4. Diet, nutrition and chronic diseases in context:
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Habits leading to noncommunicable disease development during adolescence
It seems increasingly likely that there are widespread effects of early diet on later body composition, physiology and cognition (45). Such observations “provide strong support for the recent shift away from defining nutritional needs for prevention of acute deficiency symptoms towards long-term prevention of morbidity and mortality” (45).
Increased birth weight increases the risk of obesity later, but children with low birth weight tend to remain small into adulthood (89, 92). In industrialized countries there have been only modest increases in birth weight so the increased levels of obesity described earlier must reflect environmental changes (89).
The “obesogenic” environment appears to be largely directed at the adolescent market, making healthy choices that much more difficult. At the same time, exercise patterns have changed and considerable parts of the day are spent sitting at school, in a factory, or in front of a television or computer. Raised blood pressure, impaired glucose tolerance and dyslipidaemia are associated in children and adolescents with unhealthy lifestyles, such as diets containing excessive intakes of fats (especially saturated), cholesterol and salt, an inadequate intake of fibre and potassium, a lack of exercise, and increased television viewing (10). Physical inactivity and smoking have been found independently to predict CHD and stroke in later life.
It is increasingly recognized that unhealthy lifestyles do not just appear in adulthood but drive the early development of obesity, dyslipidaemia, high blood pressure, impaired glucose tolerance and associated disease risk. In many countries, perhaps most typified by the United States, changes in family eating patterns, including the increased consumption of fast foods, pre-prepared meals and carbonated drinks, have taken place over the past 30 years (89). At the same time, the amount of physical activity has been greatly reduced both at home and in school, as well as by increasing use of mechanized transport.
The three critical questions relating to adulthood were identified as: (i) to what extent do risk factors continue to be important in the development of chronic diseases; (ii) to what extent will modifying such risk factors make a difference to the emergence of disease; and (iii) what is the role of risk factor reduction and modification in secondary prevention and the treatment of those with disease? Reviewing the evidence within the framework of a life-course approach highlights the importance of the adult phase of life, it being both the period during which most chronic diseases are expressed, as well as a critical time for the preventive reduction of risk factors and for increasing effective treatment (93).
The most firmly established associations between cardiovascular disease or diabetes and factors in the lifespan are the ones between those diseases and the major known “adult” risk factors, such as tobacco use, obesity, physical inactivity, cholesterol, high blood pressure and alcohol consumption (94). The factors that have been confirmed to lead to an increased risk of CHD, stroke and diabetes are: high blood pressure for CHD or stroke (95, 96); high cholesterol (diet) for CHD (97, 98), and tobacco use for CHD (99). Other associations are robust and consistent, although they have not necessarily been shown to be reversible (10): obesity and physical inactivity for CHD, diabetes and stroke (100-102); and heavy or binge drinking for CHD and stroke (99, 103). Most of the studies are from developed countries, but supporting evidence from developing countries is beginning to emerge, for example, from India (104).
In developed countries, low socioeconomic status is associated with higher risk of cardiovascular disease and diabetes (105). As in the affluent industrialized countries, there appears to be an initial preponderance of cardiovascular disease among the higher socioeconomic groups, for example, as has been found in China (98). It is presumed that the disease will progressively shift to the more disadvantaged sectors of society (10). There is some evidence that this is already happening, especially among women in low-income groups, for example in Brazil (106) and South Africa (107), as well as in countries in economic transition such as Morocco (108).
Other risk factors are continually being recognized or proposed. These include the role of high levels of homocysteine, the related factor of low folate, and the role of iron (109). From a social sciences perspective, Losier (110) has suggested that socioeconomic level is less important than a certain stability in the physical and social environment. In other words, an individual’s sense of understanding of his or her environment, coupled with control over the course and setting of his or her own life appears to be the most important determinant of health. Marmot (111), among others, has demonstrated the impact of the wider environment and societal and individual stress on the development of chronic disease.
4.2.5 Ageing and older people
There are three critical aspects relating to chronic diseases in the later part of the life-cycle: (i) most chronic diseases will be manifested in this later stage of life; (ii) there is an absolute benefit for ageing individuals and populations in changing risk factors and adopting health-promoting behaviours such as exercise and healthy diets; and (iii) the need to maximize health by avoiding or delaying preventable disability. Along with the societal and disease transitions, there has been a major demographic shift. Although older people are currently defined as those aged 60 years and above (112), this definition of older people has a very different meaning from the middle of the last century, when 60 years of age and above often exceeded the average life expectancy, especially in industrialized countries. It is worth remembering, however, that the majority of elderly people will, in fact, be living in the developing world.
Most chronic diseases are present at this period of life - the result of interactions between multiple disease processes as well as more general losses in physiological functions (113, 114). Cardiovascular disease peaks at this period, as does type 2 diabetes and some cancers. The main burden of chronic diseases is observed at this stage of life and, therefore, needs to be addressed.
Changing behaviours in older people
In the 1970s, it was thought that risks were not significantly increased after certain late ages and that there would be no benefit in changing habits, such as dietary habits, after 80 years old (115) as there was no epidemiological evidence that changing habits would affect mortality or even health conditions among older people. There was also a feeling that people “earned” some unhealthy behaviours simply because of reaching “old age”. Then there was a more active intervention phase, when older people were encouraged to change their diets in ways that were probably overly rigorous for the expected benefit. More recently, older people have been encouraged to eat a healthy diet - as large and as varied as possible while maintaining their weight - and particularly to continue exercise (113, 116). Liu et al. (117) have reported an observed risk of atherosclerotic disease among older women that was approximately 30%less in women who ate 5-10 servings of fruits and vegetables per day than in those who ate 2-5 servings per day. It seems that, as elderly patients have a higher cardiovascular risk, they are more likely to gain from risk factor modification (118).
Although this age group has received relatively little attention as regards primary prevention, the acceleration in decline caused by external factors is generally believed to be reversible at any age (119). Interventions aimed at supporting the individual and promoting healthier environments will often lead to increased independence in older age.
4. Diet, nutrition and chronic diseases in context:
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