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Erythrocyte sedimentation rate and cardiovascular disease
Atherosclerosis, 42 (1982)97- 107 Elsevier/North-Holland Scientific Publishers,
97 Ltd.
Erythrocyte Sedimentation Rate and Cardiovascular Disease Results from a Population Study of Women in Gateborg, Sweden Vilhjalmur Rafnsson and Calle Bengtsson Depurtnmt
of Medicine II, Suhlgrensku
Sjukhuset,
University of Gi%ehorg, Giitehorg (Sweden)
(Received 26 February, I98 I) (Revised, received 29 September. 198 I) (Accepted 30 September, 1981)
In a prospective study of a population sample of women, the erythrocyte sedimentation rate (ESR) was studied in relation to the incidence of myocardial infarction, angina pectoris, stroke and intermittent claudication. ESR could not be proved to be predictive of these manifestations of cardiovascular disease. Similar results were obtained when the population was studied cross-sectionally. The ESR was higher in women with hyperlipidaemia (serum triglyceride 2 2.0 mmol/l or 3 9 mmol/l), in women with arterial hypertension (treated or serum cholesterol untreated, with systolic blood pressure ) 160 mm Hg or diastolic blood pressure > 95 mm Hg or both) and in overweight women (women within the upper 10 centiles of weight index) compared to women of the same age in the population sample who did not fulfill the criteria according to the above definitions. ESR was similar in hyperuricaemic women (upper 5 centiles of serum uric acid) and in those who were not hyperuricaemic. No association was found between smoking habits and ESR. Weak correlations were found between ESR and serum triglycerides, serum cholesterol and serum uric acid, respectively. Although some correlations were found, ESR cannot replace other examinations in the search for risk factors for cardiovascular disease.
Cardiovascular risk factors - Erythrocyte sedimentation rate - Intermittent claudication - Ischaemic heart disease - Population study - Stroke Women
Key words:
This study was supported by Grant No. 27X-4578 from the Swedish Medical Research Council. Correspondence to: Dr. Vilhjalmur Rafnsson, Yrkesmedicinska Kliniken, Sahlgrenska Sjukhuset, S-4 13 45 Goteborg, Sweden.
0021-91/50/82/0000-0000/$02.75
0 1982 Elsevier/North-Holland
Scientific
Publishers,
Ltd.
98
Introduction The erythrocyte sedimentation rate (ESR) is a very commonly used laboratory test, especially in Scandinavia. The levels of the ESR have been found to be a risk factor for death from ischaemic vascular disease, as recently reported [l], and for myocardial infarction [2,3] in a male population. There are no previous data on women concerning this factor, and it was therefore considered of interest to study the relation between the ESR and atherosclerosis in our female population sample. Since serum lipids, high blood pressure, cigarette smoking, obesity and serum uric acid have been found to be associated with cardiovascular diseases, we have also studied the relationships between these risk factors for cardiovascular disease and the ESR. As the ESR is a simple laboratory test, it is important to determine whether the ESR can replace other more complicated examinations.
Study Population A population study of women in Goteborg, Sweden was performed in 1968-69. The women were divided into 5 age strata: 38, 46, 50, 54 and 60, altogether 1462 in number. Participation rate was 90.1%. The same women were re-studied 6 years later, in 1974-75, when aged 44, 52, 56, 60 and 66, respectively. Altogether 1302 women participated in the follow-up study, with a participation rate of 89.1% of those studied in 1968-69. Most of the studies were carried out over a 12-month period, both in 1968-69 and in 1974-75. In this way the possible influence of seasonal variation could be ruled out. The method of sampling, the high participation rate and the small differences found between participants and non-participants ensured that the women were representative of women in the general population of the ages studied [4,5].
Methods The participants were requested to arrive in the fasting state in the morning. A blood sample was drawn- with the subjects in the supine position. Approximately 120 ml of blood was drawn from a cubital vein by means of a disposable steel needle into two lOO-ml glass centrifuge tubes. Five ml of blood were mixed with 6 mg EDTA and used for routine haematological examinations. The ESR was determined according to the Westergren method from 1.6 ml blood collected in a syringe containing 0.4 ml of 3.8% sodium citrate solution [6]. The ESR was read after 1 h according to the suggestions made by the International Committee for Standardization in Haematology [7]. Serum cholesterol was determined according to the method of Levine and Zak [8] and triglycerides as described by Loftland [9]. Serum uric acid was determined by means of an enzymatic method essentially according to Praetorius [IO].
99
History of myocardial infarction was recorded as described by Elmfeldt et al. [ 1l] by means of a special myocardial infarction register. Angina pectoris was defined according to Rose [12]. The ECGs were interpreted [ 13,141. according to the Minnesota Code with the Scandinavian modification Minnesota Codes 1: 1-2, 4 : 1, 5 : l-2 (in the absence of 3 : l), 6 : 1 and 7 : 1 were defined as ‘coronary ECG’. Stroke was recorded in a special stroke register which includes all cases of stroke in the city of Goteborg since 1970 [ 151. Intermittent claudication was defined according to Rose [ 121. Blood pressures were determined about half an hour after the participant’s arrival at the laboratory. The same mercury manometer was used on each occasion. The technique of blood pressure determination was that recommended by WHO [ 16,171. Arterial hypertension was defined according to the WHO definition [ 161 as systolic blood pressure 2 160 mm Hg or diastolic blood pressure > 95 mm Hg, or both. History of arterial hypertension was obtained by interview. Subjects receiving anti-hypertensive treatment were studied separately. Information about smoking habits was obtained by interview [ 171. Body height was measured to the nearest 0.5 cm. Body weight was measured to the nearest 0.1 kg. Weight/height index was defined as body weight (kg) X 100 body height (cm) - 100 Further information about anthropometric measurements the weight indices has been presented elsewhere [ 181. Statistical
and the distributions
of
methods
Conventional methods were used for calculating mean values, standard deviations (SD) and correlation coefficients (r). The hypothesis of no differences between mean values was tested with Student’s t-test. As the logarithms of the ESR values but not the ESR values themselves have been found to be normally distributed [ 191, the statistical analyses were performed on the logarithms. The differences were considered statistically significant for values of P c 0.05.
