Abstract
Background The association between elevated blood pressure and childhood overweight and obesity has been documented in several studies. However, the linkage of blood pressure with body fat distribution in children is not well established. We investigated the relationship between both central and subcutaneous adiposity with BP in the 95th percentile or higher in Mexican children.
Methods and Results Our study, using a sample of children from the State of Guerrero, Mexico was comprised of 252 children, 124 girls and 128 boys, with an age range of 6 to 13 years. Resting blood pressure was measured in duplicate with an aneroid sphygmomanometer. Hypertension was classified as systolic or diastolic BP in the 95th percentile or higher. Additional measures included weight, height, body mass index, body circumferences, and skinfold thickness. The prevalence of obesity (26.5%) was higher than overweight (15.8%), but the prevalence of hypertension was moderate (4.7%). Both systolic and diastolic blood pressures correlated strongly with age, weight, height, and all measurements of central and subcutaneous adiposity. Interestingly, after being adjusted by age, sex, and body mass index, the BP in the 95th percentile or higher was associated with suprailiac skinfold, third tertile (OR = 11.83, P = 0.023); triceps skinfold, third tertile (OR = 6.02; P = 0.034); and biceps skinfold, third tertile (OR = 4.71; P = 0.038).
Conclusions Our data indicate that the prevalence of hypertension in children is moderate. In addition, the skinfold thickness was a better predictor of hypertension than central adiposity in the sample of children studied.
Childhood obesity is associated with many complications such as hypertension, dyslipidemia, type 2 diabetes, sleep apnea, orthopedic problems, and gall bladder disease.1Although the prevalence of hypertension during childhood is lower than that seen in adulthood, this condition is not rare in children, thus stressing the importance of evaluating blood pressure (BP).2The prevalence of hypertension among children reported by various studies ranges from 4.5% to 19.4%.3-6The association between overweight and hypertension in children has been reported in a variety of ethnic and racial groups, with practically all studies finding higher BPs and/or a higher prevalence of hypertension in overweight compared with lean children.7-9However, the prevalence of hypertension in Mexican children is unknown.
Hypertension in children has been shown to correlate with family history of hypertension, low birth weight, and excess weight.10Elevated BP during childhood and adolescence is associated with increased cardiovascular risk in later life.11Until recently, hypertension was considered to be a rare condition in children, but there is a well-documented positive relationship between body mass index and BP in children.12-14Also, it is not clear what determines hypertension during childhood. Several factors have been suggested to be related to the rise of BP levels in children. Several lines of evidence suggest that BP in US children and adolescents is increasing in parallel with weight.15
Previous studies have associated measurements of body composition with BP and the influence of central adiposity on BP level in childhood. Our aim was to gain knowledge regarding the prevalence of high BP and its relationship with body fat distribution in a sample of Mexican children.
MATERIALS AND METHODS
All children were from the State of Guerrero, with an age range of 6 to 13 years. This cross-sectional study was carried out between June and September, 2008. Participants were recruited in the urban area from the city of Chilpancingo through announcements at schools and activity centers, and word of mouth. The children used in this study included 252 girls and boys who had complete data on BP and anthropometry. There were no height or weight restrictions to entry into the study. Informed written consent was obtained from all parents or guardians before enrollment of children in the study. Approval for the study was obtained from the Research Ethics Committee of the University of Guerrero.
Clinic and Anthropometric Measurements
Body weight was determined in light clothes and without shoes using a Tanita body composition monitor (Tanita BC-553, Arlington, VA), and height was measured to the nearest 0.1 cm using a stadiometer (Seca, Hamburg, Germany). From these measurements, body mass index (BMI) was calculated (BMI = weight/height2, kg/m2). The circumferences were measured in duplicate using a diameter tape accurate to within ± 0.1 cm (Seca 201, Hamburg, Germany). Waist circumference was measured at the level of the umbilicus and the superior iliac crest. The measurement was made at the end of a normal expiration while the subjects stood upright, with feet together and arms hanging freely at the sides. Hip circumference was measured at the maximum point below the waist, without compressing the skin. The waist-to-hip ratio was calculated as waist/hip. The thickness of 4 skinfolds was measured to the nearest 0.1 mm, in duplicate, using skinfold caliper (Dynatronics Co, Salt Lake City, UT): triceps, biceps, subscapular and suprailiac. The duplicate measures were averaged.
