What is health?

In everyday parlance we use the words ‘health’, ‘fitness’, ‘wellbeing’ on the one hand, and ‘disease’, ‘illness’, ‘sickness’, ‘ill-health’, etc., on the other, more or less interchangeably, but these words become slippery and evasive when we try to define them. The World Health Organization (WHO), for example, defines health as ‘a state of complete physical, mental and social wellbeing and not merely the absence of sickness or infirmity’. On this basis, few humans could claim to possess health, although the majority may not be in the grip of obvious sickness or infirmity. Who is to say what constitutes ‘complete physical, mental and social wellbeing’ in a human being? Does physical wellbeing imply an ability to run a marathon? Does a shy and self-effacing person lack social wellbeing?

We also find health defined in functional terms, less idealistically than in the WHO’s formulation: ‘…health consists in our functioning in conformity with our natural design with respect to survival and reproduction, as determined by natural selection…’ (Caplan, 1993). Here the implication is that evolution has brought us to an optimal – or at least an acceptable – compromise with our environment, with the corollary that healthcare measures should properly be directed at restoring this level of functionality in individuals who have lost some important element of it. This has a fashionably ‘greenish’ tinge, and seems more realistic than the WHO’s chillingly utopian vision, but there are still difficulties in trying to use it as a guide to the proper application of therapeutics. Environments differ. A black-skinned person is at a disadvantage in sunless climates, where he may suffer from vitamin D deficiency, whereas a white-skinned person is liable to develop skin cancer in the tropics. The possession of a genetic abnormality of haemoglobin, known as sickle-cell trait, is advantageous in its heterozygous form in the tropics, as it confers resistance to malaria, whereas homozygous individuals suffer from a severe form of haemolytic anaemia (sickle-cell disease). Hyperactivity in children could have survival value in less developed societies, whereas in Western countries it disrupts families and compromises education. Obsessionality and compulsive behaviour are quite normal in early motherhood, and may serve a good biological purpose, but in other walks of life can be a severe handicap, warranting medical treatment.

Health cannot, therefore, be regarded as a definable state – a fixed point on the map, representing a destination that all are seeking to reach. Rather, it seems to be a continuum, through which we can move in either direction, becoming more or less well adapted for survival in our particular environment. Perhaps the best current definition is that given by Bircher (2005) who states that ‘health is a dynamic state of wellbeing characterized by physical, mental and social potential which satisfies the demands of life commensurate with age, culture and personal responsibility’. Although we could argue that the aim of healthcare measures is simply to improve our state of adaptation to our present environment, this is obviously too broad. Other factors than health – for example wealth, education, peace, and the avoidance of famine – are at least as important, but lie outside the domain of medicine. What actually demarcates the work of doctors and healthcare workers from that of other caring professionals – all of whom may contribute to health in different ways – is that the former focus on disease.

What is disease?

Consider the following definitions of disease:

We sense the difficulty that these thoughtful authorities found in pinning down the concept. The first definition emphasizes two aspects, namely deviation from normality, and dysfunction; the second emphasizes aetiology (i.e. causative factors) and phenomenology (signs, symptoms, etc.), which is essentially the manifestation of dysfunction.

Harm and disvalue – the normative view

The shortcomings of the naturalistic view of disease, which is in principle value free, have led some authors to take the opposite view, to the extent of denying the relevance of any kind of objective criteria to the definition of disease. Crudely stated, this value-based (or normative) view holds that disease is simply any condition the individual or society finds disagreeable or harmful (i.e. disvalues). Taken to extremes by authors such as Szasz and Illich, this view denies the relevance of the physical manifestations of illness, and focuses instead on illness only as a manifestation of social intolerance or malfunction. Although few would go this far – and certainly modern biologists would not be among them – it is clear that value-laden judgements play a significant role in determining what we choose to view as disease. In the mid-19th century masturbation was regarded as a serious disease, to be treated if necessary by surgery, and this view persisted well into the 20th century. ‘Drapetomania’, defined as a disease of American slaves, was characterized by an obsessional desire for freedom. Homosexuality was seen as pathological, and determined attempts were made to treat it.

A definition of disease which tries to combine the concepts of biological malfunction and harm (or disvalue) was proposed by Caplan et al. (1981):

’States of affairs are called diseases when they are due to physiological or psychological processes that typically cause states of disability, pain or deformity, and are generally held to be below acceptable physiological or psychological norms.’

What is still lacking is any reference to aetiology, yet this can be important in recognizing disease, and, indeed, is increasingly so as we understand more about the underlying biological mechanisms. A patient who complains of feeling depressed may be reacting quite normally to a bereavement, or may come from a suicide-prone family, suggestive of an inherited tendency to depressive illness. The symptoms might be very similar, but the implications, based on aetiology, would be different.

In conclusion, disease proves extremely difficult to define (Scully, 2004). The closest we can get at present to an operational definition of disease rests on a combination of three factors: phenomenology, aetiology and disvalue, as summarized in Figure 2.1.

Fig. 2.1 Three components of disease.

Labelling human afflictions as diseases (i.e. ‘medicalizing’ them) has various beneficial and adverse consequences, both for the affected individuals and for healthcare providers. It is of particular relevance to the pharmaceutical industry, which stands to benefit from the labelling of borderline conditions as diseases meriting therapeutic intervention. Strong criticism has been levelled at the pharmaceutical industry for the way in which it uses its resources to promote the recognition of questionable disorders, such as female sexual dysfunction or social phobia, as diseases, and to elevate identified risk factors – asymptomatic in themselves but increasing the likelihood of disease occurring later – to the level of diseases in their own right. A pertinent polemic (Moynihan et al., 2004) starts with the sentence: ‘there’s a lot of money to be made from telling healthy people they’re sick’, and emphasizes the thin line that divides medical education from marketing (see Chapter 21).

