Types of Silica Explained: What Absorption Studies Measured

No form of silica has been shown in a trial to do more for your health than another. The studies that compare forms measured how much silicon reached urine or blood after a dose, in 3 to 32 healthy adults; none measured hair, skin, nails or bone.¹ Silicon has no authorised health claim in Great Britain in any form: all 23 silicon wordings on the register are non-authorised, and "Only authorised claims in the Great Britain NHC register may be used in Great Britain".² The silica in this article is dietary silicon: the silicon in food, water and supplements, which is swallowed, dissolved and passed out in urine. It is not crystalline silica dust, which causes silicosis when breathed in at work and which the HSE and the food regulators assess separately, and it is not the silica gel in desiccant sachets, which is not poisonous if swallowed but whose packet can choke a small child (call NHS 111, or 999 if someone is choking).^{3, 4, 5} Part of the Wellgard silica guide and the vitamins and minerals guide.

What forms of silica are sold, and what is each one chemically?

Silicon never occurs on its own. In rock, sand and plants it is silicon dioxide (silica) or silicates; in water, silicates release orthosilicic acid, the dissolved form the gut takes up.⁵

• Orthosilicic acid solutions: silicon dissolved in water, as in mineral waters.
• Choline-stabilised orthosilicic acid: a concentrate in which choline keeps the acid from clustering; a listed silicon source in GB supplement law.⁶
• Monomethylsilanetriol, sold as "organic silicon": a small carbon-bearing silicon molecule, also listed.⁶
• Colloidal silica, silicon dioxide and magnesium trisilicate: silica particles in suspension or tablets, and an antacid silicate; silicon dioxide and silicic acid are listed sources.⁶
• Plant extracts: bamboo and horsetail, labelled by plant weight; botanicals, not listed mineral sources.⁶

Horsetail is a herb sold as a silicon source; it is a traditional herbal medicine in its own right, with its own cautions, and is not covered here. Homeopathic "silicea" and tissue-salt products are highly diluted preparations sold as remedies; they are not a dietary source of silicon and this article is not about them.

How does the body take silicon in?

As dissolved orthosilicic acid, whatever the source. In eight volunteers given orthosilicic acid in water, a median 50.3% of the dose appeared in urine.⁷ In five volunteers given 34 mg of silicon as single-molecule (monomeric) or clustered (oligomeric) silica, 53% of the monomeric dose was excreted in urine while the oligomeric form "was not detectably absorbed or excreted".⁸ Urinary silicon is the proxy every study below uses: it says how much silicon passed through the blood, not what it did there.

What did the head-to-head absorption study measure?

One study has compared sources in the same people: 32 fasted healthy adults aged 19 to 40, in sub-studies of 5 to 14 (3 for colloidal silica), two sources a week apart at the makers' maximum doses, absorption read from six-hour urine.¹

The authors' summary: "Monomeric silicates were readily absorbed, while particulate silicates were decreasingly well absorbed with increasing polymerisation."¹ A dissolution test came first: the choline-stabilised liquid, the antacid and colloidal silica dissolved enough to be taken forward, while horsetail capsules dissolved less and a "silica complex" tablet "did not dissolve"; neither of those two was given to people, so no human figure exists for either.¹ Limits: one laboratory, 3 to 14 people per source, single fasted doses that differed a hundredfold, a six-hour window that favours fast-dissolving forms, and no health outcome.

What else has been measured for each form?

• Choline-stabilised orthosilicic acid. 10 mg of silicon a day raised serum silicon against placebo in 50 women over 20 weeks and urinary silicon in 48 women over nine months; 3, 6 or 12 mg a day for 12 months in 136 women taking calcium and vitamin D3 produced no related adverse events.^{9, 10, 11} The three trials share authors and none has been repeated.
• Monomethylsilanetriol. In a four-week crossover of 22 women, 10.5 mg of silicon a day raised fasting serum and urinary silicon with no reported adverse effects; a published letter disputed the safety conclusion and the authors replied.^{12, 13}
• Orthosilicic acid stabilised with vanillin. After single doses in volunteers, EFSA judged the silicon "bioavailable" and "similar to values reported in the literature for other established sources of OSA".¹⁴
• Orthosilicic acid in three presentations, a liquid with horsetail and rosemary, one with aloe and a maltodextrin powder, each at 21.6 mg of silicon, gave 32%, 35% and 27% in six-hour urine in five men, with no significant difference.¹⁵

What has not been measured?

Facts about the literature, not verdicts on a form.

• No study has measured silicon absorption from bamboo extract in people, so no figure can be given for it in either direction.
• No trial of any form has measured hair growth or shedding, facial skin, fracture, or anything in men.
• No two forms have been compared for a health outcome; the comparisons stop at urine.

Is a liquid absorbed differently from a capsule?

