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Page Background

duty of the public health sector to





conditions of an epidemic area of

malaria and to find ways and means

of eradicating the breeding places of

the vector.

The application of the model

of the ‘epidemiological triangle’ to

chronic diseases is possible but not

advisable because of the multiple

factors linked to the causation of





particularly because of the long

time-span after exposure to the risk

factors before the final clinical occurrence of the

disease. So, for chronic diseases the ‘risk factor

model’ is a better choice for looking into disease

causing factors. Nowadays, by applying sophisticated statistical models, all categories of

environmental factors such as socio-demographic features and behavioral aspects can be added

into the search for causative factors of a given disease. It can be safely stated that the

environment is one of the important aspects in the determination of disease occurrence and

public health. However, besides environmental factors, genetic determinations also play a role

(Figure 2).

Chronic diseases, behavior, genetics and epigenetic

Chronic diseases, especially, are due to behavioural factors which are determined by the

cultural- and socio-economic environment. Prevention usually starts with attempts to influence

these factors: if smoking was entirely unknown, if alcohol was consumed in only very modest

quantities, and if everybody observed the national nutritional guidelines for food intake, a

substantial number of curative facilities and medical doctors would be superfluous. Genetic

conditions are less easy to influence: for example, it is difficult to change the fact that one is a

male or a female (even some people try hard to do exactly that), and it is difficult to work against

the fact that middle-aged females have a greater risk of suffering from cancer than men and on

the other hand middle-aged men have a greater risk of experiencing cardio-vascular diseases.

The strict distinction between environmental and genetic factors is no longer possible, at least

not as far as the phenotype is concerned. One of a fast developing field of research now is about

the question of how the environment interacts with genetics to determine the phenotype (1). This

field is called ‘epigenetic’.

Epigenetic is actually not an entirely new issue, but it is given a lot of attention

nowadays. One of the earliest hints of an interaction between environment and genetics was

expressed by Neel who published the ‘thrifty gene’ hypothesis in 1962 (2). According to the

hypothesis, ‘certain genes evolved to regulate efficient intake and utilization of fuel stores’. As

far as type 2 diabetes mellitus (T2DM) is concerned, this means that insulin resistance and

insulin deficiency delay the metabolism of glucose and that, while this is beneficial during

Model commonly used in qualitative research

Biological environment

Socio-economic environment

Cultural environment



Individual or


What makes people sick?

Populati n’s and individual's genetic conditions

Environmental factors

Fig.: 2 Factors of disease causation