A clue from pre-birth
As a medical student I remember chuckling at our professor of pathology, who had a habit of putting his spectacles on the desk, going to draw on the blackboard, and then having difficulty finding where he had put them. His lectures were charmingly old-fashioned; he was the last of the professors who had been appointed for life and had obstinately refused to retire. We sang ‘Happy Birthday’ on his 80th. But he still had his facts at his finger tips and also could been seen cycling furiously along the river bank supporting his college crews in rowing races.
And now, as I approach his age, I too forget where my spectacles are (I sometimes find them on my head) but still manage to give occasional, probably old-fashioned, lectures though I have given up cycling in Edinburgh’s traffic. People’s names sometimes escape me, so I too have become an absent-minded professor. Like me, if you are my age, you may well be able to remember poems you learnt at school but find it impossible to learn new ones. You may worry that you are becoming demented, and worry even more when the radio announces that the NHS is soon to be overwhelmed by caring for people with Alzheimer’s disease. What are the facts and what, if anything, can we do about it?
A colleague at Aberdeen University, Lawrence Whalley, has recently published a remarkable book called ‘Understanding Brain Aging and Dementia’ (Columbia University Press, New York), in which he explains the many influences on brain development and function, and what is known of cognitive decline. While accepting that a sharp increase in the prevalence of dementia has occurred as the population ages, he notes encouraging statistics in some countries, including England and Sweden, showing that there has been a fall more recently. He also notes that mild cognitive impairment associated with getting older far from necessarily leads on to the serious condition of dementia. He points out that around half of all dementia is caused by what is called Alzheimer’s disease but much is related to other causes, blood vessel disease being an important one. Indeed, it is suggested that measures taken to reduce risks of vascular disease may well be responsible for the recent apparent reductions in prevalence.
Professor Whalley takes an unusually broad approach to causation, in striking contrast to many research scientists’ emphasis only on genetic factors. This latter emphasis is directed to understanding mechanisms, usually in the hope of finding a drug to fix the problem, whereas Whalley is interested in multiple risk factors operating throughout life that influence whether or not we become impaired. Thus this essay may not only be relevant to my more elderly readers’ own health but also to what advice we give to our children and grandchildren.
Before trying to summarise what this advice should be, it is important to point to some of the difficulties in obtaining sufficient evidence on environmental effects on which public health advice, legislation or regulation might be based. For example, imagine you thought that exposure of the unborn baby to toxic substances, say in household cleaning materials or air pollution, might lead to brain damage in later life, how would you test that hypothesis? There are ways of doing this but none can give a clear unambiguous answer as to what might happen 70 years later.
It is somewhat easier to test a hypothesis relating activity or diet in middle life to decline in mental function by looking backwards for exposure to risk factors, but still we have problems of how far statistical associations indicate causation or whether the results are confounded by some other unmeasured factors. Even intuitively easier problems, such as comparing environmental exposures in individuals with and without evidence of cognitive decline, raise issues of bias from memory difficulties. These are some of the many issues that make scientists cautious about saying something causes a disease, and therefore what I write has an important caveat; in almost all cases the beneficial effects proposed are based on evidence of association rather than of proven causation.
Almost everyone will now be familiar with the first photograph of an ultrasound image of a baby, as presented to proud parents-to-be, and will have noticed the relatively large size of the head. This is determined by the size of the foetal brain, which grows very rapidly in early pregnancy and continues to grow after birth until the bones of the skull join up. It is no surprise therefore that any toxic substance to which a child is exposed in utero or early life may have potential to impair brain development; you will know about alcohol, tobacco and German measles, for example, and perhaps you remember campaigns on lead in drinking water and petrol. There are many other examples, and some are likely to be as yet undiscovered. A number of nutritional factors, including severe calorie deficiency, are known to damage the developing brain, and others wait to be discovered. There is now a known association between impairment of cognitive function in childhood and risk of dementia in later life. This is one of the reasons for public health advice in pregnancy.
Early childhood is increasingly recognised as a critical phase of brain development, a period during which nerve connections are made and rapid learning occurs from play and interaction with other children and parents. A child deprived of such stimulation in an era of working parents, television cartoons and poor opportunities for early learning, is also at greater risk of later deterioration in cognitive function. To make matters worse, such children are more likely to leave education early and thus incur another risk factor.
It seems that the longer we persist with education, the lower our risks of dementia. But as we grow older, entering teenage years, we are tempted by some of the attractions of adult life – cigarettes, drugs, alcohol and physical combat. Cigarettes and alcohol are well-known to be associated with dementia though many use them to excess without succumbing. Regular use of cannabis, cocaine and other recreational drugs are under very strong suspicion and high doses may cause acute brain injury. The currently popular so-called designer drugs are particularly worrying to doctors since they kill brain cells and it is very likely that we shall see sad future consequences from this craze.
Head injuries in boxing cause dementia (we used to call it dementia pugilistica) but the same syndrome has been recognised in American football and is very likely to be shown to occur in rugby and association football – indeed any sport in which mild concussion may occur. My own and other studies have shown an association between recurrent head injury and risk of Parkinson’s disease.
Apart from these obvious toxic and physical risk factors, it now seems very likely, from the association with vascular disease, that known risk factors for heart problems are also risk factors for dementia. Therefore, prevention and careful treatment of high blood pressure and diabetes will reduce risks. The same applies to medical treatment of head injury, stroke and severe infections, all of which also carry the threat of increasing risks of dementia. Obesity, perhaps through promoting other diseases, is also a risk factor for dementia and, thus, a good balanced diet with plenty of fruit and vegetables and low carbohydrate should be beneficial.
Incidentally Mediterranean folk and people living in primitive rural societies have very much less dementia. We remain unsure about air pollution, but there is some evidence that life in polluted cities increases risks. It may also be the case that some workplace exposures cause early dementia; lead, carbon monoxide and mercury poisoning certainly can and, again from my own studies, in rare cases exposure to high doses of pesticides and organic solvents lead to brain injury.
Finally, what about exercise, physical and mental? Regular exercise is certainly preventive of heart and vascular disease, and there is some evidence of protection against dementia. Mental exercises such as crosswords, tai chi and su doku, should in theory be beneficial and can hardly be harmful. Studies of these are difficult but it is likely that small beneficial effects will eventually be shown.
It will be appreciated that there are many opportunities throughout life to take action to reduce risks of dementia. The opportunities are there for all of us. Governments can take action to improve the early life opportunities of the less fortunate and keep hammering away at the cardiovascular risk factors. Parents can try to steer their teenagers from the usual suspects, not an easy task. We can all try to keep as physically and mentally fit as possible. Since there is no effective drug yet, and may not be for a long time, and since we can’t change our genes and most of the things we can do are both enjoyable and good for us generally, even if they aren’t yet proven to work individually, why not do all of them together? Maybe it is not quite the right expression, but really it’s a no-brainer.
By Anthony Seaton | November 2015