Global Childhood & Adolescent Obesity: Prevalence, Risk Factors & Interventions - Prof. El, Study notes of Nutrition

Download Global Childhood & Adolescent Obesity: Prevalence, Risk Factors & Interventions - Prof. El and more Study notes Nutrition in PDF only on Docsity! 151 Cent Eur J Publ Health 2006; 14 (4): 151–159 THE EPIDEMIC OF OBESITy IN CHILDREN AND ADOLESCENTS IN THE WORLD Rena I. Kosti, Demosthenes B. Panagiotakos Department of Food Science and Technology, Agricultural University of Athens, Athens, Greece & Department of Nutrition and Dietetics, Harokopio University of Athens, Greece SummaRy The prevalence of obesity has reached alarming levels, affecting virtually both developed and developing countries of all socio-economic groups, irrespective of age, sex or ethnicity. Concerning childhood obesity, it has been estimated that worldwide over 22 million children under the age of 5 are severely overweight, and one in 10 children are overweight. This global average reflects a wide range of prevalence levels, with the prevalence of overweight in Africa and Asia averaging well below 10% and in the Americas and Europe above 20%. The proportion of school-age children affected will almost double by 2010 compared with the most recently available surveys from the late 1990s up to 2003. In the European Union, the number of children who are overweight is expected to rise by 1.3 million children per year, with more than 300,000 of them becoming obese each year without urgent action to counteract the trend. By 2010 it is estimated that 26 million children in EU countries will be overweight, including 6.4 million who will be obese. Moreover, in the USA the prevalence of obesity in adolescents has increased dramatically from 5% to 13% in boys and from 5% to 9% in girls between 1966–70 and 1988–91. In this review paper we present the epidemiology of obesity in children and adolescents, including prevalence rates, trends, and risk factors associated with this phenomenon. Key words: obesity, prevalence, risk factors, children, adolescents address for correspondence: Demosthenes B. Panagiotakos, 46 Paleon Polemiston St., 16674, Glyfada, Greece. E-mail: d.b.panagiotakos@usa.net INTRODUCTION The prevalence of obesity has reached alarming levels, with more than 1 billion overweight adults of which 300 million are considered as clinically obese. Obesity is affecting virtually both developed and developing countries of all socioeconomic groups including all age groups thereby posing an alarming problem, described by the World Health Organization (WHO) as an “escalating global epidemic”(1). Worldwide, over 22 million children under the age of 5 are severely overweight, as are 155 million children of school age. This implies that one in 10 children worldwide are overweight (2). This global average reflects a wide range of prevalence levels, with the prevalence of overweight in Africa and Asia averaging well below 10% and in the Americas and Europe above 20% (3). The proportion of school-age children affected will almost double by 2010 compared with the most recently available surveys from the late 1990s up to 2003 (4). In the European Union, the number of children who are overweight is expected to rise by 1.3 million children per year, with more than 300,000 of them becoming obese each year without urgent action to counteract the trend (4). By 2010 it is estimated 26 million children in EU countries will be overweight, including 6.4 million who will be obese (Table 1) (4). A potential deluge is evident across the globe with obesity rates increasing more than twofold over the past 25 years in the U.S., almost threefold in the past 10 years in England, and almost fourfold over a similar time frame in Egypt (5). Moreover, in the USA the prevalence of obesity in adolescents has increased dramatically from 5% to 13% in boys and from 5% to 9% in girls between 1966-70 and 1988-91 (1). In a single year from 2000 to 2001, the prevalence Table 1. Prevalence and projections of overweight / obesity in children and adolescents in various regions of the World Region Overweight/ Obesity ** Obesity ** Overweight/ Obesity ** Obesity ** Projected 2010 Projected 2010 Africa (1987–2003)* 1.6 0.2 Americas (1988–2002) 27.7 9.6 46.4 15.2 Eastern Med (1992–2001) 23.5 5.9 41.7 11.5 Europe (1992–2003) 25.5 5.4 38.2 10 South East Asia (1997–2002) 10.6 1.5 22.9 5.3 West Pacific (1993–2000) 12 2.3 27.2 7 *There were insufficient data on school-age children in the WHO African Region to make estimates of projected prevalence rates **In millions 152 of obesity increased among U.S. adults from 19.8% in 2000 to 20.9% in 2001 (5.6% increase) (6). If sustained at this rate over the next 10 years, the prevalence of obesity will rise by another 74%, with fully one third of the US population becoming obese by 2030 (6). This paper presents a review of the epidemiology of obesity in children and adolescents, including prevalence rates, trends, and risk factors associated with this phenomenon, in various parts of the world. DEFINITION OF CHILDHOOD OBESITy Obesity is a consequence of an energy imbalance – i.e., when energy intake exceeds energy expenditure over an extended period of time (7). Until recently, there has been confusion in international published work about the definition of childhood obesity, rendering comparisons