Boron as the sodium salt has been used by man for over 2500 years as a flux for welding gold and as an embalming agent by the Egyptians. As supplies became easier to get, namely from Italy, boric acid and borax became increasingly used as a mild antiseptic, especially for eyes and burns.
For the last 200 years, boric acid has often been used as a food preservative, but this use has been recently stopped because it tended to disguise food that was unfit for use as being in a reasonable condition for use. People must have ingested considerable quantities without any ill effect during this period. Much has been used as a simple home remedy for stings and burns, and as a powder to prevent rash.
Boric acid and borax in a 2-3% solution will prevent the growth of most bacteria and will kill many fungi. These substances are readily absorbed by damaged skin and by mucous membranes. 50% of borate is eliminated via the kidneys in the first 12 hours, and 90% of the remainder is gone within a week, in all but extreme doses. Borates are slightly astringent and will tend to allay the pain of burns and wounds. If the dry powder is introduced to the nose, it can bring on sneezing and lacrimation.
These substances are not dangerously toxic, but large doses can be dangerous. Some workers have shown that 3gm boric acid or 5gm borax have no effect on the adult human, while others have reported symptoms at 1-2gm per day. No one is likely to take too much in their food even if they do use a supplement that has only a few milligrams per tablet. Greater absorption is likely to come from a mouthwash or if a borate is applied to damaged skin.
Extensive laboratory studies on both man and animal have not shown the exact role of boron in their metabolism. Patients have been given 10gm per day for extended periods and were still excreting boron after 7 weeks. The acute toxic dose for an adult is from 20-60gm in a single dose, but infants have died with 5gm, yet others lived after being given 9gm boric acid.
In many countries, a boron supplement is being used as a food supplement, and no claims are made, but satisfied users soon tell other people who need it. Over 250,000 people have used a particular supplement with the claim that it corrects between 80 and 90% of all arthritis. No untoward side effects have been noted, but there are some useful side-effects, such as would be noticed if boron were the limiting factor in a person's well-being. Cardiopathies have been corrected, vision has been improved, psoriasis has been much improved, balance has been corrected. Arthritis in horses, cattle, dogs, deer, and goats have all been corrected.
As we use more and more phosphates on our food crops, the availability of soil boron is decreased. It is estimated that most people in western societies ingest about 2mg boron daily. This is based on the analysis of school meals in the U.S.A, but analyses earlier in this century put the figure at 8mg. Observations suggest that boron intake at the level of 5-6mg per day is consistent with the prevention of arthritis. A higher dose may be required for treatment.
Sources of boron include non-citrus fruits such as plums, red grapes, apples, pears, and avocados, as well as in legumes and nuts. It is also present in significant amounts in coffee and red wine. Dried fruits contain a much higher amount of boron than fresh fruit. For example, fresh plums contain 0.45 mg of boron per 100g, but the same weight of dried prunes (about 12 prunes) contains 2.15mg of boron. The typical dietary boron consumption in humans is 1-2 mg/day for adults, but boron requirements may be as high as 9-12mg per day.
The prevalence of arthritis seems to follow inversely the availability of boron in the soil. Jamaica has the least boron and 70% with arthritis. Mauritius has very little and has arthritis. Northern Thailand is very short of boron and much arthritis, but no figures are available. In Fiji, the Indians have much more arthritis than do the Fijians, and the reason is that Indians eat mostly rice while Fijians eat mostly starch root vegetables, which contains more boron.
No protective effect of boron has been noted against breast, colorectal, uterine, cervical, or skin cancers.