Vitamin D tests used in this video
Your personalised vitamins
Single test, £39.99
Year plan, 2 tests and vitamin D supplies to titrate, £75
BetterYou test
£32.95
Vitamin D into the body
D3 (cholecalciferol), sun, animals or supplement
D2 (ergocalciferol), plants, supplements
Pathway
In the skin
Vitamin D, cholecalciferol, synthesised in the skin
In the liver
Converted to its major circulating form, 25-hydroxyvitamin D (25(OH)D)
Calcifediol
In the kidneys
Converted into 1,25-dihydroxyvitamin D3, or calcitriol, the principal active hormonal form of vitamin D
Vitamin D in the blood
25 hydroxy vitamin D
25-hydroxyvitamin D (25OHD)
Calcifediol
Circulating concentration of 25OHD is the accepted biomarker for vitamin D status
Many experts recommend a level between 20 and 40 ng/mL (50 to 100 nmol/L)
Others recommend a level between 30 and 50 ng/mL (75 to 125 nmol/L)
Some say higher
Serum concentrations, units
Nanograms per milliliter (ng/mL)
(1000 ng = 1 microgram)
Nanomoles per liter (nmol/L)
1 ng/mL is equal to 2.5 nmol/L
Supplements
Micrograms
International units
400 IU = 10 mcg
1,000 IU = 25 mcg
2,000 IU = 50 mcg
4,000 IU = 100 mcg
How much to take in Winter?
Do not take more than 100 micrograms (4,000 IU) of vitamin D a day (11 years to adults)
Children aged 1 to 10 years should not have more than 50 micrograms (2,000 IU) a day.
Infants under 12 months should not have more than 25 micrograms (1,000 IU) a day.
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