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Objective Nutrition

CHILDHOOD OBESITY: INFLUENCES OF SOCIOECONOMIC FACTOR
OBJECTIF NUTRITION 73 (SEPTEMBER 2004)
by Blandine de Lauzon, Dr. Marie-Aline Charles, INSERM U258, Villejuif, France

In developed countries, socioeconomic status and health concerns are strongly related. Therefore, it is important to understand to what degree social status may affect child development. An inverse relationship has clearly been demonstrated between socioeconomic level and prevalence of obesity in adults. In children, results are less consistent. In adults, socioeconomic status can be either a cause or a result of obesity. Conversely, in children, the causal relationship between socioeconomic status and obesity is relatively easy to analyze since a child's socioeconomic status only depends on that of his or her parents.

FOCUS
Body mass index (BMI = weight (kg)/height2 (m2)) is a good indication of body fat. In children, it clearly decreases from1 to 6 years of age and then increases up until the teenage years and the start of adulthood. Thus, in children, it is not possible to refer to a single BMI value. An international definition of obesity has recently been formulated by the International Obesity Task Force (IOTF): it is based on reference curves representing BMI values as a function of age. Overweight and obesity in childhood are defined by international BMI curves passing through 25 and 30 kg/(m2) at age 18.


Childhood obesity is a major health care professional concern. Although the majority of obese or overweight children have no medical complications, specific disorders can occur in the case of severe obesity and some subclinical disorders (hypertension, hypercholesterolemia, and hypertriglyceridemia, etc.) are more common in obese children. Furthermore, childhood obesity has psychosocial consequences, relating to a loss of self-esteem, worsened by the stigmatization of obesity.
The probability of continuing obesity or overweight in adulthood, when acquired during childhood, varies with the child's age and the presence of obesity or overweight in parents: it is the primary risk of childhood obesity. Thus, approximately 20% to 50% of children who were obese before puberty will remain so in adulthood, and 50% to 70% of obese adolescents will retain this obesity in adulthood.


SOCIOECONOMIC STATUS AND OBESITY

Indirect indicators such as country, region or town size can be an initial approach to the socioeconomic level in which the child grows.

Prevalence of childhood obesity in France…

The body mass index distribution curves (BMI), established during the 1960's, define obesity in France. A child whose BMI is above the 97th percentile of these curves is considered as obese in France. Therefore, the prevalence of childhood obesity was 3% in the 1960's. Consistency of estimates from different sources makes it possible to conclude that prevalence of obesity has been increasing since the 1960's: in 5-to-12 year-of-age children, this prevalence reached 6-8% during the 1980's and 13-15% at the end of the 1990's. (Figure 1). The French definition of obesity, defined by the 97th percentile of BMI curves, is close to the International Obesity Task Force (IOTF) definition of overweight. Obesity prevalence was higher with the French definition than with the IOTF definition.


Figure 1 ON 73

Figure 1: Prevalence of childhood obesity (French definition) in France since 1965 in children 5 to 12 years of age.
(ERF: French Reference Study; RP: Paris area Study; C-O: Center and West of France Study, ELP: Parisian Longitudinal Study; FLVS: Fleurbaix-Laventie Ville Santé Study; INCA: Individuals and National Survey of Food Intake).

…and in other countries

The prevalence of obesity in children aged 5-12 years has been multiplied by four in France between the 1960's and the year 2000, while this prevalence had tripled in the United States between 1971-74 and 1999 in children 6-11 years of age. Thus, although there is a lower percentage of obese children in France than in the United States, the progression rate of this epidemic is equally worrisome.

Childhood obesity does not affect all European countries with the same intensity. (Figure 2) A geographic gradient exists with higher prevalence of obesity in Eastern and Southern European countries, while the Northern European countries still appear relatively spared.


fig 2 ON 73
Figure 2 : Prevalence of overweight subjects (including obesity) in Europe in children of about 10 years of age (International Obesity Task Force).

Differences according to location of residence

In a given country, childhood obesity does not affect each area of the country in the same way. Thus, in France according to the “ObEpi 2000” survey (Figure 3), the western France region had the lowest percentage of obese children with a prevalence of 0.9%. The Mediterranean, southwest, northern and eastern regions of France are the most affected areas with a prevalence of obesity of about 3%. Regardless of cultural differences and possible genetic differences between populations, environmental variables, such as the economic development level of the region, may play an important role in the extension of obesity and partly account for regional differences.
In France, a study has been conducted in children in kindergarten (5-7 years of age) in so-called “Zones with Educational Priority (ZEP)”. The incidence of overweight (including obesity) in such children from less privileged areas was 16.5% versus 13.6% in children who attended school in areas outside such zones.


figure 3 ON 73

Figure 3 : Prevelance of obesity (IOTF definition) of children 2 to 17 years of age in France, depending on their region of residence (ObEpi 2000).