Components of disvalue

The discussion so far leads us to the proposition that the proper aim of therapeutic intervention is to minimize the disvalue associated with disease. The concept of disvalue is, therefore, central, and we need to consider what comprises it. The disvalue experienced by a sick individual has two distinct components² (Figure 2.1), namely present symptoms and disabilities (collectively termed morbidity), and future prognosis (namely the likelihood of increasing morbidity, or premature death). An individual who is suffering no abnormal symptoms or disabilities, and whose prognosis is that of an average individual of the same age, we call ‘healthy’. An individual with a bad cold or a sprained ankle has symptoms and disabilities, but probably has a normal prognosis. An individual with asymptomatic lung cancer or hypertension has no symptoms but a poor prognosis. Either case constitutes disease, and warrants therapeutic intervention. Very commonly, both components of disvalue are present and both need to be addressed with therapeutic measures – different measures may be needed to alleviate morbidity and to improve prognosis. Of course, such measures need not be confined to physical and pharmacological approaches.

The proposition at the beginning of this section sets clear limits to the aims of therapeutic intervention, which encompass the great majority of non-controversial applications. Real life is, of course, not so simple, and in the next section we consider some of the important exceptions and controversies that healthcare professionals and policy-makers are increasingly having to confront.

Therapeutic intervention is not restricted to treatment or prevention of disease

The term ‘lifestyle drugs’ is a recent invention, but the concept of using drugs, and other types of interventions, in a medical setting for purposes unrelated to the treatment of disease is by no means new.

Pregnancy is not by any definition a disease, nor are skin wrinkles, yet contraception, abortion and plastic surgery are well established practices in the medical domain. Why are we prepared to use drugs as contraceptives or abortifacients, but condemn using them to enhance sporting performance? The basic reason seems to be that we attach disvalue to unwanted pregnancy (i.e. we consider it harmful). We also attach disvalue to alternative means of avoiding unwanted pregnancy, such as sexual abstinence or using condoms. Other examples, however, such as cosmetic surgery to remove wrinkles or reshape breasts, seem to refute the disvalue principle: minor cosmetic imperfections are in no sense harmful, but society nonetheless concedes to the demand of individuals that medical technology should be deployed to enhance their beauty. In other cases, such as the use of sildenafil (Viagra) to improve male sexual performance, there is ambivalence about whether its use should be confined to those with evidence for erectile dysfunction (i.e. in whom disvalue exists) or whether it should also be used in normal men.

It is obvious that departures from normality can bring benefit as well as disadvantage. Individuals with above-average IQs, physical fitness, ball-game skills, artistic talents, physical beauty or charming personalities have an advantage in life. Is it, then, a proper role of the healthcare system to try to enhance these qualities in the average person? Our instinct says not, because the average person cannot be said to be diseased or suffering. There may be value in being a talented footballer, but there is no harm in not being one. Indeed, the value of the special talent lies precisely in the fact that most of us do not possess it. Nevertheless, a magical drug that would turn anyone into a brilliant footballer would certainly sell extremely well; at least until footballing skills became so commonplace that they no longer had any value³.

Football skills may be a fanciful example; longevity is another matter. The ‘normal’ human lifespan varies enormously in different countries, and in the West it has increased dramatically during our own lifetime (Figure 2.2). Is lifespan prolongation a legitimate therapeutic aim? Our instinct – and certainly medical tradition – suggests that delaying premature death from disease is one of the most important functions of healthcare, but we are very ambivalent when it comes to prolonging life in the aged. Our ambivalence stems from the fact that the aged are often irremediably infirm, not merely chronologically old. In the future we may understand better why humans become infirm, and hence more vulnerable to the environmental and genetic circumstances that cause them to become ill and die. And beyond that we may discover how to retard or prevent aging, so that the ‘normal’ lifespan will be much prolonged. Opinions will differ as to whether this will be the ultimate triumph of medical science or the ultimate social disaster⁴. A particular consequence of improved survival into old age is an increased incidence of dementia in the population. It is estimated that some 700 000 people in the UK have dementia and world wide prevalence is thought to be over 24 million. The likelihood of developing dementia becomes greater with age and 1.3% of people in the UK between 65 and 69 suffer from dementia, rising to 20% of those over 85. In the UK alone it has been forecast that the number of individuals with dementia could reach 1.7 million by 2051 (Nuffield Council on Bioethics, 2009).

Fig. 2.2 Human lifespan in the USA.

Data from National Centre for Health Statistics, 1998.

Conclusions

We have argued that that disease can best be defined in terms of three components, aetiology, phenomenology and disvalue, and that the element of disvalue is the most important determinant of what is considered appropriate to treat. In the end, though, medical practice evolves in a more pragmatic fashion, and such arguments prove to be of limited relevance to the way in which medicine is actually practised, and hence to the therapeutic goals the drug industry sees as commercially attractive. Politics, economics, and above all, social pressures are the determinants, and the limits are in practice set more by our technical capabilities than by issues of theoretical propriety.

Although the drug industry has so far been able to take a pragmatic view in selecting targets for therapeutic intervention, things are changing as technology advances. The increasing cost and sophistication of what therapeutics can offer mean that healthcare systems the world over are being forced to set limits, and have to go back to the issue of what constitutes disease. Furthermore, by invoking the concept of disease, governments control access to many other social resources (e.g. disability benefits, entry into the armed services, insurance pay-outs, access to life insurance, exemption from legal penalties, etc.).

So far, we have concentrated mainly on the impact of disease on individuals and societies. We now need to adopt a more biological perspective, and attempt to put the concept of disease into the framework of contemporary ideas about how biological systems work.