Nearly 10 million adults in the United States have osteoporosis – a condition where the bones have deteriorated to such a point that the person is at a significantly increased risk of fracture and mortality. Experts expect this number to increase by 30% by 2030. The estimated national cost of osteoporosis-related injury and treatment in 2008 was $22 billion. Due to the widespread impact of osteoporosis, we could all benefit from reducing the occurrence of this condition.
It is generally accepted that strength training can reduce a person’s risk of osteoporosis. However, the relationship between muscle strength, osteoporotic fracture, and ethnicity are unclear. A new study, published in September 2017, has now found that increased muscle strength is associated with reduced odds of developing osteoporosis across both genders and all ethnicities.
This means that all people can potentially benefit from regular strength training, especially as we age.
The new study, first published in September 2017 in the Journal of Strength & Conditioning Research, sought to determine (a) whether increased muscle strength was in fact associated with reduced odds of developing osteoporosis and (b) whether these odds differed based on ethnicity.
The researchers analyzed data obtained from nearly 3000 males and females ranging in age from about 46 to 70 years old and from across the United States using results from a 2013 and 2014 National Health and Nutrition Examination Survey (NHANES). Among other things, the NHANES measured handgrip strength and femoral neck density. Low handgrip strength is an accepted clinical biomarker of muscle weakness and is associated with low bone density. The femoral neck has served as a reference skeletal site for osteoporosis in many large, epidemiological studies.
The researchers adjusted for age, BMI, ethnicity, calcium intake, vitamin D intake, and supplement usage to improve validity of their statistical analysis. The researchers found that women and non-Hispanic Asian men had the highest odds of developing osteoporosis across gender and ethnicities. However, they also found that increased muscle strength was protective against osteoporosis for both genders and across all ethnicities. Specifically, for every 0.1 kg increase in hand grip strength, the odds of osteoporosis decreased by 6% for men and 10% for women.
One limitation recognized by the researchers is that, due to the cross-sectional design of the study, determining the direction of causation was difficult. In other words, does increased muscle strength cause less loss of bone density or vice versa? It is generally accepted that strength training does reduce the risk of osteoporosis, indicating that increasing muscle strength most likely does cause a decrease in loss of bone density.
Additionally, calcium and vitamin D intake were self-reported. A common issue with self-reported information is that it tends to be less accurate and this could have affected the statistical analysis. There were also a large number of participants who were excluded because of missing data for handgrip strength or femoral neck density.
Another limitation not mentioned by the researchers is that this study encompassed only a small snapshot of time and could therefore only definitively establish an association between increased muscle strength and reduced odds of osteoporosis. A longitudinal study looking at muscle strength and bone density over time (e.g., 10 years) could better establish a relationship between the two.
This study provides even more support for encouraging older adults to participate in regular strength training activities such as lifting weights. Mere weight-bearing activities like walking do not load the body enough to increase overall muscle strength. Resistance training programs that include proper progressions should be followed to reduce the risk of osteoporosis and preserve physical functioning as we age.
Read the full study here.