I recently had a blood test to determine my vitamin D storage levels.  I found out today mine is 28 which is low.  My doctor is having me take two powerful vitamin D pills, then wait 2 weeks and repeat the dosage.  After a 2 month period we will check the levels again.  I learned that many doctors do not perform this test, but that it is important because the body needs enough vitamin D to make bone tissue.  Obviously it is not uncommon for women with osteoporosis to have a low level.  This is not the amount of vitamin D we consume daily but what our bodies have stored over time.  Interestingly this problem is not very common in women who live south of Atlanta, Ga., but much more common in those who live north.........obviously because of the sun.  No matter how much calcium or bone building medicines you take, without the proper amount of vitamin D they will not benefit you.  I encourage everyone to ask their doctors to check their vitamin D storage levels.  There are no symptoms if it is low.