White blood cell count and stroke incidence and death. The NHANES I epidemiologic follow-up study

A 1982 report (J Chronic Dis 1982;35:703-14) that a relatively high white blood cell (WBC) count predicted increased incidence of cerebral thrombosis could not establish whether this association was independent of smoking. Therefore, the authors examined data from the First National Health and Nutrition Examination Survey (NHANES I) Epidemiologic Follow-up Study, conducted in 1971-1987, to assess WBC count as a risk factor for stroke in a sample of the US population. White men with a WBC count of > 8,100 cells/mm3 had a 39% increase in age-adjusted stroke incidence compared with those with a WBC count of < 6,600 cells/mm3. However, controlling for cigarette smoking reduced the association and rendered it statistically nonsignificant (relative risk = 1.26, 95% confidence interval 0.93-1.70). No significant associations of WBC count with stroke incidence were seen in white women or in blacks. In white men, elevated WBC count may be a mediator of cardiovascular effects of smoking, an indicator of smoking exposure, or both. Further studies are needed to confirm these findings and to elucidate mechanisms for the effect of smoking and WBC count on stroke incidence and death.