Traffic-related air pollution (TRAP) refers to air pollution caused by traffic activity. Vehicles emit exhaust pollutants from fuel combustion and non-exhaust pollutants from brake wear, tire wear and resuspended dust from the road. Both exhaust and non-exhaust pollutants contribute to elevated air pollution levels.
Common traffic-related pollutants include particulate matter, ultrafine particles, nitrogen dioxide, carbon monoxide black carbon, elemental carbon, hydrocarbons, and volatile organic compounds. TRAP continues to be a major public health concern around the world. People who live in urban areas or near roads with high traffic volumes are often exposed to higher levels of TRAP. Their exposure results in numerous negative health effects.
Until TRAP levels are reduced, practical shorter-term strategies are needed to help reduce the health impact from exposure to TRAP. New evidence suggests that antioxidant-rich diets and antioxidant supplements may be a promising strategy to combat adverse health effects.
Negative health effects from exposure to TRAP include premature death, cancer, respiratory diseases including asthma and wheezing, heart diseases, heart attacks, increased blood pressure, cognitive decline, diabetes, and bone conditions. TRAP can exert multiple detrimental effects on organs through wide-ranging mechanistic pathways.
A key mechanism is through oxidative stress. Oxidative stress occurs when TRAP is inhaled and the pollutants, oxidative by nature, begin to outnumber the antioxidants in the body.
While the body is equipped with powerful antioxidants to protect itself, some exposures to TRAP can overwhelm the body. A potentially effective way to prevent the negative health effects from TRAP would be increasing antioxidant intake through diet or supplements
Dietary sources of antioxidants include fruits, vegetables, oils, soy, nuts, seeds, some spices, compounds found in chocolate, wine, and whole grains. One specific diet that is rich in antioxidants is the Mediterranean diet. The Mediterranean diet focuses on plant-based foods and the consumption of fruits, vegetables, healthy fats and fish which are rich in antioxidants. Furthermore, a diet with an increased intake of fruits and vegetables, in general, is proven to be rich in antioxidants.
In the newly published review on 18th January 2020, the team concluded that adherence to the Mediterranean diet or increased fruit and vegetable intake were effective ways to prevent a wide range of negative health effects associated with TRAP exposures. For example, one study concluded that participants who adhered to the Mediterranean diet were less likely to suffer from heart diseases that have been associated with nitrogen dioxide and particulate matter exposure.
Furthermore, asthmatic children in Mexico who reported strong adherence to the Mediterranean diet or higher fruit and vegetable intake experienced less severe symptoms and increased lung functioning. Additionally, pregnant mothers who reported high fruit and vegetable intake protected their babies form cognitive impairments that can result from nitrogen dioxide and benzene exposures.
Increased fruit and vegetable intake promoted mental development in infants who may have otherwise suffered from adverse cognitive effects associated with TRAP. The results indicate that antioxidant-rich diets proved to be beneficial for healthy adults, asthmatic children, pregnant women and infants. Adhering to the Mediterranean diet or increasing fruit and vegetable intake would be a cheap and simple strategy to mitigate the negative health effects from TRAP.
In addition to the known benefits of vegetables, broccoli and other plants in the cabbage family contain the molecule sulforaphane. Sulforaphane has antioxidant properties and the potential to prevent negative health effects associated with TRAP. One study analyzed the effect of broccoli sprout extract in mango juice while another analyzed the effect of a broccoli sprout beverage.
Both studies determined that sulforaphane offered protection from exposures to diesel exhaust and benzene. While the results of these two studies were promising, participants often complained of nausea or the beverage’s bad taste. So, while broccoli and sulforaphane may be beneficial, there is still a need for researchers to find a way to make the beverages more appetizing.
Antioxidants can also be consumed as supplements which often come in the form of a pill that is taken by mouth. There are a variety of antioxidant supplements available including vitamin C, vitamin E and omega-3 polyunsaturated fatty acids (PUFA). Antioxidant supplements are relatively cheap, can be purchased over the counter and offer some protective benefits from TRAP exposure.
Fish oil and soy oil supplements were given to nursing home residents that had been exposed to elevated levels of particulate matter. In this study, the fish oil supplements protected the elderly from experiencing negative heart effects whereas the soy oil supplements did not. However, in another study analyzing the effects of fish oil and soy oil in the elderly, both groups had increased levels of antioxidant indicators.
In addition to these benefits, healthy college students who were exposed to particulate matter and consumed fish oil supplements experienced less inflammation than the students who did not consume fish oil supplements. Another study compared the effects of fish oil supplements to olive oil supplements in response to particulate matter exposure. Those given fish oil supplements were protected from heart effects while the olive oil group was not.
On the contrary, a different study comparing fish oil supplements to olive oil supplements concluded that olive oil provided protective benefits from controlled particulate matter exposure while the fish oil group remained unprotected. Due to the conflicting results regarding fish oil and olive oil supplementation, there is a need for further research to determine their effectiveness in preventing adverse health effects associated with TRAP.
In addition to fish oil, olive oil and soy oil supplementations, vitamin C and vitamin E are other inexpensive antioxidants supplements that are popular. Asthmatic children that consumed a vitamin C and vitamin E supplement experienced less severe markers of nasal inflammation in response to ozone and particulate matter exposures.
Overall, the available evidence, which comes from 11 international and peer-reviewed publications, indicates that antioxidant-rich diets and to a lesser extent antioxidant supplements can provide protection from the health effects associated with TRAP. The evidence supporting antioxidant-rich diet is more consistent than the evidence behind antioxidant supplements, and therefore is the most promising strategy.
While there is still a need for more research regarding antioxidant supplements and their effective dose, they are still an inexpensive and relatively accessible option which may provide health benefits.
Vulnerable populations such as children, pregnant women, asthmatics, the elderly, those who are exposed to TRAP in their workplace and those suffering from chronic conditions or damaged immune systems may specially benefit from increasing their antioxidant intake. Finally, the team recommend that health practitioners note the value of antioxidant-rich diets and encourage their clients to increase their antioxidant intake.
Barthelemy, J., et al. (2020). New Opportunities to Mitigate the Burden of Disease Caused by Traffic Related Air Pollution: Antioxidant-Rich Diets and Supplements. International Journal of Environmental Research and Public Health. https://www.mdpi.com/1660-4601/17/2/630