FOOD SOURCES
Fresh fruits and vegetables are the main dietary sources of boron. The estimated average daily intake for Americans is between 1.7 and 7 milligrams daily. A diet high in fresh fruits and vegetables is known to offer significant protection against osteoporosis and osteoarthritis (Murray, 1996).
If one wanted to supplement due to boron poor soils etc, I suspect the boron citrate would be good, although there are some food based boron supplements on the market that may be better.