Silicon

What it is

Silicon is a non-metal element that reaches the body from food and drink almost entirely as dissolved silicic acid. In blood it circulates as silicic acid and is not bound to proteins, and most of the silicon in the body sits in connective tissues including the aorta, trachea, bone, tendons and skin. Adult diets in the United States supply roughly 14 to 40 mg a day, mostly from beverages, grains and vegetables. Supplements use orthosilicic acid stabilised in various ways, or silica, and silica is also widely used as an anti-caking excipient in tablets and capsules.

What the research says

The human evidence is limited and mostly indirect. Animal deprivation work links silicon to bone and collagen formation, and a large cross-sectional study found higher dietary silicon went with higher hip bone density in men and premenopausal women, but not in postmenopausal women; that paper's statements about the lumbar spine contradict each other and should not be relied on either way. The one substantial randomised trial, funded by a supplement manufacturer, raised a marker of collagen formation but found no significant change in lumbar spine bone density over 12 months. No functional role for silicon in humans has been identified, so no requirement has been set, and no upper limit could be set either because there were not enough data on adverse effects.

Evidence grade: Limited evidence.

What goes wrong

A woman developed recurrent kidney stones made entirely of silicate while taking over-the-counter supplements whose excipient was silica; the stones stopped when she stopped the products and returned when she restarted them. (Source 1)

• Case report, Certainty not rated.
• Size: 1 patient.
• Who: adult woman taking three over-the-counter supplements.
• How long: not stated; recurrence on rechallenge.
• Result: Stone analysis 100% silicate.
• Funding: not stated.

The nephrolithiasis promptly abated after discontinuation of the products containing silica, then returned when the patient restarted her supplements.

The Institute of Medicine recorded that magnesium trisilicate antacids taken in large amounts for years have been associated with silicon-containing urinary stones, with fewer than 30 reported cases since the 1930s. (Source 2)

• Official position, Low certainty.
• Size: fewer than 30 reported cases of urolithiasis.
• Who: long-term users of silicate-containing antacids.
• How long: several years of use.
• Result: No incidence rate given; fewer than 30 cases found in the literature.
• Funding: independent (US Institute of Medicine)

Limited reports indicate that magnesium trisilicate (6.5 mg of elemental silicon per tablet) when used as an antacid in large amounts for long periods (i.e., several years) may be associated with the development of urolithiasis due to the formation, in vivo, of silicon-containing stones (Haddad and Kouyoumdjian, 1986).

What the evidence supports

A cross-sectional study of the Framingham Offspring cohort found dietary silicon intake associated with higher hip bone mineral density in men and premenopausal women; being cross-sectional it cannot show that silicon caused the difference. (Source 3)

• Survey study, Low certainty.
• Size: 2,847 participants (1,251 men and 1,596 women)
• Who: men and pre- and postmenopausal women aged 30-87 years.
• How long: single cross-sectional assessment.
• Result: Positive correlation with adjusted BMD at four hip sites in men and premenopausal women; differences in BMD up to 10% between highest (> 40 mg Si/day) and lowest (< 14 mg Si/day) intake quintiles.
• Funding: independent (US government research support)

Silicon intake correlated positively with adjusted BMD at four hip sites in men and premenopausal women, but not in postmenopausal women.

A 12-month randomised placebo-controlled trial of choline-stabilised orthosilicic acid added to calcium and vitamin D found that of the bone markers measured only the type I collagen formation marker PINP was significantly higher at 12 months, at the 6 and 12 mg silicon doses, and with no clear dose-response. (Source 4)

• Randomized trial, Low certainty.
• Size: 136 of 184 randomised women completed.
• Who: women with lumbar spine T-score below -1.5.
• How long: 12 months.
• Result: PINP significantly higher at 12 months for 6 and 12 mg Si/day versus placebo (p < 0.05, MANCOVA), without a clear dose-response; a trend for a dose-corresponding increase in the resorption marker CTX-I.
• Funding: industry-funded (grant from Bio Minerals n.v., the developer of ch-OSA, plus a small grant from the National Osteoporosis Society UK)

Overall, there was a trend for ch-OSA to confer some additional benefit to Ca and Vit D3 treatment, especially for markers of bone formation, but only the marker for type I collagen formation (PINP) was significant at 12 months for the 6 and 12 mg Si dose (vs. placebo) without a clear dose response effect.

