Introduction
Silica, also known as silicon, is a mineral that is often referred to as a trace element in nutrition. It is the third most abundant trace element in the human body, although it is not officially classified as an essential nutrient. Nevertheless, increasing research shows that silica can play important roles for various aspects of health, especially related to bones, connective tissue, skin, hair and nails. In this article, we explore what science says about silica: its functions, bioavailability, interactions with other minerals, dietary sources, and safe doses to support overall health.
Silica in the body and bioavailabilityWhat is silica? Silica usually refers to silicon dioxide or other silicon-containing compounds. In a biological context, silicon often acts as soluble orthosilicic acid, especially in liquids such as water and body fluids. The body contains silicon in small amounts, particularly in tissues such as bones and connective tissue.
Bioavailability, or absorption, is an important factor for silica's effect in the body. Silica exists in various chemical forms, and the ease with which it is absorbed varies considerably depending on the form. Monomeric orthosilicic acid is absorbed most efficiently, with a bioavailability that can reach up to 50%. Polymerized forms, such as silica gel, colloidal silica or silica particles from plants, on the other hand, often have a very low uptake, sometimes below 1%.In general, silicon is absorbed more poorly the more bound or polymerized it is. For example, silica in drinking water and beer is mainly in the form of orthosilicic acid and thus easily accessible to the body, while silicon bound in fiber-rich plant foods, such as bananas, can have an absorption rate of less than 2%.
Silica and bone health
One of the most studied areas of silica is its role in the skeleton. Already in the 1970s, animal experiments showed that silicon is involved in normal bone development. Animals on a diet low in silicon developed deformities in bones and cartilage, while the supply of silicon promoted bone growth, collagen formation and calcium deposition in the bone tissue. Over 30 years of research has given strong indications that silicon from the diet can contribute positively to bone mineralization and connective tissue health.
Bone mineral density and strength are key aspects of bone health. Epidemiological studies have found a clear connection between higher silica intake and better bone mineral density. In both the US and the UK, people with higher dietary silica intake have shown higher bone density, particularly among men and premenopausal women. This suggests that silica can support strong bones. Mechanistic research shows that silica is present at the active mineralization front in growing bone, indicating a function in early calcification of the bone matrix. Silicon can bind to components of the bone tissue and promote the deposition of calcium and other minerals in the skeleton. Furthermore, silica is involved in the synthesis and stabilization of collagen, the most important protein in the bone matrix and cartilage. Without sufficient collagen, the minerals cannot form a solid structure, so silica's effect on collagen can be decisive for bone strength.
In a study on postmenopausal women with a tendency to osteoporosis, silicon supplements were given together with calcium and vitamin D. The group that received silicon in addition experienced a significant increase in bone density in the femoral neck compared to the control group. This suggests a synergistic effect where silica, in the presence of calcium and vitamin D, can support bone regeneration or reduce bone loss. At the same time, other studies have not always shown major changes in the bone's mineral content with silica supplementation when the diet is already sufficient. Animal experiments have shown that extra silicon can increase the calcium content of the bones only if the diet was initially low in calcium. If the calcium intake is sufficient, silicon alone does not seem to provide extra minerals to the bones. Nevertheless, there is evidence that silica can support both bone mineral density and bone strength through effects on mineral metabolism and the collagen network.
Silica and connective tissue (collagen and cartilage)
Connective tissue includes supporting tissues in the body, such as cartilage, tendons, ligaments and other tissues that contain collagen and proteoglycans. Silica appears to be important for the maintenance of such tissue. Structures rich in connective tissue, such as artery walls, trachea and cartilage, contain particularly high concentrations of silicon. This is believed to be due to silica's role in the formation of glycosaminoglycans and proteoglycans, complex molecules that build up much of the basic substance in the connective tissue. Silicon can be integrated into these structures and contribute to cross-linking between proteoglycan complexes and collagen fibers, which increases the tissue's strength and reduces the permeability of the connective tissue matrix. Simply put, silica can help bind together the components of connective tissue to make it stronger and more resistant.
