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How is Health Defined?

Health may be defined differently by doctors and their patients, and over time and place. One of the most pervasive definitions, though, is simply normality, with illness as a deviation from the normal. The definition of disease as abnormality or damage - physiological, biochemical or psychological - held sway in modern thought for most of the last century. It is represented in lay thought by the replies commonly given in surveys to an invitation to define health: health is not being ill, health is having no disease. It is represented in clinical medicine by the whole array of tests and standards, rapidly growing in sophistication, to measure 'normal' body size and weight, blood composition, lung capacity, functioning of the liver, and so on, through every organ and system of the body.

This definition raises many problems, however. What is normal - normal for what, and for whom? (Clinical standards usually assume for a particular age and gender, but no more.) 'Normal' can have many meanings: average, most representative, the most common value, central in a distribution, the habitual or the best. Are we talking about the average for a given population, or some ideal? The 'perfect' is not only impossible of attainment, but also not necessarily to be desired. As Hippocrates noted in the Aphorisms:

In athletics a perfect condition that is at its highest pitch is treacherous. Such conditions cannot stay the same or remain at rest, and, change for the better being impossible, the only possible change is for the worse.

On the other hand, normal defined as average may not mean perfectly healthy, and the average - consider the examples of body weight or cholesterol level - may not be at all what clinicians regard as the 'norm' or ideal to be aimed for. What is normal degeneration in old age: are all the old unhealthy? Not all deviations from the normal are to be deplored or 'treated': some can be positively beneficial, and others are irrelevant to health. Erde (1979: 36) noted:

If you are 80 or running a marathon, what is normal would differ from the 'norm' of someone age 20 or asleep. Furthermore, if you can run two marathons and no one else can, you may be abnormal and yet as healthy as can be. If your IQ is 100 it is normal. If it is 140, your mind's functions are not in a normal state. We need to know what 'normal' means, before we can tell whether someone has it or is it.

In other words, normal can be descriptive or proscriptive, and if it is proscriptive it has to depend on the state of knowledge at the time, or accepted current theory. A softer version is the recognition that there is a great range of normal variability, and only that which falls outside it need be considered as ill health. The range has still to be defined, perhaps arbitrarily.

Health as the absence of illness

For a time in the mid-twentieth century there was promulgation of the idea of disease or ill health as those phenomena which deviate from the norm in such a way as to place the individual at biological disadvantage. The healthy are those who are not biologically disadvantaged. To some extent this avoids the problems of the definition of normality, since those deviations which have no consequences are irrelevant. But it created new problems in the definition of disadvantage, which was usually described very specifically as shortened life and reduced fertility.

Commentators in the field of mental health used this to argue opposed positions: though no physiological abnormalities had so far been found to account for a condition such as schizophrenia, nevertheless it was a disease, using the biological disadvantage criteria. On the other hand, it was pointed out that many forms of mental ill health did not reduce life expectancy or fertility: was it impossible to call them diseases? In general, the focus on length of life and fertility seemed too Darwinian (disease is anything which interferes with the preservation of the species) and too restrictive.

A more subjective view can be taken, of course, resting the definition of health not on measurable, clinically defined abnormality, but on people's own perception of the experience of symptoms or feelings of illness. The problem is that the norm becomes even more difficult to define. It is commonly demonstrated in studies of populations that to experience no symptoms of ill health at all - never to have pain, mild dysfunction, infection or injury - is in fact highly abnormal: most of us, most of the time, can identify something which we might call a symptom of an illness. Only a small proportion of this is taken for professional attention and diagnosis as disease, and much of it is self-limiting.

Any definition of health as the absence of self-perceived illness has to deal with the fact that this perception varies widely among individuals and depends on situations. Questions have again to be raised about normal illness - normal for this particular person, normal for this sort of individual, normal in these circumstances? - with even less certainty about what the average is, or what would be considered as the ideal.

Disease as deviance

The idea of health as the absence of disease or illness, and disease as deviation from the norm, elides easily into ill health seen as 'deviance' from social or moral norms. The objective observation of a lack of 'normality' meets a very ancient and universal tendency to see the sick person as in some way morally tainted or bewitched. Possibly, they are responsible for their own condition, and at best they are being offered the opportunity to gain merit or show their strength of character in enduring suffering. Ill health usually has negative connotations, and is spoken of as 'bad luck' for the individual. Ill health also harms the functioning or the prosperity of society: the sick are not productive, they may require resources, and they must be controlled and monitored. Thus the American sociologist Talcott Parsons's treatment of sickness as a role designed to allow 'deviants' to find conditional and provisional legitimacy was influential in early medical sociology.

Health as balance or homeostasis

A link between the concepts of health and normality lies in the ancient idea of homeostasis - the idea that the normal state of the body is order, and its systems are designed to be self-righting. This old idea was given new life when it was realized that not only a pathogen, but also a host - the body which was being invaded or harmed - was actively involved in the development of ill health. When a system was being attacked by a specific agent, or was disordered by biological error or stresses and accidents in the environment, regulatory mechanisms came into play. Restoring the normal involves not only equilibrium of the human organism - mind and body - with its environment, but also internal equilibrium within the body's functions and organs. Ill health arises when the balance is disturbed. In modern times this approach gained attraction from its association with the growth of ecology as a natural science.

As commentators such as Mishler (1981) have pointed out, this has elements of older, perhaps less scientific concepts. It echoes the classical Platonic model of health as harmony among the body's processes and systems, with disease as a state of discord, and the Galenian concept of disease as a disturbance of function. Before the rise of modern medicine, not only the cultures of the West but all the great cultures of the world, such as those of China or India, held that health is to be defined as the right balance between supernatural beings, the environment, and processes within the body. Disease as imbalance had to be corrected by the remedying of deficiency (by, for instance, diet) or the removal of excess (by, for instance, purging or bleeding).

A theory of health has to accommodate the fact that all living things have some ability to respond to changing environments. The commonly accepted stance is that the environment does not wholly determine the properties of the organism which is, at least partly, self-organized and capable of change. Modern medicine shows that in certain physiological aspects the body is indeed a homeostatic machine: for instance, the immune system responds when infection enters the system, and loss of blood by injury is responded to by vasoconstriction to keep blood pressure steady. The capacity to sustain equilibrium, or more generally the ability of the body to heal itself, can be regarded as a measure of its healthiness. These ideas, ancient in principle, are elaborated by the findings of modern science. As a total model of health, however, homeostasis has limitations. This is undoubtedly part of healthiness, but some healthy functions - reproduction, for instance - upset equilibrium rather than maintain it, and not all systems are even theoretically self-righting. It can be accepted that some aspects of equilibrium are crucial to life, without confusing the idea of homeostasis with the broader ideal of the normal.

Health as function

This does, however, move away a little from the essentially negative definitions. Another, and even more positive, way is in terms of function. Health is being able to do things. This can be a very basic definition: as a woman of 70 said, when asked what it means to be healthy,

Health is being able to walk around better and doing some work in...