What causes age-related cognitive decline?
Even in the absence of brain diseases such as Alzheimer’s or Parkinson’s, we all experience some age-related cognitive decline, including our ability to think, remember, calculate and learn.
Age-related cognitive decline occurs for a number of reasons. There is a progressive loss of brain cells (grey matter), so that when 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. 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. We appreciate these things as ‘wisdom’.
In some individuals, age-related cognitive decline is 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 superimposed brain damage due to degenerative diseases such as Alzheimer’s or Parkinson’s, or stroke.
What influences the rate of cognitive decline?
A number of factors influence age-related cognitive decline. These include:
- The elements of aging: Oxidative stress, calories, advanced glycation end products and inflammation are all associated with cognitive decline and are influenced by our choices.
- Atherosclerosis: The same process that narrows the large arteries in the heart also starves the active brain of oxygen. Therefore, interventions to prevent heart attack will help our brains work better for longer. These include lowering LDL cholesterol and systolic blood pressure, controlling our weight, preventing diabetes and quitting smoking.
- Physical activity: Individuals who remain fit and active appear to retain their cognitive faculties better throughout life.
- Chronic stress: This shrinks the parts of the brain important for working memory and is linked to cognitive disorders. Finding time to relax and making constructive lifestyle changes can help prevent chronic 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. You can, however, undertake most preventative steps regardless of knowing.
- Quality sleep: Good quality sleeps rejuvenates the mind and body. We need quality sleep to function during the day and build the brain connections that we need for tomorrow.
How does nutrition affect cognitive function?
Diet also plays an important role in slowing rates of age-related 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 can increase rates of cognitive decline.
- B vitamins, especially vitamins B9 and B1.
- Antioxidants, including vitamins E and C, carotenoids, flavonoids and enzymatic co-factors. Berries containing high levels of anthocyanins (such as blueberries, blackberries and raspberries) can have useful effects on cognitive function.
A number of herbs, including ginkgo biloba, rosemary, ginseng, sage extract and Bacopa monniera (Brahmi), have also 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 unknown
None of the associations listed above have been validated in clinical trials. This does not mean interventions are ineffective, however. It simply indicates that at present the safest way to replicate the findings is to adopt the dietary and lifestyle habits that result in these benefits (regular exercise, weight control and diets high in fruit, vegetables, cereals and fish).