[surferjoe2007]

The real reason is more likely because we eat too much calcium.  The ideal per studies at pubmed.gov is actually 650 mg calcium, not more, and 1,000-2,000 i.u. vitamin D.  More vitamin D is ok (to a point).  More calcium can actually weaken your bones.  Extra vitamin D counteracts excess calcium so the most likely explanation is that too much calcium reduces your vitamin D and then you can't absorb and/or utlize calcium as well with depleted vitamin D.

The Japanese in fact get 300 mg calcium and have less osteoporosis than Americans.

So the best way is to get plenty of vitamin D and not worry about calcium too much.

Chia seeds and nuts are high in calcium though it's poorly absorbed.  Many of the veggie sources actually leech calcium from your body.  But because the oxalic acid in these veggies is so specific to calcium only and not other minerals, you can simply take calcium powder with them.  And unlike calcium powder alone you don't have to worry about being shorted on other minerals.  The veggies have plenty of these and oxalic acid won't bind to the other minerals.  Fortified foods are no different from calcium powde.  But again other nutrients including what's in veggies makes a bigger difference to your bones.