intake have higher bone density, and that silicon supplementation can increase bone volume and density in patients with osteoporosis. Silicon is needed for synthesis of elastin and collagen, of which the aorta contains the greatest quantity in the human body, and has been considered an essential element; nevertheless, it is difficult to prove its essentiality, because silicon is very common, and hence, deficiency symptoms are difficult to reproduce. Silicon is currently under consideration for elevation to the status of a "plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO)." Safety People may be exposed to elemental silicon in the workplace by breathing it in, swallowing it, or having contact with the skin or eye. In the latter two cases, silicon poses a slight hazard as an irritant. It is hazardous if inhaled. The Occupational Safety and Health Administration (OSHA) has set the legal limit for silicon exposure in the workplace as 15 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an eight-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 10 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an eight-hour workday. Inhalation of crystalline silica dust may lead to silicosis, an occupational lung disease marked by inflammation and scarring in the form of nodular lesions in the upper lobes of the lungs. See also Amorphous silicon Black silicon Covalent superconductors List of countries by silicon production List of silicon producers Monocrystalline silicon Polycrystalline silicon Printed silicon electronics Silicene Silicon nanowire Silicon tombac Silicon Valley Transistor References Bibliography External links Chemical elements Metalloids Group IV semiconductors Pyrotechnic fuels Dietary minerals Reducing agents Native element minerals Chemical elements with diamond cubic structure Crystals in space group 227 Crystals in space group 206 Materials that expand upon freezing