Posted: Mon, November 24, 2014 | By: Brain Health
by Alexander Borch Kristensen
Air pollution affects the brain in a negative way. For many years we have known that polluted air damages the brains of children, the developing brains, the brains of the future! (The components of air pollution (PAH, PM) are explained at the conclusion of this essay.)
When science puts this invisible brain killer under the microscope – what does it find?
Before We Even Breathe
Frederica Perera, Director of Columbia Center for Children’s Environmental Development, noticed that pollutants affect our brain even before we take our first breath. Her research team examined the effect of air pollution on fetuses’ and infants’ neurodevelopment. 
Perera monitored the composition of ambient air molecules during pregnancy of 263 nonsmoking African-American and Dominican women and found that concentrated levels of PAHs lead to lower birth weight (P=0,003) and lower head circumference at birth (P=0,01) 
A follow-up study three years later showed that high prenatal (before birth) exposure to PAHs (upper quartile) was associated with approximately a 5% lower mental development measured. (This developmental delay was not race specific. )
Using the same approach, Perera found that high exposure to PAHs during pregnancy is associated with a lower verbal IQ and lower full-scale IQ of 4.67 and 4.31 points, respectively. 249 children had their IQ measured at age 5.  An average decrease of 3.8 IQ points at age 5, were associated with higher levels of PAH during pregnancy, found by a Polish study from 2012.  Perera and her team also found that exposed to second hand smoke (whether it’s before or after birth) seem to be at greater risk for a neurodevelopment delay. 
Additional results have also shown that smoking during pregnancy affects the IQ of the child. A Belgian study tested the connection between smoking during pregnancy and the IQ of the children at age 4 – 8. The study found a difference of 15 IQ points in favor of the children of the nonsmoking mothers.  An Estonian study found a 3.3 point deficit of intellectual abilities by school children, when the mother smoked during pregnancy. Other studies show the same tendency: maternal smoking leads to lower IQ . [8, 9, 10] Science reveals that tobacco smoke (whether it’s second hand or from the mother herself) prevents the child from developing maximum brain potential.
A Chinese study evaluated a connection between exposure to prenatal PAHs and environmental tobacco smoke and full-scale and verbal IQ at age 5. Contradicting other studies, the study assessed that tobacco smoke or PAH didn’t have significant impact on IQ, individually. However, the two environmental factors together seemed to have severe impact on full-scale (p=0.025) and verbal (p=0.029) 
There is also a connection between prenatal exposure to air pollution and the possibility of getting autistic spectrum disorders. 
A Brain in Development
A 2014 study initiated at the University of Montana found that children exposed to high levels of air pollutants showed a higher level of serum autoantibodies. Normally, antibodies are produced in the body to detect hostile bacteria and viruses before an inflammatory response can take place and fight off the hostile organism. When this mechanism goes wrong the body might produce autoantibodies, which basically are the same thing however they are targeting the body’s own cells for inflammation. 
As autoantibodies attribute to breakdown of the blood-brain-barrier, the brain is suddenly exposed to various neurotoxins.
Lead is a metal to which you are exposed through several media, for example through the air by inhalation. Children are most susceptible to lead exposure and high exposure to children up to 2 years of age can cause, approximately, as much as a permanent decrease of 5 – 7 IQ points. Points that can’t be recovered by lowering lead exposure later on in life!  Various studies show the same tendency that children, from birth to age 8, show permanent lower cognitive performance(IQ and school performance) due to higher levels of lead. Even low levels of lead seem to have a great impact on cognition. [15, 16, 17] In India, a study showed that children’s susceptibility to lead is somewhat connected to their genetics and Hemoglobin levels.  But that becomes really technical, so let’s just keep to the simple math.
Dr. Leonardo Trasande, a professor at New York University School of Medicine, compared this IQ loss with earning potentials and estimated that the loss of IQ, due to lead exposure, is costing developing countries $992 billion annually!! Africa’s economy takes the hardest hit with losses estimated at $137.7 billion, or 4 percent of its gross domestic product. [19, 20]
Most countries have taken the first step of phasing out leaded gasoline. MOST countries! These numbers ought to affect the remaining countries to take the same step. In the 1970s, about 88% of US children up to 5 years old had more than 10 micrograms of lead per deciliter blood, according to U.S. Environmental Protection Agency. In 2011 about 5.8% had more than 5 micrograms of lead per deciliter blood. This great decrease is attributed to the phase-out of leaded gasoline. This confirms the efficiency of unleaded gasoline!
