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Quest Vitamins LTD,
8 Venture Way,
Aston Science Park,
Birmingham,
B7 4AP.

Tel: 0121 359 0056
Fax: 0121 359 0313
Email: info@questvitamins.co.uk
Registered in England No. 2530437

D (Vitamin D)

DESCRIPTION

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 g or i.u. with the conversion factor being: 40i.u. = 1g


STABILITY

Vitamin D is stable to normal cooking procedures.


FUNCTIONS

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.


DEFICIENCY

Rickets:
Deficiency of vitamin D during childhood leads to the development of rickets. Rickets may show itself as early as two months of age, when "craniotabes" (areas of softening on the skull) are noted. Production of the first teeth may be delayed and the posture affected. Rickets also produces enlargement at the end of long bones, resulting in characteristic bowing of the legs when the child starts to walk.

Osteomalacia:
In adults, vitamin D deficiency leads to osteomalacia. The disease is essentially the same as rickets, but the symptoms are slightly different because the bones are not still developing. In osteomalacia, there is thinning and weakening of the bone and spontaneous Fractures may occur.

Osteoporosis and Hip Fracture:
Incidence of Osteoporosis (brittle bones) and hip Fracture may be increased in postmenopausal women who have an inadequate vitamin D supply.


REQUIREMENTS

Upper safe level for daily supplementation = 10g

Recommended Daily Allowance = 5g


SUPPLEMENTAL USES

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:

  • Vegetarians and especially vegans (1). (Vitamin D is found mostly in animal and dairy products).
  • Asian women and children who may not eat many vitamin D containing foods and who choose to cover up their Skin (2).
  • Lactating women whose breast-milk can be low in vitamin D especially during the winter (3).
  • The housebound elderly with a tendency to eat poorly (4).


SAFETY

There are some reports of hypercalcaemia (high blood Calcium levels) occurring in infants at an intake of 50g (2000i.u.) vitamin D a day. In adults, symptoms of vitamin D toxicity have been reported at daily intakes of 625g (25000i.u.).

However, there is also some early evidence that vitamin D at lower levels (around 1000 g) may have adverse effects unrelated to hypercalcaemia.


INTERACTIONS AND CONTRA-INDICATIONS

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.


FURTHER RESEARCH

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 SOURCES

Food (i.u./100g) (g/100g)
Cod liver oil 8500 212.5
Herring and kipper 896 22.4
Salmon, canned 500 12.5
Milk, evaporated 160 4.0
Eggs 65 1.6
Butter 32 0.8
Liver 32 0.8
Cheese, cheddar 12 0.3
Milk, whole 1.2 0.03
Milk, skimmed 0 0

HERBS

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NUTRITIONAL SUPPLEMENTS

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REFERENCES

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.
2. Dietary Reference Values for Food, Energy and Nutrients for the United Kingdom, Dept. of Health, HMSO, 1991.
3. Specker BL, Nutritional concerns of lactating women consuming vegetarian diets. Am J Clin Nutr, 59;5 suppl:1182S-1186S, 1994.
4. Russell RM. New views on the RDAs for older adults. J AM Diet Assoc, 97;5:515-518, 1997.

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