Article Figures & Data
Figures
- Figure 1.
Urine and saliva sample collection time line. Sample collection occurred during the first day shift and second night shift of the rotating shift pattern.
- Figure 2.
Salivary melatonin levels comparing chronologic time points in season 1. For comparisons between day and night workers: 3PM–5PM: P = 0.99; 11PM–1AM: P = 0.84; 5AM–7AM: P = 0.04.
- Figure 3.
Association between light intensity (lumens/m2) and log-transformed change in urinary melatonin (log ng/mg creatinine). Change in melatonin is calculated as the difference in melatonin values from the 2 urine samples. Parameter estimate = −0.05494 (P = 0.04). Model adjusted for use of antidepressants.
Tables
- Table 1.
Characteristics of study population
Variable Day shifta Night shift Pb Mean (SE)/N (%) Mean (SE)/N (%) Age 40.5 (1.02) — — BMI (kg/m2) 28.4 (0.82) — — # Years of shift work 14.0 (1.01) — — Ethnicity White 113 (95.76%) — — Other 5 (4.24%) — — Reproductive characteristics Age at menarche 12.55 (0.13) — — Number of pregnancies 1.58 (0.18) — — Ever been pregnant Yes 69 (58.47%) — — No 49 (51.53%) — — Menopausal status Premenopausal 89 (75.42%) — — Postmenopausal 29 (24.58%) — — Number of days since previous period 13.83 (1.73) 19.58 (1.71) 0.009 Sleep characteristics Sleep duration 6.91 (0.15) 5.23 (0.15) <0.0001 Sleep interrupted 15 (12.71%) 19 (16.10%) 0.45 Lights on for more than 1 hour if interrupted 3 (2.54%) 8 (6.78%) 0.09 Experience sleep problems 69 (58.47%) — — Diagnosed with sleep disorder 4 (3.49%) — — Medication use Antidepressants 12 (10.17%) — — Beta-blockers 2 (1.69%) — — Hormone replacement therapy 7 (5.93%) — — Migraine medication 6 (5.08%) — — Pain medication (NSAIDs) 29 (24.58%) 28 (23.73%) 0.86 Sedatives or muscle relaxants 6 (5.08%) 7 (5.93%) 0.74 Oral contraceptives 19 (16.10%) 15 (12.70%) 0.25 Lifestyle characteristics Pack-years smoking 2.77 (0.57) — — Smoked during 24 hours of melatonin collection 10 (8.47%) 11 (9.32%) 0.56 Caffeine consumption (# drinks during 24 hours melatonin collection) 2.61 (0.22) 2.97 (0.22) 0.10 Alcohol consumption (# drinks during 24 hours melatonin collection) 0.33 (0.07) 0.06 (0.07) 0.008 Lifetime alcohol consumption (# drinks/wk) Teen 2.52 (0.33) — — 20s 4.30 (0.38) — — 30s 2.83 (0.34; n = 95) — — 40s 2.71 (0.36; n = 66) — — 50s 2.75 (0.74; n = 26) — — Chronotype Definite morning type 3 (3.57%) — — Moderate morning type 18 (21.43%) — — Neither type 55 (65.48%) — — Moderate evening type 8 (9.52%) — — Definite evening type 0 — — Light exposure Log-transformed mean light intensity (log lumens/m2) −2.14 (0.06) −0.06 (0.06) <0.0001 Urinary 6-sulfatoxymealtoninc Morning 6-sulfatoxymelatonin (ng/mg creatinine) 27.25 (1.11) 25.49 (1.11) 0.65 Change in 6-sulfatoxymealtonin (ng/mg creatinine) 23.48 (1.14) 24.53 (1.14) 0.80 -
↵aCharacteristics assessed in the study questionnaire (administered once) are shown in the “Day shift” column.
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↵bDifferences between day and night shifts are compared using difference of least squares means estimates in a mixed model with a random subject effect for continuous variables and using McNemar's test for categorical variables.
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↵cGeometric means (calculated by back-transforming log-transformed variables) are presented here.
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- Table 2.
Association between light and urinary melatonin
Model Regression coefficient P Light exposure Full population Peak urinary melatonina −0.03301 0.49 Change in urinary melatoninb −0.03128 0.58 Night shift only Peak urinary melatoninc −0.04037 0.07 Change in urinary melatonind −0.05494 0.04 Day shift only Peak urinary melatonine −0.08371 0.47 Change in urinary melatoninf 0.04392 0.75 Premenopausal women only Peak urinary melatoning 0.04535 0.50 Change in urinary melatoninh −0.07648 0.27 -
↵aAdjusted for use of antidepressant medication and the number of caffeinated beverages consumed during the 24 hours of melatonin assessment.
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↵bAdjusted for use of antidepressants, oral contraceptives, and the numbers of caffeinated beverages consumed during the 24 hours of melatonin assessment.
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↵cAdjusted for total number of years of shift work and use of antidepressant medication.
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↵dAdjusted for use of antidepressant medication.
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↵eAdjusted for menopausal status and the number of caffeinated beverages consumed during the 24 hours of melatonin collection.
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↵fAdjusted for menopausal status, antidepressant and migraine medication use, the number of caffeinated beverages consumed during the 24 hours of melatonin assessment and total number of years of shift work.
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↵gAdjusted for total number of years of shift work, number of days since previous menstrual period, smoking, and both number of alcoholic beverages and number of caffeinated beverages consumed during the 24 hours of melatonin assessment. Four overly influential individuals removed to improve model fit.
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↵hNo variables changed the parameter estimate by more than 10%, therefore no confounders included in model.
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- Table 3.
Influence of shift work history on melatonin
Model Regression coefficient P Number of years shift work (continuous) Peak urinary melatonina 0.03251 0.02 Change in urinary melatoninb 0.03373 0.05 >20 vs. ≤20 y shift work Peak urinary melatoninb 0.55187 0.07 Change in urinary melatoninb 0.63605 0.08 Chronotypec ≤20 y shift work >20 y shift work Definite morning type 2 (3.64%) 1 (3.45%) 0.04 Moderate morning type 7 (12.73%) 11 (37.93%) Neither type 39 (70.91%) 16 (55.17%) Moderate evening type 7 (12.73%) 1 (3.45%)
Volume 20, Issue 11
