Vitamin D deficiency

Vitamin D deficiency is 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 concentration 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.

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 respiratory tract infections, tuberculosis, and COVID-19), and schizophrenia. Vitamin D deficiency/insufficiency has been associated with increased risk for morbidity and mortality associated with COVID-19.

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 concentration 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]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 sufficiency is defined by a 25-hydroxyvitamin D of 75-250 nanomoles/L (30-100 nanograms/mL). Vitamin D toxicity is usually seen when serum 25-hydroxyvitamin D concentrations >375 nanomoles/L (>150 nanograms/mL).[2]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