Abstract
Epidemiological investigations have suggested that serum 25-hydroxyvitamin D [25(OH)D] level has significantly inverse associations with various neurological and neurodegenerative diseases. However, little is known about 25(OH)D level in human cerebrospinal fluid (CSF). Thus, the aim of this study was to determine correlations of 25(OH)D level in CSF with serum total, bioavailable, and free 25(OH)D levels. This observational study enrolled a total of 117 subjects (58 patients with non-neurologic disease and 59 patients with neurologic disease) from 2017 to 2018. CSF and blood samples were collected in pairs. Total 25(OH)D levels in CSF and serum and vitamin D binding protein (VDBP) levels in serum were measured. We also performed GC genotyping for polymorphisms of rs4588 and rs7041 to calculate bioavailable and free 25(OH)D levels. CSF total 25(OH)D levels were compared with serum total, bioavailable, and free 25(OH)D levels. Mean total 25(OH)D concentrations in CSF and serum of all patients were 37.14 ± 7.71 and 25.72 ± 12.37 ng/mL, respectively. The mean total 25(OH)D concentration in CSF was generally 1.4-fold higher than that in the serum. Total 25(OH)D concentrations in CSF showed weakly positive but significant correlations with serum total, bioavailable, and free 25(OH)D concentrations (P = 0.022, P = 0.033, and P = 0.026, respectively). Serum total 25(OH)D concentration was also correlated with serum VDBP concentration (P = 0.017). However, total 25(OH)D levels in CSF of non-neurologic disease group and neurologic disease group were similar. Total 25(OH)D level in CSF has weakly positive but significant correlations with serum total, bioavailable, and free 25-hydroxy vitamin D levels in the Korean population. The distribution of CSF total 25(OH)D in Korean neurologic and non-neurologic disease patients was presented.
Highlights
Most vitamin D in humans are synthesized in the skin exposed to sunlight, some minor portions of vitamin D can be acquired form the diet
Brain and general circulation are completely separated by the blood brain barrier (BBB) which tightly controls the transport of blood substances into the brain
We demonstrated that total 25 (OH)D level in cerebrospinal fluid (CSF) had weak positive but significant correlations with serum total, bioavailable, and free 25-hydroxy vitamin D levels in a Korean population
Summary
Most vitamin D in humans are synthesized in the skin exposed to sunlight, some minor portions of vitamin D can be acquired form the diet. Two steps of hydroxylation are required to obtain active form of vitamin D. 25(OH)D is transported to kidneys where it is converted to 1α, 25-dihydroxy vitamin D [1α, 25(OH)2D], an active form of vitamin D [2,3]. Most (85%–90%) of circulating vitamin D are tightly bound to vitamin D-binding protein (VDBP), a smaller amount (10%–15%) are loosely bound to albumin. Less than 1% of circulating vitamin D are present in free unbound form [4,5,6]. Since the affinity of 25(OH) D or 1α, 25(OH)2D to albumin is weaker than that to VDBP, the loosely binding fraction and the free fraction are considered bioavailable 25(OH)D [4]
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