In rickets, the bones become deformed because there is insufficient calcium to make them strong. Malabsorption of calcium in mature adults can result from low amounts of D3 as well. You should consume a minimum of 400 i.u. of D3 per day and not exceed 1000 i.u. for extended periods except under a physicians direction. Excess D3 can be toxic if consumed at excess levels for prolonged periods. One of the manifestations of D3 toxicity is excess deposition of calcium in places where you don't want it.
Vitamin A can also be toxic if consumed in significant excess for an extended period of time.
Like vitamin D3, one of the toxic manifestations is excess deposition of calcium in undesirable places, like the joints and soft tissues. Another contributing factor in the development of osteoporosis is homocysteine. Homocysteine is a metabolite of the amino acid methionine. It has been implicated in several degenerative diseases including heart disease, arteriosclerosis, and osteoporosis. Homochsteine is detoxified into methionine by specific nutrients which are able to donate methyl groups to the chemical detoxification process.