Thursday, 5 June 2014

Life can be very long

The Challenge of Longevity

Written on March 12th 2014

Life expectation at birth in Ireland in males and females was approximately the same at about 50 years at the end of the 19th century. Early in the 20th century life expectation began to increase and continued gradually during the next 106 years when the census that year confirmed mortality among males of 76.8 years and 81.6 years in females. This increase could be attributed on the one hand to a big fall in infant mortality and to the successful control of most of the epidemic diseases in the 1920s and 1930s. My colleagues and I in our paper published by the American Journal of Public Health in 1970 studied the smoking habits and mortality data in 15 different countries and we were able to conclude that the recent mortality disparity between men and women could be largely if not entirely attributed to cigarette smoking among men after the last war.

The cigarette habit had increased dramatically among men after the war thanks to the influence of the Americans and British who were generous in supplying cigarettes to the troops and subsequently to widespread advertising by the industry.   However, it is now clear from recent data that the disparity is now falling again and it should eventually fall to a more equal level as cigarette smoking is falling rapidly among middle aged men. Also it is clear that the current cigarette is less lethal because of the use of the filter and the reduction in nicotine, tar and carbon monoxide.

It is anticipated that the results of the last census in 2010 in Ireland will show a further improvement in life expectation and a further narrowing in the disparity between men and women. In an attempt to understand the continued improvement in life expectation of both sexes, it seems worth listing the lifestyle and environmental factors which may account for the continued upward survival trend.  I am speculating in this essay on the possible opportunities of maintaining the continued rise in life expectation above the current 2006 figures by studying the life style and other factors which may be relevant to changes in human survival.

Infant mortality continues to be an important factor, having fallen from 78 per thousand after the war to a remarkable figure of 3 in 2009 and 4 in 2010 in Ireland. The figure of 3 was the lowest ever recorded in these islands. Infant mortality has obviously reached an optimum level of control.

The following list includes, firstly, the factors which are likely to contribute to the continued improvement in life expectation and, secondly, the factors which I believe are responsible for our failure to reach our optimum age. For the sake of studying the optimum age of humans I have suggested 95 years when 50% of the population will have died whatever the mode of death recorded on the death certificate.

We need to look at the human gene and its influence on longevity, How fixed is it in terms of years of survival and in its distribution around a nominal figure of, say, 95 years? And what are the prospects of increasing the survival capacity of the human gene through research? And, indeed, would it be wise if we were to extend human life through genetic manipulation? I think on this issue that I would be a vigorous opponent.

It is necessary to identify all known risk factors affecting health and survival and to give each an estimated figure of the effect it may have in shortening or prolonging life within the population. Striking a single figure might represent the mean or average of each risk factor in terms of quantity or quality. It would obviously be an empirical estimate and subject to major error but the potential errors inherent in such an approach might tend to even out when all factors are taken into account in estimating a composite influence on survival. My opinions are based on my reading, my experience as a physician, my international role as a medical epidemiologist and my social contacts over the last 70 or more years.

The following factors are proposed as affecting survival with the estimated influence they may have in figures of years:

Education, Those with a 3rd level education in the UK have a greater survival rate than those with a first education. I assume the same applies to Ireland. Benefit - 3 years.

Good housing, less air pollution, and better heating, water supply, hygiene, dental care. Benefit - 0.5 years or less survival for each factor. Obviously these are intimately related to each other and to other factors such as education, wealth and possibly medical care.

Nutrition.  Meat from domestic sources including beef, lamb, pork and high saturated fat foods shorten life. It is likely that the traditional Anglo-Irish emphasis on a high meat diet may be changing to more European foods which contain less saturated fat and salt and with a greater intake of vegetables and fruit. Vegetarians and vegans are extreme examples of the benefits of diet. Dietary changes may account for some of the progressive improvement in life expectation. Proposed benefit of healthy nutrition - 4 years.

Salt. The recent substantial rise in life expectation might be partly related to the gradual reduction in salt in commercial foods and on the table.  There is no doubt that the very high salt intake I recall in the 1930s and 1940s contributed to the frequency of stomach cancer (then the commonest cancer in the population and now one of the rarest)) and hypertension and possibly to heart disease and other chronic diseases – Risk of lifetime high salt intake - 5 years.

Alcohol – more than 21 units weekly over the long-term. This figure includes all those who are deemed to be alcoholics. Risk excess - 4 years.

Obesity. Weight at or above BMI of 30. Risk - 3 years

Medical intervention and the longer survival of the old and the decrepit, including Ivan Illich’s concept of the living death, must contribute to longer life expectation. Fifty or 60 years ago older people who were debilitated and who developed an illness usually died fairly soon afterwards. Nowadays older people can be kept alive for months or years by medical means and better nursing, even if quality of life may be reduced. The contribution of medical intervention (including health education) is particularly difficult to quantify. Clearly preventive medicine in terms of health education is very important in terms of survival, although the increasingly popular health checks, which are widely advertised by private hospitals and clinics, are of very doubtful value and are generally discouraged on the grounds of poor efficacy, unnecessary medical intervention and expense.

