Inorganic borates: Chemistry, human exposure, and health and regulatory guidelines

Risk assessment of essential or nutritionally important trace elements occurring naturally in foods and the environment poses many challenges to health advisory bodies and regulatory agencies when setting acceptable daily intake levels of these elements, especially in media such as drinking water. The use of traditional 100-fold safety factors applied to animal-derived, no-effect levels for some essential elements can unwittingly lead to calculated acceptable daily intakes below levels that are recognized as nutritional requirements. Boron (B) is widely distributed in the environment combined with oxygen to form inorganic borates. It has been known for 75 years that B is an essential micronutrient for plant growth, and as such it occurs naturally in all fruits, vegetables, grains, nuts, legumes, wine, and to a lesser extent in most other foods and beverages. Drinking waters and some mineral waters from areas naturally high in B also may contribute to human daily intake. Human and animal studies provide strong support that B is a nutritionally beneficial, if not essential, element for humans, and it is possible that B deficiency may pose potential health risks. Recent estimates show that the mean dietary intake of B in the United States is 1 mg/day, although B intakes can vary considerably across national diets, especially those that contain higher amounts of fruits and vegetables. National and international health advisory and regulatory bodies should consider both the ubiquity and nutritional importance of B as part of a healthy diet when setting standards and guidelines based on animal toxicology-derived, no-effect-levels.