Monthly income of households is a more direct measurement although incomplete. In the ObEpi 2000 survey, the lowest income households were the most affected by the child obesity epidemic (Figure 4).

figure 4 ON 73
Figure 4: Prevalence of obesity (IOTF definition of children 2 to 17 years of age according to net monthly income per person per household (Obépi 2000).
Recent studies in Sweden and the United Kingdom have demonstrated that overweight and obesity were increasing more quickly in the lower income than in the higher income groups.


SOCIOECONOMIC FACTORS OF OBESITY

Physical activity and sedentary lifestyle

The epidemic of obesity has developed concomitantly with a decrease in physical activity and an increase in sedentary activities. Time spent watching television or playing video games is a period during which the child remains seated and thus his/her energy use is relatively low. Furthermore, such leisure activities lead to snacking which results in an increase in energy intake.
Cross-sectional data often reveal an inverse relationship between BMI and physical activity, indicating that obese or overweight subjects are less active than their thinner counterparts. However, it is difficult to determine with certainty whether obese subjects are less active as a result of their obesity, or whether their low degree of activity is truly the cause of their obesity.
Socioeconomic status can have an impact on the level of physical activity or the sedentary lifestyle of subjects.  Indeed, access to leisure physical activities varies considerably between different classes of society, either due to financial reasons or to reasons involving information on the physical activity-related benefits.

Diet

In the industrialized countries, food shortages have become very rare. Groups of subjects whose socioeconomic condition is less privileged do not necessarily have a lower energy intake than subjects in a higher financial bracket. Furthermore, some studies have indicated that an increase in income results more often in the purchase of foods whose preparation and packaging are more developed or whose quality is better, rather than in an increase in their quantity. However, in the poorest population groups, diet tends to involve a higher number of calories and is characterized by a very high fat intake; vegetables, fruits, and whole grain cereals, which are generally more expensive, are eaten in lesser amounts.

Educational background and knowledge in terms of health

An inverse relationship exists between education background and BMI in the industrialized countries. This finding can be attributed partly to the fact that subjects who have completed a higher grade in school are more apt to follow dietary recommendations and to change their behavior to avoid risks than subjects who have a lower level of education. However, the advantages associated with proper nutrition knowledge seem to be limited. In fact, surveys indicate that even though some people know what a "healthy diet" is, in practice their eating habits are much less "healthy".


Teenage years

Social inequality impact on the development of childhood obesity seems to be especially felt at the time of adolescence, particularly in girls. In teenagers who come from underprivileged social classes, new cases of obesity are higher, and the regression of existing obesity is less frequent than in the more privileged classes of society.
Adolescence is a period of increased autonomy often associated with irregular eating patterns, changes in eating habits, and periods of inactivity during leisure time. These changes in behavior and lifestyle are added to physiological changes, particularly in women.
During this period of high individual sensitivity to weight gain, the ability to adjust eating habits and the level of physical activity in response to weight status can be affected by several factors such as the teenager's level of education and that of his/her parents, and (cultural and financial) access to advice.


CONCLUSION

Better understanding of the influence of socioeconomic factors in the development of obesity in children is essential to set up effective prevention policies. A policy on prevention focused solely on education measures cannot effectively solve the problem of obesity. It must also take into account the major obstacle related to the cost of access to a balanced diet and to leisure physical activity.


Blandine de Lauzon, Dr. Marie-Aline Charles
INSERM U258, Villejuif, France


References
· Duport N., Castetbon K., Guignon N. & Hercberg S. - Corpulence des enfants scolarisés en grande section de maternelle en France métropolitaine et départements d'outre-mer: variations régionales et disparités urbaines. BEH, 2003, 18-19.
· Obépi 2000, Le surpoids et l’obésité en France. Enquête épidémiologique réalisée dans un échantillon représentatif de la population française, adulte et enfant. INSERM / Institut Roche de l’Obésité / SOFRES.
· Obésité: prévention et prise en charge de l’épidémie mondiale. OMS, Série de rapports techniques, 2003, n°894.
· http://www.iotf.org/chilhood/euappendix.htm