Increased triglyceride levels in shift workers

Methamphetamine attenuates disruptions in performance and mood during simulated night-shift work

RATIONALE

Increased sleepiness while working and sleep disruptions are common complaints among shift workers. Consequently, shift workers may be more susceptible to diminished performance and work-related accidents.

OBJECTIVE

To examine the effects of the central nervous system stimulant methamphetamine on psychomotor task performance, subjective effects, and food intake during shift work under laboratory conditions.

METHODS

Seven participants completed this 23-day, within-participant design, residential laboratory study. They received a single oral methamphetamine dose (0, 5, 10 mg) 1 h after waking for three consecutive days under two shift conditions: (1) during the day shift, participants performed computerized psychomotor tasks from 0830 hours to 1730 hours and went to bed at 2400 hours and (2) during the night shift, participants performed tasks from 0030 hours to 0930 hours and went to bed at 1600 hours. Shifts alternated three times during the study; shift conditions were separated by an "off" day during which participants were not on a schedule and data were not collected.

RESULTS

When participants received placebo, psychomotor task performance and subjective effects were disrupted during the night shift, relative to the day shift. Changing shift conditions did not alter food intake significantly. Methamphetamine reversed performance and subjective-effects disruptions, and decreased food intake during the night shift.

CONCLUSION

These data indicate that shift changes produce performance impairments and mood alterations, and that a single low to moderate dose of methamphetamine attenuates many shift change-related disruptions in performance and mood.

Metabolic disturbances in male workers with rotating three-shift work. Results of the WOLF study

OBJECTIVES

The aim of the present study was to investigate the relationship between important metabolic risk factors for coronary heart disease (CHD) and type 2 diabetes in shift workers and day workers.

METHODS

Cross-sectional data from a sub-population in the WOLF study consisting of 665 day workers and 659 three-shift workers in two plants were analysed.

RESULTS

A higher proportion of shift workers than day workers had high triglyceride levels (> or =1.7 mmol/l), low levels of HDL-cholesterol (<0.9 mmol/l) and abdominal obesity (waist/hip ratio>0.9). The risk of low HDL-cholesterol was doubled in shift workers, (odds ratio (OR): 2.02, 95% confidence interval (95% CI): 1.24-3.28) after being adjusted for age, socio-economic factors, physical activity, current smoking, social support and job strain. High levels of triglycerides were also significantly associated with shift work (OR: 1.40, 95% CI: 1.08-1.83). The OR for abdominal obesity was 1.19, (95% CI: 0.92-1.56). The prevalence of hyperglycaemia (serum glucose > or =7.0 mmol/l) was similar in day and shift workers. No significant interaction was seen between shift work and abdominal obesity with regard to the associations with triglycerides and HDL-cholesterol.

CONCLUSIONS

We found a significant association between shift work and lipid disturbances (i.e. low HDL-cholesterol and high triglyceride levels). We did not find any association with hyperglycaemia.

Metabolic responses to nocturnal eating in men are affected by sources of dietary energy

Because night work is becoming more prevalent, we studied whether feeding at different times of a 24-h period would elicit different metabolic responses and whether dietary macronutrient composition would affect these responses. Seven men (26-43 y, 19.9-26.6 kg/m(2)) consumed two isocaloric diets, in a crossover design. The diets were a high carbohydrate (HC) diet [65 energy % (E%) carbohydrates, 20E% fat] and a high fat (HF) diet (40E% carbohydrates, 45E% fat). After a 6-d diet-adjustment period, the men were kept awake for 24 h and the food (continuation of respective diet) was provided as six isocaloric meals (i.e., every 4 h). Energy and substrate turnover, heart rate, mean arterial pressure (MAP), blood glucose, triacylglycerol (TAG), nonesterified fatty acid (NEFA) and glycerol were measured throughout the 24-h period. Significantly higher energy expenditure and NEFA concentration, and lower blood glucose and TAG concentrations were observed when the men consumed the HF diet than when they consumed the HC diet. Significant circadian patterns were seen in body and skin temperature (nadir, 0400-0500 h). When the men consumed the HF diet, significant circadian patterns were seen in fat oxidation (nadir, 0800-1200 h; plateau, 1200-0800 h), heat release (nadir, 0800-1200 h; plateau, 1600-0800 h), heart rate (nadir, 0000 h), blood glucose (nadir, 0800-1200 h; peak, 0000-0400 h), NEFA (nadir, 0800-1200 h; peak, 1200-2000 h) and TAG (nadir, 0800-1200 h; peak, 0400-0800 h) concentrations. Energy expenditure, carbohydrate oxidation, MAP and glycerol concentration did not display circadian patterns. Unequal variances eradicated most circadian effects in the HC-diet data. The increased TAG concentration in response to feeding at 0400 h might be involved in the higher TAG concentrations seen in shift workers. Distinct macronutrient/circadian-dependent postprandial responses were seen in most studied variables.

