AUTHOR: Dr Eamon Laird, TILDA Project at Trinity College Dublin
60 Second Summary
Interest in vitamin D has grown exponentially in the last 5 years and has often been described as the new ‘superhero vitamin’ with its health effects suggested to go beyond the traditional role in bone maintenance/prevention of osteoporosis to cancer, diabetes and cardiovascular disease.
Vitamin D technically is a steroid hormone and not a vitamin. It is made through the action of ultra-violet B (UVB) sunlight on the skin where it is then transported to the liver for hydroxylation to form 25-hydroxyvitamin D (25(OH)D). Further hydroxylation then occurs in the kidneys to the biologically active form, 1,25-dihydroxyvitamin D (1,25[OH]2 D) which acts on cells and tissues via the vitamin D receptor.
Physiological factors that can influence vitamin D levels include malabsorption syndromes (Coeliac, Crohn’s etc.) and genetic differences in the way vitamin D is processed. Low vitamin D can be a particular issue for older adults (> 50 years) as the ability of older adults to synthesize vitamin D is reduced.
The primary role of vitamin D is to facilitate and enhance calcium absorption in the small intestine.
Vitamin D status is routinely assessed through the blood measurement of 25(OH)D, the universally recognised marker of choice. The accepted gold standard of vitamin D measurement in the laboratory is liquid chromatography–tandem mass spectrometry. Other methods can be used though they have the potential to over or under estimate concentrations depending on the method used.
Currently there are no official Irish guidelines for treating vitamin D deficiency through the majority of practitioners follow either the National Institute for Health and
Care Excellence (NICE) guidelines or the National Osteoporosis Society (NOS) guidelines. In the majority of cases, 800-1,000 IU vitamin D3 daily will be sufficient to maintain a level of 50 nmol/L though higher doses will be required if there is poor gut absorption or liver disease.