Not only is osteoporosis common in women, it is inevitable if we live long enough! Huge clinical studies show that, unfortunately, good calcium intake (such as dietary sources and supplements), adequate vitamin D levels (to allow our digestive tract to absorb calcium we must have a blood level of Vitamin D above 20 and millions of men and women are found to be lower than this when their blood is tested) and exercise are not enough to prevent bone loss in women. Yoga and soy products do not over come this loss of bone either.
If we look closely at why it is that women are so much more likely to get low bone density, osteoporosis and fractures as compared to men, we can understand a lot about evolutionary biology. Women and men require minimum levels of estrogen in their blood streams in order to keep minerals stored in bones. Women inherit a biology that has been selected for over millions of years of biologic evolution. And our biology is designed to mobilize nutrients from bones to enrich breast milk after giving birth. The hormone state that prevails after women deliver their babies is a very low estrogen one. This helps initiate lactation (breast feeding) and is great for nursing babies. The same low estrogen condition activates certain enzymes which mobilizes extra fat into mothers blood streams and this is then secreted into the milk, adding more calories for the nursing baby. Men do not breast feed (obviously!) and their estrogen level remains adequate throughout their entire lives to protect their bones from low-estrogen bone loss. (Men are fortunate to not have their gonadal hormone production organ (testes) fail as do women’s’ ovaries.)
For the vast majority of evolutionary time humans did not live very long life spans. Average life expectancy in stone age cultures never made it past 32. In 1900 in the U.S. the average life expectancy was 49, so only half of women would even live to experience menopause. So these incredible mechanisms to allow robust breast feeding in human mammals did not lead to millions of disabling fractures until the last 50 years, with a life expectancy for women today being 80 years or more! 30 years of life without adequate estrogen levels to protect bone strength. Women simply did not live long enough to develop weak and fragile bones in the past.
For this reason among others, I believe estrogen is a necessary hormone for optimal quality of life with respect to bone health and vigorous old age in women. Good nutrition, active life style with both aerobic and weight-bearing exercise and a healthy hormone balance are key for women to live a vigorous good quality life with strong bones.
An in depth scientific paper about the hormonal similarities between lactation and menopause (authors Ricki Pollycove, MD, MS, James A Simon, MD, and Frederick Naftolin, MD) will be published in March, 2011, in the peer-reviewed journal, “Menopause”).