Adaptation of the circadian rhythm of 6-sulphatoxymelatonin to a shift schedule of seven nights followed by seven days in offshore oil installation workers

This study evaluated circadian adaptation in a 'swing shift' schedule (seven nights, 18:00-06:00 h; then 7 days, 06:00-18:00 h) on North Sea oil installations. Eleven healthy men provided sequential urine collections for the study period offshore. The urinary melatonin metabolite 6-sulphatoxymelatonin (aMT6s) was used as an index of circadian phase. A significant difference (P=0.0004) was found between the mean aMT6s acrophase (calculated peak time) at the start (+/-SD: 05:34+/-2.42 h) and end (+/-SD: 10.95+/-3.34 h) of the night shift week, but not between the start (+/-SD: 11:04+/-4.03 h) and end (+/-SD: 12:59+/-8.83 h) of the day shift week. As a group, the subjects adapted to the night shift but very large individual variations were seen during the day shift. These individual differences clearly require further study.

Is there an association between shift work and having a metabolic syndrome? Results from a population based study of 27,485 people

OBJECTIVES

To explore how metabolic risk factors for cardiovascular disease (CVD) differ between shift workers and day workers in a defined population. Shift work has been associated with an increased risk of CVD. Risk factors and causal pathways for this association are only partly known.

METHODS

A working population of 27,485 people from the Västerbotten intervention program (VIP) has been analysed. Cross sectional data, including blood sampling and questionnaires were collected in a health survey.

RESULTS

Obesity was more prevalent among shift workers in all age strata of women, but only in two out of four age groups in men. Increased triglycerides (>1.7 mmol/l) were more common among two age groups of shift working women but not among men. Low concentrations of high density lipoprotein (HDL) cholesterol (men<0.9 and women<1.0 mmol/l) were present in the youngest age group of shift workers in both men and women. Impaired glucose tolerance was more often found among 60 year old women shift workers. Obesity and high triglycerides persisted as risk factors in shift working men and women after adjusting for age and socioeconomic factors, with an OR of 1.4 for obesity and 1.1 for high triglyceride concentrations. The relative risks for women working shifts versus days with one, two, and three metabolic variables were 1.06, 1.20, and 1.71, respectively. The corresponding relative risks for men were 0.99, 1.30, and 1.63, respectively.

CONCLUSIONS

In this study, obesity, high triglycerides, and low concentrations of HDL cholesterol seem to cluster together more often in shift workers than in day workers, which might indicate an association between shift work and the metabolic syndrome.

Work-shift period and weight change

The present study was done to determine whether weight gain was more prevalent in workers on late shifts than in those on day shifts. A questionnaire about changes in weight, food intake, exercise, and sleep since starting the job on the current shift was given to day-shift and late-shift (evening and night) hospital workers. Data were analyzed for 85 subjects, 36 of whom worked during the day shift and 49 the late shift. The late-shift group reported a mean weight gain of 4.3 kg, which was greater than the mean weight gain of 0.9 kg for the day-shift group (P = 0.02). There were, however, no significant differences in current body mass index (26.7 +/- 5.4 SD) between groups. There was a trend for late-shift workers to report eating more since beginning the later shift (P = 0.06). When combined with those reporting exercising less (P = NS), this trend became significant (P = 0.04). Late-shift workers reported eating fewer meals (1.9 +/- 0.9 SD) than the day-shift workers (2.5 +/- 0.9; P = 0.002). In addition, late-shift workers reported eating the last daily meal later (mean = 22:27, or 10:27 PM) than day-shift workers (17:52 or 5:52 PM; P < 0.00005). Late-shift workers also reported more naps (P = 0.01) and longer naps (P = 0.05) during the work week than did day-shift workers. The reported changes in eating, exercise, and sleep may contribute to the increased weight gain of late-shift workers.

