Regarding coffee consumption and the effect it has on bones,
the results of controlled studies in humans indicate that coffee and caffeine
consumption decrease the efficiency of calcium absorption resulting in a loss
of about 4-6 mg of calcium per cup of coffee. Most studies have found no
association between caffeine consumption and change in bone mineral density
(BMD, the amount of mineral in a given area of bone. BMD is positively associated with bone strength and resistance to fracture) over time, but there is no specific mention of a negative effect of
caffeine on the uptake and absorption of vitamin D from the stomach.

It is important to stress the fact that osteoporosis is a
disease that is influenced by various factors. As such, the exact impact of coffee
or caffeine consumption on the risk of osteoporosis is still not well defined.
However, currently available evidence says that if you make sure that you are
regularly consuming adequate amounts of calcium and vitamin D, in addition to
limiting your coffee intake to no more than 3 cups/day (and preferably less),
this may help reduce your risk of osteoporosis and osteoporotic fracture,
particularly as you get older (i.e., after menopause).