Seasonal variations in coronary heart disease

Sir, We read with interest the timely review by Drs Pell and Cobbe1 on the subject of seasonal variations in coronary heart disease. Although it is an interesting and comprehensive review of the areas addressed, it has missed the first report demonstrating seasonal variation in fibrinogen.2 This work was later confirmed by Woodhouse et al. in 19943 and by van der Bom et al. in 1997.4 The sole selection of the paper by Woodhouse et al. has led the authors to conclude that ‘The winter rise in fibrinogen concentrations is likely to be due to both lower temperatures and an increase in the prevalence of respiratory infections’. It seems that the hypothesis of winter infections causing the seasonal elevation in fibrinogen concentrations via the acute phase response is becoming ‘accepted’ on the basis of the Woodhouse paper alone. Whilst it is a biologically plausible explanation, it should be noted that there is more evidence against it than in its favour. Neither we2,5 nor van der Bom et al.4 found evidence for a role of infection in the seasonal pattern of fibrinogen. In these three studies, data from 2417 subjects were reported, in contrast to the 96 subjects by Woodhouse et al.3 Although there may be an indirect effect of infection upon fibrinogen levels,6 much work remains to be done in elucidating the mechanisms responsible for the seasonal variation in fibrinogen.