Low levels of vitamin D poorly responsive to daylight exposure in patients with therapy-resistant schizophrenia

Abstract

Background: Low vitamin D levels are associated with schizophrenia, but the possible association between vitamin D levels and illness severity or duration of exposure to daylight has barely been investigated.Aims: To compare vitamin D levels in therapy-refractory severely ill schizophrenia patients and members of staff. To investigate the influence of daylight exposure on vitamin D levels in patients.Methods: Vitamin D was measured in patients with therapy-resistant schizophrenia in April, after the winter, and in patients and staff members in June, after an exceptionally sunny spring. Vitamin D levels in April and June were compared in patients, and levels in June were compared in patients and staff. The influence of daylight was taken into account by comparing the time patients spent outdoors during the day with the recommended minimum time for adequate vitamin D synthesis, and by comparing time spent outdoors in patients and staff.Results: Patients had high rates of vitamin D deficiency (79–90%) and lower levels of vitamin D than staff members (p < 0.001), independent of skin pigmentation. In patients, vitamin D levels did not normalize, despite the considerably longer than recommended exposure of the skin to daylight (p < 0.001) and the longer exposure in patients than in staff members (p = 0.003).Conclusion: The vitamin D deficiency of therapy-resistant schizophrenia patients is pronounced and cannot be explained by differences in skin pigmentation or by an inactive, indoor lifestyle on the ward. Even theoretically sufficient exposure of the patients to daylight did not ameliorate the low vitamin D levels.Clinical implications: While vitamin D deficiency probably plays a role in somatic health problems, it may also play a role in schizophrenia. Interestingly, exposure to daylight during an unusually sunny spring was not sufficient to correct the vitamin D deficiency seen in the patients. This emphasizes the need to measure and correct vitamin D levels in these patients.