of childhood obesity rates dif- ficult (8).The most widely used measurement to define obesity is the body mass index (BMI) (weight in kilos divided by height in square metres, kg/m2) where Cole et al. (9) deter- mined values of BMI to define overweight among children, using six large nationally representative data sets drawn from population surveys. CONSEqUENCES OF OBESITy IN CHILDHOOD AND ADOLESCENCE As stated in the report of a WHO Consultation on Obesity (1),“overweight and obesity lead to adverse metabolic effects on blood pressure, cholesterol, triglycerides and insulin resistance. Some confusion of the consequences of obesity arises because researchers have used different BMI cut-offs, and because the presence of many medical conditions involved in the development of obesity may confuse the effects of obesity itself. The more life- threatening problems are those associated with cardio-vascular disease (CVD), conditions associated with insulin resistance, such as type 2 diabetes, certain types of cancers, and gallbladder disease. There is a range of non-fatal health problems associated with obesity, which include respiratory difficulties, chronic musculoskeletal problems, skin problems and infertility. The likelihood of developing type 2 diabetes and hypertension rises steeply with increasing body fatness. Confined to older adults for most of the 20th century, this disease now affects obese children even before puberty. Approximately 85% of people with diabetes are type 2, and of these, 90% are obese or overweigh (1). Overweight and obesity in childhood and adolescence are associated with a range of psychosocial and medical complica- tions that are both immediate and long term (10) and have severe economic consequences (11). From the psycho-social point of view, the findings of a recent study (12) showed associations of weight status with social relationships, school experiences, psychological well-being, and some future aspirations were observed. Among girls, the pattern of observations indicates that obese girls reported more adverse social, educational, and psychological correlates. Obese as well as underweight boys also reported some adverse social and edu- cational correlates. These findings contribute to an understanding of how adolescent experiences vary by weight status and suggest social and psychological risks associated with not meeting weight and body shape ideals embedded in the larger culture. The study is a cross sectional one, of school-age adolescents (4,742 males and 5,201 females). Results showed that obese girls, when compared with their average weight counterparts, were 1.63 times less likely to associate with friends in the last week, 1.49 times more likely to report serious emotional problems in the last year, 1.79 times more likely to report hopelessness, and 1.73 times more likely to report a suicide attempt in the last year. Obese girls were also 1.51 times more likely to report being held back a grade and 2.09 times more calories and may interact with other factors (e.g., tele- vision, the built environment) to further promote weight gain (11). Obesity is not only a health but also an economic phenomenon (11). Several economic factors affect our food consumption and physical activity decisions and ultimately our weight (11). ETIOLOGy OF OBESITy Taking into serious consideration the severe consequences of obesity, it is of enormous importance to identify the risk factors. This task is not an easy one, since the etiology for child and adolescent obesity is not clear. Obesity is a complex condition with genetic, metabolic, behavioural and environmental factors all contributing to its development (8). However, the dramatic increase in the prevalence of obesity in the past few decades can only be due to significant changes in lifestyle influencing children and adults alike (8). These obesity-promoting environmental factors are usually referred to today under the general term of “obesogenic” or “obesigenic” (3). The current changing nature of this obesogenic environment has been well described in a WHO Technical Report (17) as follows: “Changes in the world food economy have contributed to shifting dietary patterns, for example, increased consumption of energy-dense diets high in fat, particularly saturated fat , and low in unrefined carbohydrates. These patterns are combined with a decline in energy expenditure that is associated with a sedentary lifestyle, motorized transport, labour-saving devices at home, the phasing out of physically demanding manual tasks in the work- place, and leisure time that is preponderantly devoted to physically undemanding pastimes.” Under the notion “lifestyle” are included dietary changes, changes in work and leisure patterns, cultural, behavioural, geographical, environmental, social and economic factors (17). Therefore, apart from genetic factors, the prerequisite for becoming obese is an imbalance between energy expenditure, modulated primarily by physical activity, and energy intake from foods and drinks (17). TRENDS IN DIETARy PATTERNS Findings from a longitudinal study (18) conducted in the U.S. showed that total fat consumption expressed as a percentage of energy intake has decreased among U.S. children. However, this decrease is largely the result of increased total energy intake in the form of carbohydrates