Letters Section Editor: Stephen J. Lurie,
MD, PhD, Senior Editor.
In Reply: Dr Hense points out that many factors
play a role in hypertension. A major issue in previous studies of blood lead
concentration and blood pressure has been whether to control for hemoglobin
level, which appears to be an established determinant of blood lead concentration,
but whose relationship to blood pressure has not been clearly established.1 However, consideration of hemoglobin is complicated
by the fact that lead is known to decrease hemoglobin levels, presumably through
inhibition of biosynthesis of heme.2 Thus,
to enter hemoglobin into the regression model may in fact introduce problems
of adjustment for factors along the causal pathway between lead exposure and
its effect on blood pressure, or even colinearity.
Nash D, Silbergeld E. Blood Lead Levels and Hypertension. JAMA. 2003;290(4):460. doi:10.1001/jama.290.4.460-a