European Journal of Preventive Cardiology

The traditional Greek diet is strongly inversely related to the risk of developing coronary heart disease. Consequently, Greek men have a longer life expectancy than men from other European countries or from North America. Several aspects of the traditional Greek diet may contribute to its beneficial role in countering the development of coronary heart disease. They include the high intake of olive oil that tends to increase the ratio of high- to low-density-lipoprotein cholesterol, the regular consumption of fibre-rich legumes and vegetables in meals cooked using olive oil, the high intake of vegetables and fruits and the associated anti-oxidant compounds, and the moderate consumption of wine with meals that tends to increase high-density-lipoprotein cholesterol without posing major risks of intoxication.

Traditional diets of the Pacific have been historically associated with very low rates of coronary heart disease. Both Pacific rim and Pacific island diets are uniformly very low in fat (approximately 10–15%) and high in complex carbohydrate, dietary fiber, and foods of plant origin. With the high burden of morbidity and mortality from cardiovascular disease in most modernized nations, it may be time to look at these traditional diets of the Pacific as one model for the prevention and reversal of these diseases.

This chapter reviews the evidence from epidemiologic studies and controlled clinical trials dealing with dietary fats and blood pressure. Trials studying the effect on blood pressure of n-3 polyunsaturated fatty acids from fish oil show a dose-response hypotensive effect that may be restricted to patients with atherosclerotic cardiovascular disease. However, fish oil is not a practical therapy for hypertension given the large dose required (10 capsules per day) for a small effect (3–4 mmHg). From numerous studies, it is clear that saturated and n−6 polyunsaturated fats have no effect on blood pressure. Monounsaturated fats also have no effect but fewer studies have examined this relation.

Although population-based studies suggest that a high-fat diet may increase the incidence of diabetes, the mechanism of this association is not clear. Controlled metabolic studies indicate that changes in fat content of the diet within the range that people normally consume have little or no effect on insulin-mediated glucose disposal. Thus, the effects of a high-fat diet on the incidence of non-insulin-dependent diabetes mellitus (NIDDM) may be mediated by inducing obesity, a known cause of insulin resistance and a risk factor for NIDDM. More research is needed in this area.

Alterations of dietary fat that reduce serum cholesterol are beneficial to people who have the highest risk of death from coronary heart disease (CHD). For other people the benefits are less clear; there is a suggestion (hotly disputed) that cholesterol-lowering by drugs, and possibly by diet, increases the risk of non-CHD death, for reasons that are not understood. Furthermore, fat intake interacts with other dietary and non-dietary factors. The consequences of altering dietary fat seem to be more complex and uncertain than have hitherto been supposed.

Aim: This study examined whether work-related aspects of stress, alone or in association with a high salt intake, are associated with a raised blood pressure.

Methods: A total of 384 male civil servants (35–51 years) collected a 24 h urine sample and were interviewed using measures of work-related stress. Their blood pressure was taken at a civil-service medical clinic and was self-measured at home.

Results: Systolic/diastolic pressure averaged (± SD) 135 ± 19/84 ± 14 mmHg at the clinic and 123 ± 16/80 ± 11 mmHg on self-measurements at home. The 24 h urinary sodium excretion was 172 ± 65 mmol. The overall stress score was categorized as low in 98 men, medium in 193 men and high in 93 men. Stress itself was not associated with an elevated pressure. However, in multivariate analyses with adjustments for age and body mass index, a stress-sodium interaction in the determination of the clinic systolic (P = 0.05) and diastolic (P = 0.08) pressure became apparent. At a sodium excretion of 100mmol/24 h (10th percentile), increasing stress from low to high was associated with a fall in pressure, averaging 4.5 mmHg for systolic pressure and 1.4 mmHg for diastolic pressure. By contrast, at 250mmol/24 h (90th percentile) the same stress increase was associated with a rise in pressure of 6.3 mmHg systolic and 5.9 mmHg diastolic.

Conclusion: The present study suggests that sodium intake and work-related stress may interact to determine blood pressure. This interaction is probably dynamic in nature, so that the contribution of each factor to blood pressure can only be determined if both are measured.

Objective: We set out to evaluate the relationship between aortic stiffness and serum lipids and lipoprotein fractions, including high-density-lipoprotein (HDL) cholesterol subfractions.

Methods: One hundred and five asymptomatic, normotensive, untreated, hypercholesterolaemic men underwent measurement of aortic pulse-wave velocity (PWV) by mecanography and assay of total cholesterol, triglycerides, HDL cholesterol and its subfractions (HLD₂ cholesterol and HDL₃ cholesterol), determined by electrophoresis.

