Bone is a dynamic and fluid tissue and is continually changing to meet the needs of the physical activity level of a particular person. Physical activity is known to strengthen both muscle and bone, and increased physical activity results in bones that are denser and more resilient to stress. On the other end of the spectrum, physical inactivity that occurs with age and immobility results in bone density loss and weakens the cortical structure of bones. This is particularly important for women who are premenopausal because greater bone mineral density prior to menopause can protect against osteoporosis. Osteoporosis is a disease that is characterized by severe loss of bone mineral density and results in fragile bones that are more prone to fracture. Elderly individuals who have osteoporosis and gait instability are at increased risk of hip fracture as a result of falls, which could portend further morbidity and immobility.
Researchers, lead by Dr. Mohammed-Salleh M. Ardawi from King Abdulaziz University Hospital in Saudi Arabia, have found that physical activity can result in greater bone density and is associated with biomarkers of bone strength in premenopausal women. The results of their study were published online in the Journal of Clinical Endocrinology and Metabolism. The investigators performed a cross sectional study of 1,235 premenopausal women and studied the influence of physical activity on serum sclerostin and insulin-like growth factor 1 (IGF-1). Sclerostin is glycoprotein produced by bone cells and decreases bone formation, while IGF-1 increases bone density and formation. The researchers found that women who were physically active for more than 120 minutes per week had 36.8% lower serum sclerostin levels and 107% higher IGF-1 levels when compared to women who performed less than 30 minutes of physical activity per week. In addition, the researchers studied the effect of a physical activity regimen on these markers of bone formation in 58 of the most physically inactive women in the study group. After 8 weeks of a physical activity regimen (120 minutes per week), the women in the exercise group had a 33.9% decrease in serum sclerostin level and a 74.2% increase in IGF-1 levels.
The authors wrote, “To our knowledge, this study is the first to report a significant association between low serum sclerostin levels and increased [physical activity] duration and IGF-I levels in premenopausal women. These cross-sectional observations were confirmed by our longitudinal study in which increasing the [physical activity] of sedentary premenopausal women for 8 consecutive weeks (4d/wk) resulted in marked changes in serum sclerostin (decrease) and IGF-I levels (increase)”. The authors concluded, “This study demonstrates that even minor changes in [physical activity] are associated with effects on serum levels of sclerostin, IGF-I, and [bone turnover markers] and suggests that sclerostin could be a link between mechanical loading and disuse osteoporosis in humans”.
This is an important study because it shows that with physical activity and exercise, premenopausal women can increase their bone density with exercise, and that bone turnover markers are affected in a beneficial fashion. This study adds to the existing evidence that physical activity is beneficial, not only for cardiovascular health, but also for bone health. This can translate into better bone health in later life for women, especially after menopause when bone mineral density can begin to decline. Women who are physically active in early life will have stronger bones and can potentially prevent the development of osteoporosis and decrease the risk of hip fractures in later life.
Mohammed-Salleh M. Ardawi et al. “Physical Activity in Relation to Serum Sclerostin, Insulin-Like Growth Factor-1, and Bone Turnover Markers in Healthy Premenopausal Women: A Cross-Sectional and a Longitudinal Study” The Journal of Clinical Endocrinology & Metabolism August 3, 2012 doi: 10.1210/jc.2011-3361