Collagen synthesis is a central process in connective tissue, and collagen is the dominant protein in skin, tendons and cartilage. Silica is believed to support collagen formation. Studies have shown that silicon can stimulate fibroblasts, connective tissue cells that produce type I collagen. It has also been suggested that silica helps to activate enzymes involved in hydroxylation of the collagen, a chemical modification that is important for the maturation and stabilization of the collagen fibers. Without sufficient silicon, these enzymes may be less effective, potentially leading to weaker collagen structure. In animal experiments, a lack of silicon has been linked to reduced collagen content in bones and cartilage, while supplementation significantly increased the amount of collagen. This substantiates that silica has an important function in collagen biosynthesis or stabilization.
Cartilage and joints depend on a durable but flexible matrix of collagen and proteoglycans. Given silica's role in both of these components, adequate silicon can contribute to healthy joints. Research on animals has shown that a silicon-poor diet led to abnormal cartilage development.Wound healing is another process where connective tissue regeneration is crucial. Collagen deposition is the key when wounds in the skin or other tissue are to heal. Silica's effect on collagen and tissue formation suggests that it may support wound healing. Clinical research on this is limited, but some reports have highlighted silicon's potential role in promoting wound healing and connective tissue repair. This may be linked to the cells having sufficient building blocks and cofactors, such as silica, to form new tissue efficiently. More research is needed to confirm how much silica can affect wound healing in humans, but the biological plausibility is there.
Silica for skin, hair and nailsSilica is well known among nutritional supplement enthusiasts for its supposed effect on skin, hair and nails, all of which are made up of strong protein networks – collagen in skin and keratin in hair and nails. These tissues are considered appendages of the skin, and silicon has been shown to be found in significant concentrations in hair and nails, where it is a dominant mineral in the composition of the nails. Many people experience brittle nails and lifeless hair as signs of nutritional deficiencies, and some experts have suggested that soft or brittle nails may indicate a systemic silicon deficiency.
The skin's elasticity and anti-ageing are affected by collagen and elastin, which provide structure and resilience. With age, these fibers gradually break down, and the skin becomes thinner and less elastic. Silica can support new collagen synthesis and slow down degradation by contributing to very good activity of enzymes that are necessary to form and maintain collagen in the skin. In a placebo-controlled study of 50 middle-aged women with sun-damaged skin, participants received two capsules daily, each containing stabilized orthosilicic acid equivalent to 10 mg of silicon per capsule, for 20 weeks. After the period a significant improvement in the microstructure of the skin surface was observedr and mechanical properties, such as elasticity, in the silicon group. The appearance of the skin, measured by roughness index and elasticity, improved, while the placebo group showed no corresponding change. This was the first double-blind, controlled study to document such effects of silica supplementation, and it suggests that silica may have a cosmetic and dermatological benefit in aging skin.
Hair growth and hair strength are affected by keratin, the main protein in hair, but also by minerals such as silicon found in the hair strands. Higher silicon content in a strand of hair is associated with a lower risk of breakage and possibly less hair loss. Silicon can contribute indirectly by transporting nutrients to the hair follicles and by binding to amino acids or keratin to strengthen the structure. In one study, 48 people with thin, brittle hair took a supplement of stabilized orthosilicic acid daily for 9 months, equivalent to 10 mg of pure silicon per day. By the end of the experiment had the hair of those who received silicon significantly higher breaking strength and thicker hair, while the placebo group showed no improvement. This suggests that long-term silica supplementation may produce stronger, fuller hair, possibly by integrating into the hair fibers or stimulating the production of hair proteins. The researchers speculated that silica may interact with the keratin structure via silanol groups that form complexes with the proteins.
Potential effects on cognitive function
Can silica affect the brain and nervous system? This is less explored than bone and skin health, but there are interesting observations. Silicon is not known as a critical nutrient for nerve cell function, but it can indirectly affect the brain through other mechanisms, especially when interacting with metal ions such as aluminium.
