Given perfect conditions, human beings are thought to be capable of living a healthy 125 years. Indeed, the oldest recorded human being was a French woman who lived to be 122 years of age (JAMA, 1997; 278: 1345-48). The vast majority of us, however, don't live that long, and why? is a question which vexes gerontologists and interested lay groups alike.
In the US, the elderly (aged 60 and over) will comprise 17 per cent of the population by the year 2000. The 50 plus age group now represents 26 per cent of the total population (World Health, 1992; 45: 15-28). The US Census Bureau predicts that one in nine baby boomers (born between 1946 and 1964) will go on to live into their nineties; one in 26 will reach 100. For a long time, ageing has been studied in the context of the diseases which were common to it more than 80 per cent of those over 60 die from preventable diseases such as cancer, diabetes and heart failure. Now, however, as the population ages, our focus has shifted to studying healthy old age.
Suddenly, research scientists are in a very big hurry to study longevity so much so that a great deal of the quoted research has been done on nematodes and flies, whose life cycles are very short. Research is particularly abundant on fruit flies (Science, 1992; 258: 461-3; Physiol Zool, 1985; 58: 380-90) and medflies (Science, 1992; 258: 457-61). It is hard to see how this information can be extrapolated to human beings, since flies are, among other things, cold blooded. However, some useful theories have emerged, namely that the longer an organism lives, the longer it can expect to live (this has been proven to be true in humans as well, see box below). The fly research began with the theory that life span is predetermined and thus, at a given age, whole groups of flies should simply die off. However, this did not happen, nor did it appear that frailty and loss of fecundity was an inevitable consequence of ageing. Many flies continued to be active and fertile long past the predicted point of decline.
Given the still strong love affair with youth, many baby boomers are enthusiastically seeking out designer cocktails of hormones (among the most popular and controversial are melatonin and the steroid hormone DHEA), in order to produce longevity and health. The efficacy of these quick fix mixtures has yet to be proven. We have also failed to give much attention to other factors, which don't find a convenient scientific pigeon hole, but which also influence longevity: socio-economic status, race, and quality of life and thus self perception. But what has shown promise, again and again, are studies into the relationship between a healthy lifestyle and healthy old age.
When the Framingham study looked at factors associated with survival to 75 years of age in 747 healthy men and 973 healthy women aged 50 or older, they found that fewer cigarettes smoked each day, lower blood pressure and higher lung capacity were associated with longevity in both sexes. In men, lower heart rate and in women, parental survival to 75 years were additional factors which predicted long term survival (Arch Intern Med, 1996; 156: 505-9).
Many other studies agree that diverse factors, including diet, physical activity and attitude, influence longevity (J R Soc Health, 1993; 113: 75-80; J R Soc Health, 1996; 116: 283-6; Med Sci Sports Exerc, 1994; 26: 857-65), though some are less emphatic than others (Am J Epidemiol, 1996; 143: 54-62).
In a study of 101 healthy men and women aged 60 plus, exercise improved psychological, behavioural and cognitive function in a relatively short time. For the first four months of the study, members of the group were randomly assigned to perform either aerobic exercise or yoga, or to be placed in a waiting list control group. Each group was then assessed and assigned a further four months of aerobic exercise. At the end of the second assessment, subjects were given the option of going on to a further six months of aerobic exercise (14 months in total). All subjects, regardless of their health status, chose to go on to the third stage. The subjects experienced a 10-15 per cent improvement in aerobic capacity, as well as some improvement in cognitive function. The authors concluded that if individuals who are relatively healthy can still derive benefit from exercise, those with greater physical and emotional impairments might benefit all the more (J Gerontol, 1991; 46: P352-61).
Although it's easy to blame debilitated old age on genes, the genetic argument takes a bit of a bashing when held up against studies into twins raised in separate environments, and those of indigenous people such as the Yi of Southwestern China.
