural aspects of dietary carbohydrates determine glycemic response and appetite?
Starch structure seems to play a role in postprandial glycemic response but has no apparent impact on appetite hormones or satiety.
Mini: When are lifestyle changes enough to treat high blood pressure and cholesterol?
We give a quick rundown of a recent scientific statement from the American Heart Association on the impact of lifestyle changes on blood pressure and cholesterol.
Can beer hit the ‘pause’ button on menopause symptoms?
While this study found that beer could help with what ales people with menopausal symptoms, design and reporting issues hold this study back from being pitcher perfect.
Beyond strict meal planning: dietary flexibility won’t hurt body composition goals
This study suggests that people looking to shed some fat for physique can do equally well with flexible and rigid diet plans.