TheS_Vitamin-D.png – Vitas Analytical Services

Vitamin D – The sunshine vitamin

Vitamin D is both a nutrient we eat and a hormone our bodies make. It is a fat-soluble vitamin only found in a few foods of marked quantities and it is produced in the skin by sun exposure and has long been known to help the body absorb and retain calcium and phosphorus; both are critical for building bone. Laboratory studies has shown that vitamin D can reduce cancer cell growth, help control infections and reduce inflammation. For most people, the best way to get enough vitamin D is taking a supplement because it is hard to get enough via food intake.

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Christian A. Drevon Consultant

Thomas E. Gundersen

DBS

teg@vitas.no
+47 928 08 973
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Anette Sauve

General Inquiries/Quotes

as@vitas.no
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Vitamin D is one (Figure 1) of the four fat-soluble vitamins; the others are vitamins A, E and K.

Figure 1. The chemical structure of the most common variant of vitamin D, vitamin D3. – Vitas Analytical Services — Figure 1. The chemical structure of the most common variant of vitamin D, vitamin D3.

The daily dosage of vitamin D needed is only 10-20 micrograms. Vitamin D is important for many functions and organs in the body but is particularly prominent for bone tissue.

How do we get vitamin D?

The most important dietary sources of vitamin D is cod liver oil and oily fish like herring, salmon, trout, mackerel, and eel, in addition to some fortified foods such as margarine and milk although these sources provide little vitamin D.

Vitamin D is also formed in the skin by conversion of 7-dehydrocholesterol (derivative of cholesterol) by ultraviolet (UV) light (Figure 2).

Figure 2. The body gets vitamin D from the diet (oily fish, cod liver oil and some fortified foods such as margarines and certain types of milk. In addition, UV radiation will convert 7-dehydrocholesterol to vitamin D in the skin. – Vitas Analytical Services — Figure 2. The body gets vitamin D from the diet (oily fish, cod liver oil and some fortified foods such as margarines and certain types of milk. In addition, UV radiation will convert 7-dehydrocholesterol to vitamin D in the skin.

Conversion of vitamin D in the body is important

Vitamin D both from diet and the skin is transported in the blood to the liver where it is converted to 25-hydroxyvitamin D = 25OHvitD, and then in the kidneys to 1,25-dihydroxyvitamin D (1,25(OH)₂vitD), which exerts its effects on most tissues of the body.

1,25(OH)₂vitD is a very potent hormone contributing to the normal concentration of calcium and phosphate in blood. Due to the extremely low blood concentrations of 1,25(OH)₂vitD, this is not possible to measure with available methods.

Vitamin D deficiency can lead to rickets in children, and osteomalacia (soft bone/ osteoporosis) in adults. In addition, 1.25(OH)₂vitD has important effects on secretion of insulin in the pancreas, many functions of the immune system, cell division, fetal development, muscle strength, and several functions of the central nervous system.

What is measured in the blood?

After many years of research, it has been concluded that the best and most practical measure of vitamin D status in the body is the level of 25OHvitD in the blood. This is the substance Vitas is measuring in plasma, serum and on DBS. Because the level of 25OHvitD in the blood is rather low (about 20 nanogram/mL), a very sensitive and advanced method (liquid chromatography combined with mass spectrometry; HPLC-MS/ MS) is used to measure the level.

What effects does vitamin D have on the body?

The most potent vitamin D hormone, 1,25(OH)₂vitD, regulates the transcription (reading) of many genes primarily affecting the metabolism of calcium and phosphate in the intestine and bone tissue. Vitamin D is also important for the metabolism in muscle, brain, pancreas, and immune cells, but we do not have enough knowledge to give precise advice on what to eat or how to be exposed to the sun to achieve the best possible health.

Vitamin D requirements

Because there are only a few foods such as oily fish and cod liver oil that contain vitamin D in significant amounts, many people get little vitamin D, and have low blood levels of 25OHvitD. Vitamin D can be stored in adipose tissue, and a large adipose tissue often gives low values of 25OHvitD in the blood. The recommended daily intake is 10-20 ug, but this should be adjusted depending on the measured blood concentrations of 25OHvitD. One strives for a blood level of at least 50 nmol/L (20 ng/mL) with a variation up to 125 nmol/L (50 ng/mL), which often is considered the upper normal range. This means that if you do not reach at least 50 nmol/L with 10-20 ug supplement, you can increase the dose up to 80 ug/day under continuous control of the blood values.

Toxicity

Large doses of vitamin D may be toxic and lead to high levels of calcium in the blood, with a risk of developing kidney stones and precipitation of calcium in kidney tissues (nephrocalcinosis) and renal failure, with large individual differences in sensitivity. People regularly taking large doses of vitamin D (over 40 ug/day) must therefore every third months measure the blood/serum concentration of 25OHvitD. Children are more sensitive than adults to high dosages of vitamin D.

Nevertheless, today scientists are less concerned than before about toxic effect of moderate/large doses of vitamin D under regular control of blood levels.