Technical Abstract: Since 1981, circumstantial evidence has been accumulating which suggests that boron is an essential nutrient for higher animals including humans; that is, a dietary deprivation of boron consistently results in changed biological functions that could be construed as detrimental, and are preventable or reversible by an intake of physiological amounts of boron. Nonetheless, boron is not generally recognized as essential or nutritionally important for humans, probably because a specific biochemical function for boron has not been elucidated, or as demonstrated for plants, it has not been shown necessary to complete the life cycle. However, findings from human and animal experiments show that boron is a dynamic trace element that can affect the metabolism or utilization of numerous substances involved in life processes including calcium, copper, magnesium, nitrogen, glucose, triglyceride, reactive oxygen, and estrogen. . Through these effects, boron can affect the function or composition of several body systems including blood, brain and skeleton. Two hypotheses have appeared to account for these multiple effects. One hypothesis is that boron is a negative regulator that influences a number of metabolic pathways by competitively inhibiting some key enzyme reactions. The other hypothesis is that boron has a function involved in cell membrane function, stability or structure such that it influences the response to hormone action, transmembrane signalling or transmembrane movement of regulatory cations or anions. Regardless of the fact that the function of boron remains undefined, the findings from human and animal studies indicate that boron should be recognized as being of nutritional importance.