A study of melatonin levels and stress in female shift workers

The aim of this study was to determine the relationship between saliva melatonin and stress levels in Thai female shift workers. Five older (38.4 +/- 1.82) and five younger (21.4 +/- 0.55) female workers voluntarily participated in this study. All participants worked both morning and night shifts at a glass manufacturing factory. Saliva was collected every three hours at the workplace and at the subjects' houses to examine melatonin profiles. The Mann-Whitney U test and the Wilcoxon signed ranks test were used. There was a significant (p < 0.05) difference between melatonin levels in younger and older subjects when measured during the night shift at 19:00. Differences between melatonin levels during the morning and night shifts in the older group were significant at 07:00 and at 19:00 in younger subjects (p < 0.05). Normal stress and mild stress were found. No significant differences in melatonin levels were found between workers with normal and mild stress levels. The onset time of increasing saliva melatonin was at 19:00, both in women working the morning shift and in those working the night shift. Peak melatonin production occurred at 22:00 for the night shift in both groups. During the morning shifts, the peak times were at 04:00 and 01:00 (in the younger and older groups, respectively), usually between 02:00 and 04:00. These findings show that melatonin levels in female shift workers adapted according to the shift worked, especially in the older group. Health surveillance programs should therefore be established to prevent further negative health effects for female shift workers.