Introduction
One of the most common questions I field during presentations is "am I at risk for getting Alzheimer's disease (AD)?" My first response is always that the greatest risk factor for AD is simply your age. Therefore, if you are blessed to live to a ripe old age of 85, you will have an almost 50% chance of having AD. But it doesn't appear as if we are entirely defenseless as a hot topic these days is the idea of "cognitive reserve". What protective effect is there against AD via "cognitive reserve"? Exactly what is it and what can be done to maximize this reserve? Since I continue to hear about this concept I decided it was time to do a little digging into some of the latest literature on the topic. This is what I found.

About Cognitive Reserve
Cognitive reserve suggests that larger brain size and greater cognitive abilities beginning early in life may be important for later protection against dementia.

"Cognitive reserve has been suggested as a concept to explain the differences among individuals in coping with the neuropathologic changes, plaques and tangles, of AD. The notion is that the ability of the mature brain to sustain normal function in the face of significant disease or injury is a function of its reserve capacity. The cognitive reserve capacity is set early in life and gradually declines as the nervous system ages. As individuals age, those with a greater reserve capacity will have a lower risk of dementia than individuals with less cognitive reserve. The impact of brain diseases or injuries will be less apparent in those with a greater reserve capacity, as healthy brain functions are able to accommodate for the cell loss. However, in those where cognitive reserve capacity is low, the effects of the same injury will be more readily apparent as the limited resources available in this situation become expended more quickly."
Source: Neurology.org accessed on September 2, 2009

Dr. Yaakov Stern goes on to say:

"Reserve can be derived from brain size or neuronal count and it can be related to the brains ability to cope with brain damage by using preexisting cognitive processing approaches or by enlisting compensatory approaches". Reference: Stern Y. What is cognitive reserve? Theory and research application of the reserve concept. J Int Neuropsychol Soc. 2002;8:448-460

Enhancing Cognitive Reserve
Therefore, with the concept that cognitive reserve is an important protective factor against AD, the question becomes, what can a person do to maximize their cognitive reserve. The recent research describes some things that have been found to enhance or maintain cognitive reserve such as:

1. Increase Size of Social Circle
   
   The recent documentary that aired on HBO about the Science of Alzheimer's Disease spotlighted the work of Dr. Bennett out of Rush University in Chicago in which he has been studying the protective effects on socialization against clinical symptoms of dementia.
   
   "People with wide social circles are more likely to engage in activities that require physical and mental activity, all of which may protect against AD. In the subdomains of cognitive function, the most pronounced effects of social network showed up on the correlation of overall pathology to semantic memory, and of tangles to episodic, semantic, and working memory. The authors concluded that their data ‘provides evidence that the extent of social networks, or something related to social networks, provides some type of reserve which reduces the deleterious effect of Alzheimer's disease pathology on cognitive abilities in old age' Different people vary widely in their ability to make and maintain social ties, and the authors point out that many of the regions of the brain involved in social cognition also support episodic and semantic memory. It is possible that the very social have a stronger underlying brain circuitry in these regions, or that they more readily access alternative circuits when the need arises." Reference: Bennett DA, Schneider JA, Tang Y, Arnold SE, Wilson RS. The effect of social networks on the relation between Alzheimer's disease pathology and level of cognitive function in old people: a longitudinal cohort study. Lancet Neurol. 2006 May;5(5):406-12
    
2. Maintain a Healthy Weight
   
   A new study finds obese people have 8 percent less brain tissue than normal-weight individuals. Their brains look 16 years older than the brains of lean individuals, researchers said today. Those classified as overweight have 4 percent less brain tissue and their brains appear to have aged prematurely by 8 years. The results, based on brain scans of 94 people in their 70s, represent "severe brain degeneration," said Paul Thompson, senior author of the study and a UCLA professor of neurology. "That's a big loss of tissue and it depletes your cognitive reserves, putting you at much greater risk of Alzheimer's and other diseases that attack the brain,"."But you can greatly reduce your risk for Alzheimer's, if you can eat healthily and keep your weight under control."  The findings are detailed in the online edition of the journal Human Brain Mapping. Source: Livescience.com accessed on Aug 25, 2009
    
3. Early Life Education and Cognitively Stimulating Activities Later In life
   
   Early life education and participation in cognitively stimulating leisure activities later in life are 2 factors thought to reflect cognitive reserve, which may delay the onset of the memory decline in the preclinical stages of dementia.  One study conducted concluded late life cognitive activities influence cognitive reserve independently of education. The effect of early life education on cognitive reserve may be mediated by cognitive activity later in life. Alternatively, early life education may be a determinant of cognitive reserve, and individuals with more education may choose to participate in cognitive activities without influencing reserve. Reference: Cognitive activities delay onset of memory decline in persons who develop dementia. Neurology. 2009 Aug 4;73(5):356-61.Hall CB, Lipton RB, Sliwinski M, Katz MJ, Derby CA, Verghese J.
    
4. Strong Literary Skills
   
   The well known "nun study" conducted by David Snowdon and colleagues found  that nuns with greater literary prowess in their teens and 20s (as measured by the relative complexity of their writing) were more likely to stay cognitively intact than nuns with lesser evidence of literary skill earlier in life.

Summary
At what point does our ability to build cognitive reserve begin to wane? I don't think there is a conclusive answer. The literature seems to suggest that there is still much debate.

One study was conducted to specifically identify whether cognitive reserve is static or dynamic. The study concluded that reserve is dynamic, but it is most amenable to change in early life with an active, engaged lifestyle, emphasizing mental activity and educational pursuits in early life, can have a positive impact on cognitive functioning in late life.

The greatest preponderance of evidence seems to demonstrate significant benefits in earl life mentally stimulating activities for development of cognitive reserve. However, some suggest such as Dr. Bennett, that late life activities, such as activity engagement in social circles, may also assist with cognitive reserve.

As you probably know there are multiple games and activities on the market today designed and marketed to enhance "brain fitness". Activities often recommended are reading, learning a new game or language, and doing crossword puzzles and Sudoku. People are essentially encouraged to do "brain exercise" at all stages of life to continue developing and maintaining cognitive reserve. A key recommendation seems to be engaging in something new and challenging. For example, if you are an old pro at bridge, you might want to throw in a new activity such as learning to speak Spanish. 

Future research will help clarify the most beneficial type of mentally stimulating activities and the life period of maximum benefit to build cognitive reserve capacity. Until then, I suggest we all do what we can to create a healthy brain that can best mitigate against the effects of brain pathology. Therefore, pardon me while I grab my crossword puzzle book and a glass of red wine (red wine has been found to maximize brain health through improved oxygenation). If your teens and 20's are as far in the rearview mirror as mine, don't give up on your brain. Maintaining a healthy lifestyle that includes keeping weight, cholesterol and stress in check along with increasing oxygen to your brain through physical exercise and natural food and drink such as blueberries and red wine are also of great value. And, just for good measure, no matter what age, I would keep up that brain exercise!

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