In order to evaluate the homogeneity of the sample, the three groups were compared at T0. For the dermatological parameters and hair mineral analysis (
Tables S1 and S2), in the majority of the evaluated items, the groups did not present at the beginning of the study any statistically significant differences (although it seems to occur in a first look, without statistical analysis). However, in the evaluation of left pore size, users of MMST and M-OSA differed significantly (
p = 0.029); Significant differences (
p = 0.045) were also observed for the Truskin
® test (left); specifically, the difference was observed between the MMST and M-OSA groups. As groups were not homogeneous at baseline, so this was considered during statistical analysis.
3.2. Skin Multispectral Imaging Evaluation
First, considering the high number of parameters and determinations, non-significative results are expressed in
Table S4. For significant results, one can refer to
Figure 1. A typical imaging from the multispectral evaluation can be found in
Figure 2.
Considering the contrasts in the evaluation of wrinkles, it was observed that there were significant differences between the baseline and the two follow-ups, both in G2 and G3, showing that there was a detectable effect on wrinkles betterment. The effect can be attributable to the use of M-OSA and MMST, as no statistically significant differences were found in the participants in the control group.
As what regards UV spots, significant differences were found in the time factor between averages of UV spots (
Figure 1). Specifically, the contrasts indicated significant differences on the G2 group between T0 and T5 and between T3 and T5. Among the users in group G3, the results showed significant differences between all the times, i.e., both M-OSA and MMST provided improvement on UV spots and on wrinkles.
For the other factors considered, we have found two situations. For skin texture, size of the pores, length of the eyelashes and cutaneous porphyrins, significative differences were found, but these did occur both for the treatments and for the control—again, this can be related to seasonal effects, once the study was conducted over two seasons. For the other parameters (red areas, brown spots, eyelashes volume and TruSkin Age
®), non-significant differences were found in any of the analyses performed (
Table S3).
3.4. Subjective Evaluation
The participants’ perception of changes in the skin, hair and nails was assessed through a self-efficacy questionnaire. To evaluate these aspects, the respondents used a scale with values between 1 and 10, in which 1 is considered that there was no improvement and 10 that there was excellent improvement. The results of these analyzes are presented in
Table 2. In relation to the control group, only the yellowing of the nails showed a statistically significant difference at T3 and T5. For G2, there was a statistically significant difference for skin oiliness, amount of darkened areas in the skin, speed of whitening of the skin, and nail stains. In relation to G3, a statistically significant difference was observed for the number of darkened areas of the face, wrinkles/lines of expression of the lips, wrinkles/forehead expression lines, hair vitality, and yellowing of the nails. It is worth noting that mean comparison tests were performed for all the variables of the self-efficacy questionnaire, and the results can be seen in the
Tables S9–S12.
Scores ranged from 1 to 10 (1—no improvement and 10—excellent improvement). Perception of improvement should be based on the baseline by the volunteers.
M = mean. SD = standard deviation. G1 = control (placebo). G2 = treated with maltodextrin-stabilized ortoshilic acid. G3 = treated with monomethylsilanetriol. T3 = 3 months of study. T5 = 5 months of study.
The difference between the groups regarding the questionnaire of perceived self-efficacy was assessed and the significant results at the end of the study (T5) are presented in
Figure 4 (complete results are presented in
Tables S9–S12). Bonferroni Post Hoc tests indicated that, for the general appearance of the skin, the participants of the MMST group (G3) differed significantly (
p = 0.02) from the control group; the same was true for the variable skin hydration (
p = 0.02). Regarding the homogeneity of the skin, the participants of the M-OSA group (G2) differed significantly from the participants in the control group (
p = 0.05). Concerning the intensity of the color of the darkened areas the participants of the MMST group (G3) differed significantly from the participants in the control group (
p = 0.01). For the variable amount of darkened areas, a significant difference was observed among G1 and G2 (
p = 0.002) and G3 (
p = 0.0002). For the skin imperfections, the participants in G3 differed significantly from the participants in the control group (
p = 0.04). The luminosity skin variable, presented a significant difference between the participants of the G3 and the participants in the control group (
p = 0.03).
Regarding the variables that assessed hair related issues, a significant difference was observed between the participants of G3 and the participants in the control group for the variables: hydration (p = 0.02); nutrition (p = 0.02); softness (p = 0.04); vitality (p = 0.01); luminosity (p = 0.01); and dandruff (p = 0.03). No significant differences were found between the participants in the G2 group and participants in the control group.
