Leading organizations in the field of disease prevention and health promotion, such as the World Health Organization (Headquarters in Geneva, Switzerland) and the Centers for Disease Control (Atlanta, USA), have since the early 1980s used healthy lifestyles as a label for a cluster of behaviours known to reduce the risk of injury, morbidity and mortality and increase the chances of good health and well-being. Health-related behaviours (health-enhancing or healthcompromising) include eating habits, physical exercise, smoking, alcohol use, use of illegal addictive substances, sexual practices, risk-taking in traffic, work etc., use of safety devices (for instance wearing safety helmets when biking), sleeping habits, oral hygiene and personal hygiene. Examples of health-related behaviours which are relevant only to specific ethnic groups are exposure to the sun in order to obtain a more tanned skin among Caucasians, or use of skin-whitening creams among ethnic groups with dark skin colours. The concept of lifestyle is also used in other contexts. In the field of marketing, analysis of consumer lifestyles means examining the way people live (their activities, interests, values and opinions) in order to better tailor marketing efforts to specific target groups. According to Elliott (1993): ... a lifestyle has been defined as a distinctive mode of living that is defined by a set of expressive, patterned behaviors of individuals occurring with some consistency over a period of time. It should be evident from this definition that the lifestyle construct is not meant to capture the totality of a person’s behaviour. There are three aspects that make lifestyles more specific: their consistency or relative stability over time, their interrelatedness (being patterned), and the meaning they convey to others as well as oneself (expressiveness). Health-related lifestyles refer to behaviours that have been shown by epidemiological and other health research to predict disease or health. A related term, ‘risk-taking behaviour’, refers to behaviour patterns which are volitional and which increase risk of disease of injury (Irvin, 1990). The lifestyle concept is less accepted as a term in developing countries. In Lalonde’s classic report on ‘The health of Canadians’ (Lalonde, 1974) the definition of lifestyle that was suggested implied that lifestyles are the result of choices made by individuals. The lifestyle of an individual is seen as the result of an aggregate of decisions made by the person him- or herself, decisions over which the person has considerable control. Environmental and social factors have, however, been shown to exert a powerful influence on health behaviours, even in affluent societies, and factors over which the individual person has limited or no control are obviously of even higher importance in developing countries (Eaton et al., 2004). When defining ‘adolescence’, several criteria are relevant, for instance secondary sex characteristics, cognitive abilities, social criteria or simply age. According to Adams et al. (1994), adolescence covers the age-groups 11–20, and distinction is made between early adolescence (11–14), middle adolescence (15–17) and late adolescence (18–20). There is no global consensus regarding the definition of adolescence. The World Health Organization defines adolescence as the period from 10 to 19 years of age. Defining adolescence as a period covering such a wide age-range may seem particularly relevant for affluent societies of the West. During recent decades, however, it has become clear that a transitional stage between childhood and adulthood is evident in most societies of the world. This expanded, more-distinct transitional period includes longer schooling, earlier puberty, later marriage, removal from full-time labour, and greater separation from the world of adults (Larson & Wilson, 2004). During this period of life, through a complex interplay between biological, physiological, psychological, social, societal and cultural factors, lifestyles are shaped.
