“A risk factor is any attribute, characteristic or exposure of a subject which increases the likelihood of developing a disease or suffer a trauma” (World Health Organization, 2013). For example, exposure of a person to a risk factor such as smoking increases the risk of developing lung cancer as smoking cessation reduces this risk. The importance of risk factor reflects the strength of association with disease. It is expressed as the relative risk observed in exposed versus non-exposed. It reflects a gradual association. This implies that the risk factor precedes the disease, the correction factor should reduce the incidence of the disease (concept of reversibility) and that this risk factor is independent of others. A modifiable risk factor is going to be a factor that we will take action. For example, it can not act on a person’s age. By cons, we can act on his smoking.
A risk factor is not a cause of disease in the strict sense, but a probability of having a disease. This notion of Epidemiology result of the work of Hill (1965) means that there is a statistical link between a factor of interest (eg smoking) and the occurrence of an event (for example, the annual number of cancer deaths lung in a country). This factor can be an individual characteristic (eg body weight) or group (for example the inhabitants of a city). Researchers can deduce the probability of the incidence of a disease in a population, monitor its development, forecasting and extrapolate a general population or patients. Professionals have a chance of developing a disease or health problem.
Analyzes of observational studies (cohort) isolate a potential pathogenic cause of other confounding factors. But this is not always so simple. Consider an example. A cohort study following thousands of people over a period of 50 years can show a link between the weekly physical activity and the risk of cardiovascular disease. But this link can also be explained by other factors, the supply of fruits and vegetables or drinking, which are linked to cardiovascular disease. It is not appropriate to consider physical activity as a risk factor and still less to propose an intervention acting on his level. It is often necessary to use intervention research by conducting a randomized controlled trial to determine the exact contribution of the risk factor and if its change causes less disease.
Major risk factors
The main risk factors not modifiable cause disease are age, sex and family history. The major modifiable risk factors at the behavioral level are overweight (especially abdominal fat), the thinness, the unprotected sex, hypertension, smoking, alcohol consumption, hygiene and physical activity. The major modifiable risk factors are the environmental level income, working conditions, social participation, access to care, prevention strategies, habitat, water quality and sanitation.
What it means for Patients
Blog in Health invites us not confuse risk factor for disease and health reasons. A risk factor is a probabilistic notion. To say that the risk factor of chronic obstructive pulmonary disease (COPD) is 90% for smoking does not mean that 90% of smokers will COPD or a smoker has a 90% chance of becoming COPD (the actual figure is estimated at between 10% and 20%). It means that a smoker has nine times more likely to become a non-smoker COPD.
What it means for Health Professionals
The epidemiology is based on the concept of probabilistic risk factor to identify modifiable factors which therapeutic or preventive measures can be recommended. Risk factors are often identified by cohort studies in the general population, in particular groups (e.g., occupational cohorts or subgroups at risk) or in patient populations. These studies follow long-term population and identify factors which modify life trajectories. This identification allows to implement specific interventions to change risk factor in the general population (in public health) or specific population (action on a group of patients). It also allows the development of additional intervention research.
What it means for Researchers
The comparison with the results of observational studies obtained in different conditions is a necessary step to collect the different elements in order to better prepare for an interventional study. The researcher must justify their choices in the development of a randomized controlled trial: the nature of the intervention, population, follow-up, outcome measures.
What it means for Policymakers
If it is legitimate to understand the mechanisms of action, important for the individual and society is that the action is effective, the goal is to prevent or slow the progression of disease. Identifying the mechanisms underlying an association between illness and modifiable risk factor is one of the objectives of epidemiology etiology but is not essential in a more pragmatic interventional approach. A do we still need to know the cause of a disease in order to influence its effect or evolution? Is it essential to understand the mechanisms that may explain the relationship between modifiable factor for disease and initiate therapeutic action? These issues still under debate (Berr 2013 In Ninot, 2013).
Berr C. (2013). Démontrer l’efficacité des interventions non médicamenteuses : Point de vue de l’épidémiologiste (pp. 103-115). In Ninot G (Ed.). Démontrer l’efficacité des interventions non médicamenteuses : Question de points de vue. Montpellier : Presses Universitaires de la Méditerranée (PULM).
Hill AB (1965). The environment and disease: Association or causation? Proceedings of the Royal Society of Medicine, 58, 295-300.
World Health Organization (2013). Glossary. Geneva: WHO Edition.
To reference this article Blog en Sante © article.
Ninot G (2014). Definition of modifiable risk factor. Blog en Sante, L4.
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