TABLE 4.

Results from regression analyses of melatonin levels by chronotype within the night shift workers (NSW)

Comparison	% difference in 6- sulfatoxymelatonin levels¶	95% Confidence Interval
Day sleep v. night sleep
Dichotomous†
Evening	−21.5%**	(−36.7%, −6.3%)
Morning*	−40.9%***	(−52.5%, −29.4%)
Trichotomous§
Evening	−17.7%	(−36.4%, +1.1%)
Intermediate	−27.9%***	(−42.1%, −13.6%)
Morning*	−52.8%***	(−65.0%, −40.7%)
Night work v. night sleep
Dichotomous†
Evening	−52.3%***	(−58.1%, −46.5%)
Morning*	−32.5%***	(−40.6%, −24.4%)
Trichotomous§
Evening	−57.3%***	(−63.6%, −51.0%)
Intermediate*	−39.8%***	(−47.3%, −32.4%)
Morning*	−27.4%***	(−39.5%, −15.3%)

^*test for difference from Evening Type category: p<0.01, using two-sided t-test

^**p<0.05, two-sided t-test

^***p<0.001, two-sided t-test

^†Evening: chronoscore 33 or less; Morning: chronoscore 34 or higher

^§Evening: chronoscore 28 or less; Intermediate: chronoscore 29–39; Morning: chronoscore 40 or higher

^¶Analyzed using the natural log transformation and adjusted for the effects of age, gender, hours of darkness, body mass index, number of alcoholic beverages consumed, and use of psychotheraputics; reference category is night sleep; e.g. in dichotomous analysis, evening type night shift workers during daytime sleep had 53.2% lower levels of 6-sulfatoxmelatonin than all night shift workers during nighttime sleep