Ethnic Differences in Fibrinogen Levels: The Role of Environmental Factors and the β-Fibrinogen Gene

Fibrinogen is a cardiovascular risk factor, but little is known about levels in ethnic groups that differ in their cardiovascular risk. Fibrinogen was measured in 479 Black individuals, 459 South Asian Indians, and 453 Whites aged 40–59 years living in south London, England, from March 1994 to July 1996. Genotype was determined at two sites in the promoter of the β-fibrinogen gene (G-455→A and C-148→T). Plasma fibrinogen levels were lower in Blacks than in Whites by 0.22 g/liter (95% confidence interval (CI): 0.08, 0.36) in men and 0.11 g/liter (95% CI: –0.01, 0.23) in women. These differences were not explained by measured environmental variables, including smoking, or by genotypes. The fibrinogen levels of South Asians were not consistently different from those of Whites. The A-455 and T-148 alleles were less common in Blacks than in either Whites or South Asians. In Whites and South Asians, but not in Blacks, there was complete allelic association between the two variants. In Blacks, the T allele rather than the A allele was associated with higher fibrinogen levels. The average fibrinogen-raising effect of the T-148 allele across all ethnic groups was 0.14 g/liter (95% CI: 0.02, 0.26 g/liter) in women and 0.15 g/liter (95% CI: 0.03, 0.27 g/liter) in men. Low fibrinogen levels in Blacks may partly explain their lower risk of ischemic heart disease in the United Kingdom.