Exercise as it relates to Disease/Can physical activity delay the onset of osteoporosis in post-menopausal women?

This is a critique of the original research article 'Physical Activity and Osteoporosis in Post-menopausal Women' written by Nancy Oyster, Max Morton and Sheri Linnell from the Department of Anatomy and Physical Education, Colorado State University. It was published in the journal Medicine and Science in Sport and Exercise, vol. 16, No. 1, pp. 44–50, 1984.

Background to the research
Osteoporosis is a skeletal disorder where by the strength and integrity of a person’s bones are compromised, increasing the risk of fractures. It is noted in this research that osteoporosis is an accepted fact of ageing in women. Post-menopausal women are a high risk demographic of developing osteoporosis because the onset of osteoporosis is linked to the decline of oestrogen that naturally occurs after menopause. Oestrogen suppresses the reabsorption of bone, therefore more bone is reabsorbed for calcium. Physical activity and weight baring exercise has been proven to increase bone mineral density which results in the delayed onset and reduced severity of osteoporosis. Therefore the purpose of this study was to determine whether regular physical activity affected the degree of osteoporosis in women, post-menopause.

Reducing the severity of osteoporosis is important in reducing the likelihood of fractures in older populations. Fractures in any bone of the body have been shown to reduce an individuals quality of life, increase the risk of sustaining another fracture and places a large burden economically on the health care system. It is not only women that are impacted, 1 in 5 men over the age of 50 also experience osteoporosis. Therefore, increasing physical activity and reducing the chances and severity of osteoporosis will benefit everyone, worldwide.

Where is this research from?
This research is from the department of Anatomy and Physical Education at Colorado State University (CSU). CSU has a very large and diverse science background, with notable programs in human and exercise sciences. This department, along with countless others at the university, continue to contribute research across many different areas of health such as nutrition, public health, infectious disease and healthy ageing. The three authors of this study were all researchers and faculty members at CSU at the time this study was conducted and are experienced individuals which makes them appropriate researchers for this particular topic  ..

What kind of research was this?
This research was a case control study. Some disadvantages to a case control study include lack of control and knowledge of external variables, there can also be recall bias of the subject leading to incorrect assumptions. This means the evidence from this study design would not be as reliable as a randomised control trial for example. There are also some advantages of a case control study. They are usually fast, in-expensive and offer insight to long term results of a behaviour in a short testing time.

Method
40 post-menopausal women aged 60–69 were selected at random from a group of volunteers. They were asked to complete a physical activity profile of a normal three day period, including one weekend day, and were asked to recall their typical activity levels including daily living, recreational pursuits, planned physical fitness participation. Intensity of these activities were also estimated. 10 of the women were deemed the most active and placed in the ‘physically active’ group, and another 10 were deemed the least active and placed in the ‘sedentary’ group. Physical activity levels were measured by estimating the oxygen consumption of the subjects based on their height, weight and activities they completed. These two groups were then compared to determine if physical activity can alter degree of osteoporosis. This was done by measuring the cortical diameter of their second metacarpal on the non-dominant hand using X-RAY technology. The authors hypothesised that the more active group would have thicker bone mineral density. This thicker bone mineral density would then result in the delayed onset of osteoporosis.

Limitations

 * 40 is a small sample group, the 40 is then split again into an even smaller group of 20. This could lead to misleading results that aren’t representative of the majority of women
 * Only asking about 3 days’ worth of activity is not representative of a lifetime of physical activity. Therefore, the hypothesis that physical activity over a lifetime impacts severity of osteoporosis is not represented in the results of this study.
 * The study does not take into account diet or calcium/oestrogen supplements over the lifetime, they only ensured they had not been taking them for the last 5 years.
 * The time since menopause beginning is largely estimated. The amount of time post-menopause is an important variable to know because the longer a women is post-menopause, the more likely osteoporosis developing is.

Results
The authors found that the ‘physically active’ groups average cortical diameter (4.305mm) was larger than the ‘sedentary’ groups (3.654mm). The researchers interpreted and compared these results using an independent t-test for small samples. The t of 2.77 was statistically significant (P value= <0.05). Importantly, the researchers also compared the women with the smallest cortical diameters (most-osteoporotic) to the women with the largest cortical diameters (least-osteoporotic), and compared their height and weight. They used an independent t-test for small samples again and found that height was not statistically significant (t= 1.52), but weight was (t= 3.02) and concluded that heavier women were the least osteoporotic, independent of physical activity.

Due to the amount of variables in this study, it is possible the authors over emphasise the implications of their findings. Some ways future studies can overcome some of these variables are to study younger subjects and implement a physical activity intervention that can be more closely controlled. Then measure the severity of osteoporosis once post-menopause. This longer study design will take more time and expenses, but results will be more indicative of the true impact physical activity has on osteoporosis.

Conclusions
Physical activity can delay the onset of osteoporosis and decrease the severity post-menopause. Physical activity results in more bone mineral density. This means that women who are physically active throughout their life have a bigger buffering capacity between reaching menopause and developing osteoporosis. Heavier women were also found to be less osteoporotic, emphasising the importance of lighter women to engage in physical activity.

The impact of physical activity on bone mineral density is a largely researched area. Resistance training in particular results in greater gains in bone mineral density. Greater bone mineral density and reduced severity of osteoporosis is also a largely researched area. Therefore, the result from this study align well with results found in similar studies.

This study however doesn’t investigate the effect physical activity has on diagnosed osteoporosis, only how physical activity during a lifetime can prevent it once post-menopausal. Which, while useful for younger women who still have time to be more physically active and develop more bone mineral density, is still not very useful for inactive, already post-menopausal women.

Practical advice
Being physically active throughout the entirety of your lifetime will delay the onset of osteoporosis post-menopause and decrease overall severity. This is important in decreasing the amount of fractures in older populations and increasing their quality of life, as well as decreasing the economic burden of the disease. Resistance training is a particularly important mode of exercise in increasing bone mineral density.

The Australian Physical Activity Guidelines for 18-64 year old adults recommend accumulating 150-300min of moderate intensity exercise, or 75-150min of vigorous exercise each week. Muscle strengthening exercises should be done at least 2 days a week. Older populations (65 years and older) should aim for 30mins of moderate activity on most or all days, including fitness, strength, flexibility and balance exercises. Before commencing a physical activity program, see a general practitioner, exercise physiologist, personal trainer or any health professional to make sure it is safe for you to do so.

Further information/resources
Osteoporosis Australia- more information and support

Exercise Physiologists in Canberra

At home strength training tips

Calcium rich, osteoporosis friendly recipes

Further reading: The world wide problem of Osteoporosis