Study reveals 'significant deviations' in the content of vit K2 and D3 supplements
There is an increasing interest in supplementing the diet with various vitamins, especially vitamin D which is widely recommended to be taken during the winter months.
The recent study was conducted by researchers at the Jagiellonian University Medical College, in Poland, to develop optimal conditions for the qualitative and quantitative determination of vitamins D2, D3 and K2 in dietary supplements available in various forms, using thin-layer chromatography with densitometric detection.
As a result, the methodology for analysing the content of three vitamins from various matrices was developed, optimised and validated in accordance with ICH requirements. The obtained results allowed the team to conclude that their methodology was reliable and met the requirements for analytical procedures used in the analysis of medicinal products.
They also found that based on the results obtained, there were significant deviations in the content of vitamin K2 and D3 in the tested supplements to that stated on pack.
"Given the vast amount of dietary supplements available around the world, quality control measures appear to be insufficient and label claims may mislead consumers," say the authors.
"For this reason, one of the objectives of our work was to check whether products containing vitamins D and K meet the quality requirements. Then, we assessed their quality in accordance with the procedure used for drugs. For this purpose, a new analytical procedure was developed that allows the simultaneous qualitative and quantitative determination of the content of vitamins D2, D3 and K2 side by side.
"The carried-out analysis suggests that quality control measures were not sufficient for the majority of advertised dietary supplements containing vitamins D and K.
"For the majority of tested products, the claims made on the labels may be misleading to consumers, and the hypothetical performance of the purchased product will be significantly limited if it does not contain the ingredient (or contains too little of it) we expect.
"In this aspect, it can be concluded that there is a need for further and more extensive research that will allow to assess the real quality of available dietary supplements.
"New analytical procedures developed for this purpose will create new opportunities for comprehensive quality control analysis of these products. Especially if they present quick, simple and relatively cheap solutions and take into account the aspect of ‘green chemistry’, i.e., focusing on the design of processes that takes into account the reduction of analysis time and minimizes the use and generation of hazardous reagents."
The main objective of the study was to determine the content of vitamins D3 and K2 (MK-4 form) in dietary supplements available on the Polish market. It was decided to (i) optimize the conditions for the separation of vitamins D3, D2 and K2 using the TLC technique with densitometric detection, (ii) develop a method of extracting vitamins from various forms of dietary supplements, (iii) validate the developed methodology, and (iv) use the developed procedure for qualitative and quantitative analysis of vitamins D and K2 in dietary supplements. For the analysis of supplements, a procedure analogous to that used in the analysis of drugs was used.
All preparations and supplements from various manufacturers were purchased in local pharmacies. The analysed 25 dietary supplements containing vitamin D3 and/or K2 were in various forms, such as tablets, power, capsules, drops, with declared contents of 5–500 µg per 1 tablet, 1 dose, 1 capsule or 1 mL. The complements were coded with letters from A to Z, for reasons of confidentiality.
Analysis of the samples found "huge variations" in the content of the vitamins. The smallest determined amount was about 62% of the content declared by the manufacturer, while in other supplements, the content of vitamin D3 ranged from 71 to 101% (average 92%).
After applying many different modifications of the analysis conditions for vitamins D2, D3 and K2 next to each other, the most optimal separation was observed using TLC Silicagel 60F254 plates activated with a solution of 10% (v/v) paraffin in cyclohexane, then dried for 10 min at 60 °C, developed in a mixture of methanol-water (19:1, v/v) as the mobile phase, over a distance of 12 cm. These conditions allowed to obtain retardation factor (RF) values for individual vitamins.
The next stage of the work consisted of checking the stability of solutions containing vitamin D and K2 under the influence of solar radiation and temperature. For this purpose, methanolic solutions were left for 48 h in a sunny place. Similarly prepared solutions were subjected to an elevated temperature (in tightly closed dark glass vials), heating them for 24 h at 60 °C and for 2 h at 90 °C.
After the specified time, the samples were applied and analyzed under the conditions described above. At the same time, a test was carried out with samples of identical composition but left in a shaded place and stored at room temperature for the same period of time, as controls.
"Quality Control of the Dietary Supplements Containing Selected Fat-Soluble Vitamins D and K"
Authors: Starek. M., et al