For many years, there have been suggestions that exposure to air pollution increases the risk of getting dementia, and now a study provides compelling evidence in support of this theory.
Most people are not aware that the majority of neurodegenerative illnesses are not purely genetic in nature, but rather require a combination of a faulty gene and some environmental toxin. In Alzheimer’s Disease (AD), the most significant risk factor of all is age, but the most significant genetic risk factor is having the APOE 4 gene. Even so, this gene accounts for less than a 50% heritable risk, suggesting other factors must be involved in triggering disease.
In a study published in January, researchers followed 3647 US women (who had this genetic risk), for more than a decade, and found a significant correlation between exposure to air pollution levels greater than those considered safe by the United States EPA, and cognitive decline. Air pollution was defined as particulate matter of a size less than 2.5 uM (PM2.5) which is a common component of exhaust fumes from traffic pollution.
The gene that is at fault here is called APOE and humans have three types, one of which as been linked to increasing risks for AD as well as heart disease*. APOE ε3 is the most common type, APOE ε2 provides protection against heart disease by lowering levels of the bad cholesterol low-density lipoprotein or LDL, and APOE ε4 is a risk factor since it increases LDL. In this study, the researchers studied women who had either one or two copies of the “risk” gene.
Most people are not aware that the majority of neurodegenerative illnesses are not purely genetic in nature, but rather require a combination of a faulty gene and some environmental toxin.
Apart from excessive levels of air pollution increasing the the risk of dementia, the type of APOE that the women had was also a significant contributor. Women who had 2 copies of APOE ε4 had a greater risk of dementias than those with one APOE ε3 and one APOE ε4 or 2 APOE ε3s. Thus, residing in places with PM2.5 exceeding EPA standards increased the risks for global cognitive decline and all-cause dementia respectively by 81 and 92%, with stronger adverse effects in APOE ε4/4 carriers.
Researchers utilised the Women’s Health Initiative Memory Study (WHIMS), a well characterized, nationwide prospective cohort of older US women. The participants were community-dwelling (>95% in urban areas) across 48 US states, aged 65 to 79 years, and free of dementia when enrolled in 1995–1999. The age of subjects at the beginning of the trial provides evidence for late-life exposure to air pollution as a common environmental factor for developing dementia.
We already have epidemiological evidence associating cognitive deficits with PM2.5 exposures among the elderly, but this is the first study to show a gene-environment interaction and importantly, that the damage occurs later in life. This is important since it gives you an opportunity to reduce your risk by reducing your exposure. All the more reason to make a sea-change to the country later in life, whilst your still have your faculties intact.
Thus, residing in places with PM2.5 exceeding EPA standards increased the risks for global cognitive decline and all-cause dementia respectively by 81 and 92%, with stronger adverse effects in APOE ε4/4 carriers.
Take home message:
• People who lived in high pollution locations had a greater risk of getting dementia.
• This was increased when they also had genetic risk factors
• Moving away from areas of excessive air pollution (ie higher than what the EPA considers safe) will reduce your risk of getting dementia
• These findings provide the first experimental evidence for gene-environment interactions involving airborne particulate matter and a genetic risk factor for Alzheimer’s disease.
*APOE ε4 combined with air pollution is also a risk factor for heart disease, as described here.