- Ultraviolet B (UVB) rays are required by the skin for the production of vitamin D. The intensity of UVB at the Dead Sea area is the lowest in the world. Low vitamin D levels are often associated with musculoskeletal symptoms. To assess the effectiveness of climatotherapy at the Dead Sea on the production of vitamin D in Norwegian patients suffering from various rheumatic diseases and to investigate possible associations between increased vitamin D serum levels, musculoskeletal symptoms and disease severity. Sixty Norwegian patients who came to the Dead Sea area for 21 days of medical rehabilitation were divided into three groups according to their diagnosis: chronic pain syndromes, i.e., low back pain or fibromyalgia (Group 1, n=33); rheumatoid arthritis (Group 2, n=16); and osteoarthritis (Group 3, n=11). Serum 25-hydroxyvitamin D (25-OH-D) levels were determined at arrival and prior to departure. The treatment protocol included daily sun exposure (climatotherapy), bathing in the Dead Sea and mineral spring water (balneotherapy), mud applications and fitness classes. 25-OH-D serum levels increased significantly from 71.3 +/- 26.6 nM at arrival to 89.3 +/- 23.2 nM prior to departure (P < 0.001). Adjusted for the initial levels of pain (assessed by a visual analog scale) and disease severity, a direct correlation was observed between increased 25-OH-D serum levels and pain reduction (P = 0.012) and reduction of disease severity (P = 0.02). Climatotherapy at the Dead Sea induces significant changes in vitamin D. Increased 25-OH-D serum levels are associated with reduced musculoskeletal pain and disease severity.