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.
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:
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.
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).
Different organizations recommend varying doses of vitamin D. For example, in cases where vitamin D formation through sunlight is deficient, the DGE currently recommends a dose of 400 IU for infants up to 1 year of age and 800 IU for children, adolescents, adults, seniors, and pregnant and nursing women.
According to vitamin D experts this recommendation is too low and only represents the minimum daily intake required to stave off rickets.
Recent studies clearly demonstrate that vitamin D3 and vitamin K2 are essential to good health. Deficiencies in both these vitamins are extremely common, which is why more and more people are taking vitamins D3 and K2 as a daily dietary supplement.
It's very important to know that if you take vitamin D3 regularly over a long period, you definitely need to take vitamin K2 as well. This raises the question of how these two key vitamins should best be combined in order to promote health and vitality.
Vitamin D ensures healthy bones and is involved in a variety of metabolic processes in the human body. In contrast to all other vitamins, the need can't be met through nutrition alone; and a lack of the vitamin can cause serious illnesses. An adequate supply of vitamin D is therefore important.