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Intake Assessment

Humans can be exposed to boron from consumption of food, dietary supplements, and drinking water from natural, municipal, or bottled sources. Airborne boron contributes very little to the daily exposure of the general population. For humans not taking supplements, diet is the major source of boron followed by the intake from drinking water.

The ninety-fifth percentile dietary intake of boron in the United States is approximately 2.3 mg/day for men, 1.6 to 2.0 mg/day for women, 2.0 mg/day for pregnant women (Appendix Table C-12), 2.7 mg/day for vegetarian males, and 4.2 mg/day for vegetarian females (Rainey et al., 1999). These dietary intakes are slightly higher than those estimated by Meacham and Hunt (1998). The average intake of supplemental boron at the ninety-fifth percentile is approximately 0.4 mg/day for adults (Appendix Table C-13). A consumption of 1 L/day of municipal drinking water in the United States contributes 0.005 to 2 mg/day (mean of 0.2 mg/day) of boron (EPA, 1987), and bottled water can contribute an average of 0.75 mg/day (Allen et al., 1989). Percutaneous absorption of boron from consumer products through intact skin has been shown to contribute very little to the total daily intake (Wester et al., 1998).

At the ninety-fifth percentile, intake of boron from the diet and supplements is approximately 2.8 mg/day. Adding to that a maximum intake from water of 2 mg/day gives a total intake of less than 5 mg/day boron at this percentile.

Risk Characterization

At the ninety-fifth percentile intake, no segment of the U.S. population has a total (dietary, water, and supplemental) intake of boron greater than 5 mg/day (Appendix Tables C-13 and D-1). Those taking body-building supplements could consume an additional 1.5 to 20 mg/day (Moore, 1997). Therefore this supplemental intake may exceed the UL of 20 mg/day.

RESEARCH RECOMMENDATIONS FOR BORON

  • The relationship between dietary boron and vitamin D metabolism; specifically, does boron influence the half-life of functional vitamin D metabolites and calcium metabolism as it relates to bone mineralization?

  • The possible influence of boron on estrogen metabolism and



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