Brains in General
When connecting air pollution to brain health most researchers are referring to the damaging effect of inflammation and oxidative stress in the brain. [21, 22, 23]
Inflammation is a mechanism of the immune system attacking foreign organisms e.g. bacteria and viruses. So this is actually a good thing. However this mechanism might also affect some of the surrounding tissue. Imagine this happening in the brain! It would be optimal to keep this response at a minimum. 
Oxidative stress; reactive oxygen species (AKA. free radicals) are molecules that are highly reactive meaning that they have the ability to pick apart another molecule (a very simple explanation). As these species react with vital molecules of the cells e.g. the DNA they can become very dangerous. Free radicals are created in the body as a waste product as the mitochondria create energy. Luckily the body acquires Antioxidants from ingested food and its own production. Antioxidants are used to keep the free radicals in “check mate”. Oxidative stress is the term for disruption of the internal balance of free radicals and antioxidants. An overload of free radicals would damage the cells from within and might often cause cell death. 
This understanding matches with the fact that living by highly trafficked roads is associated with higher exposure to ultra fine particles and fine particles (which are subtypes of Particulate Matter) at the as it’s associated with lower performance in verbal learning and memory, psychomotor speed, language and executive functioning. It also came to attention that, brain performance rose monotonically with increasing distance to the roadway. [26, (27, 28, 29, 30)]
Researchers believe that the oxidative stress and inflammation caused by air pollution may lead, or attribute, to disorders like Alzheimer’s disease (AD) and Parkinson’s disease (PD).
Exercise has shown to enhance neuro-plasticity and cognition in various ways. In other words, your brain is a great fan of exercise. Brain derived neurotropic factor (BDNF) is a protein which is believed to be connected to this enhancement. It can be put very simple:
(Aerobic) Exercise → increased levels of BDNF in various brain regions → Better brain “performance”
A review, from August 2014, summarizes studies that indicate cognition is enhanced by exercise, but is impaired if the ambient air during exercise becomes polluted. Polluted air inhibits the exercise induced BDNF-increase. This theory is not well-established and will, presumably, be supported by follow-up studies. 
Other factors might be mediating cognition besides BDNF. BDNF has just become a point of focus in relevance to cognition.
A 2008 epidemiological study looking at the adult brain showed a connection between higher ozone levels and reduced attention span, slower reaction time and compromised short term memory. 
How extensive is the impact of air pollution? How polluted does the air need to be to cause harm? Is the damage significant enough to worry about?
Additional research is definitely required, to clarify the connection between traffic-related air pollution and brain damage. How extensive is the damage formed by traffic? And how much do we need to reduce the density of traffic to see an improvement? Hopefully these question will soon be investigated.
The Components of Polluted Air
Air pollution is a heterogeneous mixture of gases (e.g. Particulate matter, ozone, nitrogen oxides, PAHs and more)
Polycyclic aromatic hydrocarbons (also known as PAHs) are non polar molecules mostly found in burned pots and pans, charred foods, diesel exhaust(DE), and cigarette smoke and are made during incomplete combustion, caused by insufficient oxygen availability. 
Particulate matter (PM) is a pollutant made from a mixture of solid particles and liquid droplets. The composition is very small which makes it even more dangerous, as it’s more simpler to inhale and easily enters the bloodstream. In fact, the smaller the particles, the more dangerous it is. PM10 and PM2,5 or fine particles indicates PM with a size less than 10μm and 2,5μm in diameter, respectively. UFPM or ultra fine particles (PM under 0,1 μm in diameter) which are often are released from diesel exhaust.
The Do’s and the Don’ts
What can be done to breathe cleaner air?
Your choice of residence – Where you live is a factor of cleanliness of the air. If you’re about to move anyway, prefer living further from dense traffic to avoid neuro-inflammation and oxidative stress.
Your choice of transportation – If public transportation or taking the bicycle is out of the option, think of this. Next time you’re buying a car, an electric or a hybrid car should be at higher priority than combusting cars (especially diesel), to improve your ambient “Brain health” environment.
Taking responsibility for the brain development of the next generation would involve not lighting your cigarette/cigar or whatever you’re smoking, in their presence or in the presence of a pregnant woman.
