Serum cholesterol levels and stroke mortality

Analysis of the MRFIT screenees: a methodological study

PURPOSE

To review the methods used in the many publications on the MRFIT screenees.

METHOD

Medline was searched for articles mentioning MRFIT screenees. The articles were collected, abstracted, and the method section and some of the result section were scrutinized in detail. The statements in different articles regarding methods used and the presentation of results were compared.

RESULT

The analyses of the MRFIT screenees seem to be retrospective studies of mortality and risk factors, where the underlying data base has been far from complete. Similar data are presented in slightly different fashions in several papers published in different scientific journals at about the same time. The control of the quality of underlying data has been uneven and is not discussed at all in most of the papers published.

CONCLUSION

The often-repeated statement that the MRFIT screenees constitute the largest and most exact data base regarding the relation of risk factors to mortality in the healthy male US population has no foundation.

Influence of total cholesterol, high density lipoprotein cholesterol, and triglycerides on risk of cerebrovascular disease: the Copenhagen City Heart Study

OBJECTIVE

To estimate the influence of plasma total cholesterol, high density lipoprotein cholesterol, and triglycerides on risk of cerebrovascular disease.

DESIGN

The Copenhagen City Heart Study is a prospective observational survey with two cardiovascular examinations at five year intervals. Non-fasting plasma lipids were measured in participants once at each examination, along with other variables. The Cox regression model was used to establish the effect of the factors recorded on cerebrovascular events of mostly, but not exclusively, ischaemic origin.

SUBJECTS

19,698 women and men at least 20 years old, randomly selected after age stratification from an area of central Copenhagen.

MAIN OUTCOME MEASURES

Initial cases of stroke and transient ischaemic attack recorded from hospital records and death certificates from 1976 through 1988.

RESULTS

660 non-haemorrhagic and 33 haemorrhagic events were recorded. Total cholesterol was positively associated with risk of non-haemorrhagic events, but only for levels > 8 mmol/l, corresponding to the upper 5% of the distribution in the study population. For lower plasma cholesterol values the relative risk remained nearly constant. Plasma triglyceride concentration was significantly, positively associated with risk of non-haemorrhagic events. The relative risk corresponding to an increase of 1 mmol/l was 1.12 (95% confidence interval 1.07 to 1.16). There was a negative, log linear association between high density lipoprotein cholesterol and risk of non-haemorrhagic events (0.53 (0.34 to 0.83)). There was no indication that the effects of plasma lipids were different in women and men.

CONCLUSIONS

The pattern of the association between plasma cholesterol and risk of ischaemic cerebrovascular disease was not log linear, and the increased risk was confined to the upper 5% of the cholesterol distribution. Further studies should concentrate on the association between plasma cholesterol and verified haemorrhagic stroke.

Serum cholesterol and acute myocardial infarction: a case-control study from the GISSI-2 trial. Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto-Epidemiologia dei Fattori di Rischio dell'Infarto Miocardico Investigators

OBJECTIVE

To examine the role of serum cholesterol in acute myocardial infarction in a population of patients with no history of coronary heart disease and to establish the nature of this association, the degree of risk, and the possible interaction between serum cholesterol and other major risk factors for acute myocardial infarction.

DESIGN

Case-control study.

SETTING

90 hospitals in northern, central, and southern Italy.

PATIENTS

916 consecutive cases of newly diagnosed acute myocardial infarction and 1106 hospital controls admitted to hospital with acute conditions not related to known or suspected risk factors for coronary heart disease.

DATA COLLECTION

Data were collected with a structured questionnaire and blood samples were taken by venepuncture as soon as possible after admission to hospital from cases and controls. Blood cholesterol concentrations were available for 614 cases and 792 controls.

RESULTS

After adjustment by logistic regression for sex, age, education, geographical area, smoking status, body mass index, history of diabetes and hypertension, and family history of coronary heart disease the estimated relative risks of acute myocardial infarction for quintiles of serum cholesterol (from lowest to highest) were 2.3 (95% confidence interval (CI) 1.6 to 3.4), 3.1 (95% CI 2.1 to 4.6), 4.1 (95% CI 2.8 to 6.0), and 5.2 (95% CI 3.5 to 7.7). The estimated relative risk across selected covariates increased from the lowest to the highest quintile of serum cholesterol particularly for men, patients under 55 years of age, and smokers. When the possible interaction of known risk factors with serum cholesterol was examined, smoking habits, diabetes, and hypertension had approximately multiplicative effects on relative risk.

CONCLUSIONS

This study indicates that serum cholesterol was an independent risk factor for acute myocardial infarction. This association was linear, with no threshold level. Moreover, there was a multiplicative effect between cholesterol and other major risk factors on the relative risk of acute myocardial infarction.