Determining human dietary requirements for boron

Abstract

A dietary requirement is defined as the lowest continuing intake of a nutrient that for a specified indicator of adequacy, will maintain a defined level of nutriture in an individual. An essential dietary component is one that the body cannot synthesize in sufficient quantities to maintain health. Recommended dietary allowances (RDAs) are based on estimates of the dietary requirements, and are designed to prevent deficiency diseases and promote health through an adequate diet. In 1996, the Food and Nutrition Board (FNB) began a revision process of the RDAs using as criteria specific indicators of adequacy and functional end points for reducing the risk of chronic disease. Boron (B) is a dietary component, and evidence from animal studies indicates that it is a dietary essential; it cannot be synthesized in tissues, and organisms exposed to very low levels of B show developmental defects. In humans, there is evidence of homeostatic regulation of B and an interrelationship with bone metabolism. To understand better the relationship between dietary B and B homeostasis, we measured the dietary B intake and urinary B losses in seven male participants of a controlled metabolic study of Zn homeostasis. Average dietary B intake for the repeated menu days, days 1, 2, and 3, was 4.56, 1.87, and 4.75 mg/d, respectively. Urinary B excretion during the 42-d collection period averaged 3.20 +/- 0.41 mg/d. When dietary B was low, urinary B loss (2.92 mg/d) was significantly lower than when B intake was higher (3.15 and 3.54 mg/d). Our study showed that urinary B excretion changes rapidly with changes in B intake, indicating that the kidney is the site of homeostatic regulation. To enable establishment of a dietary requirement for B in the future, further research of homeostatic regulation and functional markers of B metabolism need to be performed, followed by epidemiological studies to identify health conditions associated with inadequate dietary B.