Vitamin D (Calciferols)

Vitamin D, a fat-soluble vitamin, is found in many forms or vitamers, collectively known as calciferols. Vitamin D is an essential component of normal calcium function, a role which has profound implications for maintaining normal bodily processes. The most active form of vitamin D in humans is vitamin D3, cholecalciferol. This can be synthesised by humans in the skin upon exposure to ultra violet radiation – B (UVB) from sunlight, or it can be obtained directly from the diet. When exposure to UVB radiation is insufficient for the synthesis of vitamin D3 in the skin, adequate intake of vitamin D from the diet is essential.

Functions

Vitamins D has a variety of important biological functions. One of it's principal roles is regulation of the body’s calcium balance. Maintenance of serum calcium levels within a narrow range is vital for normal functioning of the nervous system, as well as bone growth and maintenance of bone density. Vitamin D is also essential for efficient utilisation of calcium by the body for many purposes, including muscle contraction. 

Other known functions include:

  • Cell differentiation – the active form of vitamin D, 1, 25 – dihydroxyvitamin D, inhibits proliferation and stimulates the differentiation of cells.
  • Immunity – there is growing scientific evidence that 1, 25 – dihydroxyvitamin D has a variety of effects on immune system function which may enhance innate immunity and inhibit the development of autoimmunity.
  • Insulin secretion – animal studies suggest that 1, 25 – dihydroxyvitamin D plays a role in insulin secretion under conditions of increased insulin demand. Also, limited data in humans suggest that insufficient vitamin D levels may have an adverse effect on insulin secretion and glucose tolerance in type 2 diabetes.
  • Blood pressure regulation - The renin-angiotensin system plays an important role in the regulations of blood pressure. It is thought that inappropriate activation of this system plays a role in some forms of human hypertension and that vitamin D levels may be important for decreasing the risk of high blood pressure.

Reference Intake (RI)


    AGE

   CHILDREN

    MALES

FEMALES

MALES

FEMALES

PREGNANCY

  YEARS

1-3

4-6

7-10

11-14

15-17

11-14

15-17

18-64

65+

18-64

65+

 

VITAMIN D

    (µg / day)

7

0*

0*

0*

0*

0*

0*

0*

10

0*

10

       10

 

    MONTHS

0-3

4-6

7-9

10-12

LACTATION

VITAMIN D (μg / day)

8.5

8.5

7

   7

       10


*certain at-risk individuals or groups may require dietary vitamin D

Food Sources

PRODUCTS

   Cod Liver Oil

   Atlantic Herring

Fortified Cereals

     Oysters

(IU / 100 g)

10001

2996

342

320

PRODUCTS

Soy Milk (fortified)

           Salami

       Eggs

   Mushrooms

   (IU / 100 g)

   49IU 

   62

37

     27

 

Deficiency / Toxicity

Deficiencies of vitamin D may result from inadequate exposure to the sun or from inadequate dietary intake. Secondary deficiencies may result from malabsorption due to insufficient dietary fat intake, GI tract diesease, or from vitamin D resistance. Signs of vitamin D deficiency may include the development of rickets in infants and children, and osteomalacia in teenagers and adults. Rickets is characterised by bone pain and deformation of weight-bearing bones, muscle tenderness, swollen joints, and delayed tooth eruption. The symptoms of osteomalacia include inadequate mineralisation of the soft bones, and bone tenderness and pain (spine, shoulder, ribs, pelvis).   

Too much vitamin D is also possible and may lead to high serum calcium levels (hypercalcemia), which could result in bone loss, kidney stones or calcification of organs such as the heart and kidneys. Overall, research suggests that vitamin D toxicity is very unlikely in healthy people at dietary intake levels lower than 10,000 IU / day.