Results ESR
in women with symptoms
suggesting cardiovascular
disease
ESR values in women with angina pectoris, ‘coronary ECG’ and intermittent claudication as found in the studies in 1968-69 and 1974-75, respectively, are shown in Table 1. Compared to the population sample, ESR tended to be slightly higher in women with these manifestations than in other women, but there were no differences of statistical significance. Data are given for the total numbers of
loo TABLE
I
ESR (mm) IN WOMEN WITH SYMPTOMS SUGGESTING ANGINA PECTORIS WITH ‘CORONARY ECG’ AND WITH SYMPTOMS SUGGESTING INTERMITTENT CLAUDICATION. AND IN WOMEN IN THE TOTAL POPULATION STUDY AS FOUND IN 1968-69 AND 1974-75. RESPECTIVELY
Age (yr)
S&L+ in 1968-69 Angina pectoris 38-60 Coronary ECG 38-60 Intermittent claudication 38-60 Total population sample 38-60 SlUd?, in 1974-75 Angina pectoris 44 52 56 60 66 44-46 Intermittent claudication 44-46 Total population 44 52 56 60 66 44-66
Mean
n
SD
Median
Range
Statistical significance
29
12.8
9.4
II
2-
34
N.S.
23
14.3
10.0
I4
2-
36
N.S.
18
17.4
17.6
I4
2-
72
N.S.
12.2
10.6
IO 13 17 17 x 65
13.1 12.6 18.4 23.4 27.9 18.9
8.1 7.2 19.9 21.3 31.8 19.3
II 13 I3 I5 I6 14
5- 30 3- 30 3- 85 g- 92 g-105 3-105
N.S. N.S. N.S. N.S. N.S. N.S.
30
16.1
16.4
12
2-
N.S.
333 385 349 163 65 1295
12.7 14.9 16.6 18.2 24. I 15.7
12.5 Il.6 13.2 13.2 20.2 13.2
9.3 Il.9 12.2 14.9
2-125 2- 70 2-100 2- 92
18.4 11.9
4- 105 2-125
1461
9.3
a
I-120
92
sample
a Compared to women manifestation studied.
of the same age in the population
sample
who were not found
to have the
subjects with the different manifestations studied, except for women with angina pectoris in 1974-75, in which group the different age strata are also presented separately. The proportion of subjects in whom an increased ESR could be explained by inflammatory diseases or other diseases [ 191 was similar in those who had manifestations indicating IHD and in those who had not. ESR in women with mani$estations period
of cardiovascular
The lo-year incidences of myocardial 1978) and the 6-year incidences (between
disease during the follow-up
infarction and stroke (between 1968 and 1968-69 and 1974-75) of angina pectoris
101
TABLE 2 INCIDENCES OF MYOCARDIAL INFARCTION AND STROKE (IO-year incidences) AND OF ANGINA PECTORIS AND INTERMITTENT CLAUDICATION (6-year incidences) TOGETHER WITH PREMORBID ESR (mm) VALUES (IN 1968-69) OF WOMEN WHO HAD THESE MANIFESTATIONS DURING THE FOLLOW-UP PERIODS AND OF WOMEN IN THE TOTAL POPULATION SAMPLE
Myocardial infarction Angina pectoris Stroke Intermittent claudication Total population sample
n
Mean
SD
Median
Range
15 53 7 29 1461
13.6 14.1 28.6 11.3 12.2
10.6 11.2 24.8 10.6 10.6
13.6 14.0 28.5 I I.2 9.3
4- 35 2- 55 I- 71 2- 36 I-120
TABLE 3 ESR (mm) VALUES AS FOUND IN 1968-69 IN WOMEN COMPARED TO WOMEN IN THE TOTAL POPULATION
Age
n
Mean
SD
WITH INCREASED SAMPLE Median
Range
(yr) Triglycerides 3 2.0 mmol/l
38 46 50 54 60 38-60
I4 32 31 21 7 105
13.6 14.8 16.7 18.7 16.1 16.1
10.6 12.3 8.8 17.3 8.0 12.1
9 12 I8 I4 I6 I4
Triglycerides 3 3.0 mmol/l
38 46 50 54 60 38-60
2 4 9 8 3 26
24.5 16.0 16.2 19.9 16.0 17.9
13.4 9.0 5.2 20.6 4.0 12.3
Cholesterol a 9 mmol/l
46 50 54 60 38-60
I1 24 I1 2 48
15.2 15.8 24.5 26.5 18.1
Total population sample
38 46 50 54 60 38-60
371 431 398 180 81 1461
10.9 II.0 12.0 15.5 17.7 12.2
a Compared
SERUM
Statistical significance
2- 34 I- 54 3- 40 I- 63 3- 29 I- 63
N.S. N.S. P-=0.001 N.S. N.S. P
24.5 14.5 I9 10.5 I6 15.2
l5- 34 7- 28 8- 25 4- 63 l2- 20 4- 63
N.S. N.S. N.S. N.S. N.S. P
II.4 8.7 32.3 10.6 17.5
13 15 8 26.5 14.5
4- 36 I- 37 4-114 l9- 34 l-114
N.S. N.S. N.S. N.S. P
II.0 8.4 8.4 15.0 13.6 10.6
7.8 8.6 10.3 11.9 14.4 9.3
I-120 I- 54 I- 72 l-114 I- 71 I-120
to women of the same age in the population
LIPIDS
a
sample who had serum lipids below these levels.
102
and intermittent claudication are shown in Table 2 together with the premorbid ESR values of the women who had these manifestations during the stated periods (ESR as found in 1968-69). There were no significant differences between these groups of women and other women in the population sample.. In a quintile analysis carried out in the same way as in the study of men by B&tiger and Carlson [ 11,the levels of ESR could not be shown to be a significant risk factor for myocardial infarction, angina pectoris or intermittent claudication, while the ESR was higher in those women who later suffered stroke. ESR in women with risk factors for cardiovascular disease Hyperlipidaemia. Table3 ‘shows ESR values in women with serum triglyceride values > 2.0 and 3.0 mmol/l, respectively, and in women with serum cholesterol values 2 9.0 mmol/l in comparison with women in the total population sample. Statistically significant differences were found between women aged 50 who had and who did not have increased serum triglycerides and for the total numbers of subjects with hypertriglyceridaemia and hypercholesterolaemia according to the definitions used. Weak correlations were found between serum cholesterol and ESR (r = 0.11) and between serum triglycerides and ESR (r = 0.15) in the study carried out in 1968-69. Similar correlation coefficients were obtained when the same analyses were carried out on the data from 1974-75. Arterial hypertension. ESR values in women with arterial hypertension as found in
TABLE 4 MEANS AND SD VALUES OF ESR (mm) IN WOMEN WITH UNTREATED ARTERIAL HYPERTENSION AND IN WOMEN RECEIVING ANTIHYPERTENSIVE TREATMENT AS FOUND IN THE STUDY IN 1968-69
Age
n
Mean
SD
Statistical
11.8 13.6 12.7 16.3 18.6 14.4
13.1 11.9 7.1 18.8 17.1 13.5
N.S. N.S. N.S. N.S. N.S. P
15.1 10.7 16.2 14.6 8.0 13.3
N.S. N.S. N.S. N.S. N.S. P
significance
’
(yr) Hypertensive 38 46 50 54 60 38-60
women, unrreuted 16 40 68 41 28 193
Women receiving untihypertensioe 38 3 46 14 50 18 54 19 60 38-60 ’ Compared
13 61
treotmem 25.7 12.2 @ 18.5 18.2 19.9
17.7
to women of the same age in the population
sample who did not have high blood pressure.
