Time After Time: Environmental Influences on the Aging Brain

Elizabeth Grossman


Environ Health Perspect. 2014;122(9):A238-A243. 

In This Article

Abstract and Introduction


The population of Americans aged 65 and older is expected to double between 2010 and 2050,[1] and by midcentury the proportion of the human population made up of people over age 80 is projected to have quadrupled since 2000.[2] So factors that affect this aging population are of increasing importance. Of particular concern are the neurological diseases and disorders typically associated with advanced age, among them Alzheimer's and Parkinson's diseases, dementia, and reduced cognitive function. Investigators are studying the effects of not just present-day exposures and environmental influences such as physical and mental exercise, but also exposures that occurred much earlier in life, whose effects may only become apparent in old age.

It was long assumed that "once the brain received its allotted quota of nerve cells, its destiny was frozen. After that, the passage of time eroded our allotment steadily and irrevocably," as professor emeritus Bernard Weiss of the University of Rochester School of Medicine and Dentistry wrote in 2007.[3] Now, however, there is increasing evidence that the brain is capable of generating new neurons and other functional brain cells even during advanced age. There is also evidence that the older brain can respond quickly and positively to external influences such as physical exercise and intellectual stimulation. This is prompting considerable interest in developing strategies for protecting and enhancing neurological function in the elderly.

The two most vulnerable periods for the brain, Weiss says, are early in life, when the organ is first developing, and later in life, when the body's defenses and compensatory mechanisms begin to falter. There is a large and growing body of evidence indicating these two vulnerable life stages can be linked when damage incurred during early development contributes to health disorders that may not become apparent until later in life.[4]

Weiss also notes that declining defense mechanisms may magnify vulnerability to contemporary environmental exposures. He says that when older adults experience cognitive problems, diagnoses rarely consider the possibility that environmental chemical exposure may be involved, simply because questions about such exposures are typically not asked as part of clinical intake. Over the past 30 years, Weiss says, research attention has focused primarily on environmental influences on early developmental stages. Far less extensively researched, but a subject of increasing interest, are environmental chemical exposures that can affect the health of the aging brain.