The 12-month randomised trial of choline-stabilised orthosilicic acid reported no supplement-related adverse events and safety bloods within the normal range. (Source 4)

• Randomized trial, Low certainty.
• Size: 136 of 184 randomised women completed.
• Who: osteopenic women.
• How long: 12 months.
• Result: No ch-OSA related adverse events; biochemical safety parameters within normal range at 3, 6 and 12 mg Si/day.
• Funding: industry-funded (Bio Minerals n.v.)

There were no ch-OSA related adverse events observed and biochemical safety parameters remained within the normal range.

Silicon in beer is absorbed about as well as a solution of orthosilicic acid, with roughly 55 per cent absorption in healthy volunteers. (Source 5)

• Blood level study, Low certainty.
• Size: 9 healthy volunteers for the absorption study; 76 beers analysed.
• Who: healthy adult volunteers.
• How long: 6 hours of serum and urine sampling after a single 0.6 litre drink.
• Result: Mean beer silicon 19.2 (sd 6.6) mg/l; ultrafilterability about 80%; absorption about 55%.
• Funding: not stated.

The ultrafilterability of Si from beer (about 80 %) and its absorption in volunteers (about 55 %) was comparable with that of a solution of OSA suggesting that Si in beer is present chiefly in a monomeric form and is readily bioavailable.

Feeding amorphous silica by mouth to rats and mice for about two years produced no evidence of tumour induction. (Source 2)

• Animal study, Low certainty.
• Size: not stated.
• Who: rats and mice.
• How long: approximately 2 years.
• Result: No evidence that orally administered silica induced tumours.
• Funding: independent (reported in the Institute of Medicine review)

There was no evidence that orally administered silica induced tumors.

What the evidence does not support

In the same cross-sectional cohort silicon intake was not associated with bone density in postmenopausal women at any site, and the correlation analysis found no significant association at the lumbar spine in any group - although the paper also reports a significant lumbar spine association in men. (Source 3)

• Survey study, Low certainty.
• Size: 2,847 participants.
• Who: men and pre- and postmenopausal women aged 30-87 years.
• How long: single cross-sectional assessment.
• Result: No significant association at the lumbar spine in any group in the correlation analysis, and no association in postmenopausal women; the categorical analysis additionally reported a significant lumbar spine association in men.
• Funding: independent (US government research support)

Limit of this finding: The paper contradicts itself about the lumbar spine. Its results section says no significant association was observed at the lumbar spine in any group, and four sentences later says a significant association at the lumbar spine in men was also observed. The two statements come from different analyses - the first from correlations with silicon intake as a continuous measure, the second from comparing intake categories - but the abstract does not reconcile them. A reader should not take either the null or the positive lumbar spine result as settled.

Silicon intake correlated positively with adjusted BMD at four hip sites in men and premenopausal women, but not in postmenopausal women. No significant association was observed at the lumbar spine in any group. Categorical analysis by Si intake, or energy-adjusted Si intake, supported these findings, and showed large differences in BMD (up to 10%) between the highest (> 40 mg Si/day) and lowest (< 14 mg Si/day) quintiles of silicon intake. A significant association at the lumbar spine in men was also observed.

In that same trial lumbar spine bone mineral density did not change significantly, and the femoral neck result came only from a post-hoc subgroup analysis. (Source 4)

• Randomized trial, Low certainty.
• Size: 136 of 184 randomised women completed.
• Who: osteopenic women.
• How long: 12 months.
• Result: Lumbar spine BMD unchanged; femoral neck significance only in a post-hoc subgroup with baseline femur T-score < -1 at the 6 mg dose.
• Funding: industry-funded (Bio Minerals n.v.)

Lumbar spine BMD did not change significantly. Post-hoc subgroup analysis (baseline T-score femur < -1) however was significant for the 6 mg dose at the femoral neck (T-test).

What official bodies say

The Institute of Medicine could not set a Tolerable Upper Intake Level for silicon because there were not enough data on adverse effects, and set no reference intake because no human function is known. (Source 6)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: all life stages.
• How long: not applicable.
• Result: No EAR, RDA, AI or UL for silicon.
• Funding: independent (US Institute of Medicine)

Due to lack of data indicating adverse effects of silicon, it is not possible to establish a UL.