Results: PWV was related to HDL cholesterol (r = 0.21, P = 0.05) and more specifically to the HDL₃ cholesterol subfraction (r = 0.29, P >0.01). The latter association remained significant after adjustment for systolic blood pressure and age. Multivariate analysis demonstrated an independent association of PWV (r² = 0.27, P <0.001) with age, systolic blood pressure and HDL₃ cholesterol.

Conclusion: Although hypercholesterolemia was not accompanied by increased aortic rigidity, there was a positive relationship between PWV and HDL cholesterol and between PWV and HDL₃ cholesterol independently of the influence of age and systolic blood pressure on PWV. These results suggest that, in hypercholesterolaemic men, HDL₃ could, in addition to its anti-atherogenic property, have a prosclerotic stiffening effect. This duality could explain why, in clinical studies, although the level of the HDL₂ subfraction is frequently associated with a lower incidence of coronary artery disease, results for the HDL₃ subfraction are less convincing and remain equivocal.

Objective: We set out to examine the association between resting heart rate and haematological factors and blood lipids, all believed to be associated with coronary heart disease.

Methods: In a cross-sectional study, 6016 industrial employees in Israel were screened between 1985 and 1987 for cardiovascular disease risk factors [the CORDIS Study (Cardiovascular Occupational Risk Factors Detection in Israeli Industries)]. Repeated measures of resting heart rates were obtained. Complete data were available for 5393 participants. The lowest mean measure was used to examine the association with individual factors.

Results: For men, of the blood lipids, only triglycerides were independently positively associated with resting heart rate after controlling for all the possible confounding factors (P <0.002). Mean heart rate was higher at elevated triglyceride levels (70 beats/min at ≤ 93mg/dl and 73.3 beats/min at >150mg/dl). Platelet count and haemoglobin were independently positively associated with heart rate (P <0.0001 in both groups). For women, low-density lipoprotein cholesterol and leucocyte count were independently positively associated with resting heart rate (P <0.05 and P = 0.006, respectively).

Conclusion: These associations suggest that the role of resting heart rate as a predictor of coronary heart disease may be partly explained by its association with triglycerides, haemoglobin, platelet count and leucocyte count, which may be confounding factors or intervening variables.

Background: Stimulated hyperinsulinaemia is observed in some patients with syndrome X, defined as angina, positive stress test and normal coronary arteriography, and may be involved in the pathogenesis of the syndrome. An increased sympathetic response to exercise may also be pathogenetically involved. However, the diagnostic value of hyperinsulinaemia as a marker of this syndrome has not been defined.

Methods: We determined blood glucose and immunoreactive insulin during fasting, at 60 and 120 min after a glucose load of 75 g in 21 patients (eight men, 1 3 women, 53.9 ± 7.1 years old) with syndrome X and in 21 healthy volunteers matched to the patients for age, sex and body mass index (eight men, 13 women, 51.6 ± 9.3 years old). Insulin values were related to the rate-pressure product increase at first exercise stage.

Results: The glucose values as well as the insulin values during fasting were similar in syndrome X patients and in controls. However, significantly higher insulin values (mU/l) were observed at 60 (P <0.01) and 120 min (P <0.005) in syndrome X patients (median 75.5 and 52, range 43–290 and 6.1–212, respectively) than in controls (median 47.5 and 24.5, range 8–195.6 and 5.2–164, respectively). A considerable overlap of insulin values, however, was observed between the two groups, with abnormal values even during fasting. For a specificity of 95%, an abnormal insulin value had a sensitivity of between 19 and 24% and a diagnostic accuracy of 57–60%. A significant positive correlation was found between insulin levels after the glucose load and the rate-pressure product increment with exercise (60 min, r = 0.60; 120 min, r = 0.65).

Conclusion: Hyperinsulinaemia may be pathogenetically involved in syndrome X patients, in close relation to the higher sympathetic drive that characterizes this syndrome. However, the wide range of insulin values, frequently overlapping with normal values, limits the usefulness of this abnormality as a marker of the syndrome.

Background: Dietary consumption of fish, rich in n-3 polyunsaturated fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), has been shown to reduce blood pressure in both animal studies and clinical trials. Although the antihypertensive mechanisms are not known, the blood-pressure-lowering effect of n-3 polyunsaturated fatty acids may be partially attributed to their vasorelaxant properties.

