GROWING OLDER, STAYING STRONGER:
HOW AGE INFLUENCES OSTEOPOROSIS
Jennifer Wider, MD
Society for Women's Health Research
March 18, 2010

Osteoporosis is a common disease that causes bones to become brittle and more likely to break.  These fractures can occur anywhere in the body, but occur more often in the hip, spine and wrist.  Osteoporosis is a wide-spread disease that affects women much more often than men.  According to the National Institutes of Health, 8 million women and 2 million men suffer from osteoporosis.

For years, experts on bone diseases have pointed to a decrease in the hormone estrogen as the main cause of osteoporosis.  Not anymore.  A recent study in the journal Cell Metabolism reveals that aging may play a more prominent role than hormones in the development of osteoporosis.

“The primary mechanism (in osteoporosis) is aging and oxidative stress, and that is true for both sexes,” says Stavros Manolagas, M.D., Ph.D., director of the University of Arkansas for Medical Sciences (UAMS) Center for Osteoporosis and Metabolic Bone Diseases.  According to the study’s findings, as the body ages, it loses its ability to fend off molecules that damage the bone, a process known as oxidative stress.  As a result, the body is rendered vulnerable to osteoporosis. 

“Aging and oxidative stress cause a decline in bone strength that is far more important that the decline in bone mass for the development of fractures in our aging population,” says Manolagas.  According to the study’s authors, the evidence causes a paradigm shift in the “estrogen-centric” model of osteoporosis to one in which age-related mechanisms play a much more important role in disease etiology. Further identification of sex differences in these age-related mechanisms will help determine why predominantly women suffer from osteoporosis.

Bone remodeling occurs throughout an adult's life, as specialized bone cells constantly renew the human skeleton while preserving its strength and density.  Cells called osteoclasts resorb old bone, while specialized cells called, osteoblasts create new bone.  As a person ages, this process gets interrupted.  “Aging decreases the number of osteoblasts (the cells that form bone) as well as the number of osteocytes or osteoblast progenitor cells (the cells that monitor bone quality and initiate its repair),” explains Manolagas. 

Aside from gender and age, there are several other factors that increase a person's risk of osteoporosis.

• Family history:  having a first-degree relative with osteoporosis or osteopenia, a condition where bone mineral density is lower than normal, increases the risk of osteoporosis.
• Race: certain studies show that Caucasian people and people of Asian descent have a higher rate of osteoporosis.
• Small body frame: women and men who have small body frames or who have a body mass index of 19 or less, have a higher risk of osteoporosis, possibly because they have less bone mass to begin with.
• Thyroid disease: too much thyroid hormone, either from hyperthyroidism or supplements to treat hypothyroidism, can cause bone loss and increase the risk of osteoporosis.
• Medical conditions: certain medical conditions and diseases including: inflammatory bowel disease, celiac disease and gastric band surgery, can interfere with the body's natural ability to absorb and properly utilize calcium.

The good news is that there are ways to lower the risk of osteoporosis.  “Keep fit and exercise, eat healthy, give up smoking, make sure that you have an adequate intake of vitamin D and calcium, and educate yourself about osteoporosis and how to assess your risk with the help of doctors,”  says Manolagas. 

For more information visit: The National Institute of Arthritis and Musculoskeletal and Skin Diseases

SOURCES

Follin, S.L. and L.B. Hansen. Current approaches to the prevention and treatment of postmenopausal osteoporosis. Am J Health Syst Pharm. 2003. 60(9): p. 883-901; quiz 903-4.

Manolagas SC. From Estrogen-centric to Aging and Oxidative Stress: A Revised Perspective of the Pathogenesis of Osteoporosis. Endocrine Reviews, published online January 5, 2010: 10.1210/er.2009-0024.

Mayo Clinic, Osteoporosis, information sheets, 2009-10.