Intervention in terms of drugs and surgery obviously contribute to better health and survival but we have to add iatrogenic problems and unnecessary intervention to the equation when we are studying longevity. In aiming at better life expectancy I would give the figure 7 to medicine in general of which 4 or more I would contribute to medical education and 3 or less to medical intervention, Medical education and medical intervention have certainly contributed to quality of life. Total benefit - 7 years

Aerobic exercise or a lifetime programme starting as late as 45 or 50 years of aerobic exercise equivalent to 5 hours walking a week or more at an optimum rate for age has been shown in many studies to benefit longevity. Occupational and anaerobic exercise does not provide the same benefit. Benefit of aerobic exercise – 4 years.

Family history (this figure is based on our own work among patients with coronary disease) We found that it is the habits shared in families which provide the risk factors for heart disease except in the rare case where an abnormal cholesterol profile of genetic origin is found in some or all members of a family. For example, smoking is an example which was often a shared habit in households while other families tend to be non-smokers.  Nutrition is another obvious shared factor. It is likely that family habits may impinge on more than heart disease, stroke and cancer, the three biggest killers. The benefit of family history is minimal but when heart disease was so prevalent 30-40 tears ago it was not unexpected to find more that one case in a family. Risk not relevant

Cigarette smoking (20 a day or more from the age of 18 inhaling) I would posit a very substantial adverse effect of cigarette smoking on survival from my experience, both as a physician and a social observer, That was thirty years or more ago, when cigarette smoking was so widespread among middle aged males and before the habit had begun to decline and the cigarette became less lethal, Some such smokers died in the thirties and forties and many died in the fifties and sixties. I would posit that 50% of all men at that time who continued to smoke and inhale 20 or more cigarettes a day would be dead between 60 and 65 years. My estimate for lifetime smokers would be 25 years for men and 30 years for women.

The figure of 25 years may possibly have been on the conservative side but clearly cigarette smoking is declining rapidly to-day among middle-aged and older people and the benefits of the decline is already apparent in the last 25 years. Cigarette smoking is not only declining rapidly, particularly among the middle aged,  but the cigarette of to-day is much less lethal than formerly thanks to the filter and the substantial butt, to the decline in the amount of tobacco in each cigarette and to a substantial reduction in their nicotine and tar content. Among smokers to-day, with the less lethal cigarette, the risk may be modified but a long term habit of smoking with to-day’s cigarette must still involve considerable risk.  Current risk 10-15years.

Other tobaccos (pipe, cigars). Their adherents were much less vulnerable because they were seldom inhalers. Risk - 1 year. Perhaps snuff adherents had some small risk too.

Occupation - less than 1 year

Social disadvantage, including accident proneness, poverty, chronic unemployment, criminality.  Risk - 4 years

Stress. Pathological rather than ordinary day-to-day concerns. Stress includes mental illness, accident proneness. suicide and poverty. Risk - 3 years

Gender – No inherent risk.

It is hardly possible to quantify an individual in terms of longevity, mainly because of earlier chance events or illnesses but with optimum knowledge of causation and a reasonable adherence to healthy living we should be confident of reaching the 9th or 10th decade.  However, one’s attitude to ageing is important. It is related to the ability to adapt to the normal physical, psychological and social changes of the third stage of life. With an appropriate acceptance of the increasing limitations which are then inevitable, it is possible to enjoy ageing and retirement as much as at other stages of life, including the gradual loss of one’s friends and contemporaries. You may become more housebound and drop more from the social scene but in this modern world there is much to occupy oneself even if mostly confined to the home. This aspect is dealt with in detail in my My Challenge to Ageing 3rd edition on Kindle and is based on observing and recording my experience of and adaptation to the 26 years of my retirement.

This estimate of allotted lifetime reduced or increased collectively in this manner is somewhat speculative. We obviously cannot be specific about the individual because of wide quantitative variations in life enhancing and risk factors and variations in time of exposure. However, if we combine the influence of two or more factors we may arrive at a more acceptable opinion about the influence of life style on long-term survival although we might still be without the support of firm evidence. A few examples may suffice here;
If an obese person with a BMI of 35 who is a heavy salt eater, who tends to eat a diet rich in beef, lamb or pork and who largely eschews vegetables and fruit, and who takes no aerobic exercise, could have the combined estimate of risk of 15 years or more. This does seem a lot of risk but I would think the risk is not far from reality.

If a person of reasonably normal weight who walks or jogs at an optimum rate of 6-8 miles or more a week, who eschews free salt and salty food, who does not smoke and who is a vegetarian (but not necessarily vegans) will very likely  reach the late 80s or the 90s, or possibility one hundred!

This combined approach to the assessment of risk continues to lack specificity but is easier to judge as rational if not firm on scientific grounds. It is of course, necessary to continue studying the role of the specific risk factors which influence health and longevity but already there is much clear evidence in the literature on such lifestyle aspects as aerobic exercise, nutrition, smoking and salt.

In Ireland we are awaiting full information about longevity derived from the 2010 census but the data available so far would suggest a further increase in both males and females with a further narrowing of the disparity between the sexes because of the dramatic reduction in cigarette smoking in middle-aged people.

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