Book excerpt: There are an estimated 55 million Americans over the age of 50 who have low bone mass. This easy-to-understand guide helps readers assess their risk and find a practical approach to the diagnosis, treatment and prevention of osteoporosis. It covers bone density tests and a wide range of treatment options for osteoporosis -- from hormone replacement therapy and acupuncture to calcium-rich foods, supplements and exercise -- and offers pointers on preventing broken hips and other common fractures.