Since this link "timed out" for at least one person, I'm posting a summary
of the points in the article:

> >What affects calcium absorption and excretion?
> http://ods.od.nih.gov/factsheets/calcium.asp

"Calcium absorption refers to the amount of calcium that is absorbed from
the digestive tract into our body's circulation. Calcium absorption can be
affected by the calcium status of the body, vitamin D status, age, pregnancy
and plant substances [phytic acid and oxalic acid] in the diet. The amount
of calcium consumed at one time such as in a meal can also affect
absorption. For example, the efficiency of calcium absorption decreases as
the amount of calcium consumed at a meal increases. ...

Calcium excretion refers to the amount of calcium eliminated from the body
in urine, feces and sweat. Calcium excretion can be affected by many factors
including dietary sodium, protein, caffeine and potassium."

Other factors: phosphorus and alcohol (minimal effect or evidence is weak)