Hypertension (HT) is the worldwide number-one risk factor for preventable death. In Turkey the overall prevalence of HT is 31·8 %, and only 40·7 % of those with HT are aware that they have it(Reference Altun, Arıcı and Nergizoğlu1). HT is believed to result from obesity, which is exacerbated by a high-energy, high-fat and high-salt diet, inadequate exercise and stress(Reference Sorof, Lai and Turner2–Reference Flyn4). Childhood HT risk factors increase the risk of HT in adulthood(Reference Raj, Sundaram and Paul5, Reference Ataei, Hosseini and Iranmanesh6). Systolic blood pressure (SBP) elevation in childhood predicts arterial stiffness in young adults(Reference Li, Chen and Srinivasan7, Reference Raitakari, Juonala and Kahonen8). Increased carotid intima-medial thickness predicts cardiovascular events(Reference Davis, Dawson and Riley9). Diastolic blood pressure (DBP) is particularly important in monitoring blood pressure (BP) in younger individuals(Reference Elkasabany, Urbina and Daniels10).
The prevalence of obesity has increased rapidly in all age groups(Reference Nielsen and Andersen11). From 1980 to 2005, in the USA the prevalence of obesity has increased by 40 % in children and adolescents(Reference Lasserre, Chiolero and Paccaud12, Reference Prineas13). Overweight predisposes children to the health problems of obesity in adulthood, including HT, dyslipidaemia, impaired glucose metabolism, hyperinsulinaemia, obstructive sleep apnoea, and orthopaedic and psychosocial problems(Reference Işık and Naçar14). High childhood BP predicts CVD in adulthood, and HT plus high BMI predicts even worse CVD in adulthood(Reference Rademacher, Jacobs and Moran15). The risk of obesity is related to factors in the antenatal environment, the early postnatal years, the adiposity rebound (at 5–6 years of age) and puberty(Reference Velasquez-Mieyer, Perez-Faustinelli and Cowan16).
The relationship between HT and BMI in children has not been studied in Ankara, which is the second largest and the capital city in Turkey. We measured height, weight and BP in 2826 students, aged 7–12 years, in Ankara, Turkey.
Method
The study was approved by the Provincial Health Directorate of Ankara and the Ethics and Research Committee of Diskapi Yildirim Beyazit Training and Research Hospital, Ankara, Turkey.
We collected the data between March and June of 2012. We expected a frequency of HT of 10 % in 7–12-year-old children, so to achieve α=0·01 we calculated that we would need 2396 subjects. The Provincial Health Directorate of Ankara selected, with a simple random-sampling method, three primary schools, in three different socio-economic regions of Ankara. There were a total of 3165 students in the three schools. Our data-collection days were predetermined and the data collectors were trained medical staff. We aimed to collect data from all 3165 students, but some students declined to participate and some were absent on our data-collection days. Response rate was 89·3 % and data on height, weight, SBP and DBP of 2826 children were recorded.
With a device that combined a weight scale and a stadiometer (DR-MOD·85 scale) we measured height to the nearest centimetre, weight to the nearest 0·5 kg, and SBP and DBP to the nearest mmHg. The weight scale/stadiometer was recalibrated before every data-collection day. The children were measured while wearing their undergarments. BP above the 95th percentile was deemed HT, according to the 2004 scheme of the High Blood Pressure Working Group(17). Overweight and obesity were defined according to the year 2000 Centers for Disease Control and Prevention growth charts(Reference Kuczmarski, Ogden and Guo18). The 85th BMI percentile was considered overweight and the 95th BMI percentile was considered obese(Reference Neyzi, Günöz and Furman19, 20).
Statistical analysis
The data were analysed with the statistical software package PASW Statistics 18 and are presented as mean and standard deviation, range and frequency values. The χ 2 test was used for categorical variables and Student’s t test was used for normally distributed data with equal variances. The effect of BMI on SBP and DBP of children was investigated with ANOVA. The Kruskal–Wallis test was used if the variables did not have a normal distribution. Statistical significance was set at P<0·05.
