A researcher at San Diego State did a comprehensive study of bone density using many local cyclists for subjects. Many of the male cyclists had fairly low numbers. Age is a factor both in men and women. Those who lifted weights regularly usually had the highest numbers. Cycling is not a load bearing activity so with age, most cyclists should lift weights, jump rope or run. Actually, studies have shown that jumping rope is really beneficial. I could get the cites if anyone is interested.
Del Mar CA