The couple that taught our NFP (Natural Family Planning) class had three children, which they planned and conceived using NFP after the wife went off of the birth control pill.
Unfortunately, she already had such severe osteoporosis that her ability to hold and carry her youngest child while standing was severely limited, under the orders of her doctor.
She wasn't even 40 yet when my husband and I took the class. Her back was already showing early signs of the "dowager's hump" that is often very pronounced in older women with advanced bone loss.
Part of the reason for her early osteoporosis was her long-term use of The Pill, according to her doctor.
Back in 2005, the connection between Birth Control Pills and bone loss was documented in a Purdue University Study, and also in 2001
This article, dated in 2007, refers to Loyola Marymount University research published in the journal Osteopororsis International that finds the same. This study was of women aged 18-25, a critical time (in addition to the teen years) for women to be doing everything they can to build up their bone mass.
Imagine what could happen with women who started taking the Pill for acne (or other reasons) as early as 12 or 13 and have spent almost their entire post-pubescent lives on the Pill. I hope someone will study that next.
Some recommend taking extra calcium and getting extra exercise to minimize this rather frightening side effect. Why not just ditch the pill, so the calcium-rich diet and exercise (which are generally good for us women anyway) can have their full effect?
Who knows, maybe one less Pill now could mean we're less likely to need one more (i.e. osteoporosis pill) later.