How to determine the Vitamin D3 level

You can measure your vitamin D levels by using a blood test to determine if you have enough vitamin D in your body. In fact, not the active form of vitamin D is measured, but the concentration of 25(OH)D (25-hydroxyvitamin D) in the blood.

The 25 (OH)D value is a precursor of vitamin D, in which form is is transported in the blood. If necessary, this form is converted into the active form of vitamin D (calcitriol).

The 25 (OH)D value shows how much vitamin D you got through nutrition or produced during sun exposure. But this value does not tell you anything about your vitamin D levels throughout the year, which will vary depending on the sun exposure and vitamin D uptake from food.

The half-life of 25(OH) Vitamin D is 2 month. This means, that the vitamin D level will fall to half of its value, provided that you no longer get any vitamin D at all.

What does the 25(OH)D value mean?

Nobody can say what the optimal 25(OH)D value is. Therefore, the suggestions vary by author. After viewing many different suggestions, we came to the following conclusion:

  • under 20 ng/ml - Vitamin D deficiency - there is an increased risk for rickets, osteoporosis, calcium deficiency, and other vitamin D deficiency symptoms
  • from 21 to 40 ng/ml - insufficient Vitamin D supply - may eventually lead to deficiency symptoms
  • from 41 to 60 ng/ml - sufficient to optimal Vitamin D supply - ideal to maintain good health
  • from 61 to 80 ng/ml - normal to high Vitamin D supply - this value is still within the normal range
  • from 81 to 100 ng/ml - slightly increased value - does not necessarily represent a health risk. These values can normally only be achieved by taking vitamin D supplements
  • from 101 to 150 ng/ml - Vitamin D over supply - these values are not yet classified as harmful
  • over 151 ng/ml - Vitamin D intoxication - the oral intake of Vitamin D and sun exposure should be discontinued
  • over 280 ng/ml - will lead to a disturbance of the calcium metabolism
  • People in southern countries who get a lot of sun exposure, have often a value of 100 ng/ml or more, but do not show any signs of overdosage. Dark-skinned people usually need a 5 to 10 times longer sun exposure than people with light skin, to produce the same amount of vitamin D in the skin.

    Vitamin D production can vary significantly

    The ability of each person to produce vitamin D through sun exposure or to increase the vitamin D level by taking vitamin d supplements, can vary significantly and depends on age, body weight, skin colour, sun exposure, and life style.

    It is not said, that each person can reach the same vitamin D level by taking the same amount of vitamin D or having the same sun exposure. Some people may need more or less vitamin D per day to achieve the same level.

    Therefore, the recommended rules for calculating the optimal vitamin D dosage are only indicative. To know your personal vitamin D level, a 25(OH)D blood test has to be performed. It shows you exactly how your vitamin D level is changing depending on the vitamin D intake and sun exposure.

    What is the difference of the 25(OH)D value shown in ng/ml or nmol/l?

    In Europe the 25(OH)D value is usually measured in ng/ml. But any laboratories also use nmol/l.

    - To calculate a test result from nmol/l to ng/ml, divide the nmol/l value by 2,5. For example, 50 nmol/l are equal to 20 ng/ml (50 ÷ 2,5).

    - To calculate a test result from ng/ml to nmol/l, multiply the ng/ml value with 2,5. For example, 20 ng/ml are equal to 50 nmol/l (20 x 2,5).

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