Serum phosphate in white-coat hypertensive patients: focus on dipping status and metabolic syndrome

Recent studies indicate an association between serum phosphate levels and blood pressure in hypertensive patients. A growing body of evidence suggests that white-coat hypertension (WCH) is associated with target organ damage. Furthermore, metabolic syndrome (MS) and a non-dipping pattern are associated with increased cardiovascular risk. The purpose of this study was to explore the nocturnal blood pressure fall in patients with WCH according to their serum phosphate levels and number of MS components fulfilled. The study included 2600 patients with WCH who attended our outpatient clinics. All patients underwent repeated office blood pressure measurements, 24-h ambulatory blood pressure monitoring and full clinical and laboratory evaluation. The diagnosis of MS was made according to the Adult Treatment Panel III criteria. Dipping pattern was defined as follows: 'dippers' had a nocturnal systolic blood pressure (NSBP) fall > or =10% but <20%; 'non-dippers' had an NSBP fall <10%; 'extreme dippers' had an NSBP fall > or =20% and 'reverse dippers' had an NSBP increase. There were 314 extreme dippers, 1337 dippers, 734 non-dippers and 116 reverse dippers. Reverse dippers presented with significantly lower levels of serum phosphate, whereas extreme dippers had significantly higher levels (3.39+/-3.29 vs. 3.58+/-3.52 mg per 100 ml, P<0.0001). The patients were classified according to the number of MS components and the main observation was the inverse relationship of serum phosphate with MS components (3.53+/-0.36, 3.50+/-0.38, 3.49+/-0.38, 3.44+/-0.36 and 3.35+/-0.31 mg per 100 ml, respectively, P=0.003). Patients with WCH and low serum phosphate levels appear to have a higher incidence of a non-dipping NSBP profile and an impaired metabolic profile. This observation may be important for the stratification of the cardiovascular risk in WCH patients.