Osteoporosis and Air Pollution

Air pollution is one of the biggest threats of modern times. It is dangerous because it is harming the environment that humans live in, as it contributes to global warming, which leads to uncertainty in weather patterns, causing recurrent floods, droughts, and severe storms in different regions of the world that were not exposed to those risks in the past. Prolonged uncertainty due to such climate change not only lowers agricultural and economic productivity, but it is also harmful to the health of humans in many ways, causing lung problems and heart diseases. New research conducted by the Barcelona Institute of Global Health and Harvard University has found that air pollution is also worsening bone health in humans, causing humans to suffer from diseases such as osteoporosis. 

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Osteoporosis is a condition in which one’s bones become weak and brittle over time. According to the World Health Organization (WHO), osteoporosis is the second leading health problem globally. In the United States alone, over three million residents are affected by the disease. Females are more likely to suffer from this condition due to the fact that the estrogen hormone, the sex hormone required for reproduction, reduces significantly from the time of menopause at around the age of fifty. Lower estrogen levels pose a higher risk of developing osteoporosis, and about a third of women over the age of fifty have osteoporosis in the U.S. 

Having osteoporosis typically leads one to break their bones more easily, especially in the hip and spine areas, as there is a higher likelihood that older people fall on their hip and back. Even a minor fall can cause a serious injury in those areas of the body, which can lead to a disability such as an inability to walk, bend, stand, and lift objects, or even cause death due to complications from hip and spine surgeries. The fractures occur because of reduced bone strength. Bones are living tissue, so they are constantly being built up and then broken down. When people are younger, typically teenagers, their bones build up faster than they break down. The strength of bones is mainly determined by bone mineral density (BMD), also known as bone mass.  Once humans are thirty years old, they have reached their peak bone mass. Low BMD is one of the main factors for older men and post-menopausal women to develop osteoporosis.

BMD levels decrease over time as people age. Although the average decline is less than 1% per year from the level of the prior year, some individuals lose BMD at faster rates than others due to genetics. However, new research shows that the effect of the exposum – non-genetic determinants, such as air pollution – over a period of an individual’s lifetime reduces BMD and causes osteoporosis to be even worse by making the bone more brittle. Therefore, genetics isn’t the only factor that influences the development of osteoporosis. 

To understand the relationship between air pollution and bones, it is important to measure the specific elements in the air that exacerbate bone degeneration. Scientists gauge air pollution by measuring the total amount of a fine particle called particulate matter 2.5 (PM 2.5) in the air. These particles are extremely small droplets, with widths of 2.5 microns or less  (microns are measurements of distance, and there are 25,000 microns in an inch). PM 2.5 is found everywhere in our daily lives, as it is emitted from cars, trucks, cooking, smoking, and elsewhere. When PM 2.5 levels increase in an area, foggy conditions are present; however, in these conditions, it feels very hard to breathe and surroundings are hazy. There is a set standard in every country for a safe level of PM 2.5. For example, the United States’ PM 2.5 standard is 12 micrograms per cubic metre. In the past, air pollution has been linked to lung problems and heart diseases, since PM 2.5 is able to slip into the respiratory tract extremely easily. While there is not yet a clear understanding of the exact scientific process by which these pollutants impact bone density, scientists have now established a clear statistical correlation between high PM 2.5 levels and lower BMD.

A recent study in India has shown the strong correlation between these two factors, and the problem of air pollution in India is severe. The World Health Organization sets the annual average guideline for PM 2.5 as 10 micrograms per cubic metre, while in 2019, cities in India were at 115 micrograms per cubic metre. A number of surveys are being done in Indian cities to show the impact it has on health.  Recently in New Delhi, India, the pollution has become so terrible that some people are setting up oxygen bars where customers can pay to breathe in pure oxygen. A sample study in 2019 was done by the CHAI Project, a project funded by the Barcelona Institute of Global Health, in 28 villages outside of the Indian city of Hyderabad, where air pollution is significantly above the safe level. Researchers surveyed different groups of population such as men, women, and different income groups to observe their exposure to PM 2.5 and black carbon. They also measured the bone mineral content (BMC) of the hip and spine for the same sample groups. The results of the statistical analysis showed that there was an inverse correlation between the ambient PM 2.5 and the BMC of the hip and spine. When PM 2.5 levels are high, there is a lower bone mineral content, which leads to lower bone mineral density, increasing the risk of osteoporosis. 

There are other studies in the U.S. that show a similar correlation between this polluting PM and osteoporosis. For example, a study done by the School of Public Health of Harvard University used a sample of 9.2 million Medicare enrollees over the age of sixty-five between 2003-2010 and found that the number of admissions of patients to hospitals for osteoporosis-related fractures was higher in the areas where concentration of PM 2.5 was high. Interestingly, the correlation between air pollution and osteoporosis-related fractures was stronger among the lower income patients. 

Although the correlation has been established, the mechanism by which air pollution affects bone density is an area of further research. Upon my request, Dr. Mone Zaidi, Professor of Medicine and Director, The Mount Sinai Bone Program, explained, “Recent studies from India and Europe that document a strong association of levels of particulate matter in the air, a surrogate for the extent of overall air pollution, and bone mineral density are indeed intriguing. A plausible explanation for such a relationship is that particulate matter initiates an inflammatory response, which is known to stimulate bone loss.  Further studies are likely to help us better understand the mechanism underlying pollution-induced bone degradation.”

Although more scientific evidence is required for understanding why air pollution directly impacts osteoporosis, the results from these statistical studies are important because it also has socioeconomic implications for the population of the world. In the U.S., the direct health cost from 2.1 million osteoporosis-related bone fractures is $20.3 billion annually. The outcome is even worse for less advanced countries where a large number of people do not have access to adequate healthcare. For example, in Indian cities, PM 2.5 is at 115 micrograms per cubic metre, a level that is 11.5 times the safe level established by the World Health Organization. People in countries such as India work largely in the informal sector with an outdoor work environment, such as construction workers, vendors, auto rickshaws drivers, and families living on the streets. Increased air pollution due to rapid industrialization also affects factory workers and the general population, including the children living in these cities. While there already has been data to show direct correlation between air pollution and lung diseases, such as asthma, in these cities, there is now an additional dimension to the problem, which is reduction of bone strength. This means that over time, worker productivity will decline because more people will suffer from osteoporosis. 

The current consumption habits and the production processes for producing goods and services are the main reasons for increased air pollution. Some argue that the habits that humans have now such as an excessive reliance on fossil fuels for transportation and electricity usage, are necessities, since they help our economies to grow. If humans do not change these habits now, pollution will essentially increase the health costs for nations as well as lower worker productivity in the long run. However, apart from an economic and health rationale for reducing air pollution, there is also an ethical obligation towards all other living things on this planet that are impacted by air pollution severely. Science tells us that it is imperative that we understand the detrimental effects of air pollution and thereby use sustainable technologies for producing goods and services that will improve air quality. 

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