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Introduction
Data accumulated over the past three decades indicate that atherosclerotic disease processes begin early in childhood. This provides compelling evidence for the worth of initiating prevention of cardiovascular disease in childhood1.
Overweight and obesity in childhood and adolescence have been associated with adverse socioeconomic outcomes as well as increased morbidity and mortality rates in adulthood2. Paediatric obesity is associated with an increase in psychological problems, cardiovascular disease, type 2 diabetes mellitus and asthma3.
There is no definition of obesity among children and adolescents that is accepted worldwide. In the USA, individuals with body mass index (BMI) >30 kg/m2 or ≥95th percentile (whichever is smaller) for age and gender are considered obese4. The most recent normative US charts were produced by the Centres for Disease Control in 20005. Similar BMI age-sex-specific reference charts have been developed in the UK, France, Germany and Denmark6,7. In Greece, BMI charts were recently published for children living in urban Athens but no data exist for the entire country8. In 2000, reference BMI criteria based on 6 pooled international data sets were developed for children from 2 to 18 years of age: the International Obesity Task Force (IOTF) standards9. The IOTF reference standards are widely used, particularly outside the USA; however, some authors believe these standards do not accurately reflect the world's population and so are unsuitable for clinical use4. It has been suggested that a single international definition of obesity may not be appropriate10. Consequently, it has been advocated that prevalence studies include both IOTF cut-offs, as well as national definitions in order to provide better comparison across populations11.
A marked increase in child and adolescent obesity in the past few decades is well established12. It essentially concerns populations that have recently adopted Western lifestyle, poor dietary habits and inactivity, combined with limited awareness of health issues13. Obesity in children between 6 and 18 years in Greece has been studied, particularly in urban areas. Its prevalence has been reported as between 8.4% and 12.3% in boys, and between 7.3% and 9.9% in girls13-15. In the rural population of Crete, childhood obesity prevalence was 9.4%16.
Hypertension in addition to obesity is a known risk factor for atherosclerotic cardiovascular disease in adults17. There is evidence that childhood hypertension predisposes an individual to adult hypertension18. For each increment of 1 to 2 mmHg in systolic blood pressure (BP), children have a 10% greater risk of developing hypertension as adults19. Increased prevalence of elevated BP in childhood and youth has been documented in recent decades and is associated with an increased prevalence of overweight1.
The primary objective of this study was, for the first time, to screen for obesity and elevated BP in school children in rural northern Greece. The significance of the findings were evaluated with respect to primary health care. The criteria for defining obesity and their impact on primary health care are discussed.
Methods
School health screening programs are compulsory for all Greek children and provide health information for parents. Because the programs are approved and organized by the Greek Ministries of Health and Education they are exempt from additional ethics committee or a human-subjects review board approval. Body mass index screening is performed in these programs to detect children at increased risk for weight-related health problems. The data collected for this study were anonymous.
The Nea Madytos Health Centre of the Greek National Health System provides primary care for all inhabitants of the eastern provinces of Thessaloniki prefecture in northern Greece, an essentially rural population. Health centre practitioners visited every nursery and elementary school in the region and examined every nursery student (from 4 to 5 years of age), and students in the 1st, 3rd and 5th class of elementary school (6, 8 and 10 years, respectively) between October and December 2007. A total of 572 children were examined (287 boys and 285 girls). The sample had social and economic characteristics in common with the rural student population of northern Greece and other rural regions of Greece.
All children had height, weight and blood pressure measured at the same visit. Height was measured without shoes with a wall-mounted stadiometer. Weight was measured without heavy clothing or shoes. Blood pressure was measured twice with the child in the seated position, by auscultation with an aneroid sphygmomanometer and appropriate-size cuff, following 5 min of quiet rest. The average of these two recordings was used for further calculations.
Obesity was defined using three different methods: (i) BMI charts of the French society of Paediatrics (FR), which define school children with BMI ≥97th percentile as obese7; (ii) US BMI charts produced by the Centers for Disease Control in 20005, which define individuals 2 to 18 years of age with BMI >30 kg/m2 or ≥95th percentile for age and gender (whichever is smaller) as obese; and (iii) the IOTF reference curves9.
Elevated BP was defined as BP ≥95th percentile based on age, gender and height using normative Greek charts20.
Results are presented as the mean ± standard deviation; 95% confidence intervals for the prevalence of obesity in male and female students were obtained using normal approximation to the binomial distribution21. To compare the risk of developing elevated BP in obese and non-obese children, 95% confidence intervals for relative risk and odds ratios were constructed using the normal distribution21.
Results
The mean age of the children in the study was 7.3 ± 2.0 years, mean height 130 ± 14 cm, mean weight 31 ± 11.2 kg, mean BMI 17.9 ± 3.6 and mean BP 98 ± 11.5 / 59 ± 10.7 mmHg.
