What is Vitamin D
Vitamin D, a fat soluble vitamin, is more appropriately categorized as a prohormone which is a collective term for a group of seco-steroids. Vitamin D is metabolised by hepatic 25-hydroxylase into 25-hydroxyvitamin D and by renal 1α- hydroxylase into the active form 1,25- dihyroxyvitamin D. This is responsible for the modulation of calcium absorption and inflammatory responses. Low circulating levels of 25-hydroxyvitamin D Is the most reliable marker of Vitamin D deficiency.
Why test for Vitamin D Deficiency
Vitamin D deficiency can be a serious problem and does not have very obvious symptoms. It increases susceptibility to other more serious conditions. Maintaining Vitamin D levels protects the body from a wide range of diseases including viruses, cardiovascular disease, bone disease including osteoporosis, rickets and osteomalcia, autoimmune disease (such as multiple sclerosis and rheumatoid arthritis), strokes, nervous system disorders (such as Parkinson’s Disease) and type 1 and 2 diabetes. Depression and breast, prostate and colon cancer have also been linked to Vitamin D deficiency.
Causes of Vitamin D Deficiency
- Deficient production
- Decreased input due to seasonal lack of exposure to sunlight
- Anything that interferes with the penetration of solar ultraviolet radiation into the skin will diminish the cutaneous production of Vitamin D3
- Dietary intake is low
- Marked decrease in the capacity of the human skin to produce vitamin D in the elderly
- Impaired absorption due to kidney or digestive diseases
Which foods contain Vitamin D
Only a few foods naturally contain Vitamin D therefore adequate levels are dependent on exposure to sunlight. The flesh of fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources. Small amounts of vitamin D are found in beef liver, cheese, and egg yolks. Vitamin D in these foods is primarily in the form of vitamin D3 (cholecalciferol) and its metabolite 25(OH)D3. Also fortified foods such as breakfast cereals, yogurt, margarine contain added Vitamin D.
Vitamin D maintains the levels of calcium and phosphate which in turn is needed for normal bone mineralisation, muscle contraction, nerve conduction and general cellular function. More specifically 1, 25-dihydroxyvitamin D is a strong steroid hormone that has a crucial role in calcium homeostasis, bone metabolism, cell growth and replication.
How does the test work
CNS uses a conventional ELISA based technology to determine levels of 25-Hydroxyvitamin D and other metabolites in serum or plasma. Calibrators, controls and samples are diluted with biotin labelled 25-OHD.
Diluted samples are incubated for 2 hours at room temperature before washing. Enzyme labelled Avidin is added and binds selectively to complexed Biotin and following a further wash step colour is developed using TMB. Colour produced is proportionate to the concentration of 25-OH D.
Adequate exposure to sunlight and appropriate supplements to maintain healthy levels of the vitamin.
Sample requirements & test turnaround
The test requires just a pin-prick blood sample. Results are available within 10-15 working days.
CNS participates in the DEQAS external quality assessment scheme for Vitamin D testing.
The CNS Vitamin D test has not been verified for use with clients under the age of 18. In some cases, under 18s may have different blood protein levels which may affect the results of most Vitamin D tests currently available.