Shiftwork and myocardial infarction: a case-control study

OBJECTIVES

Previous studies have indicated an association between shiftwork and coronary heart disease. The increased risk could be due to job strain, which could act as a mediator of disease. There is also a possibility that interaction between shiftwork and job strain could occur that may induce or modify the development of disease. We conducted this study to explore the relation between shiftwork, job strain, and myocardial infarction.

METHODS

2006 cases with acute first time myocardial infarction were compared with 2642 controls without symptoms of myocardial infarction, and obtained from the same population that gave rise to the cases (population based case-control study).

RESULTS

Myocardial infarction risk was associated with shiftwork both in men (odds ratio (OR) 1.3, 95% confidence interval (95% CI) 1.1 to 1.6) and women (OR 1.3, 95% CI 0.9 to 1.8). In the age group 45-55, the relative risk was 1.6 in men and 3.0 in women. The results cannot be explained by job strain, age, job education level, or smoking. No interaction was found between shiftwork and job strain.

CONCLUSIONS

The findings indicate that shiftwork is associated with myocardial infarction in both men and women. The mechanism is unclear, but the relation cannot be explained by job strain, smoking, or job education level.

Randomized clinical trial of melatonin after night-shift work: efficacy and neuropsychologic effects

OBJECTIVE

Melatonin has received considerable publicity for its sleep-promoting properties; however, there is little scientific evidence of its efficacy. The objective of this study is to determine whether there are measurable beneficial effects from exogenous melatonin in emergency physicians after intermittent night-shift duty.

METHODS

This randomized, placebo-controlled, double-blind, crossover trial was conducted in the emergency department of an urban tertiary care hospital. Fifteen emergency physicians were given melatonin 5 mg or placebo for 3 consecutive nights after night-shift duty with crossover to the opposite agent after a subsequent block of night shifts. The primary outcome measure was the global assessment of recovery measured by a visual analog scale. Secondary outcome measures included sleep quality, duration, and tiredness. In addition, the Profile of Mood States questionnaire and neuropsychologic testing were performed.

RESULTS

There was no difference between melatonin and placebo in the global assessment of recovery (60.4+/-16.9 and 58.9+/-14.5, respectively; P=.29). There were no differences in sleep quality, duration or tiredness scores, sleep latency, hours of sleep obtained per night, and night or early awakening at any measurement point. Profile of Mood States and neuropsychologic test performances were similar.

CONCLUSION

We found no beneficial effect of melatonin on sleep quality, tiredness, or cognitive function in emergency physicians after night-shift duty. Our results suggest that exogenous melatonin is of limited value in recovery from night-shift work in emergency physicians.

Working conditions and prevalence of pre-eclampsia, Norway 1989

OBJECTIVE

To study the associations between working conditions and pre-eclampsia.

METHODS

A cross-sectional study based on questionnaires to all parturients was conducted in Norway from 16 October 1989 to 26 November 1989, with an 87.2% response rate. Of the 5388 responders with singleton pregnancies, 3321 continued in paid work beyond the 3rd month of pregnancy. Pre-eclampsia was recorded if the woman reported hospitalization for hypertension, or if proteinuria and hypertension were diagnosed more than once in the pregnancy.

RESULTS

The prevalence of pre-eclampsia was increased in work involving the lifting of heavy loads of 10-20 kg (adjusted odds ratio (OR), 1.8; 95% CI, 1.2-2.5), hectic work pace (OR, 1.4; 95% CI, 1.0-2.0, P < 0.05), work with hands above shoulder level (OR, 1.4; 95% CI, 1.0-2.2; P = 0.07) and for parous women, shift work (OR, 2.0; 95% CI, 1.1-3.6). It was reduced when the woman had an influence on work pace (OR, 0.7; 95% CI, 0.5-1.0; P = 0.07). Prevalence was also increased with daily consumption of more than four cups of coffee (OR, 1.6; 95% CI, 1.1-2.3).

