Doctors, drugs, and the DHSS
BMJ (Clinical Research Edition)
sightly nodule in the side of the neck alongside the superior border of the thyroid cartilage. R E MAY Frenchay Hospital, Bristol BS16 1LE Blood lead concentration and blood pressure SIR,-We read with great interest the paper by Dr S J Pocock and others (6 October, p 872), dealing with the relation between blood lead concentration and blood pressure, a controversial subject.' 2 A relation was not found by Dr Pocock and others. However, data displayed in their fig 1, showing the variations of
... he variations of systolic blood pressure in relation to blood lead concentrations, seem to indicate that an increase in the blood lead value might result in an increase in systolic blood pressure up to a limiting value, while higher lead concentrations do not relate to blood pressure. Results from one of our recent studies support this hypothesis. Our population study consisted of 431 men attached to a section of the Paris civil service, aged 24-55 years (mean 41-4 years), living in the same urban area, and not occupationally exposed to lead. We measured blood lead values by flameless atomic absorption spectrometry (graphite furnace atomiser), blood pressure after resting (with a mercury apparatus), weight, and height. Daily alcohol and tobacco consumption was assessed by questionnaires. The logarithms of blood lead values were used in calculating the correlation coefficients. As in the work of Dr Pocock and others, the systolic blood pressures were adjusted for body mass index, age, and alcohol consumption using analysis of covariance. The results are summarised in the table, where blood lead was Systolic blood pressure means in relation to blood lead concentrations Systolic blood Blood pressure lead No of (,umol/l) Mean (and 2 SE) Adjusted subjects (mm Hg) mean <'060 127 (3 6) into the same classes as those used by Dr Pocock and others. The blood pressure means, not adjusted and adjusted, are shown by blood lead group: overall they differ significantly (p < 0 001). They increase from the first blood lead class (<0-60 jtmol/l) to the fourth (1-20-1-49 Hmol/l); the last two means, corresponding to 1-50 timol/l and over, do not yield much information because of the small numbers of subjects. The overall correlation coefficient between systolic blood pressure and blood lead concentration is 0-23 (p< 0 001). Its values in the age classes 24-34 years (145 subjects), 35-44 years (143 subjects), and 45-55 years (142 subjects) are 0-29 (p<0001), 0-20 (p<005), and 0-14 (not significant), respectively. Adjusting for alcohol consumption and body mass index does not modify these results. Our results in fact agree with those of Dr Pocock and his colleagues provided the following observations are made. The mean systolic blood pressure in their study is much higher than in ours, which might at least partly be explained by the different age ranges in the two studies (40-59 years in theirs, 24-55 in ours). In their study no overall correlation was found between blood lead values and systolic blood pressure, although a slight increase is to be noted as blood lead varies from 0-6 Fumol/l to 1 1 4mol/l. In our study blood lead values are significantly related to blood pressure; this correlation, highly significant in young subjects (24-34 years), decreases with age (not significant in 45-55 year olds). Thus, we may hypothesise that the increase in blood lead concentration parallels the increase in blood pressure until some limit value, so that such a trend is apparent only when other factors (such as age) do not competitively increase blood pressure by greater amounts.