Dr Paul Whelton and his colleagues at Johns Hopkins University in Baltimore, Maryland have spent years tracking indigenous Yi. As a rule, the Yi are a lean bodied people who seldom develop hypertension. Their traditional diet is mainly rice, a little meat and lots of fresh fruit and vegetables. Their consumption of grains such as oats and buckwheat also contributes to their low levels of hypertension and cholesterol (Am J Clin Nutri, 1995; 61: 366-72).
To assess the effect of rural urban migration, particularly on hypertension, Dr Whelton measured the blood pressure of 8,241 Yi farmers, 2,575 urban Yi migrants and 3,698 Han urban dwellers (Am J Epidemiol, 1991; 134: 1085-101). The Yi farmers had the lowest blood pressure and the least rise in blood pressure with age of the three groups at baseline. The Han showed signs of increasing hypertension with age. But a move to an urban setting, where diet and lifestyle are different, showed a significant rise in blood pressure in Yi males and females, approaching the level of the urban dwelling Han.
Dr Whelton and colleagues have published many studies on their findings (Am J Epidemiol, 1995; 142: 295-303; Am J Epidemiol, 1996; 144: 839-48; J Hypertens, 1995; 13: 1267-74). They have studied the phenomenon of rising blood pressure in relation to other factors such as body mass (Am J Epidemiol, 1994; 139: 380-9) and alcohol use (Hypertension, 1993; 22: 365-70). Alcohol use, in particular, was shown to have a devastating effect on the migrant farmers. In their rural setting, alcohol consumption did not appear to have a significant effect on blood pressure. But once in the city, approximately 33 per cent of hypertension in Yi migrants could be attributed to daily alcohol use, compared with only 9.5 per cent in the Han people. The conclusion is simple: it's not their genes, but their diet and lifestyle which changes.
For years we have known that physically active people have a life expectancy which is, on average, seven years longer than sedentary people (Prev Med, 1972; 1: 109-21). He or she will be prone to less depression and anxiety and experience better mental efficiency (Br J Sports Med, 1979; 13; 110-17), higher self esteem (Med Sci Sport, 1970; 2: 213-17), more restful sleep (Psychol Physiol, 1978; 15: 447-50), more relaxation, spontaneity and enthusiasm, and better self acceptance (Am Corr Ther J, 1979; 33: 41-44; J Clin Psychol, 1971; 27: 411-12).
In the 1960s, Dr Ralph Paffenbarger began tracking 17,000 Harvard alumni. At the time it was widely believed that vigorous exercise was bad for the elderly. However, Dr Paffenbarger's landmark 1986 study showed the opposite death rates fell in proportion to the number of calories they burned each week (N Eng J Med, 1986; 314: 605-13).
A few years later, Paffernbarger and colleagues studied a large group of men and women, measuring their physical fitness by a maximal treadmill exercise test. Follow up at eight years showed startling results. Mortality rates from all causes (including heart disease and cancer) fell dramatically across the board, the more fit the patients were: from 60 per 10,000 for the least fit men to 18.6 per 10,000 for the most fit men, and from 39.5 per 10,000 for the least fit women to 8.5 per 10,000 for the most fit women (JAMA, 1989; 262: 2395-401). These trends remained, even after adjusting for age, smoking, cholesterol levels, systolic blood pressure, and family history of heart disease.
Follow up of his Harvard data 10 years on confirmed that those who maintained or improved adequate physical fitness were less likely to die from all causes, and specifically from cardiovascular disease, than persistently unfit men (JAMA, 1995; 273: 1093-8). Furthermore, it was not simply exercise, but vigorous exercise which had the greatest effect on longevity (JAMA, 1995; 273: 1179-84).