Where the research disagrees

Whether dietary or supplemental silicon benefits bone in humans

• Jugdaohsingh and colleagues (Framingham Offspring cohort, JBMR 2004), cross-sectional analysis of 2,847 participants; the authors state confirmation in a longitudinal study is being sought: These findings suggest that higher dietary silicon intake in men and younger women may have salutary effects on skeletal health, especially cortical bone health, that has not been previously recognized. (Source 3)
• Institute of Medicine (2001), expert review of animal deprivation studies and limited human data; no reference intake set: A functional role for silicon in humans has not yet been identified. (Source 7)

How much

• Reference intake: No Estimated Average Requirement, Recommended Dietary Allowance or Adequate Intake has been set for silicon (Institute of Medicine, 2001), because no biological role in humans has been identified. Mean adult intakes in the FDA Total Diet Study were 40 mg/day in men and 19 mg/day in women. (Source 8)
• Upper limit: Institute of Medicine, 2001: no Tolerable Upper Intake Level could be established for silicon, because there were no adequate data demonstrating a no-observed-adverse-effect level and too little evidence of adverse effects. (Source 6)
• Studied: Choline-stabilised orthosilicic acid providing 3, 6 or 12 mg silicon per day, on top of 1000 mg calcium and 20 mcg cholecalciferol, for 12 months in osteopenic women. (Source 9)
• Studied: A single 0.6 litre serving of beer supplying 22.5 mg silicon in a bioavailability study in nine healthy volunteers. (Source 5)
• Studied: The Institute of Medicine reported a median supplemental silicon intake by US adults of about 2 mg/day. (Source 10)

A common belief, and what the research shows

The belief: Silicon supplements are proven to strengthen bones, hair and nails because silicon is a building block of collagen.

What the research shows: The collagen link rests on animal work: "Silicon contributes to prolylhydrolase activity, which is important for collagen formation (Carlisle, 1984). Chicks fed a silicon-deficient diet exhibited structural abnormalities of the skull and long-bone (Carlisle, 1984)." In people the position is weaker: "A functional role for silicon in humans has not yet been identified." The main randomised trial in women moved a collagen formation marker but not bone density - "Lumbar spine BMD did not change significantly." Silicon is also not the same thing as silicone, and much of the silica in supplement capsules is an excipient rather than a nutrient - one woman's silicate kidney stones were traced to it.

Questions and answers

What is it?

Silicon is a chemical element that reaches the body from food and water as dissolved silicic acid. It travels in blood as silicic acid rather than bound to a protein. Most of the body's silicon is in connective tissues such as the aorta, trachea, bone, tendons and skin. (Source 11)

What does it do in the body?

No function for silicon in the human body has been pinned down. In chickens and rats it appears involved in bone formation, and it supports the enzyme activity needed to make collagen. Those are animal findings; the human role is still unidentified, which is why no requirement has been set. (Source 12)

Is it good or bad for you?

Silicon occurring naturally in food and water has not been shown to cause harm, and the main year-long supplement trial reported no supplement-related adverse events. Benefit is the weaker half: the evidence for bone is an observational association plus a marker change, not a demonstrated effect on bone density. Very large, prolonged silicate intakes are a different matter and have been linked to urinary stones. (Source 2)

How do you get more of it?

Intake comes mainly from drinks and plant foods. Silicon from beer is well absorbed - roughly 55 per cent in volunteers - and serum and urine silicon rose after beer or a solution of orthosilicic acid but not after alcohol or water alone. Trials of supplements used choline-stabilised orthosilicic acid at 3 to 12 mg of silicon a day. (Source 5)

If it is harmful, what reduces it?

Silicon from ordinary food and water is not treated as something to remove. Where silica intake did cause trouble, stopping the source was what worked: in a reported case silicate kidney stones settled after the silica-containing supplements were stopped and came back when they were restarted. About half of ingested silicon is excreted in urine. (Source 1)

Why might someone be low in it or missing it?

