The role of boron in nutrition and metabolism.

A large number of responses to dietary boron occur when the boron content of the diet is manipulated. Numerous studies suggest that boron interacts with other nutrients and plays a regulatory role in the metabolism of minerals, such as calcium, and subsequently bone metabolism. Although the mechanism of action has not been defined, it may be mediated by increasing the concentration of steroid hormones such as testosterone and beta-oestradiol. Boron is obtained from a diet rich in fruits, vegetables, nuts and legumes. The daily intake has been estimated to range from 0.3-41 mg per day. The wide range is due to the variation of the analytical methods used and differences in the soil content of boron. Based on a limited number of studies, increasing dietary boron results in increases in the boron concentration of all tissues. Large amounts of boron are well tolerated while consistent signs of deficiency include depressed growth and a reduction in some blood indices, particularly steroid hormone concentrations. Via its effect on steroid hormones and interaction with mineral metabolism, boron may be involved in a number of clinical conditions such as arthritis. Further research is required before boron is accepted as an essential nutrient for humans.