Table 3.

Influence of shift work history on melatonin

ModelRegression coefficientP
Number of years shift work (continuous)
Peak urinary melatonina0.032510.02
Change in urinary melatoninb0.033730.05
>20 vs. ≤20 y shift work
Peak urinary melatoninb0.551870.07
Change in urinary melatoninb0.636050.08
Chronotypec≤20 y shift work>20 y shift work
Definite morning type2 (3.64%)1 (3.45%)0.04
Moderate morning type7 (12.73%)11 (37.93%)
Neither type39 (70.91%)16 (55.17%)
Moderate evening type7 (12.73%)1 (3.45%)
  • aAdjusted for age.

  • bAdjusted for age and light exposure between 12 AM and 5 AM during 24 hours of melatonin assessment.

  • cChronotype frequency by long-term shift work status.