Alzheimer’s disease and Type 2 diabetes are two of the most common diseases in the United States. A UCLA Fielding School of Public Health research team is uncovering how higher exposure to air pollution and pesticides may contribute to both.
In a review paper first published in February, Fielding School researchers reported that several studies have shown overlapping biological mechanisms and environmental risk factors for both diseases. After examining data from recently published studies that tracked people’s exposures and whether they did or did not develop one of the diseases, the team concluded that there is much evidence that exposures to higher levels of air pollution and pesticides increase the risk of Type 2 diabetes. Fewer studies have reported a link between air pollution and pesticide exposure and Alzheimer’s disease, they found. The people included in the studies were exposed to air pollution through their immediate surroundings and to pesticides through a variety of sources.
Learning more about factors that increase the risk of both Alzheimer’s disease, which affects an estimated 5.7 million Americans, and diabetes, which affects an estimated 30 million Americans, could inform prevention strategies with significant public health implications for the U.S. and beyond.
“We believe it is very important to show how these environmental factors may contribute to diabetes and Alzheimer’s,” says Dr. Beate Ritz, a co-author of the review paper and professor of epidemiology and environmental health sciences at the UCLA Fielding School of Public Health. “Even if the environmental factors contribute only in small ways, they are so prevalent at the population level that it can mean a big effect in terms of the number of people who develop diabetes or Alzheimer’s and might also develop the diseases earlier than they otherwise would.”
Dr. Michael Jerrett, FSPH professor and chair of the department of environmental health sciences and co-author of the paper, adds, “Many of these exposures can be controlled more effectively than they are now, so there could be big population health benefits that affect both of these important chronic diseases.”
Dr. Kimberly Paul, a Fielding School postdoctoral scholar and lead author of the paper, notes that a 2013 meta-analysis that included data from 15 longitudinal studies found that having diabetes raises a person’s risk of developing Alzheimer’s disease by 57 percent. Drs. Paul and Ritz explain that insulin resistance and oxidative stress, a process by which free radicals damage cells, may be behind both diseases — causing people to accumulate excess proteins in the brain, a marker of Alzheimer’s disease, or in the pancreas, a characteristic of diabetes.
Drs. Paul, Ritz, and Jerrett are now analyzing data from the Sacramento Area Latino Study on Aging (SALSA) series with Dr. Mary Haan at UCSF, a project that is tracking the incidence of Alzheimer’s, diabetes and other diseases in 1,789 elderly Latinos living in the Sacramento region of California. The researchers plan to use this data set to further examine connections between exposure to air pollution or pesticides and onset of Alzheimer’s disease or Type 2 diabetes.
“A lot of non-genetic research on these two diseases is focused on lifestyle factors, such as smoking and diet, but we hope this paper encourages researchers to start thinking about environmental exposures such as air pollution or pesticides,” Dr. Paul says.