Relationship between white blood cell count and incident hypertension

To the Editor: Shankar et al1 have extended our knowledge of the positive relationship between elevated white blood cell (WBC) count and hypertension, using data from a large population-based follow-up study. They found that elevated WBC count was associated with incident hypertension, independent of smoking and other traditional cardiovascular risk factors, with a risk ratio of hypertension increasing in a dose-dependent manner with increasing WBC count tertiles. They speculated that this relationship might be explained by chronic low-grade inflammation, increased catecholamine levels, or sympathetic nervous system activity.1 Another possibility is that the relationship reflects a subtle increase in cortisol activity. Total leukocyte count and blood pressure are increased by cortisol administration in normal human subjects,2 and a degree of neutrophilia and hypertension are commonly seen in Cushing’s syndrome.3 The leukocytosis of glucocorticoid excess is characterized by neutrophilia, associated with lymphopenia and eosinopenia. There is also increased interest in the possible role of cortisol in essential hypertension.4 There is evidence for variations in the glucocorticoid receptor gene in essential hypertension,5 increased sensitivity to topical glucocorticoids and prolonged cortisol half-life in essential hypertension,6 and a blood pressure-lowering effect of low-dose dexamethasone in essential hypertension but not normotensives.7 Thus, it seems plausible that some of the increase in WBC count in essential hypertension might reflect subtle alterations in corticosteroid metabolism.