In another study, Paffenbarger further concluded that other lifestyle modifications, such as quitting smoking, also had a positive effect on longevity (Med Sci Sports Exerc, 1994; 272-857-65). What is more, the physically active were less likely to take their own lives prematurely. Another analysis of the Harvard data showed that the physically active and sports players had a better mental attitude. Depression was higher among cigarette smokers, and among those who reported insomnia, exhaustion and self consciousness. Suicide rates were also higher among smokers and those who reported depression (Acta Psychiatr Scand Suppl, 1995; 272: 16-22).
This brings to mind the question of how important emotional life is to longevity. A number of studies have looked at this aspect of ageing and concluded that among the most important emotional predictors of longevity are connectedness with other people, purposefulness and even curiosity.
In a Scandinavian study of 1,062 elderly individuals aged 67 plus, physical health and activity were the overall most important factors influencing longevity. But among the youngest elderly, mental health was a more important predictor of survival than physical health, and greater also than social networks, mobility and spiritual life (Scand J Soc Med, 1996; 24: 90-101). The implication may be that good mental health is not the single most important thing, but that life is a moveable feast and each age group may require different mental/emotional stimuli to sustain health.
Self esteem, social ties and life satisfaction came out high in another
study (Arch Fam Med, 1997; 6: 67-70) which questioned how these feelings influenced the way we take care of ourselves.
There is also some evidence that living alone may have a negative impact on health, especially on men (Am J Pub Health, 1992; 82: 401-6). This is reinforced by several studies which show that married persons tend to live longer. There is dispute as to why this may be (Soc Sci Med, 1995; 40: 1717-30). The Terman Life cycle study, initiated in 1920 by Lewis Terman (Health Psychol, 1996; 15: 94-101) looked at marital history in mid life (in 1950) and mortality of a group of 1,077 individuals. Its finding was that consistently married people lived longer than those who have experienced marital break up.
This may not be due to any protective effect of marriage per se since individuals who waited until mid life to marry were at even higher risk of early death than those who had experienced a divorce. What seems to be important is the protective effect of learning to be in a relationship at an early age.
The same study also showed that psychological and emotional health was a good predictor of mortality. Researchers found that mental health problems were strongly related to deaths from injury and cardiovascular disease (Health Psychol, 1995; 14: 381-7).
Curiosity and taking an interest in the world around you may also have an important role to play. A prospective examination of the relationship of curiosity to longevity was made in a five year study of 1,118 community dwelling older men, at a mean age of 70.6 years.
Among survivors, curiosity was the most significant factor, even after adjusting for other factors such as common health problems. The same study also looked at curiosity in 1,035 women and found the same strong association (Psychol Ageing, 1996; 11: 449-53).
Personality may well play a part in successful ageing but contrary to common perceptions, this may not mean that the most cheerful and optimistic personalities survive the longest.
In one study, cheerfulness (defined as optimism and a sense of humour) was inversely related to longevity (J Pers Soc Psychol, 1993; 65: 176-85)! Other research along similar lines has shown that stability of personality and a sense of routine may be the most important factors (J Gerontol, 1991; 46: 285-91).
Another interview study of the views of 12 centenarians as to of why they live so long came up with many common themes. Among these were: relationships with others, a sense of productivity and worth, and faith in God. Researchers determined that centenarians might best be described as "survivors" (J Holist Nurs, 1997, 15:199-213).
This idea is underscored by findings from a retrospective study in which the factors influencing 17 long surviving American Civil War nurses, including Louisa Mae Alcott, Dorothea Dix and Clara Barton, were explored. Its findings were that social and marital status, altruism and religion were all important.
But more than any other tangible factor, the presence of a pioneering spirit (interest in new things and change) seemed to be at the root of their longevity (Nurse Forum, 1991; 26: 9-16).
As the number of studies on longevity continues to mount, the normal human life span increases and the elderly become more healthy, what is clear is that many of our long held beliefs about the human life cycle will be challenged.
Motivating elderly people to take charge of their lives can be difficult. However, we can no longer afford to pedal the idea to them or to ourselves that age is a disease state, or that disease is an inevitable consequence of ageing.