Shiftwork and mortality from ischaemic heart disease.

OBJECTIVES: To investigate the relation between shift work and death from ischaemic heart disease (IHD). METHODS: A nested case-control approach was used. The cohort comprised male manual workers who joined an industrial company aged 50 years or under between 1 January 1950 and 31 December 1992 and worked there for at least one month. Cases were 467 cohort members who died during the same period aged 75 years or under, with ischaemic heart disease (IHD) (international classification of diseases (ICD) 410-414) coded from the death certificate. For each case a control worker was chosen, who joined the company at the same age and in the same period but who survived the case. Work status (shift work or day work) was assigned to cases for their entire employment and to controls for that part of their employment which preceded the matching case's death. The main source of information was historical personnel records containing pay codes which differed for day work and shift work. Information on weight, height, blood pressure, and smoking from a pre-employment medical was available. RESULTS: Two thirds of subjects had been employed for at least one month as shift workers and there was evidence that they had slightly better health at recruitment than day workers. The odds ratio for shift workers during the period starting 10 years after shift work began, and after adjustment for height, body mass index, blood pressure, smoking, duration of employment, and job status (skilled or unskilled) was 0.90 (90% confidence interval (90% CI): 0.68-1.21). There was no relation between risk of IHD death, and duration of shift work, but there was evidence of a reduced risk when actively employed as a shift worker, together with an increased risk in the first five years after leaving shift work to do day work. CONCLUSIONS: Shift work did not increase the risk of death from ischaemic heart disease in this study. Those workers with poorer cardiovascular health may be under represented in groups with longer shift work experience because of health related selection out of shift work.     

Excess winter mortality from ischaemic heart disease and stroke during colder and warmer years in Israel

Most data on winter excess mortality from cardiovascular diseasehave been reported from countries with large seasonal temperaturevariations. In this study, the contribution of environmentaltemperature to ischaemic heart disease (IHD) and stroke mortalitywas evaluated in a country with relatively small variationsin seasonal temperature. The association between monthly temperatureand cause-specific monthly proportion of annual mortality wasstudied in the population of Israel aged 45 years and over forthe period 1976-85. Population size in this group averaged nearly1 million people during the study period, and about 40% of alldeaths were due to IHD or stroke. For men, IHD mortality was51% higher and stroke mortality 48% higher in mid-winter thanin mid-summer; for women the respective figures were 48% and40%. In cosinor analysis for months above and below the medianminimum temperature, it was shown that excess mortality in winterwas greater in years below the median minimum temperature inalmost all age-sex categories. In partial correlation analysis,most of the variation in IHD and stroke mortality was explainedby variation in minimum monthly temperature. These findingsstrongly support the role of environmental temperature in excesswinter mortality from cardiovascular disease over a wide agerange, and efforts should be directed at identifying interventionmeasures which could significantly reduce the incidence of prematuremortality.     

Occupational noise exposure and ischaemic heart disease mortality

Aims

To investigate the hypothesis that long term exposure to excessive noise can increase the risk of ischaemic heart disease.

Methods

A case‐control design, nested within a cohort of nuclear power workers employed at two sites in England over the period 1950–98, was used. Cases were men who died from ischaemic heart disease (ICD‐9: 410–414) aged 75 or under; each was matched to a surviving control of the nearest age who joined the same site at the same time. Personal noise exposure was assessed retrospectively for each man by hygienists using (1) company work histories, (2) noise survey records from 1965–98, and (3) judgements about likely use of hearing protection devices. Men were classified into four groups according to their cumulative exposure to noise, with men whose exposure at the company never exceeded 85dB(A) for at least one year being considered “unexposed”. Risks were compared via odds ratios (ORs) using conditional logistic regression and adjusted for systolic and diastolic blood pressure, height, BMI, and smoking, as measured at recruitment to the company.

Results

Analysis was based on 1101 case‐control pairs. There was little difference between the exposure groups at recruitment. There was no evidence of increased risk at site A: the ORs for ischaemic heart disease mortality among low, medium, and high exposure categories, compared to unexposed men, being 1.04, 1.00, and 0.77. The corresponding ORs (95% CIs) at site B were 1.15 (0.81–1.65) 1.45 (1.02–2.06), and 1.37 (0.96–1.96). When the comparison was confined to men with at least five years of employment, these dropped to 1.07 (0.64–1.77), 1.33 (0.88–2.01), and 1.21 (0.82–1.79) respectively.

