Abstract
Background and Purpose: The objective of this study was to determine the risk factors of stroke incidence and mortality.
Methods: Our data are based on a prospective cohort study of men aged 40 to 49 years after 12 years of follow-up.

Stroke is the third most common cause of death in men in Norway after myocardial infarction and cancer (1990 data). During the 10-year period from 1980 to 1990, stroke mortality in men declined by 4% . ' The incidence and mortality of stroke vary greatly among populations.2-11 During the last decades stroke mortality has steadily declined in many countries, including the United States, Canada, Japan, and European countries other than Eastern European countries.12 However, there have been reports of a change in trend toward an increase in stroke incidence. 13, 14 Although new poststroke treatment strategies reduce mortality and hospitalizations,15 increased knowledge of risk factors is still important in the prevention of stroke. Major risk factors in stroke for men are hypertension, clinical evidence of cardiac disease, transient ischemic attacks, high hematocrit, diabetes mellitus, elevated blood cholesterol and lipids, cigarette smoking, excessive alcohol intake, physical inactivity, and obesity.16
In this article we present the results after 12 years of follow-up with regard to the incidence and mortality of stroke and the long-term predictivity of certain risk factors for men with no known symptoms or diseases of cardiovascular origin or diabetes.
Subjects and Methods
During 1972 and 1973 all men in Oslo aged 40 to 49 years and a 7% sample of men aged 20 to 39 years were invited to a screening. This study reports on the 25 915 men aged 40 to 49 years. A total of 16 209 men attended the screening from May 1972 to December 1973. The screening'7 included answering a questionnaire on medical history with regard to cardiovascular symptoms or diseases, smoking habits, physical activity, and stress factors. The men had their blood pressure measured with a mercury sphygmomanometer; the first and the fifth Korotkoffs sounds determined the systolic blood pressure (SBP) and diastolic blood pressure (DBP), respectively. A blood sample was taken in the nonfasting state to determine total serum cholesterol, triglycerides, and glucose. Height and weight were measured. The risk factor analysis is based on the baseline measurements. Also included in this report are the men who later participated in the dietary and smoking intervention trial (n= 1232)18 and the hypertension trial (n=785). 19 Our institute collected the data on stroke morbidity from all Oslo hospitals and two hospitals in the neighboring county. It was not feasible to collect morbidity data on men leaving the Oslo area to attend other hospitals. Data on all deaths were supplied from the Central Bureau of Statistics. Mortality data are complete except for those who emigrated. The eighth revision of The International Classification of Diseases was used (stroke codes 430 through 438). The diagnoses were not reviewed by the investigators. We included those men with stroke as major event. The follow-up period ended on December 31, 1984.
For comparative reasons the men were grouped in accordance with other Norwegian studies20,21 as follows: A total of 98 men died of stroke, and the mortality rate was 0.33 per 1000 person-years. The nonattenders tended to have a higher rate compared with healthy men than men with symptoms of cardiovascular diseases. The number of events in some groups was low. The nonattenders had a rate ratio of 2.85 compared with all attenders.
The mean values of the risk factors SBP, DBP, daily cigarette smoking, and total cholesterol together with the rate of mortality from the first quintile to the second. In the lowest quintile of the SBP distribution (Fig 2) , no cases of stroke mortality occurred. The incidence risk was of the same magnitude for SBP and DBP for the lowest quintile. The risk leveled off for the fourth and fifth quintiles.
Cholesterol was a significant risk factor for mortality, but for incidence it was only of borderline significance W(P=.08) (Fig 3) . Increasing age was a significant risk factor for incidence but not (Table 5 ). The x2 tests for a linear trend were not screening compared with 45% in significant for mortality (P>.10) or incidence (P=.09). oke.
The proportional-hazards multiple regression analy-SBP and DBP at screening were sis for incidence gave a somewhat different result from ,sed rates of incidence and morthat of mortality (Table 6 ). DBP and daily cigarette to be a highly significant predicsmoking were independent risk factors for both end and mortality in the age-adjusted points. Age and physical activity at leisure were inderds regression analysis (Table 3) . pendent risk factors for incidence but not mortality. sortant risk factor for both inciTotal cholesterol was of no significance for either end was SBP. The coefficient value point. dictability of risk factors when ,nd mortality. The coefficients for greater for mortality than for Fig 1) the trend showed a falling Discussion The mortality rate of all men invited to screening in this study during a 12-year period was 0.20 compared with the Bergen study22 rate of 0.55 in men aged 40 to 49 years followed for 20 years. The difference in rate is due most likely to different durations of follow-up.
Men from this cohort have been participating in two intervention trials, in which a total of 1010 men were in the treated groups. There was a significant difference in stroke events after 5 years of follow-up in the hypertension trial (intervention, 0; control, 7) but no difference in the dietary and smoking trial (intervention, 3; control, 3). Consequently, the effect of treatment is evident in the results.
Results of this study indicate that DBP is a stronger predictor than SBP. This is at variance with the results of the British regional heart study.2 SBP and DBP both predict mortality better than incidence. The association between a single baseline measurement of DBP and the risk of stroke is underestimated due to measurement error. 23 Assuming a universal correlation between withinperson measurements of DBP, the method presented by MacMahon et a123 by correcting for regression dilution of 60% can be applied to this study. The increased risk in DBP by an increase of 1 SD of 10.6 mm Hg after adjusting for age, total cholesterol, daily cigarette smoking, and physical activity at leisure is 2.14 (1.61) for stroke incidence and 2.96 (1.97) for stroke mortality. We have not controlled for any treatment effect by antihypertensive medication during the follow-up period. Treatment of hypertension may be the reason that SBP The results of the univariate analysis were largely confirmed in the multiple regression analysis, which found age, DBP, daily cigarette smoking, and physical activity at leisure to be independent risk factors for stroke incidence. DBP and daily cigarette smoking were found to be independent risk factors for stroke mortality. Because the number of fatal cases was low, no conclusions can be firmly drawn from the results that age and physical activity at leisure were of no significance in the multiple regression analysis of stroke mortality.
This study failed to find body mass index, height, weight, glucose, triglycerides, and physical activity at work as risk factors in an age-adjusted univariate analysis for stroke in healthy middle-aged men.
In conclusion, this study confirmed that increased blood pressure and daily cigarette smoking were the main risk factors for stroke. Total serum cholesterol was of less importance, possibly because of young age. The infarction risk score was highly predictive of stroke incidence and mortality.

{'paper_id': '15153592', 'title': 'Risk factors of stroke incidence and mortality. A 12-year follow-up of the Oslo Study.', 's2_url': 'https://api.semanticscholar.org/CorpusID:15153592', 'source': 'S2ORC'}