Silica, aluminum and cognitive health is an area of interest. Aluminum has long been suspected of having a role in neurodegenerative processes, although the connection has not been conclusively proven. Silicon appears to be able to counteract aluminum by binding it to itself and forming insoluble aluminum silicates in the gastrointestinal tract, which can prevent absorption in the body. This can act as a natural way to reduce the potential negative effects of aluminium. A large French cohort study followed almost 2,000 elderly people over the age of 15 and examined mineral intake via drinking water in relation to cognitive health. They found that those who ingested more silicon from drinking water had a lower risk of cognitive challenges - an increase of 10 mg silicon per day was associated with approx. 11% reduced risk. Conversely, higher aluminum intake was associated with increased risk. These findings suggest that silica may have a protective effect on the brain, possibly by preventing aluminum from accumulating in brain tissue. Small studies have shown that people who drank silicon-rich mineral water over time had reduced aluminum content in the body and tendencies towards improvement in cognitive function in some. The data base is nevertheless thin, and silica cannot be recommended as a prevention or treatment of cognitive challenges. A moderate intake of silica via diet and water is probably beneficial for general health and can have positive side effects on the brain by helping to reduce potentially harmful substances such as aluminium.Potential effects on the immune system
The link between silica and the immune system is complex. Inhalation of silica particles, such as stone dust, can overstimulate the immune system in the lungs and lead to harmful effects, but this applies to crystalline silica that is inhaled, not dietary supplements or silicon from the diet. The question is whether silica in food supplements has immune-strengthening or immune-regulatory properties.
There is limited direct human research looking at silica supplementation and immune function, but animal studies provide some indications. In an animal model of induced joint inflammation, silicon supplementation was found to attenuate the autoimmune response, suggesting that silica may enhance anti-inflammatory responses and modify immune responses in a beneficial direction during chronic inflammation. A reduction in the number of circulating lymphocytes during inflammation was also observed in the animals that received silica, which can be interpreted as a dampening of excessive immune activity.On a general level, some sources have suggested that silicon can support the immune and hormonal systems and help maintain a balanced pH in the body, which in theory could create a less favorable environment for pathogens. These statements often derive from laboratory or animal experiments, or holistic perspectives, and not from large clinical trials. Indirectly, silica can support the immune system by contributing to healthy mucous membranes and skin, which are the body's first line of defense against infections. A sufficient silicon intake can provide stronger connective tissue in the skin and mucous membranes and thus better barrier function. This is a logical implication rather than something directly measured, but robust tissue can help prevent bacteria and viruses from penetrating the defences.
In summary, there may be immune-related benefits to silica, particularly related to its potential anti-inflammatory properties. Boron, another trace element, is better known to affect immune response and inflammation, and it is possible that silicon has similar, milder effects. So far, we lack clinical studies showing that healthy people get a stronger immune system from silica supplements, so claims should be cautious.
Interaction with other minerals: boron, calcium and magnesium
Minerals in the body rarely work alone; they form part of complex networks where they can enhance or inhibit each other's uptake and functions. Silica has interesting interactions with several minerals, especially those that have overlapping roles in bone health.
Calcium interacts with silica both in the gut and in the bone tissue. High levels of dietary calcium can potentially reduce the absorption of silicon, possibly by forming poorly absorbable complexes, while low calcium can increase silicon absorption. In the skeleton, they work together: calcium is the main mineral in the hydroxyapatite crystals that make bones hard, while silica probably helps these crystals to be deposited efficiently in the collagen matrix. Some researchers have suggested that silica may affect how calcium and magnesium are transported or used in the body. The amount of silicon excreted in the urine often correlates with calcium excretion, which may indicate that they follow some of the same metabolic pathways. Practically, this means that silica supplements for bone health should be combined with an adequate intake of calcium and vitamin D for a very good effect, as shown in studies where silicon has shown positive results on bone density.
