Alertness After Night Shifts Among Workers in the Aluminium Industry

Abstract

Objective: This case-crossover study aimed to evaluate changes in alertness following night shifts among workers in the aluminium industry, and the potential impact of the number of consecutive night shifts and shift length.

Methods: We estimated alertness on 87 aluminium workers by a 3-minute version of the Psychomotor Vigilance Test after both day and night shifts. Linear mixed models were used for statistical analysis.

Results: The level of alertness was significantly lower after three and four consecutive night shifts, compared with after a day shift. No significant differences in alertness were observed between three and four consecutive night shifts, nor between periods of three consecutive 8 + 8 + 8-hour versus 8 + 12 + 12-hour night shifts.

Conclusions: Our findings indicate reduced alertness after three and four consecutive night shifts, compared with after day work. No significant dose-response effect was observed.

Keywords: neurobehavioral performance; night work; occupational health; psychomotor vigilance task; reaction time; shift work; working time.

Graphical abstract

FIGURE 1

Shift plan with marked PVT time points. 3 N, after three consecutive 8-hour nightshifts; 3 NL, after three consecutive 8 + 12 + 12-hour nightshifts; 4 N, after four consecutive 8-hour nightshifts; D, after three consecutive 8-hour day shifts; D8, 8-hour dayshift; N8, 8-hour nightshift; N12, 12-hour nightshift; X, day off.

FIGURE 2

PVT results for all outcome measures, with day shift PVT as reference. Comparisons between time points with statistically significant difference are marked *P < 0,05. **P < 0,01. *** P < 0,001. 3 N, after three consecutive 8-hour nightshifts; 3 NL, after three consecutive 8 + 12 + 12-hour nightshifts; 4 N, after four consecutive 8-hour nightshifts; D, after three consecutive 8-hour day shifts; Lapses, number of response times >355 milliseconds; Mean 1/RT, mean reciprocal response time, measured in seconds; Slowest 10% Mean 1/RT, the slowest 10% of reciprocal response times, measured in seconds; RT, response time in milliseconds.

FIGURE 3

PVT results for the rehearsal tests for the outcome measure mean response time. Reh1, first rehearsal test; Reh2, second rehearsal test; Reh3, third rehearsal test; 3 N, after three consecutive 8-hour nightshifts; 3 NL, after three consecutive 8 + 12 + 12-hour nightshifts; 4 N, after four consecutive 8-hour nightshifts; D, after three consecutive 8-hour day shifts; RT, response time in milliseconds.

FIGURE 4

Differences in mean response time between groups. 3 N, after 3 consecutive 8-hour nightshifts; 3 NL, after 3 consecutive 8 + 8 + 12-hour nightshifts; 4 N, after 4 consecutive 8-hour nightshifts; D, after three consecutive 8-hour dayshifts; RT, response time. * P < 0,05.

FIGURE 5

Relationship between aluminium levels in urine, adjusted and nonadjusted for creatinine, and mean response time for the PVT test taken the same day as the urine sample, excluding outliers. Al, aluminium; Creat, creatinine; RT, response time.