There is no defined deficiency, so this is about intake rather than a deficiency state. Intake tracks the diet: plant foods, beer, coffee and water carry most of it, refining strips silicon out of foods, and a high-fibre diet supplied more than twice as much as a low-fibre one in a controlled feeding study. (Source 8)

Which whole foods contain it or feed it?

Plant foods carry more silicon than animal foods. In the FDA Total Diet Study beverages including beer, coffee and water supplied 55 per cent of intake, grains and grain products 14 per cent and vegetables 8 per cent. Refining reduces the silicon content of foods. (Source 13)

What happens if you do not have it?

No human deficiency syndrome has been described. In animals deprivation does cause problems - chicks fed a silicon-deficient diet developed abnormal skull and long-bone structure - but nothing equivalent has been shown in people, and no reference intake exists for that reason. (Source 7)

How can you test for it?

There is no validated test of silicon status. Silicon can be measured in serum and urine in research settings, and the Institute of Medicine listed finding a reliable status indicator as an outstanding research need, so a lab result cannot currently be read as adequate or deficient. (Source 14)

We searched: Searched Europe PMC for silicon status biomarker, serum silicon reference range and orthosilicic acid status, and the Institute of Medicine 2001 silicon chapter; measurement methods exist but no validated status test was found.

References

1. American Journal of Kidney Diseases. Silicate nephrolithiasis after ingestion of supplements containing silica dioxide. 2009. PMID 19100669, DOI 10.1053/j.ajkd.2008.10.042. Read the source
2. Institute of Medicine (US), National Academies Press. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - Chapter 13: Arsenic, Boron, Nickel, Silicon, and Vanadium. 2001. DOI 10.17226/10026. Read the source
3. Journal of Bone and Mineral Research. Dietary silicon intake is positively associated with bone mineral density in men and premenopausal women of the Framingham Offspring cohort. 2004. PMID 14969400, DOI 10.1359/jbmr.0301225. Read the source
4. BMC Musculoskeletal Disorders. Choline-stabilized orthosilicic acid supplementation as an adjunct to Calcium/Vitamin D3 stimulates markers of bone formation in osteopenic females: a randomized, placebo-controlled trial. 2008. PMID 18547426, DOI 10.1186/1471-2474-9-85. Read the source
5. British Journal of Nutrition. The silicon content of beer and its bioavailability in healthy volunteers. 2004. PMID 15005826, DOI 10.1079/bjn20031082. Read the source
6. Institute of Medicine (US), National Academies Press. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - Chapter 13: Arsenic, Boron, Nickel, Silicon, and Vanadium. 2001. DOI 10.17226/10026. Read the source
7. Institute of Medicine (US), National Academies Press. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - Chapter 13: Arsenic, Boron, Nickel, Silicon, and Vanadium. 2001. DOI 10.17226/10026. Read the source
8. Institute of Medicine (US), National Academies Press. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - Chapter 13: Arsenic, Boron, Nickel, Silicon, and Vanadium. 2001. DOI 10.17226/10026. Read the source
9. BMC Musculoskeletal Disorders. Choline-stabilized orthosilicic acid supplementation as an adjunct to Calcium/Vitamin D3 stimulates markers of bone formation in osteopenic females: a randomized, placebo-controlled trial. 2008. PMID 18547426, DOI 10.1186/1471-2474-9-85. Read the source
10. Institute of Medicine (US), National Academies Press. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - Chapter 13: Arsenic, Boron, Nickel, Silicon, and Vanadium. 2001. DOI 10.17226/10026. Read the source
11. Institute of Medicine (US), National Academies Press. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - Chapter 13: Arsenic, Boron, Nickel, Silicon, and Vanadium. 2001. DOI 10.17226/10026. Read the source
12. Institute of Medicine (US), National Academies Press. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - Chapter 13: Arsenic, Boron, Nickel, Silicon, and Vanadium. 2001. DOI 10.17226/10026. Read the source
13. Institute of Medicine (US), National Academies Press. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - Chapter 13: Arsenic, Boron, Nickel, Silicon, and Vanadium. 2001. DOI 10.17226/10026. Read the source
14. Institute of Medicine (US), National Academies Press. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - Chapter 13: Arsenic, Boron, Nickel, Silicon, and Vanadium. 2001. DOI 10.17226/10026. Read the source