Are lead, cadmium and mercury risk factors for resistant hypertension?

Background: Lead (Pb), cadmium (Cd) and mercury (Hg) are toxic trace elements that represent a public health problem as risk factors for cardiovascular disease and hypertension (HT) and could also contribute to the development of resistant hypertension (rHT) Aims: To compare the blood concentrations of Pb, Cd and Hg in subjects with resistant and non-resistant HT and to define whether there is a relationship between its levels and rHT. Methods: Cross-sectional study. Subjects aged >= 21 to <= 80 years with a body mass index < 40 kg/m2 were recruited on a discretionary basis from October 2001 to October 2004 in a hypertension unit of a tertiary hospital amongst those sent to the hypertension unit by their family physician. Resistant hypertension was defined according to the American Heart Association (AHA) criteria. Whole blood concentrations of Cd, Pb and Hg were measured by electrothermal atomic absorption spectrometry. Results: 46 out of 73 included subjects (63%) suffered from rHT. Blood Pb median: HT 3.9 (IQR 2.7-5.2) vs. rHT 3.6 (IQR 2.8-6.0) <mu>g/dL (p=0.941). Blood Cd median: HT 0.07 (IQR 0.07-0.80) vs. rHT 0.30 (IQR 0.07-0.65) mu g/ L (p=0.681). Blood Hg median: HT 7.9 (IQR 5.8-12.9) vs. rHT 7.3 (IQR 4.6-13.3) mu g/L (p=0.611). Considering the 75th percentile of each element (Pb: 5.55 mu g/dL, Cd: 0.75 mu g/L, Hg: 13.15 mu g/L), a multiple logistic regression analysis (adjusted for age, BMI, diabetes mellitus, clearance of creatinine and only for Cd the smoking habit) showed an OR = 3.44 (0.84-14.10, p=0.086) for Pb, OR = 1.80 (0.39-8.24, p=0.451), for Cd and OR = 2.31 (0.59-9.14, p=0.232) for Hg. Moreover, the stratified analyses showed that men with Pb >= 5.55 mu g/dL have a 14 times higher risk of suffering from rHT (p=0.026). Interestingly, a 9 -fold increased risk was found for non -obese subjects with elevated Pb levels, above 5.55 mu g/dL (p=0.029). Also in men, the probability of suffering from rHT was more than 7 times higher if Cd levels were >= 0.75 mu g/L (p=0.076). Most smokers had higher Cd levels, with a high risk of suffering from rHT (ORa 12.6 (0.8-200.2), p=0.072). Conclusion: A higher blood Pb levels, defined by the 75th percentile (Pb >= 5.55 mu g/dL), is associated with a greater risk of suffering from rHT and to a lesser extent in the case of Cd and Hg.