Haemostatic variables, such as plasma fibrinogen, have been found to have lower mean levels in higher occupational grades (Rose, 1985), with fibrinogen implicated as a CHD risk factor (Rosengren, 1990; Wilhelmsen, 1984; Stone, 1984). High plasma concentrations of fibrinogen are independently associated with increased CHD risk (Meade, 1986a; Stone, 1985; Kannel, 1987b).
There are several biological reasons for fibrinogen’s importance as a risk factor (Smith, 1981; Lowe, 1979; Meade, 1986a, b; Davies, 1976; Nicolaides, 1977). In the haemostatic system fibrinogen and Factor VII levels are related to the incidence of CHD (Meade, 1986a) and may be the “biological pathway” to explain occupational differences in mortality (Marmot, 1989b), with fibrinogen levels higher in lower grade men. The Northwick Park Hospital Study found higher plasma concentration of fibrinogen and clotting factors VII and VIII in association with risk of subsequent CHD mortality (Meade, 1980b). Raised concentrations of fibrinogen may therefore contribute to raised CHD mortality (Markowe, 1985) found in low grade civil servants Marmot, 1984a), or generally in lower social classes (OPCS, 1978).
For some time clinical research has implicated poor fibrinolytic activity (Fearnley, 1964) and higher plasma fibrinogen concentrations (Dormandy, 1973) in the onset of thrombo-embolic disease, with the pathogenetic mechanism behind the association between fibrinogen concentration dependent upon plasma viscosity (Lowe, 1980) and platelet aggregation (Meade, 1983).
Plasma fibrinogen concentrations are significantly raised in men in lower employment grades (Markowe, 1985). The Whitehall Study showed substantial differences in CHD mortality between different grades (Markowe, 1985), risk in lower grades (e.g., messengers) was three times that found in higher grades e.g., administrators (Marmot, 1978b; 1984a). Differences in mean fibrinogen concentrations were large, 3.39 g/1 in lower grades, 2.95 g/1 in higher grades (Markowe, 1985). It is estimated that elevated fibrinogen might account “…for up to a quarter of the excess risk of mortality from coronary heart disease in subjects in the lower grades of employment.” (Markowe, 1985). In the Northwick Park study fibrinogen levels were higher in CHD deaths than in AMI survivors (Meade, 1980b). However, one study found no independent association between occupational class and fibrinogen concentration (Rosengren, 1990). Elsewhere it is argued “…differences in fibrinogen concentration may contribute substantially to social class differences in mortality from coronary heart disease…” (Markowe, 1985), and occupational/social class variations indicate that “…affluence and risk can be separated…” (Rose, 1985).
Appendix 177. MPhil Thesis: Population Variation for Risk Factors in Ischaemic Heart Disease. CNAA. Oxford Polytechnic and Oxford Brookes University, September 1992.
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