Magnesium is another key mineral for bones and connective tissue. Silica and magnesium can affect each other in a similar way as silica and calcium. Animal experiments have shown that silicon supplementation sometimes lowers magnesium concentration in serum or increases magnesium excretion, but this did not lead to less magnesium in the bone tissue – bone magnesium remained stable. This can be about complex buffer or distribution mechanisms. Both magnesium and silicon are involved in enzyme processes linked to collagen synthesis and bone growth, so they can have complementary roles. If silica supplementation is considered, one should also ensure sufficient magnesium intake, as very good bone and connective tissue health depends on both.
Boron is a trace element which, like silicon, is not officially recognized as essential, but which has clear effects on bones and hormones. Boron and silica are often found together in plant foods such as fruit and vegetables and are both linked to bone health. Boron can affect the turnover of calcium, magnesium and vitamin D in a positive way by reducing the excretion of calcium and magnesium and increasing the activation of vitamin D, which in turn benefits the skeleton. Silica and boron can thus support the skeleton through slightly different mechanisms: boron regulates the mineral balance, while silica contributes to the structure. Both promote bone growth in animal models, and a lack of either can cause weakened bones in experimental animals. Although direct interactions between boron and silicon have not been extensively explored, it is logical that a diet that supports bone health includes adequate amounts of both of these trace elements, along with calcium, magnesium, and vitamins such as D and K.
In summary, silica cooperates with calcium and magnesium by supporting their integration into bone and connective tissue, and can prevent the absorption of potentially unwanted minerals such as aluminium. Boron and silica complement each other by strengthening bones – boron helps mineral metabolism, while silica contributes to the physical structure. Balance is the key to overall health, and a varied diet will usually supply these micronutrients in sufficient quantities. In cases where plant or water intake is low, such as in vegans with little processed grains or people with limited access to mineral-rich water, silica intake may be lower, and supplementation may be considered.
Silica is found in a number of common foods and beverages. Plants generally contain more silicon than animal products, as they take up silicon from the soil and incorporate it into their structures. Here are some important sources:
Whole grains and grain products are among the richest sources of silica. Oats, barley, millet and brown rice in particular have a high silicon content. Refined grains lose some silica because it is in the bran and fiber. A typical whole grain breakfast cereal can contain around 5–20 mg of silicon per 100 g. In many Western diets, 30–50% of the silicon intake comes from cereal products, and in Finland, cereals make up approx. 68% of children's silica intake.
Vegetables and legumes also contribute, especially those with edible skins or roots that may contain soil particles. Root vegetables can have silica from the soil they grow in, but it is recommended to wash them well, although a little soil particles can increase the silicon intake. Certain types of beans, such as green beans, have a relatively high silicon content, with analyzes showing up to approx. 8 mg per 100 g. Leafy greens and other common vegetables have lower levels, but all contribute a little.
Fruit generally contains little silica, with the exception of banana and dried fruit such as apricots, dates and raisins, and nuts. A medium-sized banana can contain around 5 mg of silicon, but the bioavailability is low, less than 2%, so the practical benefit is limited. Dried fruit and nuts may have more concentrated levels of silica because water has been removed, but the intake amount is often small.
Herbs and special plants such as ryegrass, also called horsetail, are known for their extremely high silica content and have traditionally been used as a source of silicic acid. Other plants in the grass family, such as bamboo shoot and sugar cane, also accumulate silicon. Some dietary supplements are extracted from bamboo extract or horsetail, as they may naturally contain 5-10% silicon by dry weight.
Drinking water is a significant source of silica, depending on the geology of the area. Silicon from water occurs as dissolved orthosilicic acid, which is very easily absorbable. In countries with mineral-rich water, it can contribute a few milligrams per litre, while the levels are lower in areas with soft water. European mineral waters vary from approx. 4 mg/L up to 16 mg/L silicon, and some commercial waters can have as much as 30–40 mg/L, which has been used in studies to reduce aluminum in the body. In general, drinking water and other beverages can account for 20% or more of the daily silica intake.
