The Crucial Role of Bioavailable Silica
Silicon (Si) is an important trace element for human health, playing a vital role in the formation and maintenance of connective tissues like skin, hair, nails, and bones. It is particularly crucial for the synthesis of collagen, which provides structure and flexibility to these tissues. However, the human body cannot readily absorb all forms of silica (silicon dioxide, SiO2) found in nature or supplements. The key factor is bioavailability—the proportion of the ingested nutrient that is absorbed and utilized by the body. In the context of silica, bioavailability is dictated by the molecule's chemical form and stability in the digestive tract. Without a highly absorbable form, much of the ingested silica simply passes through the body unused.
Understanding Silica Bioavailability: Monomers vs. Polymers
The fundamental difference between highly and poorly absorbed silica lies in its molecular structure, specifically whether it is a monomer or a polymer. The highly absorbable form is orthosilicic acid (OSA), a simple, water-soluble monomeric molecule. However, OSA is inherently unstable at the higher concentrations found in many supplements. When concentrated, OSA molecules undergo a process called polymerization, linking together to form larger, insoluble chains (polysilicic acids) and eventually a gel. These larger, polymeric structures are poorly absorbed in the gut, drastically reducing the amount of silicon the body can use. The challenge for supplement manufacturers is to stabilize OSA and prevent this polymerization, ensuring the silica remains in its bioavailable monomeric form until absorption.
Monomethylsilanetriol (MMST): The Most Bioavailable Silica
Among the various silica forms, Monomethylsilanetriol (MMST), often marketed as "organic silicon," is consistently recognized as the most bioavailable. A 2009 study comparing eight different silica sources found that MMST had the highest absorption rate at 64%, surpassing even orthosilicic acid in beer and unstabilized OSA solutions.
MMST is a stabilized analog of orthosilicic acid, meaning a single methyl group replaces one of the hydroxyl groups on the silicon atom. This modification significantly improves its stability, allowing it to remain in its highly absorbable monomeric form even at higher concentrations. When ingested, MMST is readily absorbed in the intestinal tract and then appears to be metabolized into orthosilicic acid in the body for biological use. Its superior stability and high solubility make MMST the most effective option for dietary supplementation.
Stabilized Orthosilicic Acid (ch-OSA)
Choline-stabilized orthosilicic acid (ch-OSA) is another form of stabilized silica developed to prevent the polymerization of OSA. In ch-OSA, choline acts as the stabilizing agent, forming hydrogen bonds with OSA to prevent it from aggregating into less absorbable polymers. Clinical studies have shown ch-OSA to be more bioavailable than herbal or colloidal silica, producing a significant increase in serum silicon concentrations after ingestion. However, its absorption rate is lower than MMST, with the 2009 study showing an absorption of around 17%. Still, it is a highly effective and proven form for increasing bioavailable silicon levels.
Ineffective Forms of Silica
Unfortunately, many commercially available silica sources have very low bioavailability, rendering them largely ineffective. This includes some of the more well-known natural options:
- Horsetail Extract: Despite being famously rich in silica (containing up to 25% silica by dry weight), the silica in horsetail is in a poorly absorbed polymeric form. Some sources report its absorption rate is as low as 3%, despite the high total silicon content.
- Colloidal Silica Gel: This form consists of finely dispersed solid particles in a liquid. Studies have shown that colloidal silica is poorly absorbed, with one study reporting an absorption rate of only 1%.
- Diatomaceous Earth: As a food-grade supplement, this contains amorphous silica. While it is technically possible for it to be converted to OSA, the bioavailability is presumed to be low and similar to other poorly absorbed forms.
- Silicon Dioxide (E551): Used as an anti-caking agent in foods, this synthetic amorphous silica is poorly absorbed by the body.
Comparative Bioavailability of Silica Sources
To provide a clear comparison, the following table summarizes the bioavailability data from a key study and general scientific understanding based on chemical form.
| Silica Source | Type / Form | Bioavailability | Key Factor(s) Affecting Absorption |
|---|---|---|---|
| Monomethylsilanetriol (MMST) | Liquid, organic monomer | Very High (~64%) | Methyl group enhances stability, prevents polymerization |
| Orthosilicic Acid (OSA) in Beer | Liquid, natural monomer | High (~55%) | Present as monomeric OSA due to processing |
| Orthosilicic Acid (OSA) in Water | Liquid, natural monomer | High (~43%) | Absorbed in monomeric form before polymerization occurs |
| Green Beans | Food source | Moderate (~44%) | Specific plant matrix allows for decent absorption |
| Choline-Stabilized OSA (ch-OSA) | Liquid or solid, stabilized monomer | Moderate (~17%) | Choline prevents polymerization, but absorption is less efficient than MMST |
| Horsetail Extract | Plant-based supplement | Very Low (~3%) | Silica exists in poorly absorbed polymeric form |
| Diatomaceous Earth | Amorphous silica powder | Very Low (Assumed) | Insoluble, conversion to OSA is poor |
| Colloidal Silica | Solid particles in liquid | Very Low (~1%) | Highly polymerized and poorly absorbed |
Factors Influencing Silica Absorption
Beyond the specific chemical form, other elements can influence how well your body absorbs silica:
- Concentration: As discussed, even naturally bioavailable OSA will polymerize and become poorly absorbed at higher concentrations. This is why stabilized forms like MMST and ch-OSA are superior in supplements designed to deliver a high dose.
- Food Matrix: The food in which silica is delivered plays a significant role. For example, while bananas have a high total silica content, it's in a highly polymerized form, leading to poor absorption. In contrast, the processing of grains in beer results in more bioavailable OSA.
- Stabilizing Agents: The use of stabilizing agents like choline or methyl groups is essential for preventing the polymerization of soluble OSA in supplements, thereby maximizing its bioavailability.
Conclusion: Choosing the Right Silica Supplement
For anyone looking to increase their silica intake for its documented benefits to connective tissue health, the most critical factor is bioavailability. While natural food sources like whole grains and some vegetables contribute, supplementation offers a targeted way to ensure adequate intake of a highly absorbable form. Based on comparative studies, Monomethylsilanetriol (MMST) stands out as the most bioavailable silica. Choline-stabilized orthosilicic acid (ch-OSA) is also a proven, effective option with good absorption rates. In contrast, traditional sources like horsetail and colloidal preparations offer very poor bioavailability despite marketing claims. When selecting a supplement, prioritize liquid or stabilized formulations that have been clinically tested for high absorption rates to get the most benefit for your bones, skin, and hair.