Methods: Aortic rings, with and without endothelium, from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR), 16–17 weeks old, were suspended in tissue baths and isometric tension was measured. Concentration-response curves were generated for DHA and EPA (1–100 μmol/l) in norepinephrine-contracted rings. Blood pressure was measured using the tail-cuff method and aortic media thickness was determined.

Results: Blood pressure was significantly increased in SHR (n = 10; 194 ± 4.4 mmHg) compared with WKY (n = 10; 124 ± 1.2 mmHg, P ≤ 0.0001). DHA (1–100μmol/l) relaxed aortic rings from WKY (-3.3 ± 0.7 to −13 ± 2.3%, P ≤ 0.001) and from SHR (-6.5 ± 1.8 to −22.9 ± 4%, P ≤ 0.01) in a concentration-dependent manner. EPA (1–100μmol/l) evoked greater relaxation in SHR (−10.1 ± 2.0 to-33 ± 3.9%, P <0.01) than in WKY (−2.9 ± 1.1 to −18.3 ± 2.1%, P <0.01) aortic rings. The relaxant effect of DHA in both WKY and SHR and of EPA in WKY were not dependent on an intact endothelium. However, EPA (1–10μmol/l) induced greater responses in intact SHR rings (−10.1 ± 2.0 to −14.5 ± 3.1%) than in de-endothelialized SHR rings (0 to −2.1 ± 1.7%, P = 0.001).

Conclusion: The direct relaxant effects of n-3 fatty acids as seen in WKY and SHR may contribute, in part, toward the blood-pressure-lowering effect of dietary fish and fish-oil supplementation.

Background: Endothelin-1 (ET-1) may play an important role in the development and maintenance of hypertensive states. In patients with essential hypertension, ET-1 plasma concentration increases or remains unchanged. The aim of the present study was to investigate ET-1 plasma concentration in patients with mild-to-moderate essential hypertension and its interrelationship with catecholamines, neuropeptide Y and atrial natriuretic peptide (ANP).

Methods: The study included 37 patients (mean age 38.2 ± 1.6 years) with mild-to-moderate essential hypertension. The control group consisted of 21 healthy volunteers (mean age 35.6 ± 1.4 years). ET-1, neuropeptide Y and ANP were determined by radioimmunoassay methods and catecholamine plasma concentration was determined radioenzymatically.

Results: Our study shows that plasma ET-1 and neuropeptide Y levels are elevated in patients with essential hypertension compared with a control group. No correlation was found in either of the groups between plasma ET-1 level and plasma neuropeptide Y, catecholamine or ANP concentrations.

Conclusion: Our results suggest that ET-1 is relevant in the development and maintenance of elevated blood pressure.

Background: Several reports on the possible association between low-level lead exposure and blood pressure reflect diverging views. This meta-analysis aimed to find a common denominator in the published literature and to estimate whether a relationship exists between blood pressure and levels of lead in the blood.

Methods: Of the studies reviewed, 23 provided sufficient details to be considered. The meta-analysis included 33 groups with a total of 33 141 subjects, who had been recruited from the general population in 13 surveys and from occupational groups in 10 studies. In all but four studies the results were adjusted for age, and most studies took into account additional confounding factors.

Results: The association between blood pressure and blood lead was similar in both men and women. In the combined studies, a twofold increase in blood lead concentration was associated with a 1.0mmHg rise in systolic pressure (confidence interval 0.4–1.6mmHg; P = 0.002) and with a 0.6mmHg increase in diastolic pressure (confidence interval 0.2–1.0mmHg; P = 0.02). The association with systolic pressure strongly relied on the inclusion of a large study (n = 3851) in which women's blood pressure was measured at the end of pregnancy. The association with diastolic pressure was largely due to a population survey in the USA (n = 6289). There was no relationship across studies between the strength of the blood pressure-blood lead relationship and the mean blood lead concentration.

Conclusion: The published evidence suggests that there can only be a weak positive association between blood pressure and lead exposure. Any such relationship may not be causal and is unlikely to entail any public-health implication in terms of hypertension-related complications. Nevertheless, these assumptions need to be confirmed in prospective population studies.

This bibliography is produced in association with Current Opinion in Cardiology (Current Science, USA) and is compiled from the journals listed at the end of the issue. Each issue of the Journal of Cardiovascular Risk lists papers relevant to cardiovascular risk published over a two-month period. This issue consists of literature scanned between 1 December 1993 and 31 January 1994.