and not necessarily due to decreased fat consumption. The majority of children aged 5–17 years are not meeting recommendations for energy intake. Much of this 155 heavier than the non-overweight youth, which limited analysis to the non-overweight youth. Particularly because accelerometry in youth is strongly related to energy expenditure assessed by double-labelled water, an important research need for future studies is to identify methods of estimating total energy intake that are not associated with watching television, then this might offer opportunities for intervention (24). However, a Swedish study (25) refutes the speculation that reduced physical activity (PA) is associated with increased fat mass (FM). Specifically, results showed that PA was independent- ly associated with FM in males but not in females. The data also showed an intergenerational association of FM between mothers and their daughters, but not between mothers and their sons. The study is a cross-sectional one in 445 17-year-old adolescents and their mothers. According to the results, males were significantly more active than were females. PA was significantly and inver- sely associated with FM in males but not in females. However, FM and percentage FM in females were significantly associated with maternal FM and education level. No such associations were observed in males. Several limitations should be considered in interpreting the findings from the present study. First, it is not possible to infer a causal relation from cross-sectional data such as those in the current study. Second, the subjects may not be representative of Swedish adolescents in general. Third, self- reported PA is associated with recall bias. In conclusion, a clear sex difference was observed for the association between PA and FM in adolescents. Data also suggest a behavioural intergenera- tional association of FM between mothers and their daughters. Future studies, incorporating precise measures of exposures and outcome variables in parents and their offspring are needed, to test whether such an association also exists between fathers and their sons (25). OTHER RISK FACTORS ASSOCIATED WITH THE PREVALENCE OF OBESITy IN CHILDREN AND ADOLESCENTS This review indicates that various other risk factors are asso- ciated with the development of obesity in childhood and adoles- cence. The protective effect of breast-feeding against later obesity may not last through to adulthood, but obesity in later childhood is itself a predictor of adult disease, even if weight is lost and the adult is not obese (26). Therefore if breast-feeding protects against childhood obesity, that in itself may reduce the risk of adult diseases (overall morbidity and mortality from heart disease are both linked to adolescent obesity, irrespective of adult weight) (26). Furthermore, changes in maternal and, therefore, foetal nutrient supply at specific stages of gestation have the potential to substantially increase the risk of those offspring becoming obese in later life (27). The extent to which changes in dietary habits, both during pregnancy and in later life, may act to contribute to the current explosion in childhood and adult obesity still remains a scientific and public health challenge (27). In addition, during puberty, changes in body composition occur, when girls tend to increase fat mass as a result of matura- tion while boys tend to increase muscle and other non-fat body mass (3). A recent study (28) showed that parental overweight status is an important determinant of whether a child is overweight at either stage or changes from being not overweight at 5 years to becoming so at 14 years. This is a population based- prospective birth cohort study of 2,934 children who were examined at ages 5 and 14 years. The authors concluded that the results could suggest that children whose parents were overweight or obese were more likely to change from being not overweight at age 5 years to being overweight at 14 years and were more likely to be overweight at both ages. Maternal overweight status in particular was asso- ciated with these transitions. However, the study has limitations since the participation rate at both ages was 41% and the other important factors related to physical activity and diet, known to be important determinants of childhood BMI are not assessed, due to the lack of relevant information (28). The authors suggest that tackling adult obesity is likely to be important both for their own health benefit and that of their offspring and has to be taken into serious consideration in the design of intervention studies (28). In addition, apart from gender and ethnicity, the following risks factors should be mentioned (29): a) earlier adiposity rebound is associated with increased body fatness in adolescence; b) socio-economic status is another risk factor. In some developed countries, poorer children or those who live in rural settings are more at risk of obesity, whereas in countries undergoing economic transition childhood obesity is associated with a more affluent lifestyle and with living in urban regions; c) underlying medical disorders; d) prescription drugs (29). ASSOCIATIONS OF THE “MOSTLy BLAMED” DIETARy PATTERNS WITHIN THE “OBESOGENIC” ENVIRONMENT Let us first discuss the mostly blamed dietary patterns within the obesogenic