103
mm 14-l
SMOKERS EXNONSMOKERSSMOKERS 1-4 5-S lo-14 15-19 >20 GIG/D 759 108 91 152 201 84 63 N Fig.1.ESR (mm) values (means) in relation
to smoking
habits
in women aged 38-60
years as found in
the study in 1968-69.
1968-69 are shown in Table4. Statistically significant differences were found between the total numbers of women with arterial hypertension and those on antihypertensive treatment on the one hand and non-hypertensive women on the other. Smoking. No association was found between smoking and ESR, as shown in Fig. 1, where ESR values of non-smokers and different categories of smokers are shown. The data presented in Fig. 1 relate to the study carried out in 1968-69. Similar results were obtained when analyzing the data from 1974-75. Obesity. Table 5 shows the ESR values in overweight women (upper 10 centiles of weight index). Statistically significant differences were found between women in the age strata 38,46 and 50, and for the total number of subjects who were and were not overweight (higher ESR in overweight women). Serum uric acid. No definite association was found between hyperuricaemia and increased ESR, as indicated by Table6. However, a weak correlation was found
TABLE 5 MEANS AND SD VALUES OF ESR (mm) IN OVERWEIGHT WEIGHT INDEX); DATA FROM 1968-69
WOMEN
(UPPER
significance
Age (Y0
n
Mean
SD
Statistical
38 46 50 54 60 38-60
38 41 33 18 8 138
18.6 14.0 16.2 14.7 14.8 15.9
16.5 7.7 7.8 15.2 8.5 II.9
f
’ Compared
to women of the same age in the population
IO CENTILES
OF
a
sample who had weight index below these levels.
104
TABLE 6 MEANS AND SD VALUES OF ESR (mm) IN HYPERURICAEMIC OF URIC ACID); DATA FROM 1968-69
WOMEN
n
Mean
SD
Statistical
38 46 50 54
18 21 20 8
16.4 10.2 14.0 19.8
21.9 7.6 14.7 22.4
N.S. N.S. N.S. N.S.
60 38-60
4 71
11.8 14.0
6.8 15.9
N.S. N.S.
Age
(UPPER
significance
5 CENTILES
a
(Y0
’ Compared
to women of the same age in the population
sample who were not hyperuricaemic.
between serum uric acid and ESR (r = 0.11) in the study in 1968-69. A similar correlation coefficient was found in 1974-75.
Discussion This paper deals with the ESR as found in a longitudinal population study of women with special reference to subjects with manifestation of cardiovascular diseases and risk factors for cardiovascular diseases. A detailed description of the ESR in the female population has been given elsewhere [ 191.The study showed that the intra-individual differences in ESR during the 6-year period were rather small. ESR and cardimascular disease
In this study the ESR could not be proved to predict myocardial infarction or angina pectoris. These results are to some extent in contrast to those of Carlson and B&tiger [2] who, in a 9-year follow-up of men, found the levels of the ESR to be a risk factor for ischaemic heart disease (IHD). In a 1Cyear follow-up of the same individuals, Carlson et al. [3] found, by multivariate statistical analysis, the levels of the ESR to be an independent risk factor for myocardial infarction. The levels of the ESR were also an independent risk factor [l] for death from ischaemic vascular disease. In a population study of male inhabitants in Goteborg born in 1913, the ESR was not found to have any predictive value for the risk of nonfatal myocardial infarction or fatal IHD [20]. No association was found between ESR and intermittent claudication in this series. As far as we know, there are no previous clinical or epidemiological studies on the relationships between ESR and intermittent claudication. The ESR tended to be increased in subjects who later suffered stroke, but the number of subjects was too small to allow proper evaluation. As a whole, the incidences of cardiovascular diseases were rather low in this
105
series, as might be expected consideration when evaluating
in a study the results.
of women.
This
should
be taken
into
Risk factors for cardiovascular diseases Arterial hypertension, hyperlipidaemia, obesity, smoking and hyperuricaemia have been found to be risk factors for IHD in prospective and cross-sectional studies [ 1,2,17,20-231. Both in prospective and in retrospective studies, cigarette smoking, hypertension, hypertriglyceridaemia and raised urate levels have been found to be associated with intermittent claudication [22,24,25]. Arterial hypertension is the most important risk factor for stroke [26-281. Increased serum cholesterol and obesity also contributed to the risk of stroke [26,27].
ESR in relation to serum lipids The results from previous studies are contradictory concerning the relationship between ESR and serum lipids. An association between increased serum lipid levels and raised ESR was suggested as early as in 1930 [29] but denied by other investigators [30,31]. Such an association between ESR and the levels of serum cholesterol and serum triglycerides was subsequently reported from the Stockholm prospective study [32,33]. Swank [34] found serum cholesterol to be correlated to the ESR in healthy adult women. When studying the ESR with a modified Westergren method in a highly selected sample of males, Pincherle and Shanks [35] found a significant correlation between ESR and serum cholesterol in a multiple regression analysis. In a previous report on our population sample, significantly higher triglyceride levels were found in women with high ESR [ 191. When the data were analysed in the way presented in this paper, weak correlations were found between ESR, and serum cholesterol and serum triglycerides, respectively. Whether this finding is of clinical importance, as has been claimed previously [35], seems doubtful in our opinion.
ESR in relation to smoking habits High haemoglobin values have been considered to be associated with decreased ESR [36]. There is an association between smoking and high haemoglobin values [27,37] which might to some extent mask an association between smoking and ESR. No such association was found in this study. In addition, low haemoglobin values are associated with a high ESR [19]. Contrary to our results, Pincherle and Shanks [35] found an association between cigarette smoking and increased ESR.
