Foods High in Silica: UK Portions, Water and Beer

The foods highest in silica per UK portion are draught beer (a pint of lager about 16 mg of silicon), green, fine and runner beans (5 to 9 mg a serving), dried dates (7.5 mg for three), granola and oat products, bananas (4.8 mg), brown rice and boiled spinach; per 100 g the richest are the less refined cereals, led by oat bran.¹ Food tables measure silica as silicon, not silicone, the man-made polymer; every figure here is from the UK provisional database of 207 foods analysed for the Food Standards Agency.¹ Silicon has no authorised health claim in Great Britain: all 23 silicon wordings in the register, from collagen and bone to hair, nails and skin, are Non-authorised, and there is no nutrient reference value.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 The trials are on the Wellgard silica guide.

Which foods are highest in silica, per UK portion?

Values are as published in the UK database, food as eaten.¹ The last column is the share of the dose recovered in urine over six hours in the absorption studies, measured for that food in 5 to 9 people, or for its food group in three people where marked "group".^{4, 5, 6}

Eighteen of the 207 foods held more than 5 mg per 100 g, eleven of them breads and cereals; per portion, beers filled seven of the top twelve places. Meat, poultry, fish and seafood were not analysed because earlier work found very little silicon in them, the reverse of foods high in zinc.¹ Processing sets the ranking: cereal silicon sits in the husk and the hairs of the grain, so wholemeal bread held 4.8 mg per 100 g against 1.8 mg for white; drying concentrates it in dates and sultanas; brewing extracts it from barley husks; and tap-water treatment removes it, so spring and mineral waters tend to hold more.¹

Which fruits, vegetables and herbs contain silica, and do eggs?

Among fresh fruit the database found the most in bananas (4.8 mg per 100 g), pineapple (3.9 mg) and mango (3.2 mg), with dried dates (16.6 mg) and sultanas (8.9 mg) richer still; apples, pears, grapes and plums carry under 0.5 mg, and oranges were undetectable.¹ The banana has a catch: in the absorption study only about 4% of its silicon was recovered in urine, against 44% from cooked green beans.⁴ Among vegetables the beans lead, then spinach 5.1 mg per 100 g and cucumber 2.5; potatoes, carrots, peppers and broccoli sit under 1 mg, and tomatoes and onions were undetectable. Red lentils, at 4.4 mg, were the only pulse above 1 mg. Eggs were not among the 207 foods analysed, so there is no UK figure. The only culinary herb in the database is fresh coriander, 8.4 mg per 100 g but 0.17 mg in a 2 g sprinkling.¹ 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. Bamboo extract is also sold as a silicon source, and no study has measured how much of its silicon people absorb.

Is there silica in water, and which waters have the most?

Tap water in the UK database averaged 0.25 mg per 100 ml, so a litre gives about 2.5 mg; still mineral and spring waters averaged 0.54 mg per 100 ml and sparkling mineral waters from outside England 0.70 mg.¹ Water silicon is well absorbed: 49% from tap water and 52% from mineral water.⁴ In the one trial of silicon-rich water, 17 postmenopausal women with low bone mass drank a litre a day of water at 86 mg per litre of silica, or purified water, for 12 weeks: urinary silicon more than doubled on the silicon water, and the bone-resorption and bone-formation markers did not change in either group.⁷

Does beer contain silica, and does that make it good for your bones?

Across 76 beers the mean silicon content was 19.2 mg per litre, and when nine volunteers drank 0.6 litres (22.5 mg of silicon) about 55% was absorbed, while 4.6% ethanol on its own did nothing to serum or urinary silicon.⁶ Alcohol-free beer carries the same silicon: 660 ml containing 22.9 mg gave 64% recovery in the head-to-head study.⁴ In the Framingham Offspring cohort (1,182 men and 1,537 women), hip bone density was 3.4 to 4.5% greater in men drinking one to two drinks a day of beer than in non-drinkers, and after adjustment for silicon intake the beer differences were no longer significant.⁸ That is an observational association, and it points at the silicon, not the alcohol. The bone evidence is on can you rebuild bone density; the nutrient with authorised bone wording is calcium, on foods high in calcium.

How much silicon do UK diets supply, and is there a recommended amount?

