Cognitive function and the aging brain

Dr Merlin Thomas

Merlin Thomas is a physician and a scientist. His research laboratory is at the JDRF/ Danielle Alberti Memorial Centre for the study of Diabetes Complications at the Baker IDI Heart and Diabetes Institute in Melbourne.
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If life was a game, the winner would be the one with the most marbles at the end.

Even in the absence of brain diseases such as Alzheimers or Parkinsons, as we age we all experience some decline in our cognitive skills – our ability to think, remember, calculate and learn. But one trick to slow aging is holding on to your cognitive functions when all about you seem to be losing theirs.

Age-related decline in cognitive function occurs for a number of reasons.  There is a progressive loss of brain cells (grey matter), so that by the time you reach the age of 90, on average, one in every 10 brain cells is gone. More important is the loss of nerve fibers and connections (white matter), which may result in you ending up with less than half of what you had in your prime.

More marked changes are seen in some areas of the brain, reflecting local mismatches between supply and demand, protection and overload.  And this means that some functions, such as processing speed, attention span, working memory and learning, are affected more significantly than others. For example, as you age, it may take you longer to think through a problem or make a calculation. It may become more common for you to forget the simple things, such as where you left the car keys. At the same time, other things, such as vocabulary, past knowledge and skills, remain relatively intact. These things are appreciated as ‘wisdom’.

In some individuals, cognitive deficits are more severe and widespread, and the ability to function independently is compromised. This is known as dementia and can be the result of accelerated, age-related processes, or of superimposed brain damage due to degenerative diseases, such as Alzheimer’s or Parkinson’s, or a stroke.

A number of factors influence the rate of cognitive decline:

• The elements of aging: oxidative stress, calories, advanced glycation and inflammation are all associated with cognitive decline and can be influenced by the choices we make.
• Atherosclerosis: the same process that narrows the large arteries in the heart also starves the active brain of oxygen, so the things we can do to prevent heart attack (lowering ‘bad’ LDL cholesterol and systolic blood pressure, controlling weight, preventing diabetes, quitting smoking), will also help to keep our brains working better for longer.
• Physical activity: Individuals who remain fit and active appear to retain their cognitive faculties better throughout life.
• Chronic stress: has been shown to shrink those parts of the brain important for working memory and is unequivocally linked to cognitive disorders.  So find time to relax and make constructive lifestyle changes that help prevent stress. Equally, cognitive enhancements can help you deal better with stress.
• Genetic predisposition: some genes are associated with a higher risk of dementia. Although you can now test for many potential genetic disorders if you have a family history, the tests are not 100% reliable and most of your options for prevention can be undertaken regardless.
• Quality sleep: poor sleep doesn’t just make you tired the next day. We need quality sleep to function during the day and build the brain connections that we need for tomorrow.
• Nutrition: our diet may play an important role in slowing rates of cognitive decline and dementia.

Especially beneficial are diets naturally high in:

• Omega-3 fatty acids, found in fish, fish oils, nuts and omega-3 supplements. By contrast, a high intake of trans fats and saturated fats is associated with increased rates of cognitive decline.
• B vitamins, especially Vitamins B9 and B1
• Antioxidants, including Vitamins E and C, carotenoids, flavonoids and enzymatic co-factors. In particular, berries containing high levels of anthocyanins (such as blueberries, blackberries and raspberries) have been shown to have useful effects on cognitive function

None of the associations listed above have been validated in clinical trials.  This does not mean interventions are ineffective, but it does indicate that at present the safest way to replicate the findings is to adopt the dietary and lifestyle habits that have been shown to result in these benefits (such as regular exercise, weight control and diets high in fruit, vegetables, cereals and fish).

A number of herbs, including ginkgo biloba, rosemary, ginseng, sage extract and Bacopa monniera (Brahmi), have been shown to have positive effects on working memory and other aspects of cognitive functioning in some individuals, but their long-term impacts on cognitive decline remain to be established.