ESR in relation to hypertension Pincherle and Shanks [35] found an association between In this study the ESR seemed to have a weak association
ESR and blood pressure. with blood pressure, but
106
this finding probably has no clinical importance, as stated by Popp more than 50 years ago [38]. As most of the women on antihypertensive treatment received saluretic diuretics [39], which may decrease the extracellular fluid and produce some haemoconcentration, slightly higher ESR values can be expected in women on antihypertensive treatment. ESR in relation to serum uric acid A weak correlation was found between ESR and serum uric acid in this study, suggesting a possible role of the uric acid content of plasma as one factor influencing the ESR. But the clinical significance of this finding is again doubtful. The ESR has been reported to be elevated in subjects with gout [40]. ESR in relation to ooenveight Investigations into the relationship between obesity and ESR are scarce. An increased prevalence of, for example, cholelithiasis and diabetes [41,42] in the obese, with their complications, makes such an association probable. Furthermore, body weight has been found to be correlated with lipid levels [ 181.As already mentioned, an association between increased serum lipids and increased ESR was found in this study.
General Conclusions
Based on this study of a representative sample of women, we do not consider the ESR to be of predictive value for IHD, and the ESR cannot replace other examinations in the search for risk factors for cardiovascular disease.
References 1 B&tiger, L.E. and Carlson, L.A., Risk factors for ischaemic vascular death for men in the Stockholm prospective study, Atherosclerosis, 36 (I 980) 389. 2 Carlson, L.A. and B&tiger, L.E., Ischaemic heart disease in relation to fasting values of plasma triglycerides and cholesterol, Lancet, i (1972) 865. 3 Carlson, L.A., Bottiger, L.E. and Ahlfeldt, P.-E., Risk factors for myocardial infarction in the Stockholm prospective study,’ Acta Med. Stand., 206 (1979)35 1. 4 Bengtsson, C., Blohme, G., Hallberg. L. et al., The study of women in Gothenburg 1968-1969. A population study, Acta Med. Stand., 193 (1973) 311. 5 Bengtsson, C., Hallberg, L., Hallstrom, T. et al., The population study of women in Goteborg 1974-1975-The second phase of a longitudinal study, Stand. J. Sot. Med., 6 (1978) 49. 6 Westergren, S., The technique of the red cell sedimentation rcactlon, Amer. Rev. Tuberc.. 14 (1926) 94. 7 International Committee for Standardization in Haematology, Reference method for the erythrocyte sedimentation rate (ESR) test on human blood, Brit. J. Haematol., 24 (1973) 671.
107
8 Levine, J.B. and Zak, B., Automated determination of serum total cholesterol, Clin. Chim. Acta. IO (1964) 381. 9 Loftland, Jr., H.B., A semiautomated procedure for the determination of triglycerides in serum, Ann. B&hem., 9 (1964)393. IO Praetorius, E., An enzymatic method for the determination of uric acid by ultraviolet spectrophotometry, &and. J. Clin. Lab. Invest., I (1949) 222. I I Elmfeldt. D., Wilhelmsen, L., Tibblin, G. et al., A postmyocardial infarction clinic in Goteborg. Sweden, Acta Med. Stand., 197 (1975) 497. I2 Rose, G.A.. The diagnosis of ischaemic heart pain and intermittent claudication in field surveys. Bull. WHO, 27 (1962) 645. I3 Astrand. A., Areskog. N.-H., Carlsten, A. et al., The ‘Minnesota code’ for ECG classificationAdaption to CR leads and modification of the code for ECG’s recorded during and after exercise, Acta Med. Stand. (Suppl. 481) 1967. I4 Blackburn, H., Keys, A., Simonson, E. et al., The electrocardiogram in population studies, Circulation, 21 (1960) 1160. I5 Harmsen. P. and Tibblin. G., A stroke register in Goteborg, Sweden, Acta Med. Stand., 191 (1972) 463. I6 Arterial Hypertension and Ischaemic Heart Disease-Report of an Expert Committee (WHO Tech. Rep. Ser. No. 23 I), World Health Organization, Geneva, 1962. I7 Bengtsson, C., Ischaemic heart disease in women-A study based on a randomized population sample of women and women with myocardial infarction in Gbteborg. Sweden, Acta Med. Stand. (Suppl. 549). 1973. IX Noppa, H., Bengtsson, C., Bjomtorp, P. et al., Overweight in women-Metabolic aspects. Acta Med. Stand., 203 (1978) 135. I9 Rafnsson. V., Bengtsson, C.. Lennartsson, J. et al., Erythrocyte sedimentation rate in a population sample of women with special reference to its clinical and prognostic significance, Acta Med. Stand., 206 (1979) 207. 20 Tibblin, G.. Wilhelmsen, L. and Werkii, L., Risk factors for myocardial infarction and death due to ischaemic heart disease and other causes, Amer. J. Cardiol.. 35 (1975)5 14. 2 I Fessel, W.J.. Siegelaub, A.B. and Johnson, E.S., Correlates and consequences of asymptomatic hyperuricemia, Arch. Intern. Med., 132 (1973) 44. 22 Gordon, T. and Kannel, W.B., Predisposition to atherosclerosis in the head, heart and legs, J. Amer. Med. Ass., 221 (1972) 661. 23 Kannel, W.B., Some lessons in cardiovascular epidemiology from Framingham, Amer. J. Cardiol.. 37 (1976)269. 24 Hughson, W.G., Mann, J.I. and Garrod. A.. Intermittent claudication-Prevalence and risk factors. Brit. Med. J., i (1978) 1379. 25 Hughson, W.G., Mann, J.I., Tibbs. D.J. et al., Intermittent claudication: factors determining outcome, Brit. Med. J., i (1978) 1377. 26 Heyman. A., Karp, H.R., Heyden, S. et al., Cerebrovascular disease in the biracial population of Evans County, Georgia, Ann. Int. Med., I28 (1971) 949. 27 Kannel, W.B., Gordon, T., Wolf, P.A. et al., Haemoglobin and the risk of cerebral infarction-The Framingham study, Stroke, 3 (1972) 409. 28 Paffenbarger, Jr., R.S., Laughlin, M.E., Gima, A.S. et al., Work activity of longshoremen as related to death from coronary heart disease and stroke, N. Engl. J. Med., 282 (1970) I 109. 29 Theorell, H., Studien iiber die Plasmalipoide des Blutes, B&hem. Z., 223 (1930) 94. 30 Ehrly, A.M., Gramlich, F. and Mtiller, H.E.. fiber den Einfluss von Lipiden, insbesondere von unveresterten Fettsauren, auf den Mechanismus der Blutkorperchensenkungsgeschwindigkeit, Klin. Wchschr.. 43 (1965) 913. 3 I Ohlson, B. and Rundqvist, 0.. ober die Bedeutung der Plasmalipoide fur die Suspensionsstabilit’ des Blutes, Biochem. Z., 247 (1932) 249. 32 Bottiger, L.E., Carlson, L.A., Ekelund, L.G. et al., Raised erythrocyte sedimentation rate in asymptomatic hyperlipidaemia, Brit. Med. J., ii (I 973) 68 I,
