Summary of the Opinion: Boron occurs in foods as borate and boric acid. Boron has not been established to be an essential nutrient for humans and no specific biochemical function for boron has been identified in higher animals or man. There is some evidence that, in humans, boron intake within the usual dietary range may influence the metabolism and utilisation of other nutrients, particularly calcium, and may have a beneficial effect on bone calcification and maintenance. Recommended intakes for boron have not been established.
Studies of dietary deprivation of boron in animals have reported adverse effects (e.g. on growth, serum steroid hormone concentrations and bone calcification) that can be corrected by increasing boron intake. The effects of low boron intakes are more marked when accompanied by low status for other nutrients (e.g. vitamin D, magnesium).
Data on boron intake in EU countries are limited. In the UK mean intake in adults from food is estimated at 1.5 mg/day, with the 97.5 percentile of 2.6 mg/day, while mean intake from water is estimated to be in the range of 0.2-0.6 mg/day. The main dietary sources of boron are plant foods, and foods rich in boron include fruits, leafy vegetables, mushrooms, nuts and legumes, as well as wine, cider and beer. Supplements may contain 1.5-10 mg boron/dose.
Boron as borate is readily absorbed (>90%) from the human gut and is evenly distributed throughout the tissues and organs, and can cross the placenta, of animals and humans. Absorbed boron is readily excreted in urine.
Ingestion of boron at dose levels of greater than 13 mg/kg body weight/day in short and long term studies in a number of animal species (e.g. mouse, rat, dog, pig) has been shown to result in a range of adverse effects, with developmental and reproductive effects being the most critical. Studies of boron in mice and rats and in vitro showed no evidence of carcinogenicity or genotoxicity.
There are many case reports of boron intoxication in humans. Ingestion of boric acid at daily dose levels of 0.14-0.43 g boric acid/kg body weight (equivalent to about 25-76 mg boron/kg body weight) over periods ranging from days to weeks, resulted in a variety of symptoms, the most common being gastrointestinal effects such as vomiting, diarrhoea and abdominal pain.
It was considered that the data on adverse effects of boron in humans were not adequate for establishing a tolerable upper intake level (UL). The UL was based on the adverse effect occurring at the lowest intake levels in animals, i.e. decreased foetal body weight in rats resulting from maternal boron intake during pregnancy. The no observed adverse effect level (NOAEL) for this effect (9.6 mg/kg body weight/day) was extrapolated to humans by dividing by an uncertainty factor of 60 (to allow for variability between rats and humans and between-person variability in humans) to give an UL of 0.16 mg/kg body weight/day, which is equivalent to an UL of 10 mg/person/day in adults. This UL also applies to pregnant and lactating women. UL values for children were derived by extrapolating from the UL for adults on a body surface area basis, giving values (mg/day) of 3, 4, 5, 7 and 9 for children aged 1-3, 4-6, 7-10, 11-14 and 15-17 years of age, respectively. These UL values apply only to the intake of boron as boric acid and borates.
Based on the limited data available, boron intakes from food and water in EU are below the UL. The consumption of some supplements containing boron may lead to intakes which exceed the UL.
[Source: EFSA]
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