Differences between younger and older people

A starting point for the scientific appraisal of human ageing is to compare young people with older people and the general view of ageing is derived, explicitly or implicitly, from such comparisons.3 However, the result can be deceptive because differences between young and old people can arise through processes other than ageing (Table 26.1).

Differences not attributable to ageing

Some differences have come about, not because old people have changed due to ageing, but because they have always been different from younger people with whom they are being compared.

Table 26.1 Differences between young and old


True ageing

Selective survival


Cohort effects


Differential challenge



Individual adaptation

Specific adaptation

  • ? Selective survival is the result of people with advantageous genes or social environment, or healthy lifestyles, surviving longer than the less fortunate people born at the same time.
  • ? Cohort effects are the differences between generations of people born at different times and therefore exposed, especially in developing societies, to different influences and experiences, particularly early in life. Such cohort differences can be considerable. A study in the 1960s demonstrated that a major part of what appears in cross-sectional studies to be age-associated change in some types of psychological functioning was due to cultural, especially educational, differences between generations.4 Although prominent in the sphere of psychological function, which reflects educational standards and practices during childhood, cohort effects will contribute to cross-sectional estimates of age-associated variation in physical variables such as height, serum lipids, and obesity, as well as to risk of diseases such as lung cancer. Cohort comparisons reflect differences between generations in their lifestyle and behaviour as well as in changes in the physical environment.
  • ? Differential challenge. If ageing is to be defined in terms of reduced adaptability, it can only be assessed by offering equal challenges to people at different ages. Social policy often leads to our offering more severe challenges to older people than to younger ones and then attributing differences in outcome to the effects of ageing. Ageism, in its various guises, is so deeply engrained in British society that discrimination against older people is universal.

Differences attributable to ageing (true ageing)

There has long been debate about distinguishing ‘diseases’ from ‘normal ageing, but the distinction is meaningless in scientific terms.5 True ageing comprises all the ways in which individuals change as time passes. Some of the responsible processes, for reasons that range from the medical to the political, may come to be called ‘diseases’.

Primary ageing is loss of adaptability due to the effects of many different processes in the tissues and organs of the body. These ageing processes are the product of interactions between extrinsic (environmental and lifestyle) influences and intrinsic (genetic) factors. Some of these interactions may be specific: for example, it is likely that excess dietary salt raises blood pressure only in people with particular genes. Other interactions are more general: habits of physical exercise, for example, affect a wide range of body systems, presumably through genetically determined pathways. Diet is important in healthy ageing, notably through deficiencies and imbalance. Dietary factors are also probably involved in ageing effects, due to the generation and insufficiently rapid destruction of free radicals (highly active oxygen molecules) generated in mitochondria that damage cell components including DNA.

Secondary ageing is a term usefully reserved to designate those adaptations made by individuals—or by a species through natural selection—that counter the effects of ageing. At the individual level, secondary ageing is most obvious in the realm of psychological and behavioural functioning. Mildly obsessional behaviour making an ordered environment substitute for memory is a common and successful adaptation. (If we always put our car keys on the hall table, we do not have to waste brain-power remembering where we have left them today.) Older workers may develop apparently idiosyncratic ways of carrying out familiar tasks that are efficient—for them— in conserving effort and circumventing specific problems, such as a stiff joint.

Social factors are important extrinsic determinants of ageing. One of the most significant and much studied correlates of healthy ageing is higher educational level. This will partly reflect the health benefits of relative affluence and occupations that are less damaging physically. Education will also be relevant to the ability of the individual to know of medical advances and to understand their implications for prevention or therapy, and to profit from them. Social class effects on health and disability are highly complex and there may be subtle psychosocial and work-related determinants of health in middle and later life. People in lower grade jobs have less sense of control over their patterns and pace of working, and this leads to chronic ‘stress’ arousal, associated with changes in endocrine and immune function, that may have pervasive effects on susceptibility to age-associated illness and disability, especially cardiovascular disease.6

Obviously, the effects of ageing processes on body functions depend in part on how good those functions were initially. Both men and women lose muscle tissue at the same rate with ageing but, because women start with less muscle (on average) than men, they are more likely (on average) to become immobile and dependent in later life. A similar model applies to bone tissue, and to the high rates of fractures in older women, although women also experience a higher rate of bone loss with ageing. Two determinants of how soon brain damage, produced by Alzheimer’s disease, for example, shows itself in the clinical syndrome of dementia, are the original intelligence and the education level of affected individuals.7 The better the brain, perhaps, the longer it can compensate for progressive damage.

Because we start from different baselines, carry different genes and live different lives, we age at different rates and in different ways. Although, on average, we deteriorate with age, some people in their 80s will be functioning better than would be regarded as normal for people in their 30s. It is therefore unscientific, as well as unjust, to make judgments about individuals’ capabilities simply on the basis of their age—as unjust in fact as to make such judgments from their sex, skin colour, or social class. In all the discussion of age-associated changes in health and function in this chapter, we describe what happens on average in the population; it must not be assumed that such changes affect every ageing individual.

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