97 Ltd.
Erythrocyte Sedimentation Rate and Cardiovascular Disease Results from a Population Study of Women in Gateborg, Sweden Vilhjalmur Rafnsson and Calle Bengtsson Depurtnmt
of Medicine II, Suhlgrensku
Sjukhuset,
University of Gi%ehorg, Giitehorg (Sweden)
(Received 26 February, I98 I) (Revised, received 29 September. 198 I) (Accepted 30 September, 1981)
In a prospective study of a population sample of women, the erythrocyte sedimentation rate (ESR) was studied in relation to the incidence of myocardial infarction, angina pectoris, stroke and intermittent claudication. ESR could not be proved to be predictive of these manifestations of cardiovascular disease. Similar results were obtained when the population was studied cross-sectionally. The ESR was higher in women with hyperlipidaemia (serum triglyceride 2 2.0 mmol/l or 3 9 mmol/l), in women with arterial hypertension (treated or serum cholesterol untreated, with systolic blood pressure ) 160 mm Hg or diastolic blood pressure > 95 mm Hg or both) and in overweight women (women within the upper 10 centiles of weight index) compared to women of the same age in the population sample who did not fulfill the criteria according to the above definitions. ESR was similar in hyperuricaemic women (upper 5 centiles of serum uric acid) and in those who were not hyperuricaemic. No association was found between smoking habits and ESR. Weak correlations were found between ESR and serum triglycerides, serum cholesterol and serum uric acid, respectively. Although some correlations were found, ESR cannot replace other examinations in the search for risk factors for cardiovascular disease.
Cardiovascular risk factors - Erythrocyte sedimentation rate - Intermittent claudication - Ischaemic heart disease - Population study - Stroke Women
Key words:
This study was supported by Grant No. 27X-4578 from the Swedish Medical Research Council. Correspondence to: Dr. Vilhjalmur Rafnsson, Yrkesmedicinska Kliniken, Sahlgrenska Sjukhuset, S-4 13 45 Goteborg, Sweden.
0021-91/50/82/0000-0000/$02.75
0 1982 Elsevier/North-Holland
Scientific
Publishers,
Ltd.
98
Introduction The erythrocyte sedimentation rate (ESR) is a very commonly used laboratory test, especially in Scandinavia. The levels of the ESR have been found to be a risk factor for death from ischaemic vascular disease, as recently reported [l], and for myocardial infarction [2,3] in a male population. There are no previous data on women concerning this factor, and it was therefore considered of interest to study the relation between the ESR and atherosclerosis in our female population sample. Since serum lipids, high blood pressure, cigarette smoking, obesity and serum uric acid have been found to be associated with cardiovascular diseases, we have also studied the relationships between these risk factors for cardiovascular disease and the ESR. As the ESR is a simple laboratory test, it is important to determine whether the ESR can replace other more complicated examinations.
Study Population A population study of women in Goteborg, Sweden was performed in 1968-69. The women were divided into 5 age strata: 38, 46, 50, 54 and 60, altogether 1462 in number. Participation rate was 90.1%. The same women were re-studied 6 years later, in 1974-75, when aged 44, 52, 56, 60 and 66, respectively. Altogether 1302 women participated in the follow-up study, with a participation rate of 89.1% of those studied in 1968-69. Most of the studies were carried out over a 12-month period, both in 1968-69 and in 1974-75. In this way the possible influence of seasonal variation could be ruled out. The method of sampling, the high participation rate and the small differences found between participants and non-participants ensured that the women were representative of women in the general population of the ages studied [4,5].
Methods The participants were requested to arrive in the fasting state in the morning. A blood sample was drawn- with the subjects in the supine position. Approximately 120 ml of blood was drawn from a cubital vein by means of a disposable steel needle into two lOO-ml glass centrifuge tubes. Five ml of blood were mixed with 6 mg EDTA and used for routine haematological examinations. The ESR was determined according to the Westergren method from 1.6 ml blood collected in a syringe containing 0.4 ml of 3.8% sodium citrate solution [6]. The ESR was read after 1 h according to the suggestions made by the International Committee for Standardization in Haematology [7]. Serum cholesterol was determined according to the method of Levine and Zak [8] and triglycerides as described by Loftland [9]. Serum uric acid was determined by means of an enzymatic method essentially according to Praetorius [IO].
99
History of myocardial infarction was recorded as described by Elmfeldt et al. [ 1l] by means of a special myocardial infarction register. Angina pectoris was defined according to Rose [12]. The ECGs were interpreted [ 13,141. according to the Minnesota Code with the Scandinavian modification Minnesota Codes 1: 1-2, 4 : 1, 5 : l-2 (in the absence of 3 : l), 6 : 1 and 7 : 1 were defined as ‘coronary ECG’. Stroke was recorded in a special stroke register which includes all cases of stroke in the city of Goteborg since 1970 [ 151. Intermittent claudication was defined according to Rose [ 121. Blood pressures were determined about half an hour after the participant’s arrival at the laboratory. The same mercury manometer was used on each occasion. The technique of blood pressure determination was that recommended by WHO [ 16,171. Arterial hypertension was defined according to the WHO definition [ 161 as systolic blood pressure 2 160 mm Hg or diastolic blood pressure > 95 mm Hg, or both. History of arterial hypertension was obtained by interview. Subjects receiving anti-hypertensive treatment were studied separately. Information about smoking habits was obtained by interview [ 171. Body height was measured to the nearest 0.5 cm. Body weight was measured to the nearest 0.1 kg. Weight/height index was defined as body weight (kg) X 100 body height (cm) - 100 Further information about anthropometric measurements the weight indices has been presented elsewhere [ 181. Statistical
and the distributions
of
methods
Conventional methods were used for calculating mean values, standard deviations (SD) and correlation coefficients (r). The hypothesis of no differences between mean values was tested with Student’s t-test. As the logarithms of the ESR values but not the ESR values themselves have been found to be normally distributed [ 191, the statistical analyses were performed on the logarithms. The differences were considered statistically significant for values of P c 0.05.