environment. In a recent survey (30), the associ- ation between food habits and weight status was investigated in children who participated in the Bogalusa Heart Study. A 24-h dietary recall was collected over a 21-year period on a cross-secti- onal sample of 1,562 children aged 10 year. Results show that numerous eating patterns were associated with overweight status. Particularly, consumption of sweetened beverages (58% soft drinks, 20% fruit flavour drinks, 19% tea, and 3% coffee) , sweets (desserts, candy, and sweetened beverages), meats (mixed meats, poultry, seafood, eggs, pork, and beef) and total consumption of low-quality foods were positively associated with overweight status. The total amount of food consumed, specifically from snacks, was positively associated with overweight status. There was a lack of congruency in the types of eating patterns associated with overweight status across four ethnic-gender groups. The interaction of ethnicity and gender was significantly associated with overweight status. However, the study has the following limitations: Firstly, it was a cross sectional analysis and thus causal inferences cannot be made. Secondly, only a single 24- hour dietary recall was collected on each participant. Finally, the researchers suggest that additional studies are needed to confirm these findings in a longitudinal sample having multiple days of assessment (30). Furthermore, the findings from a prospective cohort study in the US (31) including more than 10,000 boys and 156 girls aged 9–14 years, showed that the consumption of sugar- added beverages was associated with small BMI gains during the corresponding year and may contribute to weight gain among adolescents, probably due to their contribution to total energy intake. A major limitation of their study was the necessity of col- lecting data (including height, weight, and beverage intakes) by Food Frequency Questionnaires (FFQ) on youth by self-report on mailed questionnaires. Their FFQ did suggest portion sizes, but did not specify the number of ounces in a can or glass, so confu- sion over this may have further biased their estimates toward the null. In addition, authors cannot claim that the children of nurses are a representative sample of U.S. children. The study suggests that beverage intake, including limiting the consumption of soft drinks, is a potential target for diet improvement (31). Another study (32) however refutes widespread speculation that carbohydrated soft drinks are responsible for the increase in overweight among children and adolescents. 3,111 children and adolescents of both gender participated in the study. Data from these participants from the years 1994–1996 and 1998 were col- lected by the U.S. Department of Agriculture. The total amount and the types of beverages consumed were analyzed according to age, race, and gender. It was found that age, race, and gender play a significant role in the total amount, types, and relative proportions of beverages consumed by children and adolescents. The relationship between body mass index (BMI) and beverage consumption is unclear. More specifically, researchers found that BMI was only related to consumption of diet carbonated bevera- ges and milk, while those relationships were weak and that total beverage consumption and beverage choices are strongly related to age, race, and gender. Older teens tend to drink more carbonated beverages, fruit drinks/ades, and citrus juice, but less fluid milk and non-citrus juice. White adolescent boys are heavy consumers of most beverages, including carbonated soft drinks, milk, and fruit drinks/ades. BMI is positively associated with the consump- tion of diet carbonated beverages and negatively associated with the consumption of citrus juice. BMI was not associated with the consumption of milk, regular carbonated beverages, regular or diet fruit drinks/ades, or non-citrus juices. Finally, researchers suggest that careful monitoring of children’s beverage intake is nevertheless warranted because caloric contributions must be balanced with energy expenditure (32). Similarly the findings from a study (33) that assessed whether intake of snack foods was associated with weight change among children and adolescents refute the widespread speculation and suggest that, although snack foods may have low nutritional value, they were not an important independent determinant of weight gain among children and adolescents. In this prospective cohort study, 8,203 girls and 6,774 boys 9–14 years of age participated. The results showed that boys consumed more snack foods than girls during the entire study period. There was no relation between intake of snack foods and subsequent changes in BMI z-score among the boys, but snack foods had a weak inverse association with weight change among the girls. The association between servings per day of snack foods and subsequent changes in BMI z-score were not significant in either gender. However, the most important limitation of this study apart from the fact that weight and height information was based on self-report is that, the study does not represent a random sample of all US adolescent males and females, since the participants are children of nurses, and thus the study includes relatively few children of low socioeco- nomic status in the sample. Moreover, the study