Importance of Vitamin D
It is no secret that Vitamin D helps prevent bone disease. More recent research suggests that its role is far wider.
Too little Vitamin D is related to an increased risk of severe chronic conditions including cancers (lung, prostate, ovarian, pancreatic), heart disease and hypertension, diabetes, infectious diseases (upper respiratory tract and tuberculosis).
Vitamin D deficiency has also been indicated in an increased incidence of schizophrenia, Parkinson’s disease, cognitive dysfunction and depression.
Natural occurrence of Vitamin D in food is scarce, and the body relies on its production in the skin with the use of UV light. However, lifestyle changes (time spent indoors and additional protection against skin cancer) have rapidly decreased the amount of exposure to sunlight. As a result, up to 50% of adults in the UK can be defined as Vitamin D ‘insufficient’ or ‘deficient’, and Vitamin D deficiency is the most common nutritional deficiency in the world.
The potential effects of supplementation are not yet clear. However, there is every possibility that correcting an existing deficiency could improve other outcomes. It should be noted that patients in mental health hospitals should be considered as at high risk of deficiency, but neither NICE nor RCPsych are yet to issue guidance on this.
The most commonly used Vitamin D blood test measures serum concentration of one of its inactive metabolites – calcifediol (25-hydroxycholecalciferol or 25OH-D). 25OH-D is created in the liver through hydroxylation of the original molecule. This metabolite is further hydroxylated in the kidneys to form an active calcitriol (or 1-alpha,25-dihydroxycholeclaciferol).
The kidney process is controlled by the parathyroid hormone while the liver hydroxylation depends only on the blood levels of Vitamin D and liver function. It is worth noting that alfacalcidol (OneAlphaTM), used for people with kidney disease, should not be used to correct Vitamin D deficiency as it has no effect on the 25OH-D concentrations and can cause hypercalcaemia.
Vitamin D Deficiency is defined as serum 25OH-D levels lower than 50 nmol/l (20 ng/ml) and insufficiency as 52-72 nmol/l (21-29ng/ml). Normal levels are those above 75 nmol/l (30 ng/ml). The upper limit has not been clearly defined and different values may be found in other sources. Test results should always be interpreted together with calcium and phosphate levels to exclude underlying conditions e.g. hyperparathyroidism.
Deficiency in adults is initially corrected with short term high doses (up to 50 000 IU per week for 6 to 8 weeks). Serum levels should then be checked again and a maintenance dose prescribed (400 to 1000 IU daily) once blood levels reach desired values. For treatment of children and adolescents please see product information.
If serum levels remain low after the initial treatment then other causes such as absorption defects (Crohn’s disease), liver disease or inherited metabolic disorders should be considered.
Follow-up serum 25OH-D measurements should be made approximately three to four months after initiating maintenance therapy to confirm that the target levels have been maintained.
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