Results ESR
in women with symptoms
suggesting cardiovascular
disease
ESR values in women with angina pectoris, ‘coronary ECG’ and intermittent claudication as found in the studies in 1968-69 and 1974-75, respectively, are shown in Table 1. Compared to the population sample, ESR tended to be slightly higher in women with these manifestations than in other women, but there were no differences of statistical significance. Data are given for the total numbers of
loo TABLE
I
ESR (mm) IN WOMEN WITH SYMPTOMS SUGGESTING ANGINA PECTORIS WITH ‘CORONARY ECG’ AND WITH SYMPTOMS SUGGESTING INTERMITTENT CLAUDICATION. AND IN WOMEN IN THE TOTAL POPULATION STUDY AS FOUND IN 1968-69 AND 1974-75. RESPECTIVELY
Age (yr)
S&L+ in 1968-69 Angina pectoris 38-60 Coronary ECG 38-60 Intermittent claudication 38-60 Total population sample 38-60 SlUd?, in 1974-75 Angina pectoris 44 52 56 60 66 44-46 Intermittent claudication 44-46 Total population 44 52 56 60 66 44-66
Mean
n
SD
Median
Range
Statistical significance
29
12.8
9.4
II
2-
34
N.S.
23
14.3
10.0
I4
2-
36
N.S.
18
17.4
17.6
I4
2-
72
N.S.
12.2
10.6
IO 13 17 17 x 65
13.1 12.6 18.4 23.4 27.9 18.9
8.1 7.2 19.9 21.3 31.8 19.3
II 13 I3 I5 I6 14
5- 30 3- 30 3- 85 g- 92 g-105 3-105
N.S. N.S. N.S. N.S. N.S. N.S.
30
16.1
16.4
12
2-
N.S.
333 385 349 163 65 1295
12.7 14.9 16.6 18.2 24. I 15.7
12.5 Il.6 13.2 13.2 20.2 13.2
9.3 Il.9 12.2 14.9
2-125 2- 70 2-100 2- 92
18.4 11.9
4- 105 2-125
1461
9.3
a
I-120
92
sample
a Compared to women manifestation studied.
of the same age in the population
sample
who were not found
to have the
subjects with the different manifestations studied, except for women with angina pectoris in 1974-75, in which group the different age strata are also presented separately. The proportion of subjects in whom an increased ESR could be explained by inflammatory diseases or other diseases [ 191 was similar in those who had manifestations indicating IHD and in those who had not. ESR in women with mani$estations period
of cardiovascular
The lo-year incidences of myocardial 1978) and the 6-year incidences (between
disease during the follow-up
infarction and stroke (between 1968 and 1968-69 and 1974-75) of angina pectoris
101
TABLE 2 INCIDENCES OF MYOCARDIAL INFARCTION AND STROKE (IO-year incidences) AND OF ANGINA PECTORIS AND INTERMITTENT CLAUDICATION (6-year incidences) TOGETHER WITH PREMORBID ESR (mm) VALUES (IN 1968-69) OF WOMEN WHO HAD THESE MANIFESTATIONS DURING THE FOLLOW-UP PERIODS AND OF WOMEN IN THE TOTAL POPULATION SAMPLE
Myocardial infarction Angina pectoris Stroke Intermittent claudication Total population sample
n
Mean
SD
Median
Range
15 53 7 29 1461
13.6 14.1 28.6 11.3 12.2
10.6 11.2 24.8 10.6 10.6
13.6 14.0 28.5 I I.2 9.3
4- 35 2- 55 I- 71 2- 36 I-120
TABLE 3 ESR (mm) VALUES AS FOUND IN 1968-69 IN WOMEN COMPARED TO WOMEN IN THE TOTAL POPULATION
Age
n
Mean
SD
WITH INCREASED SAMPLE Median
Range
(yr) Triglycerides 3 2.0 mmol/l
38 46 50 54 60 38-60
I4 32 31 21 7 105
13.6 14.8 16.7 18.7 16.1 16.1
10.6 12.3 8.8 17.3 8.0 12.1
9 12 I8 I4 I6 I4
Triglycerides 3 3.0 mmol/l
38 46 50 54 60 38-60
2 4 9 8 3 26
24.5 16.0 16.2 19.9 16.0 17.9
13.4 9.0 5.2 20.6 4.0 12.3
Cholesterol a 9 mmol/l
46 50 54 60 38-60
I1 24 I1 2 48
15.2 15.8 24.5 26.5 18.1
Total population sample
38 46 50 54 60 38-60
371 431 398 180 81 1461
10.9 II.0 12.0 15.5 17.7 12.2
a Compared
SERUM
Statistical significance
2- 34 I- 54 3- 40 I- 63 3- 29 I- 63
N.S. N.S. P-=0.001 N.S. N.S. P
24.5 14.5 I9 10.5 I6 15.2
l5- 34 7- 28 8- 25 4- 63 l2- 20 4- 63
N.S. N.S. N.S. N.S. N.S. P
II.4 8.7 32.3 10.6 17.5
13 15 8 26.5 14.5
4- 36 I- 37 4-114 l9- 34 l-114
N.S. N.S. N.S. N.S. P
II.0 8.4 8.4 15.0 13.6 10.6
7.8 8.6 10.3 11.9 14.4 9.3
I-120 I- 54 I- 72 l-114 I- 71 I-120
to women of the same age in the population
LIPIDS
a
sample who had serum lipids below these levels.
102
and intermittent claudication are shown in Table 2 together with the premorbid ESR values of the women who had these manifestations during the stated periods (ESR as found in 1968-69). There were no significant differences between these groups of women and other women in the population sample.. In a quintile analysis carried out in the same way as in the study of men by B&tiger and Carlson [ 11,the levels of ESR could not be shown to be a significant risk factor for myocardial infarction, angina pectoris or intermittent claudication, while the ESR was higher in those women who later suffered stroke. ESR in women with risk factors for cardiovascular disease Hyperlipidaemia. Table3 ‘shows ESR values in women with serum triglyceride values > 2.0 and 3.0 mmol/l, respectively, and in women with serum cholesterol values 2 9.0 mmol/l in comparison with women in the total population sample. Statistically significant differences were found between women aged 50 who had and who did not have increased serum triglycerides and for the total numbers of subjects with hypertriglyceridaemia and hypercholesterolaemia according to the definitions used. Weak correlations were found between serum cholesterol and ESR (r = 0.11) and between serum triglycerides and ESR (r = 0.15) in the study carried out in 1968-69. Similar correlation coefficients were obtained when the same analyses were carried out on the data from 1974-75. Arterial hypertension. ESR values in women with arterial hypertension as found in
TABLE 4 MEANS AND SD VALUES OF ESR (mm) IN WOMEN WITH UNTREATED ARTERIAL HYPERTENSION AND IN WOMEN RECEIVING ANTIHYPERTENSIVE TREATMENT AS FOUND IN THE STUDY IN 1968-69
Age
n
Mean
SD
Statistical
11.8 13.6 12.7 16.3 18.6 14.4
13.1 11.9 7.1 18.8 17.1 13.5
N.S. N.S. N.S. N.S. N.S. P
15.1 10.7 16.2 14.6 8.0 13.3
N.S. N.S. N.S. N.S. N.S. P
significance
’
(yr) Hypertensive 38 46 50 54 60 38-60
women, unrreuted 16 40 68 41 28 193
Women receiving untihypertensioe 38 3 46 14 50 18 54 19 60 38-60 ’ Compared
13 61
treotmem 25.7 12.2 @ 18.5 18.2 19.9
17.7
to women of the same age in the population
sample who did not have high blood pressure.