Conclusions

The authors did not find statistically robust evidence of increased risk but the estimates at site B are consistent with those in a major cohort study. A strength of the present study is that the validity of noise estimation at site B has been demonstrated elsewhere.Excessive noise, at work or in the wider environment, has been linked with increased blood pressure and risk of ischaemic heart disease. A meta‐analysis¹ of nine cross sectional, “well matched” occupational studies concluded that an increase of 5dB(A) on the 8‐hour A‐weighted scale was associated with an increase of 0.51 mmHg (95% CI 0.01 to 1.00) in systolic blood pressure and of 14% (1%–29%) in the prevalence of hypertension. However, the authors noted that the results of the studies were inconsistent and there was some evidence of a publication bias against small negative studies. An earlier review of occupational exposure² concluded that there was considerable evidence that noise has short term effects on cardiovascular function and catecholamine levels but that, although there was a suggestion that chronic noise exposure might lead to sustained increases in blood pressure, there was a lack of convincing evidence that it caused cardiovascular disease. This was, in part, due to poor quantification of noise exposures and inadequate consideration of confounders.Another problem is that there have been few longitudinal studies: although some of the reviewed studies incorporated estimates of cumulative exposure, they were essentially cross sectional with the emphasis on prevalence. One longitudinal study³ of miners with high exposures who remained in work for at least 10 years found no evidence of a link with blood pressure. Lang et al⁴ found effects on blood pressure only among those exposed at work to levels above 85dB(A) for at least 20 years, but there may have been insufficient power at lower durations. Recently, the findings from a large cohort study⁵ of lumber mill workers, including workers with 20 or more years at levels over 85dB(A), have been reported. Among workers who terminated employment before the introduction of hearing protection devices, there was a exposure‐response relation between ischaemic heart disease mortality and years of exposure above 85dB(A), with a relative risk of 1.3 (p = 0.04) in those with 20 or more years'' exposure above 85dB(A) compared to less than three years, after adjustment for age, calendar year, and ethnicity. Twenty or more years above 95dB(A) produced an RR of 1.5 (95% CI 1.1 to 2.2).According to the Netherlands Health Council committee on Noise and Health, the “no adverse effect level” for industrial workers is at most 85dB(A) on the 8‐hour A‐weighted scale and, for general environmental noise, 70dB(A) on the 24‐hour L_dn scale.^6,7 A large cohort study⁸ of road traffic noise and incidence of ischaemic heart disease found no statistically significant effects, perhaps because the maximum L_dn was less than 70 dB(A). On the other hand, a recent, large case‐control study⁹ found an OR of 1.8 (95% CI 1.0 to 3.2) for myocardial infarction among men who lived for at least 10 years in homes with daytime traffic noise levels above 70dB(A). Other cross sectional studies^10,11 found a relation between aircraft noise, up to 76dB(A) on the L_dn scale, and use of medication for cardiovascular diseases.Given these results and the ubiquity of noise exposure, there is a need for further longitudinal studies. We report here on a longitudinal study of occupational exposure and mortality from ischaemic heart disease among a cohort of nuclear power workers in England.     

Childhood risk factors for ischaemic heart disease and stroke

To explore the relation between environmental influences in early life and risk of cardiovascular disease in adulthood, case-control comparisons were made on 99 patients with acute myocardial infarction and 55 patients with recent hemisphere stroke. After allowance for smoking habits and current social class, risk of myocardial infarction was higher in subjects of lower social class at birth, smaller stature, and with a history of infant and especially perinatal death in a sibling. Stroke was also associated with infant or perinatal death in a sibling. Although none of these associations was statistically significant at a 5% level, they support other evidence that implicates the pre and early postnatal environment in the aetiology of cardiovascular disease.     

Childhood risk factors for ischaemic heart disease and stroke

Summary. To explore the relation between environmental influences in early life and risk of cardiovascular disease in adulthood, case-control comparisons were made on 99 patients with acute myocardial infarction and 55 patients with recent hemisphere stroke. After allowance for smoking habits and current social class, risk of myocardial infarction was higher in subjects of lower social class at birth, smaller stature, and with a history of infant and especially perinatal death in a sibling. Stroke was also associated with infant or perinatal death in a sibling. Although none of these associations was statistically significant at a 5% level, they support other evidence that implicates the pre and early postnatal environment in the aetiology of cardiovascular disease.     

