Terminology of Vit-D : Vitamin D2

Vitamin D3

Calcidiol (25-hydroxy-vitamin D)

Calcifidiol (25-hydroxy-vitamin D)

Calcitriol (1,25 dihydroxy-vitamin D)

Formal name: 25-hydroxy-vitamin D

1,25 dihydroxy-vitamin D

25-hydroxycholecalciferol.

The main role of Vitamin D is:

To help regulate the absorption of calcium, phosphorus, and (to a lesser extent) magnesium.

Vitamin D is vital for the growth and health of bone; without it, bones will be soft, malformed, and unable to repair themselves normally, resulting in diseases called rickets in children and osteomalacia in adults.

Vitamin D has also been implicated in the regulation of autoimmunity, metabolic function, and cancer prevention.

Why Get Tested?

To determine if you have a vitamin D deficiency;

To determine if your vitamin D supplementation level is appropriate, if you are receiving vitamin D therapy

.

When to Get Tested?

If you have an abnormal calcium, phosphorus, and/or parathyroid hormone level,

If you have evidence of bone disease or bone weakness,

If your doctor suspects that you might have vitamin D deficiency,

If you are going to start drug treatment for osteoporosis, or to monitor treatment of vitamin D deficiency;

Sample Required?

A blood sample drawn from a vein in the patient’s arm.

What is being tested?

There are two forms of vitamin D that can be measured in the blood:

25-hydroxyvitamin D [25(OH)D]

1,25-dihydroxyvitamin D [1,25(OH)(2)D]

Vitamin D comes from two sources:

Endogenous, which is produced in the skin on exposure to sunlight

Exogenous, which is ingested in foods and supplements.

Good Sources : Poor sources :

Milk

Egg

Fish

Fish oil

Rice

corn

The chemical structures of these types of vitamin D are slightly different, and they are named vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

The D2 form is found in foods and in most vitamin preparations and supplements.

Vitamin D3 is the form produced in the body and is also used in some supplements.

Vitamin D2 and D3 are equally effective.

Recommended daily allowances for Vit-D :

Age (years) RDA (g/day)

0-1 7.5-10

1-24 10

>25 5

Pregnant/lactation 10

<20 nm/L Deficiency

20-47 nm/L Insufficient

47-147 nm/L Sufficient (Normal)

>147 nm/L Potential intoxicated

25-hydroxyvitamin D

Low blood levels of 25-hydroxyvitamin D may mean that:

You are not getting enough exposure to sunlight

You are not getting enough dietary vitamin D to meet your body’s demand

There is a problem with its absorption from the intestines.

Occasionally, drugs used to treat seizures, particularly phenytoin (Dilantin), can interfere with the production of 25-hydroxyvitamin D in the liver.

High blood levels of 25-hydroxyvitamin D usually reflect excess supplementation from vitamin pills or other nutritional supplements.

1,25-dihydroxyvitamin D

Low levels of 1,25-dihydroxyvitamin D can be seen in kidney disease and are one of the earliest changes to occur in persons with early kidney failure.

High levels of 1,25-dihydroxyvitamin D may occur when there is excess parathyroid hormone or when there are diseases, such as sarcoidosis or some lymphomas, that can make 1,25-dihydroxyvitamin D outside of the kidneys.

Methods of Vit-D measurement :

HPLC [High performance liquid chromatography]

Radio Immunoassay

ELIZA [ Enzyme-linked immunosorbent assay ]

ICMA [ Immunochemiluminometric assay ]

UV absorption

References

1. Henry’s clinical diagnosis and management

by : Laboratory methods

22nd Edition-21012

2. Fundamentals of clinical biochemistry

by : Tietz

3. The vitamins – Fundamental aspects in nutrition and health

by: Gerald F. Combs JR.

4. Harrison's

5. Davidson’s