Compensation by Solar Irradiation of Depletion of 25(OH)D in CAPD Patients

M.E. Martinez, Servicio de Bioquímica, ‘LA PAZ’,, Paseo de la Castellana 261, E-28050 Madrid (Spain) Dear Sir, Low levels of 25(OH)D in serum have been described in patients on continuous ambulatory peritoneal dialysis (CAPD) [1, 2], attributed to a peritoneal loss of this metabolite and its transport protein [3, 4]. There are also studies which show a progressive decrease in the values through the time that the patient is on CAPD [2]. In previous studies we have been able to show that, in our geographic area, the levels of 25(0H)D are lower in the patients on CAPD than in normal controls [5], after the period of lowest solar radiation (March-April), but there is no progressive decrease in their levels through the time on dialysis. Since in our geographic area there are important variations in the levels of 25(OH)D throughout the year in normal controls which are dependent on the season, we have quantified the levels of this metabolite in patients on CAPD, to find out whether solar radiation might compensate for the peritoneal loss. We have studied 51 patients on CAPD through 2 years with a total of 167 determinations. They were not restricted in their protein intake nor did they receive treatment with either vitamin D or 25(OH)D. The control group consisted of 73 normal subjects with a total of 80 determinations through 2 years. Both groups were of similar age and were resident in the Madrid area of Spain within a radius of 50 km. The levels of 25(OH)D were quantified by protein binding by a commercial method (Bülhman), after purification by HPLC [6]. In the ‘patients on CAPD we found, as in the normal controls, significant variations in the levels of 25(OH)D throughout the year (fig. 1). In any season of the year the levels were always lower in patients on CAPD than in the normal controls, but the percentage of patients with lev-