Abstract

The debate about the nature of 'disease' and 'health' is complex and satisfactory definitions of these words continue to prove elusive. This debate is not helped by the lack of clarity over whether it centres merely on the way in which these words are used or on their accuracy as biological descriptors. Given that 'disease' and 'health' are words that portray underlying biological states, a better conceptual comprehension of those states would assist the understanding of the notions of 'disease' and 'health'. To that end, a graphical model serving to describe these states is presented.

Biological states, it is suggested, exist between an optimal (perhaps asymptotic) level and one of complete non-function. One's position between these limits varies, according to lifestyle, along a curve – the shape and extent of which are primarily influenced by genetic constitution, although other factors may also have a bearing. This model is meant primarily as a descriptive tool that focuses on the biological state of (or within) an organism and so can be used to represent the biological state of the whole organism or specific parts thereof. By focusing more on 'biological state', rather than the specific words 'disease' or 'health', some of the connotations associated with these words may be avoided and a clearer view of the biological object achieved.

This poster represents work in progress. Constructive criticism based on the poster or its web copy is most welcome.

Introduction

The words 'disease' and 'health' continue to generate much debate about their precise meaning (Hofmann, 2001). However, it is frequently unclear the extent to which that debate is informed by objective biological knowledge rather than a more general familiarity with the experiences to which these words relate. Furthermore, since the words 'disease' and 'health' pre-date the emergence of modern biological science, there is also a danger that the latter can easily slip into using these words uncritically. It may be useful, therefore, both to the debate and to biological science, to explore ways of comprehending the underlying biological states that come to be interpreted as 'diseased' or 'healthy'. Only rarely have graphical models of health been presented (Boorse, 1987, 1997). In such cases, they have used the concept of population norms or averages and have been based on the notion that health is the absence of disease – understood as biological functioning that is statistically below normal for the species concerned. The following provides an example of this viewpoint:

A disease is the sum of the abnormal phenomena displayed by a group of living organisms in association with a specific common characteristic or set of characteristics by which they differ from the norm for their species in such a way as to place them at a biological disadvantage.

(Scadding, 1967)

This approach, in effect, compares individual biological functions or states with those typical of the rest of the species. There will be those at the functional extremes but most will occupy a middle ground. Boorse (1987; 1997) proposes that the extremes represent a pathological state, at one end, and a (possible) state of 'positive health', at the other. Between these lies a state interpreted as 'normal' where the 'healthy' majority reside. Such models as these have not met with universal agreement, however, and an essentially scientific model describing disease and health remains to be fully worked out.

From a different perspective, the WHO defined health as:

'… a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.

The enjoyment of the highest attainable standard of health is one of the fundamental rights of every human being …'

(WHO, 1948)

This definition has been strongly criticised for its apparent lack of realism. By definition, nobody, it seems, can ever be considered healthy. Taylor gives one such criticism:

This perfectionistic view of health is, of course, of no practical help. Ideal norms are by definition unattainable in our imperfect world. To adopt them has the inevitable result of denouncing all human beings as substandard physically, mentally, and socially. Indeed it would make abnormality a universal attribute not only of mankind, but of all biological organisms.

To be practically useful the concept of abnormality must be approached from a statistical angle. From this viewpoint, abnormality is a characteristic of those attributes which occur in only a minority of the members of a domain. Attributes are thus abnormal in a domain, if they are unusual in it.

(Taylor, 1979)

Such criticisms are consistently levelled at the first sentence of the definition while, in the second sentence the apparently more realistic reference to the 'highest attainable standard of health' is largely overlooked. 'Complete physical, mental and social well-being' is an ideal that is certainly unattainable but it has been suggested elsewhere (oral presentation What the 'body-beautiful' might be telling us about the 'body-healthy') that physical ideals associated with health are not necessarily alien to our outlook on our own species – especially when associated with sexual interests. It was suggested that 'sex-appeal' rests (perhaps even relies) upon a more fundamental 'health-appeal'. Therefore, when it comes to exploring definitions of disease and health, we might do well not to discard approaches associated with notions of ideals too readily simply on the grounds of unattainability.

The WHO definition of health focuses primarily on the individual whereas biological science deals with groups and avoids drawing conclusions from individual phenomena. Thus, a biological or otherwise scientific approach to the problem of disease and health that is primarily concerned with individuals is potentially problematic. From a biological perspective, the WHO definition of health, therefore, poses (at least) two problems: the introduction and use of ideals and a focus on the individual as opposed to the group.

A Model of Biological State

The conceptual basis, and a simple description of a model, that seeks to focus on the underlying biological states which come to be interpreted as 'diseased' or 'healthy', is presented here for the first time. This model, although still in development, attempts to include the notions of the ideal and individuality rather than using any notion of 'species norms'.

