Nearly 43% of African American adults and 53-70% of African American adolescents in the US have vitamin D deficiency (VDD), ten times more than is seen in Caucasians. VDD is also quite common in sickle cell disease (SCD) with prevalence rates of 65-100%. Pain is a hallmark symptoms of SCD accounting for the majority of SCD morbidity. Some patients with SCD develop debilitating chronic pain with an unclear etiology and unsatisfactory response to treatment. Both VDD and SCD can cause chronic pain, compression fractures and myopathy. We hypothesize that VDD is implicated in the poor musculoskeletal health and chronic pain of SCD. Therefore we aim \[1\] to demonstrate that pediatric sickle cell patients have high rates of VDD and those with chronic pain have lower levels of vitamin D compared to those without chronic pain \[2\] to evaluate the musculoskeletal health, pain status, opioid analgesic use, depression and quality of life in SCD patients with and without chronic pain and determine if the presence or severity of VDD is associated with a more severe clinical phenotype and \[3\] to demonstrate that administration of replacement doses of vitamin D will correct VDD, improve musculoskeletal health and ameliorate chronic pain. An additional aim of this project is to \[4\] evaluate and describe any correlates between vitamin D status and serum levels of inflammatory cytokines, markers of oxidative stress and vitamin D receptor polymorphisms in SCD patients with and without chronic pain.

We will evaluate 60 SCD subjects aged 7-21 years (30 with chronic pain and 30 without chronic pain) for VDD and to determine specific baseline characteristics including 25(OH)D levels, bone turnover rates measured by C telopeptide serum levels (CTx), opioid analgesic use, neuromuscular strength, evidence of skeletal complications on chest radiograph, depression and quality of life, serum levels of inflammatory cytokines and oxidative status and characteristics of the vitamin D receptor (VDR). These characteristics will be compared between those with chronic pain and those without chronic pain. We will have a 30 day run in observation period during which baseline pain status will be determined by daily pain diary report. All subjects with then be randomly assigned to receive vitamin D replacement therapy or placebo for six weeks and prospectively followed for six months. All subjects will be given daily recommended daily allowance (RDA) of calcium and vitamin D in the form of a soft chew containing 500 mg calcium and 200 IU vitamin D throughout the study period. The primary endpoints are changes in serum 25(OH)D and CTx levels and opioid analgesic use (mg/kg morphine equivalent). Secondary endpoints include changes in pain status as documented by diary, depression scores, quality of life scores, neuromuscular strength and changes in serum cytokine levels and markers of oxidative stress.

In this study we hypothesize that VDD either contributes to or exacerbates sickle cell chronic pain and that correcting VDD in SCD will result in decreased pain, depression and opioid analgesic use; an improvement in musculoskeletal health; as well as a reduction in degree of inflammation and oxidative stress. This is a pilot study in preparation for a larger prospective trial evaluating the role of VDD in the pathobiology of SCD pain and musculoskeletal health.