The prevalence of obesity varied according to the definitional method used from 13.6% to 31.7% for boys, and from 14.4% to 35.1% for girls (Table 1). It must be noted that an additional 21.3% of boys and 23.2% of girls were classified as overweight according to the IOTF standards. Therefore, even using the rather conservative IOTF standards, 34.9% of boys and 37.6% of girls could be expected to be either overweight or obese at age 18.
Forty-five children (7.9%) had elevated systolic or diastolic BP (≥95th percentile), 27 children had elevated systolic BP, 30 had elevated diastolic BP, and 12 had elevated systolic and diastolic BP. Elevated BP was more common in obese children, from 17.8% to 27.5% depending on the method used to define obesity (Table 2). Therefore, obesity was associated with an increased risk of elevated BP (relative risk of 5.2 to 6.2).
Table 1: Prevalence of obesity in male and female students, according to age group
Table 2: Prevalence of elevated blood pressure in obese and not obese school children
Discussion
This study applied three methods to define obesity: (i) the IOTF criteria; (ii) the French standards; and (iii) US BMI charts. France was chosen as a country with a low cardiovascular risk profile, similar to other Mediterranean countries such as Greece and with no major obesity problem. The USA has a population with a higher cardiovascular risk and a high prevalence of childhood obesity22.
The prevalence of obesity found in previous Greek studies useing IOTF criteria was: 11.8% for boys and 7.5% for girls in the city of Ioannina14, 8.4% for boys and 7.3% for girls in the city of Thessaloniki13, 12.3% for boys and 9.9% for girls in urbanised northeast Attica15, and 14.1% in urban provinces of Crete16. It was therefore surprising to find the obesity prevalence in rural northern Greece at 13.6% for boys and 14.4% for girls, which is higher than in the mainly urban Greek populations previously studied. Obesity in rural northern Greece is also more prevalent than in rural Crete, where a rate of 9.4% has recently been reported16.
Why are children in rural areas more obese? Although multinational fast food chains are absent from rural Greece, in almost every village there is a cantina well stocked with junk food. In addition, the rural population is less educated in health issues and there is a general perception that being overweight is a sign of good health. These suggestions need to be verified in a future survey of children. Such research should include a questionnaire about childrens' fast-food consumption, and also the frequency and intensity of their sporting activity.
Using the French or US criteria (rather than IOTF), obesity was much more prevalent in our study (Table 1). For example, with the US charts, 23.7% of boys and 21.1% of girls in our study were obese. Childhood obesity appears to be more prevalent in Greece than in the USA where prevalences of 18% and 22% have recently been reported12,22-23.
Our data revive the question of which childhood obesity criteria are optimal for use in general practice. The IOTF criteria seemed to underestimate obesity in the present study population and may not be the best for use in primary care where preventive strategies, public education and treatment are far more important than an essentially epidemiological approach.
Childhood obesity tends to persist into adulthood24. Therefore, an obesity epidemic could be predicted for populations with a high prevalence of childhood obesity, as in Greece. In Europe, according to the SCORE project, two different tables are proposed to calculate an individual's cardiovascular risk: the first for populations at high risk (as in northern Europeans), and the second for populations at low risk (as in Mediterraneans)17. If the high prevalence of obesity in Greece continues unabated, the overall cardiovascular risk of the Greek population can be expected to rise. In the near future, Greece may have a population at high cardiovascular risk who are better represented by the model used for northern Europeans.
In the present study BP was measured on one occasion, although the current recommendation for diagnosing hypertension in children is detecting elevated BP on each of 3 different occasions25. Elevated BP was found in 7.9% of school children, which is similar to reported rates of 7.2% in Delaware and Pennsylvania, USA12, 9.6% in Sousse, Tunisia26, and 5.6% in Italy27. It must be noted, however, that BP is labile in children followed longitudinally27. A 19.4% prevalence of hypertension on first screening has been reduced to only 4.5% after three screenings23. Therefore, the single measurement in the present study may have overestimated the prevalence of elevated BP.
This study confirms the previously described relationship between higher BP and increasing BMI (OR 6.33-7.73)12,23,28, with odds ratios for overweight school children having been reported as 2.4 for diastolic BP and 4.5 for systolic BP28, and present in all age groups12.
Conclusion
A high rate of childhood obesity was found in rural northern Greece, and this may imply that children in rural areas are developing an unhealthy lifestyle. The IOTF criteria may underdiagnose obesity substantially, so GPs should also use national reference charts where they are available. Because obese children have a substantially increased risk of cardiovascular disease as adults, the detection, prevention and early treatment of childhood obesity is important.
Acknowledgement
The authors thank Professor JS Schutz MD for his editorial assistance.
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