As mentioned earlier a lot of countries have already taken a giant step towards cleaner air, as they’ve phased out leaded gasoline. The results on brain development should be a great encouragement for the remaining countries to take the same step.
It’s also advised that countries and states take action towards lowering traffic-related pollution, especially in highly populated areas. A step like this would potentially mean a better cognitive functioning by the general population, and thereby higher work efficiency. We might also experience a decrease in cases of Alzheimer’s and Parkinson’s disease. People would be able to stay at work for longer time.
4. Prenatal airborn polycyclic aromatic hydrocarbon exposure and child IQ at age 5 years - http://www.ncbi.nlm.nih.gov/pubmed?term=19620194
5. Prenatal exposure to airborne polycyclic aromatic hydrocarbons and children’s intelligence at 5 years of age in a prospective cohort study in Poland. - http://www.ncbi.nlm.nih.gov/pubmed/20406721
7. The smoking addiction of pregnant women and the consequences on their offspring’s intellectual development - http://www.ncbi.nlm.nih.gov/pubmed/9216801
8. The smoking addiction of pregnant women and the consequences on their offspring’s intellectual development. - http://www.ncbi.nlm.nih.gov/pubmed/9216801
9. Effect of birth weight, maternal education and prenatal smoking on offspring intelligence at school age. - http://www.ncbi.nlm.nih.gov/pubmed/20634008
10. A dose-response relationship between maternal smoking during late pregnancy and adult intelligence in male offspring. -http://www.ncbi.nlm.nih.gov/pubmed/15670102
11. Effects of prenatal polycyclic aromatic hydrocarbon exposure and environmental tobacco smoke on child IQ in a Chinese cohort. - http://www.ncbi.nlm.nih.gov/pubmed/22386727
14. Effects of metals on the nervous system of humans and animals. - http://www.ncbi.nlm.nih.gov/pubmed/11764847
15. The burden of disease from pediatric lead exposure at hazardous waste sites in 7 Asian countries. - http://www.ncbi.nlm.nih.gov/pubmed/22999658
16. Impact of low blood lead concentrations on IQ and school performance in Chinese children. - http://www.ncbi.nlm.nih.gov/pubmed/23734241
17. Childhood blood lead levels and intellectual development after ban of leaded gasoline in Taiwan: a 9-year prospective study. - http://www.ncbi.nlm.nih.gov/pubmed/22280932
18. Hemoglobin, lead exposure, and intelligence quotient: effect modification by the DRD2 Taq IA polymorphism. - http://www.ncbi.nlm.nih.gov/pubmed/21205584
21. Brain Inflammation and Alzheimer’s-Like Pathology in Individuals Exposed to Severe Air Pollution - http://www.ncbi.nlm.nih.gov/pubmed/15513908
22. Neurotoxicants are in the air: convergence of human, animal, and in vitro studies on the effects of airpollution on the brain. - http://www.ncbi.nlm.nih.gov/pubmed/24524086
23. Human brain derived cells respond in a type-specific manner after exposure to urban particulate matter (PM). - http://www.ncbi.nlm.nih.gov/pubmed/24999231
25. What is oxidative stress? - http://www.ncbi.nlm.nih.gov/pubmed/10693912
26. Physical Activity, Air Pollution and the Brain – http://www.ncbi.nlm.nih.gov/pubmed/25119155
27. Concentration and size distribution of ultrafine particles near a major highway. - http://www.ncbi.nlm.nih.gov/pubmed/12269664
28. Ultrafine particles near a major roadway in Raleigh, North Carolina: Downwind attenuation and correlation with traffic-related pollutants - http://www.sciencedirect.com/science/article/pii/S1352231008010832
29. Long-term exposure to traffic-related particulate matter impairs cognitive function in the elderly. - http://www.ncbi.nlm.nih.gov/pubmed/19733348
30. Residential proximity to nearest major roadway and cognitive function in community-dwelling seniors: results from the MOBILIZE Boston Study. - http://www.ncbi.nlm.nih.gov/pubmed/23126566
Alexander Borch Kristensen is 20 years old. He studies biotechnology at the Danish gymnasium of Grindsted, where he graduated in the summer of 2014. He’s a brain enthusiast and always eager to learn more about the brain. He’s currently taking the ‘Certificate in Brain Health and Social Policy’ course at Brighter Brains Institute.