Conceptual Background – Individual Biological Ideals

It is a truism to suggest that no two individuals are the same. Each results from unique developmental and life histories; each has a unique structure and set of physiological functions at whatever level of organisation (from organism to cell) they are considered. Each individual is also a product – the result of genetically based developmental processes influenced by external factors. Thus, even the same set of genes will produce different organisms under different circumstances. Although genetic clones, identical twins, for example, are never strictly identical and even the most similar such twins are two materially unique beings. Significantly, each individual is not entirely determined by his or her genome; they are never exactly as 'planned' but are instead what the genome produced given the circumstances that prevailed during that individual's development. That being the case, given theoretically ideal developmental conditions, an individual's genome might be expected to give rise to an organism that is the optimum it can produce (the so-called 'genetic ideal' in Figure 1). Thus, every individual has a unique 'genetic ideal' – the projected or virtual organism that their genome might have produced given ideal circumstances. This also represents an asymptotic biological state specific to each individual. Since no organism is a perfect rendition of its genetic plan there exists instead a 'resultant organism'. How closely that is able to approach the 'genetic ideal' is affected, firstly, by how well it was able to develop and, secondly, by what it experiences during life.

There also exists a state of complete biological non-function that occurs following death. This is the natural end of all organisms and this time, there are no individual differences in that end state – only in what precedes it. Thus, as envisaged here, life exists between two boundary states: an asymptotic genetic ideal and complete non-function.

A Graphical Representation of Biological State

Let the biological states that an organism can attain be represented graphically by the vertical position of a point on a curve as given in Figure 2. That point is not fixed but can move up or down following the line as (for various reasons) the organism's biological state varies. Figure 2 has been given two axes when a single vertical axis, with the point rising or falling on it, might have been expected to suffice. However, for descriptive purposes, the vertical axis has been expanded horizontally and the line the point follows has been given a curved shape. By doing this, ways in which the point moves may be conveyed more readily. In reality, this movement is not necessarily linear or simple (and may even be impossible to describe mathematically).

At any given time, a single line represents the whole range of biological states available to the organism. Where the point is situated on the line represents the organism's current biological state. As with health, biological states, and so the position of the point on the line, can vary (up or down) due to a number of factors such as diet, exercise regime, age, or the permanent effects of illness or injury.

The shape and extent of the line is also envisaged as being under numerous influences and not to be constant. Figure 3 represents the curves for an individual at two different ages. At the older age, the curve is shallower and represents the fact that that individual is no longer able to reach the biological states achievable at the younger age.

Since it concerns already extant, living organisms in possession of a biological status, the curve has been shaped so as to be higher on the left than on the right. Since biological state ultimately declines, a tailing-off to the right seems more appropriate (even though the horizontal axis does not represent time) than a rise by the curve in that direction.

The Organism's Components

So far, the point on the line has represented the overall biological state of the organism. However, the component parts of that organism can also be represented graphically. Each organism is made of various component organs. No two such organs are anatomically or physiologically identical. The same can be said of the cells and tissues that comprise these organs. Thus, in terms of structure and function, each organism is anatomically and physiologically unique at all levels of organisation. Each component, be it organ, tissue or cell, has its own biological state situated between its 'genetic ideal' and that of non-function. Together, these constitute what might be described as 'internal component biological states' that combine and interact with each other to produce an 'overall biological state' experienced at organism level. This notion is depicted in Figure 4.

The curve representing 'overall biological state' is not meant to represent any form of mathematical summation of the curves below it. Even though graphs are used, this is not meant as a mathematical or numerical model as such. The graphical format is used for convenience to portray a conceptual approach. The precise shape of each curve is unlikely to be as given here. Each individual, and their components, is likely to be represented by a uniquely shaped line – the result of the interaction between that individual's genome and developmental and life experiences.

Note

This model does not seek to quantify the states associated with disease and health per se – it seeks to provide a conceptualisation of the underlying biology that leads to the experiences that elicit the use of these words. Whether the individual is deemed 'healthy' or otherwise is an experiential interpretation of their underlying 'biological state' as suggested in Figure 5.

Conclusion

This poster represents work in progress. But it has, so far, proved possible to entertain the concepts of idealism and individuality without recourse to any other organisms. By introducing the notion of 'biological state', it is hoped that the underlying biology will not be overlooked when words like 'disease' and 'health' are used. It is believed that the term 'biological state' is justifiable as a general descriptive term on the grounds that words like 'health' are used in very similar general ways.

Certain aspects have been omitted here and examples have been kept to a minimum. One deliberate omission has been the possibility of making comparisons between different individuals. There are also further developments still to be made – in particular, to consider the use of this model within different environmental contexts.

References

Boorse, C. (1987). Concepts of health. In D. Van De Veer & T. Regan (Eds.), Health Care Ethics: An Introduction (pp. 359-393). Philadelphia: Temple University Press.

Boorse, C. (1997). A rebuttal on health. In J. Humber & K. Almeder (Eds.), What is disease? Totowa, New Jersey: Humana Press.

Hofmann, B. (2001). Complexity of the concept of disease as shown through rival theoretical frameworks. Theoretical Medicine and Bioethics, 22(3), 211-236.

Scadding, J. (1967). Diagnosis: the clinician and the computer. The Lancet, 2, 877-882.

Taylor, F. (1979). The concepts of illness, disease and morbus. Cambridge: Cambridge University Press.

WHO (1948) Preamble to the Constitution of the World Health Organization as adopted by the International Health Conference, New York, 19-22 June, 1946; signed on 22 July 1946 by the representatives of 61 States (Official Records of the World Health Organization, no. 2, p. 100) and entered into force on 7 April 1948.