Vitamin D deficiency

The most common nutritional deficiency worldwide, characterised by serum 25-hydroxyvitamin D <50 nanomoles/L (<20 nanograms/mL). Vitamin D insufficiency is regarded as a serum 25-hydroxyvitamin D level between 52-72 nanomoles/L (21-29 nanograms/mL).

Main causes include sun avoidance, using sun protection, increased skin pigmentation, inadequate dietary and supplemental vitamin D intake, malabsorption syndromes, obesity, and medication use.

Acquired and inherited disorders that either reduce or prevent the metabolism of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D also present with biochemical and skeletal abnormalities seen with vitamin D deficiency, but in a more severe form.

Most patients are asymptomatic. Severe, prolonged vitamin D deficiency causes growth retardation and rickets in children and osteomalacia, osteopenia, and osteoporosis in adults.

Both vitamin D deficiency and vitamin D insufficiency are corrected by giving vitamin D2 or vitamin D3 in treatment doses followed by lifelong maintenance doses; adequate, sensible sunlight exposure should be encouraged.

Additional replacement with 1,25-dihydroxyvitamin D or one of its active analogues is necessary for those with disorders of vitamin D metabolism, including patients with chronic kidney disease.

To maximise vitamin D effects on the skeleton and on calcium metabolism, serum 25-hydroxyvitamin D level should be >75 nanomoles/L (>30 nanograms/mL). Therefore, vitamin D deficiency is defined as a serum 25-hydroxyvitamin D level of <50 nanomoles/L (<20 nanograms/mL), whereas vitamin D insufficiency is regarded as a 25-hydroxyvitamin D level of between 52-72 nanomoles/L (21-29 nanograms/mL).[1]Hossein-Nezhad A, Holick MF. Vitamin D for health: a global perspective. Mayo Clin Proc. 2013 Jul;88(7):720-55. http://www.mayoclinicproceedings.org/article/S0025-6196(13)00404-7/fulltext http://www.ncbi.nlm.nih.gov/pubmed/23790560?tool=bestpractice.com [2]Malabanan A, Veronikis IE, Holick MF. Redefining vitamin D insufficiency. Lancet. 1998 Mar 14;351(9105):805-6. http://www.ncbi.nlm.nih.gov/pubmed/9519960?tool=bestpractice.com [3]Holick MF. Vitamin D deficiency. N Engl J Med. 2007 Jul 19;357(3):266-81. http://www.ncbi.nlm.nih.gov/pubmed/17634462?tool=bestpractice.com [4]Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011 Jul;96(7):1911-30. https://academic.oup.com/jcem/article/96/7/1911/2833671 http://www.ncbi.nlm.nih.gov/pubmed/21646368?tool=bestpractice.com

Vitamin D deficiency is the most under-diagnosed medical condition in children and adults. This is largely because patients do not typically present with overt clinical signs and symptoms until the deficiency is severe and prolonged. Children with established vitamin D deficiency present with features of rickets (skeletal abnormalities, developmental delay, failure to thrive), whereas adults present with signs and symptoms of osteomalacia (bone pain and tenderness, proximal muscle weakness reported as difficulty in rising from a sitting position).

In addition to the skeletal effects, it is now recognised that vitamin D deficiency increases the risk of many chronic diseases, including cancer, autoimmune diseases, type 2 diabetes, heart disease and hypertension, neurocognitive dysfunction, infectious diseases (including upper respiratory tract infections and tuberculosis), and osteoarthritis, as well as depression and schizophrenia.[1]Hossein-Nezhad A, Holick MF. Vitamin D for health: a global perspective. Mayo Clin Proc. 2013 Jul;88(7):720-55. http://www.mayoclinicproceedings.org/article/S0025-6196(13)00404-7/fulltext http://www.ncbi.nlm.nih.gov/pubmed/23790560?tool=bestpractice.com