In 209 healthy women over 60 in Dundee, mean intake was 18.6 mg a day, with cereals supplying about 30%.⁹ The European Scientific Committee on Food put the British intake at 20 to 50 mg a day, 55% from water, coffee and beer, 14% from grain products and 8% from vegetables, and judged that "These intakes are unlikely to cause adverse effects".¹⁰ There is no recommended amount: "A Recommended Intake for silicon has not been established due to insufficient data and lack of functional criteria".¹⁰ The minerals that do have UK amounts are on the vitamins and minerals guide.

Are there signs of silica deficiency, and how do you raise your silica level?

No deficiency of silicon has been described in people and there is no test for it: the UK Expert Group on Vitamins and Minerals says that "Silicon deficiency has not been observed in humans" and that "Methods of assessing silicon status have not been established".¹¹ So no blood test can show you are low and there is nothing to replenish: silicon is absorbed as orthosilicic acid and passed out in urine within hours; the table above is how to eat more. The hair, nail and skin changes behind most "silica deficiency" searches have recognised causes of their own, covered on does zinc help with hair loss and collagen for hair and nails; those are the questions to take to a GP.

Should you take a silica supplement as well as eating these foods?

A supplement adds the silicon stated on its label to a day's food, which in the UK runs from about 19 to 50 mg. Silicon reaches the blood as orthosilicic acid, and how much a product delivers depends on how readily its silicon dissolves into that form, which has been measured for some sources and not for others; the measurements are on types of silica explained.⁴ The European committee found "little evidence of adverse effects of orally ingested silicon" and set no upper level because the data were "inadequate to derive a tolerable upper intake level".¹⁰ Who should ask a GP or pharmacist first is on is it safe to take silica every day.

Frequently asked questions

Do oats contain silica?

Yes, more than any other cereal in the database: oat bran 23.4 mg per 100 g, oatcakes 18.3 mg and dry porridge oats 11.4 mg, so a 30 g serving of porridge oats gives 3.4 mg and two oatcakes 4.8 mg.¹

What is the richest source of silica?

By concentration, oat bran at 23.4 mg per 100 g. By portion, a pint of draught lager at 16.3 mg. By absorbed silicon, drinks and green beans, with 44% to 64% recovered in urine against 4% from bananas and 17% from dried fruit.^{1, 4}

Which foods contain silicon dioxide?

Silicon dioxide (E551) and silicates are added to some powders and processed foods as anti-caking agents; the database flagged low-energy drinking chocolate (10.3 mg a mug) and corn chips as items whose figure probably reflects an added particulate silicate, which dissolves little in the gut, and excluded processed foods for that reason.^{1, 10} The additive is a label ingredient, not a food source.

Sources

1. Powell JJ, et al. A provisional database for the silicon content of foods in the United Kingdom. British Journal of Nutrition, 2005. PubMed 16277785.
2. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. gov.uk.
3. Health and Safety Executive. Silicosis: causes and risk controls. hse.gov.uk.
4. Sripanyakorn S, et al. The comparative absorption of silicon from different foods and food supplements. British Journal of Nutrition, 2009. PubMed 19356271.
5. Jugdaohsingh R, et al. Dietary silicon intake and absorption. American Journal of Clinical Nutrition, 2002. PubMed 11976163.
6. Sripanyakorn S, et al. The silicon content of beer and its bioavailability in healthy volunteers. British Journal of Nutrition, 2004. PubMed 15005826.
7. Li Z, et al. Absorption of silicon from artesian aquifer water and its impact on bone health in postmenopausal women: a 12 week pilot study. Nutrition Journal, 2010. PubMed 20946656.
8. Tucker KL, et al. Effects of beer, wine, and liquor intakes on bone mineral density in older men and women. American Journal of Clinical Nutrition, 2009. PubMed 19244365.
9. McNaughton SA, et al. Dietary silicon intake in post-menopausal women. British Journal of Nutrition, 2005. PubMed 16277786.
10. Scientific Committee on Food. Opinion on the tolerable upper intake level of silicon, 2004, in EFSA, Tolerable Upper Intake Levels for Vitamins and Minerals, 2006. efsa.europa.eu.
11. Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals: silicon, 2003. UK Government Web Archive.

This article is general information, not medical advice. If your hair, nails or skin have changed, ask your GP or pharmacist.