Coffee and Caffeine FAQ

From the Journal of AMA: (JAMA, 26 Jan. 1994, p. 280-3.)
"There was a significant association between (drinking
more) caffeinated coffee and decreasing bone mineral density at
both the hip and the spine, independent of age, obesity, years
since menopause, and the use of tobacco, estrogen, alcohol,
thiazides, and calcium supplements [in women]."
Except when:
"Bone density did not vary [...] in women who reported
drinking at least one glass of milk per day during most of their
adult lives."
That is, if you drink a glass of milk a day, there is no need
to worry about the caffeine related loss of calcium.