3.5. Discussion
Silicon as an element (Si) was discovered in 1823 by the Swiss chemist Jacob Berzelius, who isolated it from potassium fluorosilicate (K
2SiF
6) and named it from the Latin
silex (“quartz”). Although the focus of this work is on its dermatological use, Si is one of the most used elements by humankind, including its use as a semiconductor in electronic components, and as the main component in ceramics, building materials, glass, silicones and other product [
19,
20]. Its importance in human health has been reported from Louis Pasteur, who was aware of the antiseptic, antimicrobial and antifermentative properties of silicates and predicted that silicon would play a significant role in the treatment of various diseases [
21]. However, until a few decades ago the medical emphasis given to Si was directed primarily at the concern about the potential toxicity of its particulate insoluble chemical forms (silicates and crystalline silica), which could cause urolithiasis when ingested orally and especially pneumoconioses (silicosis, asbestosis) caused by inhalation of airborne particles from occupational exposure [
19,
22,
23]. However, more recent experiments and studies employing bioavailable and non-toxic forms of silicon have increasingly contributed to its establishment as a quasi-essential element and/or as a therapeutic adjuvant, emphasizing its structural role in connective tissue and a possible metabolic importance [
3,
19,
24].
Nowadays, silicon-based compounds exist in a high number of commercial products. There is also a current burden of using it for dermatological purposes. Different trademarks and forms to stabilize it are present in the market. In fact, Kalil et al. [
18] affirm that one of the diverse Si supplements in the most prescribed oral product for skin rejuvenation in Brazil. However, there is still little evidence on its effects on skin, hair and nails, and the mechanics on the differences found for the many sources of this mineral.
The main point on using Si is its low bioavailability and fixation in the body, reason why there are so many different silicon supplements, each one using a different mechanism to promote better absorption. In general terms, there appear to be two distinct steps involved in biodistribution of dietary silicon after oral absorption: first, the rapid urinary excretion for most of the ingested silicon [
9,
15,
25]; the other step would consist of tissue storage and/or metabolism for the minor part of the ingested Si, proportional to physiological balance [
25]. In a human study using Si radioactive, Popplewell et al. [
25]. demonstrated that 90% of circulating orthosilicic acid was rapidly excreted without any form of cellular processing. Afterwards, Pruksa et al. [
26] reported that ingestion of a dose of soluble dietary silicon by healthy subjects resulted in the same amount being excreted within 24 h. In relation to MMST, it is kwon that there is a rapid majority urinary excretion, but the storage of minor part of Si occurs for an extended period—and then, there is the bioconversion (metabolism) of MMST to orthosilicic acid (dietary silicon) [
17].
To corroborate the importance of the chemical form of silicon, Sripanyakorn et al. [
16] studied the comparative absorption of silicon, supplemented as MMST and six other sources which contained high silicon content (non-alcoholic beer, bananas, green beans, orthosilicic acid solution, choline stabilized silicon supplement, colloidal silica and trisilicate of magnesium). The study showed that silicon uptake, based on urinary excretion, was higher for MMST (64% of the dose) and for non-alcoholic beer (60% of the dose), followed by green beans (44%), orthosilicic acid (43%), choline stabilized silicon supplement (17%), bananas and magnesium trisilicate (4%) and colloidal silica (1%). Peak plasma concentration occurred in about 30 min for MMST and green beans, 1.5 h for orthosilicic acid and non-alcoholic beer, 2 h for the choline stabilized silicon supplement and colloidal silica and 4 h for magnesium trisilicate. Monomeric silicates were rapidly absorbed, while particulate silicates presented a decrease in absorption with increased polymerization. The authors concluded that MMST silicon was very well absorbed, presenting higher absorption when compared to the other silicon sources studied.
Similarly, the bioavailability of silicon from M-OSA was previously evaluated by Boqué and Arola [
27] and the results showed an approximate oral bioavailability of 30% in terms of elemental silicon. Therefore, the results of this study showed that the absorption of silicon from M-OSA was in percentage terms higher than the values obtained in the study by Spripanyakorn et al. [
16] for OSA stabilized on choline, magnesium trisilicate and colloidal silica (respectively 16%, 4% and 1%).
