Silicon (Si), the second most abundant element on Earth, plays an increasingly recognized role in human health. While often overlooked, this trace mineral is involved in various physiological processes, particularly in the formation and maintenance of connective tissues, bone health, and skin integrity. This article explores diverse dietary sources of silica, its bioavailability, health benefits, and safety considerations.
Introduction to Silica and Its Importance
In recent decades, silicon has garnered significant interest as a trace element vital for both plant and human physiological and metabolic functions. Present in all organisms and soil, silicon plays a crucial role in connective tissue metabolism, essential for the biosynthesis of collagen and glycosaminoglycan, which are necessary for bone formation. Silicon is also required for the function of polyhydroxylase, responsible for the formation of collagen, elastane, cartilage, and other connective tissues.
Silicon deficiency can lead to weak and malformed bones, osteoporosis, Alzheimer’s disease, bone decalcification, cardiovascular disease, and atherosclerosis. It also impacts the maintenance and growth of hair and nails. The human body contains approximately 1 g of silicon, making it the third most abundant trace element after iron and zinc. It is primarily deposited and stored in the connective tissue of the aorta, trachea, tendons, bones, and skin, with stored silicon declining with age.
Silica (silicon dioxide, SiO2) is one of the most important silicon compounds, serving as the basic component of many minerals used in industry. In nutrition, orthosilicic acid (OSA) and its salts (silicates) are considered the best sources of silicon. Natural sources include cereals, fruits, and vegetables. Although the essentiality and specific functional roles of silicon for humans are not fully established, a silicon intake level of 20-50 mg per day is generally considered safe, with a tolerable upper level set at 700 mg per day for adults.
Dietary Intake of Silica
The typical Western diet provides approximately 19 to 31 mg of silicon per day, with the average American diet containing about 30 mg. These levels are generally lower compared to diets rich in vegetables and unprocessed cereals, such as those in India and China, where consumption ranges from 140 to 204 mg/day. This higher intake correlates with a lower incidence of bone fractures in these populations, suggesting that increased silicon consumption may have beneficial effects.
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The primary sources of silicon in the diet are plant-based foods, water, and beverages, with animal products contributing to a lesser extent. Silicon may also be present in processed foods as the additive E551, an anticaking and antifoaming agent high in silicon.
Key Dietary Sources of Silica
Vegetables
Vegetables are among the richest sources of silicon, particularly those that grow underground, such as potatoes and beets. The highest concentration of silica is found in the skin or peel of these vegetables. Green beans are also a notable source, with one cup containing approximately 7 mg of silica, contributing about 25% to 35% of the average American’s daily intake.
Leafy green vegetables like spinach, kale, and lettuce are excellent sources of silica. For example, a 2-tablespoon serving of spinach contains 4.1 mg of silica. These vegetables support healthy skin and hair while also promoting connective tissue health, including bones, tendons, and cartilage.
Fruits
Bananas are one of the most significant fruit sources of silica, with a medium-sized peeled banana containing 4.77 mg of silicon dioxide. Apples are also good sources of silicon.
Whole Grains and Cereals
Whole grains such as oats, barley, wheat, and rice bran are significant contributors to dietary silicon intake. Brown rice, in particular, has a high silica content, with three heaped tablespoons containing 4.51 mg of silica. Cereal products, especially those containing oats, are also high in silica. For instance, two tablespoons of oat bran provide 3.27 mg of silica.
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Legumes
Lentils, especially red lentils, are protein-rich beans that provide silica. One tablespoon of red lentils contains 1.77 mg of silicon dioxide.
Beverages
Water is an important source of silicon, with the content varying based on its geological origin. Silicon consumption from water can account for up to 20% of total intake. Studies have shown that at least 50% of the silicon present in mineral water is absorbed, making it a good source.
Beer, particularly non-alcoholic beer, is another significant source of dietary silicon due to the presence of barley and hops. The brewing process decomposes silicon compounds into OSA, an easily absorbable form, with up to 55% of the silicon in beer being absorbed.
Other Sources
Other sources of silicon include fish and animal meat, eggs, milk, juices, and pharmaceutical supplements. However, food processing can significantly reduce silicon content, so unprocessed whole-grain products are preferable.
Bioavailability of Silicon from Foods
Silicon compounds of greatest nutritional importance include silicic acids and their salts (silicates). OSA is considered the best form due to its high absorption rate and bioavailability, approximately 43%. However, at concentrations exceeding 0.1%, polysilicic acids form, which have lower bioavailability.
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Silicon is most effectively absorbed from cereal products and, to a lesser extent, green beans and dried fruits. In contrast, the silicon present in bananas, despite significant quantities (5 mg/portion), is only about 5% absorbed, likely due to its highly polymerized form.
Studies on beer have shown that about 55% of its silicon content, primarily in the form of OSA, is absorbed, with 42-72% of the absorbed silicon being excreted in urine. Similarly, studies on OSA from water reported urinary excretion between 21% and 74%.