does not provide information on the father’s weight status, thus there is incomplete information on parental weight status. Another limitation is that the study assessed snack foods, but not snacking occasions. There- fore the authors did not assess snacking on other foods, such as cereal and sandwiches, which may contribute an equal number of calories as snack foods. Since their definitions of snacking were based on types of foods eaten, not eating occasion, they may have misclassified some youth in terms of snacking patterns. It is possible that their results are therefore biased towards the null, which could explain the lack of positive association. Future studies are needed which assess snacking patterns, including snacking on items other than ‘snack foods,’ and the role snack foods play in overall dietary intake and weight changes. However, since most snack food items are of poor diet quality, thus regardless of the lack of association between intake of snack foods and subsequent weight gain, it would be prudent to recommend consuming snack foods only in moderation (33). At the same time, marked changes in eating culture and behaviour have occurred at an extremely rapid pace (17). Firstly, a U.S. study showed (34) that portion sizes and energy intake for specific food types have increased markedly with greatest increases for food consumed at fast food establishments and at home. The sample of the study consists of 63,380 individuals, from two surveys, aged 2 years and older. Specifically, portion sizes vary by food source, with the largest portions consumed at fast food establishments and the smallest at other restaurants. Between 1977 and 1996, food portion sizes increased both inside and outside the home for all categories except pizza. The energy intake and portion size of salty snacks increased by 93 kcal, soft drinks by 49 kcal, hamburgers by 97 kcal, French fries by 68 kcal, and Mexican food by 133 kcal. Some potential limitations of the study are that the USDA changed its methods for collecting dietary data during the period 1989–1998 and that persons who are overweight most likely under-report their energy intake (34). Finally, the results of this study propose that control of portion size must be systematically addressed both in general as it relates to fast food pricing and marketing (34). These observations are justified by the findings of another study (11) which mentioned that reductions in the relative price of energy-dense foods and an increased prevalence of marginal cost pricing , i.e. “supersizing” have resulted not only in an incre- ase in food consumption between meals, but also in an increase in the amount of food consumed at each meal (11). Moreover, since it has been estimated that children are exposed to almost 10 commercials per hour of viewing, most for fast foods, soft drinks, sweets, and sugar-sweetened cereals (5), it is obvious and can be expected that television may increase demand for these products more than computer or video game use. In addition, another study (35) showed that children who increase their consumption of FFA tend to gain weight. The cohort sample consists of 7,745 girls and 6,610 boys aged 9 to 14 years, at baseline. Results showed that at baseline, frequency of eating FFA was associated with greater intakes of total energy, sugar sweetened beverages, and trans fat, as well as lower consumption of low-fat dairy foods and fruits and vegetables. Moreover, results showed that adolescents who increased their consumption of FFA over 1 year gained weight over and above the expected gain from normal growth and matu- 157 ration during the adolescent period. The study also observed that cross-sectionally, adolescents who consumed greater amounts of FFA were heavier and were more likely to have poorer diet quality. However, the severe limitations of the study are the following: a) the researchers measured consumption of FFA and not fast food consumption or food purchased away from home directly; b) although they observed cross-sectional and longitudinal associ- ations between consumption of FFA and BMI, these associations were inconsistent across age and gender; c) researchers used self- reported heights and weights to calculate BMI; d) although the participants in this study came from all 50 U.S. states, ability to generalise may be limited because the participants are sons and daughters of registered nurses and the cohort is > 90% white. The study suggests that eating large quantities of FFA, year after year, accumulates to larger weight gains that are clinically significant. Findings from this study suggest that consumption of FFA and fast foods may have pernicious effects on body weight and diet quality, and since families may eat dinners together but away from home in fast food outlets or restaurants, one public health strategy for promoting adolescent weight maintenance may be to increase nutrition education for adolescents and their parents on the importance of a well-balanced diet (35). Another study (36) examined trends in fast-food consumption and its relationship to calorie, fat, and sodium intake in black and white adolescent girls. As it was shown, dietary intake of fast food is a determinant of diet quality in adolescent girls. In this longitudinal cohort study 2,379 black and white girls participated. Fast-food