Regionalizing mortality data: ischaemic heart disease in Norway

The way regions are delimited has a bearing on the geographical patterns and time trends which emerge from cause specific mortality analysis. Whenever possible, alternative regionalizations should be used to explore the full information potential of the data. For statistical reasons, the size of the regional units (populations-at-risk) should be selected according to the frequency of the cause of death, number of years in the time period, etc. A geographical mortality information system for Norway, based on individual death records and with quick and flexible retrieval options is described. As a demonstration, geographical time trends in ischaemic heart disease from 1970 to 1985 are studied, using different schemes of regionalization. A clear tendency towards regional convergence appears in the rural-urban dimension, but there is no convergence between the five subnational regions of the country. There is no evidence that counties which have received heart disease intervention projects fare any better than those which have not, but here a more thorough analysis is recommended. Within the intervention counties, there are large variations both in mortality levels and trends.     

Geographical variation mortality from ischaemic heart disease in England and Wales

Analysis ofthe proportional mortality attributed to ischaemic heart disease, adjusted for age, reminds us that many of the well known geographical, environmental, social, and economic variations within England and Wales are not disease specific.     

Age and sex differences in the management of ischaemic heart disease

Objective

To investigate age and sex differences in the utilisation of hospital services for ischaemic heart disease.

Design

Analysis of routine mortality data and hospital activity data.

Setting

South West Thames Regional Health Authority.

Subjects

Residents of the South West Thames Regional Health Authority who in 1991 either died from ischaemic heart disease or were admitted to an NHS hospital in England and Wales with a main diagnosis of ischaemic heart disease.

Main outcome measures

Ratio of consultant episodes to deaths from ischaemic heart disease (as a proxymeasure of the utilisation of hospital care), and the percentages of consultant episodes in which further investigation (angiography or catheterisation) or revascularisation treatment (coronary artery bypass grafting or angioplasty) were carried out.

Results

The ratio of episodes to deaths was similar in men and women (odds ratio for men vs. women 0.96, 95% confidence intervals 0.90 to 1.03). The percentage of episodes in which further investigation was carried out was higher in men than women (odds ratio for men vs. women 1.46, 95% confidence intervals 1.25 to 1.70) as was the percentage of episodes in which revascularisation treatment was carried out (odds ratio for men vs. women 1.46, 95% confidence intervals 1.20 to 1.77). The ratio of episodes to deaths, the percentage of episodes in which further investigation was carried out, and the percentage of episodes in which revascularisation treatment was carried out all declined with age (all p values <0.001).

Conclusions

Women with ischaemic heart disease are as likely as men to be admitted to hospital, but afteradmission are less likely to undergo further investigation and revascularisation treatment. Elderly patients with ischaemic heart disease are less likely than younger patients to be admitted to hospital; after admission, they are also less likely to undergo further investigation and revascularisation treatment. Further research is needed to determine whether these age and sex differences in the use of hospital services are clinically justified.     

Regional differences in mortality from ischemic heart disease

The geographical distribution of mortality from ischaemic heart disease in the Netherlands has changed dramatically since 1950. In 1950-1954 mortality was highest in high-income, urbanized areas, in 1980-1984 the reverse was true. This development resembles the one observed in the United States of America. The changes in geographical distribution cannot be attributed to differences in cause-of-death certification. The change in the association with income and the association between mortality and a number of ischaemic heart disease risk factors found in 1970-1974, suggest that at least part of the explanation is a change in the geographical distribution of risk factors.     

Geographical variation mortality from ischaemic heart disease in England and Wales.

Analysis ofthe proportional mortality attributed to ischaemic heart disease, adjusted for age, reminds us that many of the well known geographical, environmental, social, and economic variations within England and Wales are not disease specific.     

Milk drinking, ischaemic heart disease and ischaemic stroke II. Evidence from cohort studies