The head-to-head study compared chemical forms, not formats: every source given to people was a liquid, a suspension or a food; capsules and tablets were screened only for dissolution.¹ The one study to compare presentations found no significant difference between a powder and two liquids at the same orthosilicic acid dose.¹⁵ What the studies track is how readily the silicon dissolves and how many milligrams the label states.

How do you read a silica label?

"Silica", "silicon", "extract" and "herb equivalent" are four different numbers: 500 mg of bamboo extract is not 500 mg of silicon, and "7,500 mg herb equivalent" describes the plant, not the silicon in the capsule; if no silicon figure is given, ask the maker for it. No UK advisory body has set a reference intake for silicon, so no label can show "% NRV" for it.⁵ The stabiliser or mineral salts on a liquid label are permitted sources under the same law; is it safe to take silica every day has the detail.

Does the form change what the trials found?

The three outcome trials used one form, choline-stabilised orthosilicic acid, at 10 mg of silicon a day (3 to 12 mg in the bone trial), and measured forearm skin roughness, hair-fibre strength and a bone-collagen marker.^{9, 10, 11} No trial has looked at any other form on those measures. Absorption is not a health outcome, and the register lists the hair, skin, nail, bone and joint wordings as non-authorised whatever the form.² The silicon in foods and drinks is on foods high in silica.

Frequently asked questions

What is orthosilicic acid used for?

It is the dissolved form of silicon, the one the gut takes up, sold as a solution or stabilised with choline or vanillin, and the form the three outcome trials used.^{5, 9} "Monosilicic acid" is another name for it.

Is orthosilicic acid the same as silicon dioxide?

No. Silicon dioxide is solid silica, the particle form in colloidal silica, tablets and the food additive E 551; orthosilicic acid is what silica becomes when it dissolves in water.⁵

Is there a best silica for hair or bones?

One form has a hair or bone trial, choline-stabilised orthosilicic acid: in 48 women hair-fibre break load changed by -2.2% against -10.8% on placebo, and in 136 women a bone-collagen marker rose at 6 and 12 mg a day while lumbar spine density did not change significantly.^{10, 11} No other form has been tested for either; the register refused the hair, nail and bone wordings for every form.² Hair shedding and bone density are questions for a GP.

Is bamboo silica absorbed?

It has not been measured: no human study of bamboo extract exists. Silicon from solid plant foods is absorbed once it dissolves (a mean 41% of ingested silicon from foods in 3 to 8 volunteers; 44% from green beans), but whether a given bamboo extract dissolves the same way has not been tested.^{1, 16}

Sources

1. Sripanyakorn S, et al. The comparative absorption of silicon from different foods and food supplements. British Journal of Nutrition, 2009. PubMed 19356271.
2. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. gov.uk.
3. Health and Safety Executive. Silicosis. hse.gov.uk.
4. Lavon O, Bentur Y. Silica gel: non-toxic ingestion with epidemiologic and economic implications. Israel Medical Association Journal, 2015. PubMed 26665312.
5. Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals, 2003. UK Government Web Archive.
6. Directive 2002/46/EC on food supplements, Annex II, as retained in Great Britain. legislation.gov.uk.
7. Reffitt DM, et al. Silicic acid: its gastrointestinal uptake and urinary excretion in man and effects on aluminium excretion. Journal of Inorganic Biochemistry, 1999. PubMed 10612067.
8. Jugdaohsingh R, et al. Oligomeric but not monomeric silica prevents aluminum absorption in humans. American Journal of Clinical Nutrition, 2000. PubMed 10731501.
9. Barel A, et al. Effect of oral intake of choline-stabilized orthosilicic acid on skin, nails and hair in women with photodamaged skin. Archives of Dermatological Research, 2005. PubMed 16205932.
10. Wickett RR, et al. Effect of oral intake of choline-stabilized orthosilicic acid on hair tensile strength and morphology in women with fine hair. Archives of Dermatological Research, 2007. PubMed 17960402.
11. Spector TD, et al. Choline-stabilized orthosilicic acid supplementation stimulates markers of bone formation in osteopenic females. BMC Musculoskeletal Disorders, 2008. PubMed 18547426.
12. Jugdaohsingh R, et al. The silicon supplement 'Monomethylsilanetriol' is safe and increases the body pool of silicon in healthy pre-menopausal women. Nutrition & Metabolism, 2013. PubMed 23622499.
13. Vanden Berghe DA. There are not enough data to conclude that monomethylsilanetriol is safe. Nutrition & Metabolism, 2013. PubMed 24499245.
14. EFSA ANS Panel. Safety of orthosilicic acid-vanillin complex (OSA-VC) as a novel food ingredient and bioavailability of silicon. EFSA Journal, 2018. PubMed 32625656.
15. Boqué N, et al. Relative absorption of silicon from different formulations of dietary supplements. Scientific Reports, 2021. PubMed 34389753.
16. Jugdaohsingh R, et al. Dietary silicon intake and absorption. American Journal of Clinical Nutrition, 2002. PubMed 11976163.

General information, not medical advice; see a GP about symptoms.