Silicon of Mineral Origin in Functional Foods and Supplements
As processed foods increasingly dominate diets, supplementation may be necessary to ensure adequate silicon intake. Silicon can be added to functional foods and supplements in various forms, with varying degrees of bioavailability. Products commercially recommended as concentrated sources often use OSA solutions and its stabilized forms.
To prevent the polymerization of silicic acid during manufacturing, stabilization methods have been developed, such as introducing a methyl group to obtain monomethylsilanetriol (MMST), stabilizing with choline to form choline-stabilized orthosilicic acid (ch-OSA), or combining with vanillin to form orthosilicic acid vanillin complex (OSA-VC). Amorphous diatomaceous earth is also of interest as a source of organic silicon.
Silicic acids are considered the best sources of silicon due to their high bioavailability (approximately 40%) and natural occurrence in food. OSA, formed by the hydration of silicon dioxide (SiO2), plays a vital role in providing elemental silicon to cells.
The solubility of silicon depends on the pH of the environment, dissolving more easily in an almost neutral environment (characteristic of the intestinal pH) compared to acidic conditions (in the stomach). Studies comparing absorption from various sources found that MMST and beer had the highest absorption rates (64%), followed by green beans (44%), OSA (43%), ch-OSA (17%), bananas and magnesium trisilicate (MTBP) (4%), and colloidal silica (CS) (1%).
Health Benefits of Silica
Bone Health
Silica plays a crucial role in bone formation and maintenance by influencing the activity of osteoblasts and osteoclasts, which are involved in bone remodeling. It supports the balance between bone resorption and bone formation and promotes the synthesis of collagen, a key component of bone tissue. Adequate silica intake is essential for preventing bone loss and fractures, making it a vital nutrient for overall bone health.
Skin Health
Silica is essential for collagen synthesis, which is vital for maintaining skin elasticity and reducing wrinkles. It enhances the cross-linking of collagen fibers, improving skin firmness and promoting a youthful appearance. Silica also aids in the production of glycosaminoglycans, which enhance the skin's ability to stay hydrated.
Hair and Nail Health
Silica is essential for the production of keratin and collagen, which are vital for healthy hair and nails. It boosts elasticity and hydration, promoting radiant skin and strong nails while preventing brittle hair and sagging skin.
Cardiovascular Health
Silica strengthens blood vessels and muscle tissue, contributing to heart health. Studies suggest that silica may reduce the risk of atherosclerosis and lower cholesterol levels.
Joint Health
Silica plays a critical role in collagen production, strengthening cartilage and improving joint flexibility. It can reduce inflammation and help alleviate arthritis symptoms, keeping joints flexible and pain-free.
Digestive Health
Silica helps strengthen digestive tissues and rebuild damaged stomach muscles, promoting overall digestive health.
Safety Considerations and Potential Risks
While silica offers numerous health benefits, it is essential to be aware of potential risks associated with excessive intake, particularly in certain forms.
Silicosis
Long-term exposure to silica dust can lead to silicosis, a lung disease. While this is primarily a concern for those exposed to silica at work, it underscores the importance of not exceeding safe intake levels.
Kidney Stones
High dietary silica, especially when combined with a high calcium to phosphorus ratio and alkali-forming potential, can promote the formation of silica urolithiasis, or kidney stones, in animals.
Reproductive Toxicity
Research has indicated that silica nanoparticles, when combined with a high-fat diet, can exacerbate reproductive toxicity in male Wistar rats. This combination was found to decrease sperm concentration and mobility, increase abnormality rates, and damage testicular structure.
Silica Gel Consumption
Silica gel packets, often found in food packaging, are not meant for consumption. While typically non-toxic, swallowing them can lead to choking or intestinal blockage.
Practical Strategies to Increase Silica Intake
- Include Silica-Rich Foods in Your Diet: Incorporate a variety of silica-rich foods like green beans, bananas, leafy greens, brown rice, cereals, and lentils into your daily meals.
- Choose Whole Grains: Opt for unprocessed whole-grain products over refined grains to maximize silicon content.
- Drink Mineral Water: Choose mineral water with a known silicon content to contribute to your daily intake.
- Consider Nettle Leaf Tea: Sip on nettle leaf tea, which contains orthosilicic acid, a readily absorbable form of silica.
- Balance Your Diet: Ensure a balanced intake of silica with other essential minerals like calcium, magnesium, manganese, and copper for optimal health benefits.
Expert Opinions and Recommendations
Experts emphasize the importance of silica for maintaining optimal wellness. Nutritionists and scientists highlight that silica, in the form of silicon dioxide, is a crucial trace mineral our bodies need for various physiological processes.
They also point out that silica's bioavailability varies depending on the dietary source. Consuming foods rich in silica, such as horsetail and diatoms, is beneficial, but the absorption of silica from these sources might differ. It's therefore essential to consume a varied diet with multiple sources of silica.