intake was positively associated with intake of energy and sodium as well as total fat and saturated fat as a percentage of calories. Fast-food intake increased with increasing age in both races. With increasing consumption of fast food, energy intake increased with an adjusted mean of 1,837 kcal for the low fast-food frequency group versus 1,966 kcal for the highest fast- food frequency group. Total fat in the low fast-food frequency group was 34.3% as opposed to 35.8% in the highest fast-food frequency group. Saturated fat increased from 12.5% to13% and sodium increased from 3,085 mg to 3,236 mg in the lowest ver- sus the highest fast-food frequency group. These results suggest that decreasing fast-food consumption to a lower level could be a useful strategy for reducing intake of total calories and further reducing total and saturated fats. However, additional dietary strategies and changes in the food supply and market may be needed to reduce dietary sodium (36). Finally, in developing countries and economies undergoing transition, many of the same factors may be influencing the deve- lopment of obesity (8). Thus, the observed trend which combines a reduced physical activity, with significant changes in food habits and eating behaviour is of major concern. INTERVENTION STUDIES There are three critical aspects of adolescence that have an impact on chronic diseases, as in the case of obesity: (i) the development of risk factors during this period; (ii) the tracking of risk factors throughout life; and, in terms of prevention, (iii) the development of healthy or unhealthy habits that tend to persist throughout life (17). This emphasis on the environmental causes of obesity leads to certain conclusions: first that the treatment for obesity is unlikely to succeed if we deal only with the child and not with the child’s prevailing environment, and second that the prevention of obesity – short of genetically engineering each child to resist weight gain – will require a broad-based, public health programme (3). A systematic review (37) suggests that following the assess- ment of the effectiveness of many interventions designed to pre- vent obesity in childhood and adolescence (individuals aged less than 18 years old) through diet, exercise, and/or lifestyle and social support are not effective in preventing weight gain, but can be effective in promoting a healthy diet and increased physical levels. The selected studies from 1990–2004 were randomised controlled trials and controlled clinical trials with minimum duration twelve weeks. The selected intervention studies employed educational, health promotion and/or psychological/family/behavioural thera- py/counselling/management strategies. Twenty-two studies were included; ten long-term (at least 12 months) and twelve short-term (12 weeks to 12 months). Nineteen were school/preschool-based interventions, one was a community-based intervention targeting low-income families, and two were family based interventions targeting non-obese children of obese or overweight parents. Six of the ten long-term studies combined dietary education and physical activity interventions; five resulted in no difference in overweight status between groups and one resulted in improve- ments for girls receiving the intervention, but not boys. Two studies focused on physical activity alone. Of these, a multi-media approach appeared to be effective in preventing obesity. Two studies focused on nutrition education alone, but neither were effective in preventing obesity. Four of the twelve short-term studies focused on interventions to increase physical activity levels, and two of these studies resulted in minor reductions in overweight status in favour of the intervention. The other eight studies combined advice on diet and physical activity, but none had a significant impact (37). The studies were heterogeneous in terms of study design, quality, target- population, theoretical underpinning, and outcome measures, making it impossible to combine study findings using statistical methods. In addition, there was an absence of cost-ef- fectiveness data (37). Following the review, the absence of a sound effectiveness from the intervention studies could be justified by the fact that the length of time over which interventions are being conducted is too short to modify weight status (37). However, it is worth mentioning to include recognition of the complexity of the problem and its determinants, the sophistication of the intervention content, and the research methods required, in order to produce sound and sustainable outcome changes (37). The strongest recom- mendation is that all interventions are accompanied by a carefully considered evaluation design that enables sufficiently powered analysis of what is working, or not, and for whom (37). Finally, the authors recommend that a focus on short-term behaviour change is unlikely to be sustainable or effective in impacting on weight status of children and thus not an effective strategy in the absence of corresponding interventions which would impact on the sus- tainability of the interventions and a conducive and supporting environment (37). The reviewed interventions rarely considered the impact of parents’ and family’s increasingly complex working and living arrangements, yet the potential for change at the family