OBJECTIVE: Milk consumption is considered a risk factor for vascular disease on the basis of relevant biological mechanisms and data from ecological studies. The aim was to identify published prospective studies of milk drinking and vascular disease, and conduct an overview. DESIGN: The literature was searched for cohort studies, in which an estimate of the consumption of milk, or the intake of calcium from dairy sources, has been related to incident vascular disease. MAIN OUTCOME MEASURES: Ischaemic heart disease and ischaemic stroke. RESULTS: In total, 10 studies were identified. Their results show a high degree of consistency in the reported risk for heart disease and stroke, all but one study suggesting a relative risk of less than one in subjects with the highest intakes of milk. A pooled estimate of relative odds in these subjects, relative to the risk in subjects with the lowest consumption, is 0.87 (95% CI 0.74-1.03) for ischaemic heart disease and 0.83 (0.77-0.90) for ischaemic stroke. The odds ratio for any vascular event is 0.84 (0.78-0.90). CONCLUSIONS: Cohort studies provide no convincing evidence that milk is harmful. While there still could be residual confounding from unidentified factors, the studies, taken together, suggest that milk drinking may be associated with a small but worthwhile reduction in heart disease and stroke risk. SPONSORSHIP: The University of Wales College of Medicine and Bristol University. Current support is from the Food Standards Agency.     

Deaths from ischaemic heart disease and infant mortality in England and Wales.

Death rates from ischaemic heart disease (IHD) in English and Welsh counties are correlated, in both men and women, with the infant mortality rates of those counties when the individuals whose deaths are considered were young, thus confirming previous findings in Norway. In England and Wales, however, there is an equally good correlation between deaths from IHD and infant mortality patterns up to and including that for the same time period as the IHD deaths. The British data provide no grounds for concluding from these relationships that living conditions during early life per se bear a causal relationship to deaths from IHD.     

Milk drinking, ischaemic heart disease and ischaemic stroke I. Evidence from the Caerphilly cohort

OBJECTIVE: To test the hypothesis that milk drinking increases the risk of ischaemic heart disease (IHD) and ischaemic stroke in a prospective study. DESIGN: In the Caerphilly Cohort Study dietary data, including milk consumption, were collected by a semiquantitative food frequency questionnaire in 1979-1983. The cohort has been followed for 20-24 y and incident IHD and stroke events identified. SUBJECTS: A representative population sample in South Wales, of 2512 men, aged 45-59 y at recruitment. MAIN OUTCOME MEASURES: In total, 493 men had an IHD event and 185 an ischaemic stroke during follow-up. RESULTS: After adjustment, the hazard ratio in men with a milk consumption of one pint (0.57 l) or more per day, relative to men who stated that they consumed no milk, is 0.71 (0.40-1.26) for IHD and 0.66 (0.24-1.81) for ischaemic stroke. At baseline, 606 men had had clinical or ECG evidence of vascular disease, and in these the vascular risk was even lower (0.37; 0.15-0.90). The hazard ratio for IHD and ischaemic stroke combined is 0.64 (0.39-1.06) in all men and 0.37 (0.15-0.90) in those who had had a prior vascular event. CONCLUSION: The data provide no convincing evidence that milk consumption is associated with an increase in vascular disease risk. Evidence from an overview of all published cohort studies on this topic should be informative. SPONSORSHIP:: The Medical Research Council, the University of Wales College of Medicine and Bristol University. Current support is from the Food Standards Agency.     

Ethnic differences in coronary heart disease case fatality rates in Auckland

Abstract: Data from the Auckland Coronary or Stroke (ARCOS) study for the years 1983 to 1992 were analysed to describe 28–day case fatality rates from coronary heart disease among Europeans, Maori and Pacific Islands people in Auckland, New Zealand. The case fatality rate was consistently higher in each age group and for both sexes among Maori and Pacific Islands people than in Europeans. Age–standardised case fatalities for Maori and Pacific Islands people were similar at around 65 per cent, compared with around 45 per cent among Europeans, and these differences were not explained by ethnic differences in possible underreporting of nonfatal myocardial infarction, in socioeconomic status, smoking, symptoms or past myocardial infarction. There was evidence of a more rapid progression of acute coronary events to a fatal outcome among Maori and Pacific Islands people, partly explained by delays in access to life support and coronary care: greater proportions of Pacific Islands people than Maori or Europeans who died did so within an hour of onset of symptoms (56 per cent of Pacific Islands people, 47 per cent of Maori, 45 per cent of Europeans). Pacific Islands and Maori people with acute coronary events took longer to reach a coronary care unit (mean times: Pacific Islands people 8.6 hours, Maori 7.4 hours, Europeans 6.7 hours, P < 0.05), although the median times were not significantly different; life–support units were used by a majority of Pacific Islands people and Europeans (57 per cent and 55 per cent, respectively), compared with only 46 per cent of Maori, but hospital care was similar for the three groups. Further qualitative and quantitative research is needed to investigate the reasons for these ethnic disparities in case fatality rates.     

