Air Pollution and Osteoporosis - An Overview

Introduction

In the current situation, air pollution accounts for not only the impact of climate change but also its impact on the general population’s health. Harmful substances present in air pollution are the major risk factor for various health disorders. The particulate matter (PM) with a small diameter present in the pollutants is the major risk factor for causing diseases. Recent studies show evidence of an association between exposure to a particular matter and the risk of osteoporosis. This article discusses the relationship between air pollution and osteoporosis in detail.

What Is Air Pollution?

Air pollution is becoming a major risk factor for health issues in both developed and undeveloped countries. The industrial revolution developed the world in terms of technology, transportation, and various other multiple services. Still, it has become the primary cause of introducing pollutants into the environment affecting human health. Multiple studies have shown a strong correlation between air pollution and the incidence of lung diseases, heart problems, metabolic disorders, neurological disorders, and even cancer.

Air pollution contains toxic pollutants in gaseous forms. Air pollution contains particulate matter (PM) and all the gaseous pollutants such as ammonia, Sulfur dioxide, Carbon monoxide, Nitrogen dioxide, ground-level ozone, as well as water, dust, and variable particles.

What Is Meant by Particulate Matter?

The particulate matter is blamed for the harmful effects of air pollution. They are usually made up of droplets of liquid, acids, elemental carbon, organic carbon, mineral dust, metal dust, and sulfate compounds. The particulate matter is classified based on its diameter.

• The coarse particles with a diameter of fewer than 10 microns are PM10.

• Finer particles with a diameter of fewer than 2.5 microns (PM2.5) and less than one micron (PM1).

• Ultrafine particles of a diameter of fewer than 0.2 microns are also investigated.

They are mainly caused by burning fossil fuels, vehicle emissions, and industrial emissions. Exposure to this particulate matter could lead to various health effects. Long-term exposure to the particulate matter results in cardiac diseases, neurological problems, and even death. PM1 and PM2.5 could enter the deeper areas of the respiratory system and subsequently cross the barriers, reach the bloodstream and enter several other organs. PM2.5 comprises cancer-inducing properties.

What Is Osteoporosis?

Osteoporosis is a disease of the bone often caused by a low bone mineral density and bone mass or when there is any structural abnormality of the bone. This disease results in brittle and weakened bone and often predisposes to fractures. Osteoporosis occurs more commonly in females than in males due to their high risk of developing reduced bone density and decline of bone mass after menopause. Bone mass measurement is indicated in BMD (bone mineral density) which is the indicator of bone strength. Generally, the BMD of an individual is compared to a healthy person and given a T-score. The differences between the BMD of the individual and the healthy person are measured in a unit called standard deviation (SD). A person with osteoporosis has a T-score of less than 2.5SD.

What Is the Association Between Air Pollution and Osteoporosis?

Several factors predispose the decline in bone strength, such as age, sex, low body mass index, sedentary lifestyle, menopause, kidney failure, alcohol consumption, smoking, malnutrition, and diabetes. The most unexpected risk factor is the role of air pollution in declining bone strength and a higher risk of osteoporosis. Its association with osteoporosis has also been recognized in multiple studies that show the effect of this particulate matter on the occurrence of osteoporosis.

How Does Air Pollution Affect Bone Strength?

• The particulate matter present in air pollutants has the properties of promoting inflammatory reactions. This results in increased production of inflammatory cells and increased plasma concentrations of protein levels in response to an inflammatory reaction.

• These cellular reactions often result in inflammatory-related diseases like arthritis, cardiac diseases, and airway inflammation.

• Proinflammatory cytokines enhance the effect of inflammation over the bone, which is mainly responsible for maintaining bone formation as well as bone destruction.

• Inflammatory cytokines such as Tumor necrosis factor-α, Interleukin-1, and Interleukin-17 are all a type of signaling molecule that is developed by the body’s immune system and other cells that promote inflammation in response to an inflammatory reaction.

• Recent studies have shown the effects of inflammatory cytokines in inducing osteoclast (a type of cell that breaks down bone tissues) activation and stimulating bone resorption.

Other studies show the association between receptor activators of the nuclear factor-kappa B pathway (they are involved in the activation and proliferation of osteoclasts) with particulate matter (PM2.5 and PM10). The studies concluded that longer exposure to PM2.5 and PM10 is strongly associated with osteoclastogenic properties of the nuclear factor-kappa B pathway.

What Is the Association Between Vitamin D Synthesis and Air Pollution?

Vitamin D is essential for maintaining all three bone cells (osteoclast, osteoblast, and osteocytes). Vitamin D deficiency can result in osteoporosis. Cholecalciferol and the inactive form of vitamin D require two oxidation reactions for activation, one in the liver and the other in the kidney.

• Recent studies conducted by Afsar et al. show that long exposure to particulate matter in the air pollutants is associated with the oxidation reaction in the kidney in converting the inactive 25-hydroxyvitamin D to active 1,25-dihydroxy vitamin D.

• Additionally, toxic contents of the metal dust in air pollution have the property of deteriorating kidney functions, affecting vitamin D synthesis.

• Vitamin D synthesis requires sunlight, especially ultraviolet (UV)radiation between the wavelength of 290 and 315 nanometers. Particulate matter from air pollution reduces the surface solar and ultraviolet radiation, thus affecting the biological vitamin D synthesis in kidneys.

Several studies have reported that people, including adolescents and children who were exposed to high levels of particulate matter, have lower serum vitamin D levels.

Conclusion

Air pollution has some severe effects on the body’s respiratory, cardiovascular, and neurological systems. Recently, it has become a risk factor for osteoporosis by affecting bone strength and biological vitamin D synthesis. Particulate matter in the polluted air, especially PM2.5 enters the body and results in harmful health issues. Several studies have shown evidence of lower levels of bone mineral density in areas with higher concentrations of particulate matter, especially with an aero diameter of fewer than 2.5 microns.