103
mm 14-l
SMOKERS EXNONSMOKERSSMOKERS 1-4 5-S lo-14 15-19 >20 GIG/D 759 108 91 152 201 84 63 N Fig.1.ESR (mm) values (means) in relation
to smoking
habits
in women aged 38-60
years as found in
the study in 1968-69.
1968-69 are shown in Table4. Statistically significant differences were found between the total numbers of women with arterial hypertension and those on antihypertensive treatment on the one hand and non-hypertensive women on the other. Smoking. No association was found between smoking and ESR, as shown in Fig. 1, where ESR values of non-smokers and different categories of smokers are shown. The data presented in Fig. 1 relate to the study carried out in 1968-69. Similar results were obtained when analyzing the data from 1974-75. Obesity. Table 5 shows the ESR values in overweight women (upper 10 centiles of weight index). Statistically significant differences were found between women in the age strata 38,46 and 50, and for the total number of subjects who were and were not overweight (higher ESR in overweight women). Serum uric acid. No definite association was found between hyperuricaemia and increased ESR, as indicated by Table6. However, a weak correlation was found
TABLE 5 MEANS AND SD VALUES OF ESR (mm) IN OVERWEIGHT WEIGHT INDEX); DATA FROM 1968-69
WOMEN
(UPPER
significance
Age (Y0
n
Mean
SD
Statistical
38 46 50 54 60 38-60
38 41 33 18 8 138
18.6 14.0 16.2 14.7 14.8 15.9
16.5 7.7 7.8 15.2 8.5 II.9
f
’ Compared
to women of the same age in the population
IO CENTILES
OF
a
sample who had weight index below these levels.
104
TABLE 6 MEANS AND SD VALUES OF ESR (mm) IN HYPERURICAEMIC OF URIC ACID); DATA FROM 1968-69
WOMEN
n
Mean
SD
Statistical
38 46 50 54
18 21 20 8
16.4 10.2 14.0 19.8
21.9 7.6 14.7 22.4
N.S. N.S. N.S. N.S.
60 38-60
4 71
11.8 14.0
6.8 15.9
N.S. N.S.
Age
(UPPER
significance
5 CENTILES
a
(Y0
’ Compared
to women of the same age in the population
sample who were not hyperuricaemic.
between serum uric acid and ESR (r = 0.11) in the study in 1968-69. A similar correlation coefficient was found in 1974-75.
Discussion This paper deals with the ESR as found in a longitudinal population study of women with special reference to subjects with manifestation of cardiovascular diseases and risk factors for cardiovascular diseases. A detailed description of the ESR in the female population has been given elsewhere [ 191.The study showed that the intra-individual differences in ESR during the 6-year period were rather small. ESR and cardimascular disease
In this study the ESR could not be proved to predict myocardial infarction or angina pectoris. These results are to some extent in contrast to those of Carlson and B&tiger [2] who, in a 9-year follow-up of men, found the levels of the ESR to be a risk factor for ischaemic heart disease (IHD). In a 1Cyear follow-up of the same individuals, Carlson et al. [3] found, by multivariate statistical analysis, the levels of the ESR to be an independent risk factor for myocardial infarction. The levels of the ESR were also an independent risk factor [l] for death from ischaemic vascular disease. In a population study of male inhabitants in Goteborg born in 1913, the ESR was not found to have any predictive value for the risk of nonfatal myocardial infarction or fatal IHD [20]. No association was found between ESR and intermittent claudication in this series. As far as we know, there are no previous clinical or epidemiological studies on the relationships between ESR and intermittent claudication. The ESR tended to be increased in subjects who later suffered stroke, but the number of subjects was too small to allow proper evaluation. As a whole, the incidences of cardiovascular diseases were rather low in this
105
series, as might be expected consideration when evaluating
in a study the results.
of women.
This
should
be taken
into
Risk factors for cardiovascular diseases Arterial hypertension, hyperlipidaemia, obesity, smoking and hyperuricaemia have been found to be risk factors for IHD in prospective and cross-sectional studies [ 1,2,17,20-231. Both in prospective and in retrospective studies, cigarette smoking, hypertension, hypertriglyceridaemia and raised urate levels have been found to be associated with intermittent claudication [22,24,25]. Arterial hypertension is the most important risk factor for stroke [26-281. Increased serum cholesterol and obesity also contributed to the risk of stroke [26,27].
ESR in relation to serum lipids The results from previous studies are contradictory concerning the relationship between ESR and serum lipids. An association between increased serum lipid levels and raised ESR was suggested as early as in 1930 [29] but denied by other investigators [30,31]. Such an association between ESR and the levels of serum cholesterol and serum triglycerides was subsequently reported from the Stockholm prospective study [32,33]. Swank [34] found serum cholesterol to be correlated to the ESR in healthy adult women. When studying the ESR with a modified Westergren method in a highly selected sample of males, Pincherle and Shanks [35] found a significant correlation between ESR and serum cholesterol in a multiple regression analysis. In a previous report on our population sample, significantly higher triglyceride levels were found in women with high ESR [ 191. When the data were analysed in the way presented in this paper, weak correlations were found between ESR, and serum cholesterol and serum triglycerides, respectively. Whether this finding is of clinical importance, as has been claimed previously [35], seems doubtful in our opinion.
ESR in relation to smoking habits High haemoglobin values have been considered to be associated with decreased ESR [36]. There is an association between smoking and high haemoglobin values [27,37] which might to some extent mask an association between smoking and ESR. No such association was found in this study. In addition, low haemoglobin values are associated with a high ESR [19]. Contrary to our results, Pincherle and Shanks [35] found an association between cigarette smoking and increased ESR.
