Thus, life expectancy at birth in wealthier Japan is more than 80 years while in incomparably poorer Sierra Leone it is only 34 years - a difference which is shocking to say the least (Marmot 2005).
However, growing inequalities in health in the UK and other developed and developing countries, coupled with the increasing disparities in wealth and income, have forced many researchers to rethink the traditional narrow approach to exploring the contributors to such situation. Social and economic circumstances have been associated though not as heavily as these days, with health inequalities for many decades. Socio-economic status strongly influences people's physical and mental health, their use of health care, and mortality rates. Many recently published works on socio-economic determinants of health inequalities clearly demonstrate that these exist in the UK and elsewhere in the world, even in the richest societies (Krieger et al. 1997).
However, none of the existing definitions or even groups of definitions comprehensively reflects the essence of the highly complex and multilateral concept which is health. Probably the most common and widely adopted definition of health is the one suggested by the World Health Organization: "health is positive concept that emphasises social and personal resources, as well as physical capabilities. It involves the capacity of individuals - and their perceptions of their ability - to function and to cope with their social and physical environment, as well as with specific illnesses and with life in general" (WHO, 1984). Evidently, this definition seeks to emphasize the complexity and multitude of factors influencing human health in the modern world.
The same broad approach in defining the concept of health has also been adopted by authors of other popular definitions and models. Thus, Dahlgren and Whitehead (1991) in one the most widely used models of health identify the following levels of individual health:
The first-layer factors including age, gender and genetic inheritance;
The second-layer factors including behavioural patterns (physical activity, smoking, dieting);
The third-layer factors including social position, economic resources and the material environment;
The fourth-layer factors including the wider or underlying determinants, consisting of social and community networks, work environment, housing and living conditions, education and transport.
And finally, the fifth-layer factors including the economic, cultural, political and environmental conditions in the society in general (p.41-42).
In 2006, a group of U.S. scientists carried out an interesting qualitative study in an attempt to finally determine which of the existing