Quest Vitamins LTD,
D (Vitamin D)
Vitamin D is technically a hormone as it is formed in one place but carries out its action in another. The vitamin is made in the Skin by the action of sunlight on cholesterol.
Vitamin D is measured in µg or i.u. with the conversion factor being: 40i.u. = 1µg
Vitamin D is stable to normal cooking procedures.
Vitamin D is converted in the body to an important Calcium - controlling hormone (1,25-dihydroxycholecalciferol) and all its functions are related to this hormone's effects.
The principle action of vitamin D hormone is to increase the level of clcium in the blood by promoting the absorption of calcium and Phosphorus from the intestine and promoting the release of these minerals by bone. To maintain the body's physiological ratio of calcium to phosphorus vitamin D hormone also increases the excretion of phosphorus - but not calcium - from the kidney.
Upper safe level for daily supplementation = 10µg
Recommended Daily Allowance = 5µg
There are certain categories of people who are theoretically much more likely to be at risk of vitamin D deficiency and who may therefore need to supplement with this nutrient. These include:
There are some reports of hypercalcaemia (high blood Calcium levels) occurring in infants at an intake of 50µg (2000i.u.) vitamin D a day. In adults, symptoms of vitamin D toxicity have been reported at daily intakes of 625µg (25000i.u.).
However, there is also some early evidence that vitamin D at lower levels (around 1000 µg) may have adverse effects unrelated to hypercalcaemia.
The following list is not exhaustive and anyone taking medication should consult their general practitioner before using vitamin D supplements.
Adverse reactions for vitamin D have been associated with certain heart drugs such as Verapamil.
Combined Oestrogens can elevate blood levels of vitamin D and so vitamin D supplements should be avoided by people using these drugs.
It has been suggested that vitamin D supplements can increase the activity of anticoagulants such as Warfarin. The evidence for this interaction is contradictory but it would be prudent for people using anticoagulant drugs to avoid vitamin D supplements as a precaution.
Vitamin D should not be taken at the same time as thiazide diuretics as there is some evidence to suggest that this combination might raise blood levels of Calcium.
Primary Vitamin D deficiency in children
In recent years, the prevalence of vitamin D deficiency has increase and rickets has re-emerged in the UK and other developed countries as a public health problem. Infants, toddlers and adolescents in at risk are ethnic minorities (e.g. Asian, African Carribean and Middle Eastern) are particularly likely to be vitamin D deficient or to have rickets. Also at particular risk are babies and toddlers who have been exclusively breast fed during infancy without receiving vitamin supplements or whose mothers did not have vitamin D supplements during pregnancy.
Drug Ther Bull. 2006 Feb; 44 (2):12-6
Food (i.u./100g) (µg/100g)
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1. Parsons TJ. et al. Reduced bone mass in Dutch adolescents fed a macrobiotic diet in early life. J Bone Miner Res,12;9:1486-1494, 1997.