ESR in relation to hypertension Pincherle and Shanks [35] found an association between In this study the ESR seemed to have a weak association
ESR and blood pressure. with blood pressure, but
106
this finding probably has no clinical importance, as stated by Popp more than 50 years ago [38]. As most of the women on antihypertensive treatment received saluretic diuretics [39], which may decrease the extracellular fluid and produce some haemoconcentration, slightly higher ESR values can be expected in women on antihypertensive treatment. ESR in relation to serum uric acid A weak correlation was found between ESR and serum uric acid in this study, suggesting a possible role of the uric acid content of plasma as one factor influencing the ESR. But the clinical significance of this finding is again doubtful. The ESR has been reported to be elevated in subjects with gout [40]. ESR in relation to ooenveight Investigations into the relationship between obesity and ESR are scarce. An increased prevalence of, for example, cholelithiasis and diabetes [41,42] in the obese, with their complications, makes such an association probable. Furthermore, body weight has been found to be correlated with lipid levels [ 181.As already mentioned, an association between increased serum lipids and increased ESR was found in this study.
General Conclusions
Based on this study of a representative sample of women, we do not consider the ESR to be of predictive value for IHD, and the ESR cannot replace other examinations in the search for risk factors for cardiovascular disease.
References 1 B&tiger, L.E. and Carlson, L.A., Risk factors for ischaemic vascular death for men in the Stockholm prospective study, Atherosclerosis, 36 (I 980) 389. 2 Carlson, L.A. and B&tiger, L.E., Ischaemic heart disease in relation to fasting values of plasma triglycerides and cholesterol, Lancet, i (1972) 865. 3 Carlson, L.A., Bottiger, L.E. and Ahlfeldt, P.-E., Risk factors for myocardial infarction in the Stockholm prospective study,’ Acta Med. Stand., 206 (1979)35 1. 4 Bengtsson, C., Blohme, G., Hallberg. L. et al., The study of women in Gothenburg 1968-1969. A population study, Acta Med. Stand., 193 (1973) 311. 5 Bengtsson, C., Hallberg, L., Hallstrom, T. et al., The population study of women in Goteborg 1974-1975-The second phase of a longitudinal study, Stand. J. Sot. Med., 6 (1978) 49. 6 Westergren, S., The technique of the red cell sedimentation rcactlon, Amer. Rev. Tuberc.. 14 (1926) 94. 7 International Committee for Standardization in Haematology, Reference method for the erythrocyte sedimentation rate (ESR) test on human blood, Brit. J. Haematol., 24 (1973) 671.
107
8 Levine, J.B. and Zak, B., Automated determination of serum total cholesterol, Clin. Chim. Acta. IO (1964) 381. 9 Loftland, Jr., H.B., A semiautomated procedure for the determination of triglycerides in serum, Ann. B&hem., 9 (1964)393. IO Praetorius, E., An enzymatic method for the determination of uric acid by ultraviolet spectrophotometry, &and. J. Clin. Lab. Invest., I (1949) 222. I I Elmfeldt. D., Wilhelmsen, L., Tibblin, G. et al., A postmyocardial infarction clinic in Goteborg. Sweden, Acta Med. Stand., 197 (1975) 497. I2 Rose, G.A.. The diagnosis of ischaemic heart pain and intermittent claudication in field surveys. Bull. WHO, 27 (1962) 645. I3 Astrand. A., Areskog. N.-H., Carlsten, A. et al., The ‘Minnesota code’ for ECG classificationAdaption to CR leads and modification of the code for ECG’s recorded during and after exercise, Acta Med. Stand. (Suppl. 481) 1967. I4 Blackburn, H., Keys, A., Simonson, E. et al., The electrocardiogram in population studies, Circulation, 21 (1960) 1160. I5 Harmsen. P. and Tibblin. G., A stroke register in Goteborg, Sweden, Acta Med. Stand., 191 (1972) 463. I6 Arterial Hypertension and Ischaemic Heart Disease-Report of an Expert Committee (WHO Tech. Rep. Ser. No. 23 I), World Health Organization, Geneva, 1962. I7 Bengtsson, C., Ischaemic heart disease in women-A study based on a randomized population sample of women and women with myocardial infarction in Gbteborg. Sweden, Acta Med. Stand. (Suppl. 549). 1973. IX Noppa, H., Bengtsson, C., Bjomtorp, P. et al., Overweight in women-Metabolic aspects. Acta Med. Stand., 203 (1978) 135. I9 Rafnsson. V., Bengtsson, C.. Lennartsson, J. et al., Erythrocyte sedimentation rate in a population sample of women with special reference to its clinical and prognostic significance, Acta Med. Stand., 206 (1979) 207. 20 Tibblin, G.. Wilhelmsen, L. and Werkii, L., Risk factors for myocardial infarction and death due to ischaemic heart disease and other causes, Amer. J. Cardiol.. 35 (1975)5 14. 2 I Fessel, W.J.. Siegelaub, A.B. and Johnson, E.S., Correlates and consequences of asymptomatic hyperuricemia, Arch. Intern. Med., 132 (1973) 44. 22 Gordon, T. and Kannel, W.B., Predisposition to atherosclerosis in the head, heart and legs, J. Amer. Med. Ass., 221 (1972) 661. 23 Kannel, W.B., Some lessons in cardiovascular epidemiology from Framingham, Amer. J. Cardiol.. 37 (1976)269. 24 Hughson, W.G., Mann, J.I. and Garrod. A.. Intermittent claudication-Prevalence and risk factors. Brit. Med. J., i (1978) 1379. 25 Hughson, W.G., Mann, J.I., Tibbs. D.J. et al., Intermittent claudication: factors determining outcome, Brit. Med. J., i (1978) 1377. 26 Heyman. A., Karp, H.R., Heyden, S. et al., Cerebrovascular disease in the biracial population of Evans County, Georgia, Ann. Int. Med., I28 (1971) 949. 27 Kannel, W.B., Gordon, T., Wolf, P.A. et al., Haemoglobin and the risk of cerebral infarction-The Framingham study, Stroke, 3 (1972) 409. 28 Paffenbarger, Jr., R.S., Laughlin, M.E., Gima, A.S. et al., Work activity of longshoremen as related to death from coronary heart disease and stroke, N. Engl. J. Med., 282 (1970) I 109. 29 Theorell, H., Studien iiber die Plasmalipoide des Blutes, B&hem. Z., 223 (1930) 94. 30 Ehrly, A.M., Gramlich, F. and Mtiller, H.E.. fiber den Einfluss von Lipiden, insbesondere von unveresterten Fettsauren, auf den Mechanismus der Blutkorperchensenkungsgeschwindigkeit, Klin. Wchschr.. 43 (1965) 913. 3 I Ohlson, B. and Rundqvist, 0.. ober die Bedeutung der Plasmalipoide fur die Suspensionsstabilit’ des Blutes, Biochem. Z., 247 (1932) 249. 32 Bottiger, L.E., Carlson, L.A., Ekelund, L.G. et al., Raised erythrocyte sedimentation rate in asymptomatic hyperlipidaemia, Brit. Med. J., ii (I 973) 68 I,