In our study, we used two different forms of Si: M-OSA and MMST. Specifically, we have used the commercial products SiliciuMax
® Powder and SiliciuMax
® Liquid, respectively, used after quality control tests (assay). M-OSA and MMST did produce an increase in mean hair Si content, but for MMST this did not reach statistical significance. Jugdaohsingh et al. [
17] also studied the metabolism of MMST in a 4-week supplementation study, using the blood and urine as biological matrices. Their data showed that 4 weeks of MMST supplementation significantly increased total serum silicon concentrations with median 272 μg/L versus baseline median of 173 μg/L (
p = 0.0002) or placebo median of 191 μg/L (
p = 0.003). In urine, total silicon concentrations after silicon supplementation for 4 weeks resulted in an average of 17.0 mg/L versus baseline of 8.5 mg/L (
p = 0.008) or placebo median of 7.8 mg/L (
p = 0.007).
We have chosen hair as the biological matrix because of its widespread applications in toxicological, clinical, environmental and forensic investigations [
28]. It also reflects long-term exposition, and not the momentary status of a given element within the body, as occurs with the blood. It has a particular interest in the biomonitoring of heavy metals, as it is a vehicle for excretion of such substances because the metal cations are able to bind to the sulphur present in the keratin of the hair matrix [
29,
30]. In this sense, a related result was found for the use of M-OSA and MMST, as both treatments reduced, after 5 months, the hair levels of aluminum. Magnesium and phosphorus also showed different levels among the three groups, but the effect could not be related to the treatments themselves, only to time. On the contrary, aluminum reduction was actually correlated directly to the consumption of M-OSA and MMST. This effect is in accordance with the literature: epidemiological studies already suggested that silicon can prevent the absorption of aluminum and/or increase its excretion [
31,
32,
33,
34]. Indeed, in nature, silicon readily forms complexes with aluminum and therefore, aluminosilicates are the most prevalent form of silicates [
3]. Reduction of aluminum levels in the body is of sheer importance because of its neurotoxicity, mainly in Alzheimer’s disease pathogenesis, and because we live and in a world in which is virtually impossible not to be exposed to such element [
35,
36]. To the best of the authors’ knowledge, this is the first report of the aluminum detox activity for M-OSA and MMST.
Other important result found in our study was the reduction of facial wrinkles and UV spots—the link between sun exposure and hyperpigmentation is clear from the literature, as what occurs in melasma [
37]. Recent studies with organic Si stabilized by other chemical forms also shows similar results. For example, Kalil et al. [
18] showed that in a small population, the use of OSA stabilized by hydrolyzed collagen (daily dose = 600 mg) provided positive results on firmness, hydration and skin texture. However, these results were found during the clinical evaluation by the dermatologist, not by multispectral imaging evaluation, although they have used the same device as the one used in this study. No changes in wrinkles or UV spots was found, which corroborated the hypothesis that the chemical form of stabilization the Si really affects its effects on human body.
Barel et al. [
6] also evaluated the effects of OSA on skin, nails and hair, but using a molecule stabilized with choline (Si daily dose = 10, during 20 weeks, in 50 women with photodamaged skin). They have assessed the effects of this supplement using a corneometer (to measure skin hydration), a reviscometer (for visco-elastic properties of the skin) and a visiometer (for microrelief/roughness), and also biochemical parameters in serum. They found out an increase in serum Si concentration, and positive effects on skin surface and skin mechanical properties, and on nail fragility, but no mention to wrinkles or UV spots was made.
With concerns to our results, together with the proven effects directly related to Si consumption, skin texture and eyelashes length also changed throughout the study for all groups. These effects can be attributable to the role that Si plays on collagen synthesis (it stimulates type I collagen synthesis), on enzyme activation and cross-linking in connective tissues, and on the increase of elastic fibers density [
7,
9,
21]. The reduction of collagen, proteoglycans and glycosaminoglycans, as well as the degradation of elastic fibers, are key factors on the skin aging, which can be observed as sagging. In addition to that, Si also was shown to provide important connections among hyaluronic acid, proteoglycans and water [
38]. All of these data are strong points that corroborates the findings of our study on the betterment of facial skin parameters. What also corroborates the analytical results is the patients’ self-reported satisfaction with the treatment, in scale of 1–10. Comparison between control x treatments showed a higher number of parameters well evaluated for the ones who used MMST instead of M-OSA. But in a general manner both treatments were able to provide satisfaction in the volunteers in hair, nail and skin parameters.
To our knowledge, this is the first clinical study on both M-OSA and MMST to evaluate the parameters here described, which adds evidence to what is already in literature for these substances. As future perspectives, one envisions a continuity of this work with a higher follow-up period and a greater sample population, as these were two limitations of the study. Histopathological evaluations are also recommended, as well as the use of enhanced tools to allow the visualization of the results on hair and nail quality.