Results
We collected data from 2826 children (89·3 % of the 3165 total students in the three schools; Table 1). Of these, 1496 (52·9 %) were male and 1330 (47·1 %) were female. All the children were between 7 and 12 years old. The mean BMI, SBP and DBP all increased with age in both sexes (P<0·001) and all were higher in boys than in girls.
Mean BMI, systolic blood pressure (SBP) and diastolic blood pressure (DBP) by sex and age in 2826 children aged 7–12 years, Ankara, Turkey, March–June 2012
HT was present in 222 children (7·9 %): 124 boys (55·9 %) and ninety-eight girls (44·1 %; P=0·40). In the whole cohort, 101 (3·6 %) had only systolic HT, twenty-one (0·7 %) had only diastolic HT and 100 (3·5 %) had both systolic and diastolic HT.
Overall, 2040 (72·2 %) of the children had normal weight, 393 (13·9 %) were overweight and 393 (13·9 %) were obese. Obesity was significantly more common in boys (16·2 %) than in girls (11·3 %, P<0·001 via χ 2 test; Table 2).
BMI category by sex and age in 2826 children aged 7–12 years, Ankara, Turkey, March–June 2012
Among the children with normal BP, 264 (10·1 %) were obese. Among the children with HT, 129 (58·1 %) were obese (Table 3). There was HT in fifty (2·5 %) of the normal-weight children, forty-three (10·9 %) of the overweight children and 129 (32·8 %) of the obese children. HT was significantly more common in the obese children (P<0·001). As BMI increased, SBP and DBP also increased: P<0·001 for the relationship between BMI and SBP, and P<0·001 for the relationship between BMI and DBP.
Relationship between blood pressure (BP) category and BMI category in 2826 children aged 7–12 years, Ankara, Turkey, March–June 2012
Mean SBP and DBP of the boys were significantly higher than those of the girls (all P<0·001; Table 4), and mean SBP and DBP increased with age (P<0·001; Table 5).
Mean systolic blood pressure (SBP) by sex, age and BMI category in 2826 children aged 7–12 years, Ankara, Turkey, March–June 2012
Mean diastolic blood pressure (DBP) by sex, age and BMI category in 2826 children aged 7–12 years, Ankara, Turkey, March–June 2012
Discussion
The overall prevalence of HT in our cohort was 7·9 %. Previous studies in Turkey reported prevalence between 3·9 % and 17·8 %, but those studies had smaller sample sizes(Reference Dişcigil, Aydoğdu and Başak21–Reference Çetinkaya24). The range of reported overall prevalence of HT among children in the USA is 2·7 % to 16·9 %(Reference Falkner25). Two studies in Japan found HT prevalences of 11·0 % and 7·2 %, and HT was more common in boys(Reference Matsuoka and Awazu26, Reference Zhang, Tse and Deng27).
In our cohort the HT was predominantly systolic. Systolic HT in children is associated with more than fourfold increased risk of coronary artery disease(Reference Zhang, Tse and Deng27) and childhood systolic and diastolic HT predict CVD in adult life(Reference Li, Chen and Srinivasan7–Reference Elkasabany, Urbina and Daniels10), so our findings are important and concerning.
According to our study, the mean BP increased with age, but increasing age did not correlate with an increase in the number of hypertensive children. Other studies in Turkey agree with these findings(Reference Irgıl, Erkenci and Aytekin22, Reference Sarıkan28, Reference Dinç, Saatli and Baydur29). In contrast, our findings regarding the relationship of sex and HT do not agree with previous studies. Çetinkaya found that 9·4 % of boys and 5·6 % of girls in Ankara had HT(Reference Çetinkaya24). In the Van region of Turkey, Arslan found an equal prevalence of HT in boys and girls (9·4 % v. 8·7 %)(Reference Arslan30). Contrary to our findings, two other studies in Turkey found a higher prevalence of HT in girls than boys (20 % v. 15 %; 21 % v. 15 %)(Reference Dişcigil, Aydoğdu and Başak21, Reference Dinç, Saatli and Baydur29). In our study HT was non-significantly more common in the boys.
