0403 Plasma Melatonin Profiling in Insomnia Disorder and Good Sleepers

Abstract Introduction Research on the role of circadian rhythms in Insomnia Disorder are mixed. Some studies in small samples have found alterations in melatonin patterns, with reduced levels at night compared to good sleepers, while other studies have failed to confirm these patterns. It can be difficult to draw conclusions because most studies either used melatonin sampling only at night or did not control for lighting levels. The current study examined group differences in melatonin secretion over two days in controlled settings. Methods Forty subjects (20 good sleepers, 20 with insomnia) were recruited to spend 4 nights in a laboratory setting as part of a larger study. Subjects (50% male, 50% female, mean age (SD)=33.5 (7.2)) were kept for 48 hours in light settings below 100 lux and had an IV placed for blood sampling every 2 hours over a 48-hour period. Plasma samples were analyzed with a melatonin radioimmunassay. Melatonin profiles were modeled with a cosinor analysis to compute mesor, acrophase, and amplitude. Results Melatonin parameters did not differ significantly between good sleeper and those with insomnia. Although the insomnia group had a higher mesor value (M=108.32, SD=103.95) than good sleepers (M=77.07, SD=59.02), this difference was not statistically significant (p=0.33). Amplitude between good sleepers (M=294.66, SD=742.40) and those with insomnia (M=107.69, SD=81.12) was also not significant (p=0.34). Finally, acrophase values were nearly identical between participants with insomnia (M=4.15, SD=3.47) and healthy subjects (M=4.28, SD=3.07) (p=0.92). Conclusion The current findings suggest that Insomnia Disorder may not be strongly associated with abnormalities in circadian rhythms of melatonin at the group level. However, the variability observed in melatonin parameters, particularly mesor and amplitude, suggests individual variability that may hide clinically relevant subpopulations. These findings are consistent with clinical trial evidence showing that exogenous melatonin administration is generally not effective for most individuals with insomnia, though some may benefit. Support (if any) NIH/NINR 5R01NR018836