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Vitamin D supply[1]

Parameter Concentration Vitamin D status Vitamin D supplemantation and treatment regimes
25(OH)D 0-20 Deficiency It is recommended to start supplementation according to the current guidelines.
It is also recommended to repeat the test after 3 months of starting the supplementation. In case of very low vitamin D levels (below 10 ng/ml), it is advised to consult a doctor for the treatment of vitamin D deficiency.
20-30 Suboptimal It is recommended to start supplementation according to the current guidelines.
If supplementation is continued, the dose should be increased by 50% and a repeat vitamin D test should be performed in 6 months. According to general worldwide guidelines, a concentration above 20 ng/ml is considered optimal. However, it should be emphasised that this concentration refers only to the prevention and treatment of rickets. Regarding all other potential benefits of vitamin D supplementation, it is recommended to maintain 25(OH)D concentrations in the optimal range of 30-50 ng/ml.
30-50 Optimal It is recommended to continue the current management.
A concentration within this range is considered optimal by most Endocrine Societies.
50-100 High It is usually recommended to reduce the dose by 50% or even to stop supplementation for a period of 1-2 months.
However, it should be noted that in some cases concentrations above 50 ng/ml may even be advisable. This depends on a person's general wellbeing and health. Nevertheless, it is advisable to consult a doctor to discuss supplementation strategies.
>100 Toxic It is recommended to discontinue supplementation and test the concentration of 25(OH)D at monthly intervals.
It should be emphasized that the toxic effects of vitamin D do not result solely from high levels of 25(OH)D, but also from accompanying hypercalcemia and hypercalciuria. Therefore, a doctor should be contacted for appropriate investigations.
[1] „Vitamin D Supplementation Guidelines for General Population and Groups at Risk of Vitamin D Deficiency in Poland-Recommendations of the Polish Society of Pediatric Endocrinology and Diabetes and the Expert Panel With Participation of National Specialist Consultants and Representatives of Scientific Societies-2018 Update”, Rusińska A, Płudowski P, Walczak M, et al., Front Endocrinol (Lausanne), 2018, 9:246, doi: doi:10.3389/fendo.2018.00246

Vitamin D bioavailability

Parameter Value Clinical interpretation Recommendations
25(OH)D3 : 24,25(OH)2D3 Ratio* < 6,98
Resistance to vitamin D supplementation
Supplementation only under medical supervision.
This condition is the result of increased 24-hydroxylase enzyme activity, which may contribute to resistance to vitamin D supplementation. In situations of low 25(OH)D concentrations, it is suggested to increase the intake, but this should be done under medical supervision.
6,98 - 23,64
Optimal vitamin D supplementation
Supplementation in accordance with current guidelines.
This indicates normal activity of 24-hydroxylase, which is characteristic for most of the population. No action is needed if total 25(OH)D concentration is normal. In the presence of a deficit, supplementation according to current guidelines should be applied.
> 23,64
Lack of or insufficient vitamin D supplementation
Supplementation only under medical supervision.
The condition is most often caused by insufficient 25(OH)D concentrations. It can also be the result of bone disease, renal dysfunction, or calcium homeostasis disorders. It is worth mentioning that there is a small group of people who have a mutation in two genes: CYP24A1 and SLC34A1. The first is associated with impaired or lost 24-hydroxylase function, while the second is characterised by excessive calcitriol synthesis. In both cases, there is an increased risk of hypervitaminosis D. Therefore, supplementation should only be carried out under medical supervision. Individuals with these mutations usually have optimal or high 25(OH)D concentrations.
* The metabolite 24,25(OH)2D3 is formed from 25(OH)D3 by the action of the enzyme 24-hydroxylase. An increase in the concentration of 24,25(OH)2D3 primarily indicates an increased concentration of the active form of vitamin D (calcitriol), but also suggests ongoing bone regeneration processes (e.g., after a fracture).