CONCLUSION

Prenatal care should include assessment of working conditions, as early improvements may reduce the risk of pre-eclampsia.

Carbon disulphide. III. Risk factors for coronary heart diseases in workers in the viscose industry

To evaluate risk factors for coronary heart disease and factors which can influence the course of acute myocardial infarction in workers exposed to CS2 we performed a cross-sectional study of 247 workers in the viscose industry. The control group of 222 men from the same plant was comparable for age, social status and physical work. The CS2 exposure determined by personal air sampling ranged from < 0.2 ppm to 65.7 ppm (median: 4.0 ppm) and the duration of exposure ranged from 4 to 220 (median: 66) months. Using a multiple linear regression model we found neither higher blood pressure at rest or after exercise, nor hyperlipoproteinaemia in a higher degree, nor lower high-density lipoprotein (HDL) or lower apolipoprotein A-I levels, nor higher blood glucose values, nor indicators of direct cardiotoxic effects or signs of disturbances in blood coagulation in the exposed group in comparison to controls. Regarding the influence of chronic exposure on the investigated parameters, we found an inverse correlation of the cumulative exposure (mean CS2 exposure in the department multiplied by the duration of work in this department) with the HDL concentration. The HDL levels correlated with the duration but not with the intensity of exposure. In the same way the apolipoprotein A-I levels showed a negative association with the duration of exposure in the exposed group as well as in the control group. The HDL concentrations showed the same trend for the controls. It therefore seems that this finding is more likely due to confounding factors than to the CS2 exposure. As all subjects (exposed and controls) have done shift work, in some cases for a long time, this kind of work could be responsible for the negative relationship between the duration of employment as a shift worker and the apolipoprotein A-I and HDL levels. At the current air-borne levels no significant differences were found between the exposed persons and the controls in the distribution frequency for blood pressure values, lipoproteins, blood glucose, blood coagulation and indicators of direct cardiotoxic effects.

Gender and employment grade differences in blood cholesterol, apolipoproteins and haemostatic factors in the Whitehall II study

In the first Whitehall study, plasma cholesterol was a strong predictor of coronary heart disease (CHD) but it showed a positive association with grade of employment: the higher the grade the higher the level. Because it could not explain the higher rate of CHD in lower employment grades, further investigation of biochemical CHD risk factors has been conducted with data from the baseline examination of the Whitehall II cohort in 1985-88. These data also allow investigation of gender differences and the effect of menopause. Serum cholesterol (6860 men and 3374 women) and apolipoproteins A-I and B (apo AI and apo B) were measured in those aged 35-55 working in the London offices of twenty Civil Service departments. Plasma fibrinogen and factor VII were determined in 45-55 year olds. The apo B/apo AI ratio (95% confidence interval) after age adjustment is lowest in premenopausal women: 0.557 (0.549-0.565), intermediate in postmenopausal women: 0.601 (0.589-0.613) and highest in men: 0.703 (0.698-0.709). After age adjustment fibrinogen is higher in postmenopausal (2.90 (2.85-2.95) g/l) than in premenopausal women (2.78 (2.71-2.84) g/l), who have higher levels than men (2.64 (2.62-2.67) g/l). A positive association with employment grade is seen for apo AI and a negative association is seen for fibrinogen, apo B (women only) and the apo B/apo AI ratio, after age adjustment. These patterns are consistent with the higher rates of CHD in lower grades. Cholesterol and factor VII show no gradient with our sensitive measure of social position. After adjusting for the effects of smoking rates, alcohol consumption, exercise and dietary pattern, as well as age, ethnicity, body mass index and report of symptoms, the regression coefficient for apo AI on employment grade is reduced by 43% in men and 70% in women. Corresponding reductions for fibrinogen are 53% and 65%. These attenuations suggest that a considerable part of the social gradients in apo AI and fibrinogen are explained by variations in health related behaviours. The remaining gradients may represent effects independent of these behaviours.