The Immune and Clinical Impacts of Vitamin D in Patients With Chronic Musculo-skeletal Pain

The immune and clinical impacts of vitamin D in patients with chronic musculo-skeletal pain

Background Vitamin D is a group of fat-soluble secosteroids, the two major physiologically relevant forms are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D without a subscript refers to either D2 or D3 or both. Vitamin D3 is produced in the skin following exposure to UVB light from the sun or artificial sources, and occurs naturally in a small range of foods. Vitamin D is carried in the bloodstream to the liver, where it is converted into the prohormone calcidiol. Circulating calcidiol may then be converted into calcitriol, the biologically active form of vitamin D, either in the kidneys or by monocyte-macrophages in the immune system. When synthesized by monocyte-macrophages, calcitriol acts locally as a cytokine, defending the body against microbial invaders (1).

When synthesized in the kidneys, calcitriol circulates as a hormone, regulating among other things, the concentration of calcium and phosphate in the bloodstream, promoting the healthy mineralization, growth and remodeling of bone, and also vital to the normal function of the different arms of the immune system (1;2).

Vitamin D receptor activation in the intestine, bone, kidney, and parathyroid gland cells leads to the maintenance of calcium and phosphorus levels in the blood (with the assistance of parathyroid hormone and calcitonin) and to the maintenance of bone content. Vitamin D increases expression of the tyrosine hydroxylase gene in adrenal medullary cells. Vitamin D is involved in the biosynthesis of neurotrophic factors, synthesis of nitric oxide synthase, and increased glutathione levels. Adequate vitamin D may also be associated with healthy hair follicle growth cycles (3). Vitamin D insufficiency can result in thin and brittle bones, whereas sufficiency prevents rickets in children and osteomalacia in adults and helps to protect elderly from osteoporosis. Vitamin D has also direct on muscle strength and function (4;5). Nevertheless, there is no persuasive evidence of lower vitamin D status in chronic pain sufferers.

There are also associations between low 25(OH)D levels and peripheral vascular disease (6), certain cancers (7-10), multiple sclerosis (11), rheumatoid arthritis (12-15), juvenile diabetes (16-18), Parkinson's and Alzheimer's disease (19;20). However these associations were found in observational studies and vitamin D vitamin supplements have not been demonstrated to reduce the risks of these diseases.