‘Sedentary lifestyle led to lighter bones in humans’

Study suggests increased physical activity could be a way to counter weak bones

By Sabreen Haziq
Published: Monday 29 December 2014

Recent research suggests that sedentary lifestyle is responsible for modern humans having lighter bones as compared to hunter-gatherers.

The new study additionally proposes that while human hunter- gatherers from around 7,000 years ago had bones similar in density to current orangutans, 6,000 years later farmers had altogether lighter and weaker bones, more prone to breaking.

The study was carried out by Timothy M Ryan, associate professor of anthropology and information science and technology, Penn State, and Colin N Shaw of the University of Cambridge, UK, and other scientists. It says even though reduction in physical activity is the root cause of degradation in human bone strength, two more explanations have emerged which are less likely to be true. One being that humans and nonhuman primates have varied bone structures because of genetics, as a result of which humans are advancing to a more frail and lighter bone structure, and another being that the large joint surfaces required for upstanding, two-legged movement reduce the brunt on bone, therefore, limiting the development of strong bones. The study was published on December 22in the Proceedings of the National Academy of Sciences.

As a part of this study, the researchers investigated the trabecular structure of the bone (spongy supportive connective tissues of bones found in arm and leg joints) from the head of femur of four specific archaeological human populaces, representing hunter-gatherers and agriculturalists, all found in the same zone of the US state of Illinois. It was found that even though the trabecular structure is very similar in all populations, there appeared one notable exception within the mesh, the honeycomb-like structure encased within cortical shell or outer shell of most bones that allows flexibility. The hunter-gatherers evidently have a great deal larger amount of actual bone density. The altering shape of the trabecular bone depends on the loads imposed on it that can alter its structure from being rod like to significantly thicker. The thickening of the bone is directly related to the constant loading on the bone, depending on the physical activity being undertaken. Although exertion results in minor harm, it can lead the bone mesh to grow back thicker and stronger.

The study also focused on how modifications in eating plans can alter the density of bones which directly affects the weight of the skeleton. Shaw says that human bones can be as sturdy as orangutan’s if they expose their bones to sufficient loading, which in turn delays the onset of degradation of bones.

The study suggests that increased physical activity could be a way to counter weak bones. This can also lower the risk of fractures and conditions such as osteoporosis in later life as exercise in early life would result in a higher peak of bone strength around the age of 30, meaning the inevitable weakening of bones with age is less detrimental.

One in three women and one in five men above 50 years of age around the world carry the chances of being affected by osteoporosis. Osteoporosis has been recognized as the third-most common disease prevalent in India by World Health Organization (WHO). Usually, nutritional deficiencies, including the high prevalence of vitamin D deficiency are considered to be majorcontributor to low bone mass. CS Yadav, professor with Department of Orthopedics at All India Medical Institute, New Delhi, told Down To Earth, “India is a developing country and unfortunately the basic nutritional needs of people specially belonging to the lower strata of the society are almost never met. On top of that the consumption of tobacco and alcohol worsens osteoporosis.  Just like people work out in the gym to build muscles, bones too need some sort of strength training so as to increase their density.”

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