## 1 Introduction
### Sources of Silicon of Mineral Origin Used in Functional Foods and Food Supplements
#### 1.2.3 EFSA Opinion on MMST as a Novel Food Ingredient Used in Supplements  
According to Directive 2002/46/EC [43; 47], MMST is one of the sources of Si that can be used in dietary supplement production in the form of an aqueous solution at a concentration of 4.1 mM. A daily recommended intake of MMST in the amount of 60-90 mL corresponds to a Si content of approximately 7-10 mg. The receiving of MMST has two stages. In the first stage, potassium methylsiliconate is synthesized under highly alkaline conditions. After that, the obtained material is diluted, and the pH is adjusted to the value of 6.6 [40]. The solubility of MMST in water is up to 21 mM (about 588 mg silicon/L) at 21 \({}^{\circ}\)C and does not irreversibly polymerize after 2 months. Studies by [PERSON] et al. (1998) [50] and [PERSON] et al. (2014) [51], conducted in humans with the use of silicon, showed that most of the silicon is excreted. With regard to MMST, it is known that when this compound is ingested, most Si is rapidly excreted in the urine, but a small proportion of Si is stored for a longer period, and then bioconversion of MMST to orthosilicic acid occurs. These and other studies [52; 53; 54; 55; 56] would support the metabolism of MMST to OSA. In [PERSON] et al. 's study (2013) [57], total silicon was measured twice in fasting serum and urine samples at baseline and after 4 weeks of supplementation with MMST. The results showed an increase in total silicon. Urinary MMST accounted for about 10.3% of the increase in the total silicon excreted, consistent with the conversion of MMST to OSA in the body. In addition, this study concluded that there were no significant changes in any of the biochemical measurements taken or changes in well-being after 4 weeks of the maximum daily dosage of MMST (i.e., consumption of 10.5 mg Si per day). [PERSON] et al. (2009) [43] conducted a study comparing the absorption of silicon from eight sources with high silicon levels: bananas, alcohol-free beer, green beans, MMST, ch-OSA, supplemental CS, and magnesium trisilicate (MTBT) compared with OSA (positive control). Urinary excretion of silicon was the highest for MMST (64%), followed by OSA (43%), ch-OSA (17%), MTBP (4%), and CS (1%). Taking into account the available information in the literature studies and the results cited above, the EFSA concluded that MMST is unlikely to raise any safety concerns as a novel food ingredient for the proposed single-use and that OSA is released from MMST and is likely to have comparable or higher bioavailability from MMST than from other sources [40]. 2.4 EFSA Opinion on the Safety and Bioavailability of Silicon from ch-OSA That Is Added for Nutritional Purposes in Food Supplements  
Ch-OSA consists of orthosilicic acid (OSA) and choline chloride (CAS) and occurs in both liquid and pellet form with the silicon content (mainly as OSA) of 1.7-2.39% (_w/v_) and 0.6-1.0% (_w/v_), respectively [35; 39]. [PERSON] (2000) [58] showed that incubated solutions of ch-OSA dissolved in water contain Si primarily in the form of OSA. During the manufacturing process of ch-OSA liquid, choline chloride is subjected to a chemical reaction with dry hydrochloric acid and silicontetrachloride, and, after that, water is added. Sodium hydroxide is then added to the ch-OSA solution for neutralization, followed by the concentration of the entire solution by distillation under vacuum. At the end, glycerol is added. Ch-OSA pellets are formed by adding microcrystalline cellulose to the concentrated solution. After adding water, the mass is extruded, and the resulting pellets are dried. The absorption of Si from ch-OSA was investigated in human studies using a crossover method. Each fasting subject received ch-OSA, herbal silica, CS, or mineral water as a placebo. For ch-OSA, a significant increase in serum silicon concentration was observed, which was achieved earlier compared to the placebo. After ch-OSA supplementation, urinary silicon excretion was also significantly higher than the placebo [59].