By Julia Bird
We can live for weeks without food, days without water, but only a few minutes without air. The quality of the air we breathe is likewise extremely important for overall health and wellbeing. Air pollution is a major cause of mortality and illness in the world. While there are several natural sources of air pollution, human activities (especially industry, heating and transport) have made a significant contribution to air pollution over centuries (1), particularly after the onset of the industrial revolution in the late 1700s. Nowadays, outdoor air pollutants include fine particles from industry, agriculture or burning fossil fuels, noxious gases, ozone, and tobacco smoke. Indoor air pollution levels are partly related to how well ventilated indoor spaces are. Indoor air pollutants include gases and particulate matter from heating or cooking, various household chemicals, building materials, tobacco smoke, and mould spores. Reducing air pollution is best tackled at the regional or national level. The move to renewable energy sources (2) has the potential to drastically reduce air pollution levels by avoiding one of the major causes of air pollution: burning fossil fuels.
The World Health Organization estimates that around one in eight deaths globally can be attributed to both ambient and indoor air pollution (3). These deaths are primarily from cardiovascular disease, while pulmonary diseases are the second most common cause of death from air pollution. A wide variety of different substances are responsible for air pollution. Air pollution negatively impacts health through stimulating damaging inflammatory and oxidative stress pathways (4).
Setting emissions regulations has been useful in the past for reducing dangerous air pollution levels from industry (5). However, there is still considerable progress to be made to reduce the cause of air pollution, particularly in developing countries that bear the greatest burden of air pollution. The enactment of air pollution regulations and the transition of industry and transport to cleaner energy sources require considerable time and resources to implement. Good nutrition, which has been shown to have a measureable impact on the effects of air pollution, offers an immediate means to mitigate some negative effects. Several micronutrients have clear anti-oxidant and anti-inflammatory actions, and preventing deficiency counteracts oxidative stress in general. The vitamins, minerals and fatty acids provided by a nutritious diet could boost body defences against the effects of air pollution (6, 7).
Marine omega-3 polyunsaturated fatty acids (PUFAs)
In Mexico City, air pollution levels exceed World Health Organisation standards, and private vehicle bans have been put in place to reduce the amount of deadly smog (8). The elderly are at greatest risk of illness and death from air pollution. A research group conducted two randomized controlled trials to investigate whether marine omega-3 PUFAs affect health in the face of heavy air pollution. Omega-3 fatty acids have been identified as having anti-inflammatory properties, and have been implicated in reducing asthma symptoms (9). In the first study, 50 nursing home residents in Mexico City were randomly assigned to 2 g per day fish oil or soy oil for five months. The soy oil group found that heart rate variability declined around 50% when air pollution levels increased, but there was only a small change (7%) in heart rate variability during high air pollution in the fish oil supplemented group (10). A low heart rate variability is a sign of chronic stress (11). In the second study, 52 nursing home residents were once again randomly assigned to 2 g per day fish oil or soy oil for five months. During periods of high air pollution, levels of the antioxidant enzymes superoxide dismutase and glutathione were suppressed while lipid peroxidation products increased. Supplementation with fish oil increased superoxide dismutase and glutathione levels and suppressed lipid peroxidation products (12). One further study in 29 healthy older Americans randomized to fish oil or olive oil found that fish oil prevented negative changes in heart rate variability and plasma lipids caused by inhaling fine particulate matter (13).
B vitamins – folate, B6, B12
Many of the B-vitamins work together to support DNA and protein synthesis. When folate, vitamin B6 or B12 are lacking, levels of homocysteine, a protein building block, rise. Certain genetic differences also result in an increase in homocysteine concentrations in the blood. High homocysteine levels cause negative changes in the lining of arteries, increased oxidative stress and reduced ability of the veins and arteries to expand (14). Interestingly, both cigarette smoking and air pollution are associated with elevations in homocysteine (15). This has led researchers to investigate whether air pollution and B-vitamin deficiency are linked, as both cause an increase in homocysteine levels. Within a cohort study of 549 elderly men, subjects with genes corresponding to a higher homocysteine level had a reduction in heart rate variability, and this effect was stronger if these men were exposed to greater levels of air pollution (16). In addition, having better intakes of folate, vitamin B6 and B12 reduced the negative effects of air pollution on heart rate variability.
Antioxidant vitamins C and E
Vitamins C and E work together to provide antioxidant protection to the body. Regular smokers have a greater need for vitamin C and tend to have lower levels in their body (17, 18); dietary intake recommendations are greater in smokers (19). It stands to reason that air pollution and vitamin C may also interact. In a study conducted in workers exposed to coal-electric plant emissions, a high dose supplement of vitamins C and E could improve workers’ antioxidative capacity (20).
Vitamin D is named “the sunshine vitamin” because it is produced by sunlight on the skin. However, vitamin D is only produced when the sunlight reaches a certain threshold of intensity: sunshine on a summer’s day is ideal, weak wintery light through cloud cover is not. Current estimates find that vitamin D deficiency is widespread in many countries, particularly in infants and the elderly (21). Besides cloud cover, air pollution is a further risk factor for low vitamin D status. Air pollutants such as aerosols and ozone gas reduce the amount of sunlight reaching people located on the ground, thereby reducing the amount of vitamin D their skin can produce. Studies in diverse populations such as postmenopausal women living in Belgium, and infants and young children living in India, show that living in areas with high levels of air pollution is a risk factor for vitamin D deficiency (22, 23).
Air pollution is a major cause of poor health throughout the world. It causes an increase in oxidative stress and inflammation in the body that raises risk of cardiovascular and lung diseases. Nutrients including omega-3 PUFA, the B-vitamins, vitamin C and E can potentially work against some of the negative effects of air pollution. Air pollution can also reduce the amount of sunlight that we are exposed to, which in turn can mean a reduction in vitamin D production. An adequate intake of essential nutrients can be a strategy to prevent some of the negative health effects of air pollution.