Han J, et al. - In this cross-sectional study, researchers investigated vitamin D deficiency (VDD)-related risk factors for sickle cell disease (SCD). In 65% of adult SCD patients, the presence of VDD was detected. An independent, as well as positive correlation of 25-OHD levels, was seen with older age and vitamin D supplementation. Relative to the general African-American population, higher 25-OHD levels were detected in SCD patients over 40 years of age. Both lower 25-OHD levels and increased pain frequency were found to be related to increased expression of SLC6A5 encoding glycine transporter-2, a protein involved in neuronal pain pathways.