Beer is a surprisingly good source of silica for many adults. Barley malt and hops release silicon during brewing, and beer contains orthosilicic acid in concentrations of approx. 5–20 mg per litre, depending on the type. studies have shown that beer drinkers, especially men, can have a significantly higher silica intake than non-drinkers; in Finland, 44% of men's silicon intake came from beer. Silicon from beer is also efficiently absorbed, shown by high excretion levels in urine after consumption. This is not a call for increased alcohol consumption, but illustrates how dietary habits affect silicon levels. Alcohol-free beer or malt extracts could theoretically provide similar benefits without alcohol.
A diet rich in whole grains (preferably not wheat), vegetables, beans and mineral water automatically provides some silica. In Western countries, the average intake is estimated to be 20–50 mg of silicon per day, twice the typical intake of iron or zinc, although silicon receives less attention. In plant-based diets, such as in India and China, intake can reach 140–200 mg/day, while it can be lower than 20 mg in groups with little plant intake or limited water consumption.
Recommended intake and dosage for health benefits
There is no official recommended daily intake (RDI) for silica in Norway, the EU or the USA, but an adequate intake is estimated at 10–25 mg per day for adults. Most people get this through their diet, with an average of 20–30 mg/day in Western countries.
Silica is found in multivitamins and supplements for skin, hair and nails, often in doses from 5–25 mg per day. Studies show that 10 mg daily can have positive effects on skin and hair, while 20-30 mg per day, together with calcium and vitamin D, can support bone health. Higher doses (40–50 mg/day) have not shown a clearly better effect, as the body does not absorb unlimited amounts.
Silica supplements are considered safe in moderate doses. A 20-week study at 20 mg/day reported no side effects. Surpluses are efficiently excreted via the urine, but very high doses can theoretically strain the kidneys. EFSA considers silicon dioxide to be safe in normal amounts, but extreme doses should be avoided.
For general health, including skin, hair and nails, 5–10 mg per day is recommended. For bone health, 10–20 mg per day can be considered, especially with calcium and vitamin D. Start with a low dose and consult a doctor in case of medical conditions or use of diuretics. Silica supplements should supplement, not replace, a balanced diet.
Concluding remarksSilica appears as an exciting trace element with many biological compounds. Although it has long been underestimated, modern research suggests that silicon has important support functions in the body – from contributing to solid bone structure and healthy connective tissue to supporting beauty-related aspects such as the youthfulness of the skin and the strength of the hair. There are also promising links to cognitive health and immune balance, mainly indirectly through mechanisms such as aluminum detoxification and anti-inflammatory effects.
For specific goals, such as strengthening hair and nails, a supplement can be considered in consultation with healthcare professionals, with reasonable doses and realistic expectations. As with all dietary supplements, it is important to follow guidelines and avoid unrealistic claims. Silica is no miracle cure, but it is undoubtedly a contributing factor in the body's intricate biochemistry to keep bones strong, connective tissue supple and external attributes healthy. Continued research will hopefully provide better insight into how this mineral can promote health in a safe and effective way.
- Silicon and bone health
- The role of silicon in connective tissue health
- Silicon and its role in bone formation
- The biological role of boron in humans: A review
- Boron and its role in nutrition and health: A review
- Boron: A key element in bone health, calcium metabolism, and prevention of arthritis
- Nutritional Bioavailability of Silicon
- Effect of oral intake of choline-stabilized orthosilicic acid on hair tensile strength and morphology in women with fine hair
- Effect of oral intake of choline-stabilized orthosilicic acid on skin, nails and hair in women with photodamaged skin
- Silicon supplementation and bone health: A review of the evidence
- Dietary silicon intake is positively associated with bone mineral density in men and premenopausal women of the Framingham Offspring cohort
- Silicon intake and Alzheimer's disease: Results from the PAQUID cohort