Trends in mortality from ischaemic heart disease in Singapore, 1959 to 1983

Mortality from ischaemic heart disease in Singapore has been studied from vital statistics for the 25 years from 1959 to 1983. The age-standardized rates for ages 30 to 69 years increased in men from 106.8 per 100 000 in 1959-1963 to 204.5 in 1979-1983, while for women they increased from 30.7 to 72.0 per 100 000. The male to female ratios in the age-standardized rates for ischaemic heart disease fell from 3.5 to 2.8 in the period, while remaining steady for all causes. However, while mortality rates for ischaemic heart disease have increased steadily over the period in the older age groups, they have recently declined in the younger ages with a birth cohort effect. For males the decline started with the 1932-1936 birth cohort (men now aged around 50 years), while for females it was the 1937-1941 birth cohort (women now aged around 45 years). The reasons for this decline are discussed but no clear explanation is at present apparent and it would be useful to have future monitoring of lifestyles and coronary risk factors.     

Ischaemic heart disease mortality among men in Norway: reversal of urban-rural difference between 1966 and 1989.

OBJECTIVE--This study aimed to examine regional urban-rural differences in mortality from ischaemic heart disease, including sudden death of unknown cause (IHD/SUD) in Norway from 1966-89, for men and women aged 30-69 years. DESIGN--Analysis was based on vital statistics. Regional mortality rates were obtained by aggregating the 443 municipalities in Norway into urban, rural, and intermediate municipalities. SETTINGS AND SUBJECTS--Norway. RESULTS--In 1966-70 the age adjusted IHD/SUD mortality in the age group 30-69 years was higher in urban than in rural areas; for men by 31% (95% CI 27%, 36%) and for women by 28% (95% CI 19%, 36%). In 1986-89 the IHD/SUD mortality for men showed a reversed urban-rural gradient: it was 8% (95% CI 2%, 13%) higher in rural than in urban areas. The mortality rates for women were equal for both these aggregates. For men the results indicate that IHD/SUD mortality peaked first in urban municipalities and then, but at a lower level, in rural areas. For women there was a substantial decline in IHD/SUD mortality between 1966 and 1989, but an actual peak could not be demonstrated in any of the three aggregates during the period. The decline in IHD/SUD mortality among women was steepest in urban municipalities and least noticeable in rural municipalities, but the decline tapered off towards the end of the study period. CONCLUSION--The results confirm a phase-shifted peak in IHD/SUD mortality, which began in towns and ended in rural areas, and provides clues to the main underlying factors in the IHD epidemic at the population level.     

Selenium in ischaemic heart disease

Ecological between-area comparisons, hospital-based case-control studies and cross-sectional angiography studies have provided data on the role of selenium (Se) deficiency in the aetiology of ischaemic heart disease (IHD), but this evidence is, at best, suggestive because of the potential selection biases and the lack of certainty of the temporal direction of the observed associations. Out of the four cohort-based population studies published so far, one observed a moderate association between a reduced serum Se and an increased risk of IHD and all cardiovascular (CVD) deaths, one was equivocal and two did not find any association between serum Se and IHD. There are, however, several potential sources of biases acting towards the null hypothesis in these studies. In the pooled data of the two separate cohorts from eastern Finland including 377 people who experienced a CVD death or a non-fatal myocardial infarction and equally many event-free risk-factor matched controls, people with serum Se of less than 45 micrograms/l had a 1.7-fold (95% confidence interval 1.2-2.7) risk of an CVD event compared to those with higher serum Se. This association could, however, be explained by the covariation of Se with other nutrients, as for example n-3 polyunsaturated fatty acids. As the evidence concerning the role of serum Se in IHD is inconclusive, we need new epidemiological studies to test the association and experiments exploring the possible mechanisms.     

Occupational differences in ischemic heart disease mortality and risk factors in Australia

Mortality rates from ischemic heart disease in Australia declined by about 25% over the period 1969-1978. The greatest declines were experienced by the professional occupations, while lower socioeconomic groups had higher mortality rates at the beginning of the period and experienced smaller declines. From a national survey in 1980, significantly and consistently lower risk levels of blood pressure, triglyceride, cigarette smoking, body mass and exercise were found among higher status occupation groups. This suggests that there is a pattern of coronary prevention behavior spanning multiple risk factors that is associated with a reduction in ischemic heart disease.