In our children the prevalence of overweight and obesity were both 13·9 %, and more boys than girls were obese. A study of 15–18-year-olds in Turkey found that 3 % were overweight and 11 % were at risk for being overweight(Reference Dinç, Saatli and Baydur29). Another study, which included 1899 Turkish children aged 6–14 years, found that a higher percentage of boys than girls were at or above the 85th percentile of BMI(Reference Gundogdu31). The 2007–2008 National Health and Nutrition Examination Survey (NHANES) in the USA found that 16·9 % of 2–19-year-olds were obese(Reference Ogden, Carroll and Curtin32). We also found a high incidence of obesity.
Our results showed a statistically significant relationship between obesity and HT. There was HT in 2·4 % of the normal-weight children and 32·8 % of the obese children. As BMI increased, SBP and DBP also increased. A study in Istanbul, Turkey found that obese children had higher SBP and DBP(Reference Öktem33), and several studies in other countries had findings similar to ours(Reference Wolff, Hoang and Flannery34–Reference Moore, Stephens and Wilson39). In Italy, Di Bonito et al. found HT in 17·7 % of obese children and 1·5 % of normal-weight children aged 6–16 years(Reference Di Bonito, Forziato and Sanguigno40). In the USA, a prospective study that included 22 071 individuals found a positive relationship between BMI and BP(Reference Gelber, Gaziano and Manson38).
The impact of sex on the relationship between BMI and BP is controversial. A study of 7–18-year-olds in Iran found a stronger association between BMI and BP in boys than in girls(Reference Hosseini, Ataei and Aghamohammadi35). Two studies in Turkey found results similar to our study: BMI was higher in boys and there was a positive relationship between BMI and HT(Reference Gundogdu31, Reference Şimşek, Ulukol and Berberoğlu41). Overweight was a critical determinant of BP in both girls and boys(Reference Kawabe, Shibata and Hirose42, Reference Paradis, Lambert and O’Loughlin43). On the other hand, Gundogdu found that sex had no effect on the relationship between BMI and BP(Reference Gundogdu31). The possible reasons for sex differences are not clear. The reported higher prevalence of HT in young and middle-aged men (than in women) and the higher prevalence of HT in older women (than in men) suggest that sex hormones may affect BP(Reference Martins, Nelson and Pan44). SNP of oestrogen receptor genes was reported to be important in the development of HT. Men inheriting the ‘a’ allele of the oestrogen receptor α had significantly higher BP than did men with other genotypes(Reference Ellis, Infantino and Harrap45), but there was no significant association between oestrogen receptor genes and BP in women. This suggests that sex differences affect BP via sex steroids(Reference Dasgupta, O’Loughlin and Chen46). The effects of sex hormones in sodium excretion and renal haemodynamic response may explain the hormonal control of BP(Reference Hosseini, Ataei and Aghamohammadi35).
Limitations
Our study included only three schools. We tried to prevent selection bias with the Provincial Health Directorate of Ankara’s randomized selection of schools from three different socio-economic levels. Since our study was not designed to determine the reasons for obesity, we do not think our results were importantly affected.
We did not collect data from 339 students (11 %) who declined or were absent during the data-collection days. Refusal to participate may have been related to obesity, body image or self-esteem. However, we did reach our calculated necessary sample size, so we believe our results are valuable.
Future studies
We plan on multi-centre studies of BP and BMI in other cities in Turkey, which will provide percentile curves and important additional data on the relationship between BP, weight, age and sex.
Conclusions
Our study is the first study to be representative of Ankara with the highest number of sampling. In children aged 7–12 years in Ankara, Turkey, HT was more prevalent in the overweight and obese children and more prevalent in boys than in girls. As age, weight, height and BMI increased, the mean SBP and DBP increased. BP measurement should be routine and frequent in children, especially overweight children.
Acknowledgements
Acknowledgements: The authors wish to thank all the children and teachers who participated in the study. Financial support: This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. Conflict of interest: None. Authorship: S.G. and C.A. designed the study and helped the data analysis. M.P. and H.Y collected the data, conducted the data analysis and wrote the paper. Ethics of human subject participation: The present study protocol was accepted by the Ethics and Research Committee of Diskapi Yildirim Beyazit Training and Research Hospital (Protocol No. KAEK 07/22).