Blood pressure was measured on the right arm of children seated at rest for at least 5 minutes. Two consecutive measures were obtained at 1-minute intervals with an aneroid sphygmomanometer (Riester CE 0124, Jungingen, Germany). Prehypertension was classified as BP in the 90th percentile or higher for systolic or SBP but less than the 95th percentile. Hypertension was defined as the average of the 2 measurements where the systolic BP (SBP) or DBP is in the 95th percentile or higher for age and sex.16The classification of overweight and obesity was made using the 2000 Center for Disease Control and Prevention growth charts defining as underweight less than fifth percentile; normal weight, fifth to 85th percentiles; overweight, 85th to 95th percentiles; obesity, 95th percentile or higher.17
Statistical Analysis
Statistical analysis was performed with STATA software (V.9.2). P <0.05 was considered significant. Differences in baseline characteristics between participants were evaluated using the χ2 test for categorical variables and the Mann-Whitney U test for continuous variables without symmetrical distribution (the data were presented as median and 25th-75th percentiles). Pearson correlation coefficients were used to evaluate the relationships between SBP and DBP and anthropometric measurements; some nonnormally distributed data were analyzed after logarithmic transformation. Logistic regression was used to determine the association between hypertension and anthropometric measurements categorized by tertiles; the lowest tertile was used as the reference category.
RESULTS
The participants were 252 children, 124 girls and 128 boys, with an age range of 6 to 13 years. The descriptive characteristics of the sample are summarized in Table 1. The mean age of the children was 9 years (range, 6-13 years), without a difference between boys and girls. Both SBP and DBP were significantly higher in boys than in girls. Regarding anthropometric measurements by sex, no significant differences were observed; only the waist-to-hip ratio was significantly higher in boys in comparison with girls (0.9 vs 0.8, P = 0.01).
In all children, obesity and overweight were detected in 26.5% and 15.8%, respectively. There were no significant differences by sex for overweight, obesity, and BP in the 95th percentile or higher. Of all children studied, 4.7% had hypertension (Table 2). Interestingly, of 12 children with BP in the 95th percentile or higher, 6 were obese (4 boys and 2 girls) and 6 nonobese (2 boys and 4 girls). Also prehypertension was determined: six children had prehypertension, 4 systolic prehypertension (2 with obesity and 2 with overweight) and 2 diastolic prehypertension (one was obese and the other was overweight) (data not shown).
Table 3 displays the correlation coefficients between systolic and diastolic BP and other variables investigated. Both systolic and diastolic BP correlated positively with age, weight, height and all measurements of central and subcutaneous adiposity.
After adjustment for age and sex, BP in the 95th percentile or higher was associated with increases in all body circumference and skinfold thickness measurements (all measurements were grouped into tertiles and were analyzed using the first tertile as a reference). However, after adjustment for BMI, the association was observed only between BP in the 95th percentile or higher and suprailiac skinfold, third tertile (OR = 11.8, P = 0.023); triceps skinfold, third tertile (OR = 6.0, P = 0.034); and biceps skinfold, third tertile (OR = 4.7, P = 0.038; Table 4).
DISCUSSION
Our results indicate that a sample of children aged 6 to 13 years, from the south of Mexico, had a high prevalence of obesity (26.5%) but moderate prevalence of BP in the 95th percentile (4.7%) or higher. Similar prevalence of hypertension (4.5%) was obtained in the school-based screening performed in 5102 students aged 10 to 19 years in 8 Houston public schools.6A review of 8 large US studies of BP in children and adolescents reported an overall prevalence of hypertension of 4% for SBP and 3% for DBP.18Different results were observed in 1884 subjects aged 6 to 13 years participating in the Ellisras Longitudinal Study where the prevalence of hypertension was 1% to 5.8% for boys and 3.1% to 11.4% for girls.15In another school-based survey of a representative sample of youth aged 9, 13, and 16 years in Quebec, Canada, the prevalence of elevated SBP was 12%, 22%, and 30% among 9-, 13-, and 16-year-old boys, respectively, and 14%, 19%, and 17% among same-aged girls.14
However, in a sample of children from Mexico City, 3.6% had systolic hypertension, 14.2% had diastolic hypertension, and 22.8% had mixed hypertension. In this study, the prevalence of elevated BP was higher in comparison with our results; however, those findings seem related to increases in overweight and obesity in children from Mexico City.19
In this study, we identified 6 children with prehypertension where the systolic prehypertension was more prevalent that the diastolic prehypertension. These results show that the relatively young age of the participants influenced the moderate prevalence of prehypertension and hypertension in the sample of children studied. The prevalence of prehypertension tends to be higher among young adults compared with older adults, whereas hypertension is lower.20Because both BP level and hypertension prevalence increase with age, individuals with prehypertension progress to the hypertension threshold. Lifestyle changes that modify BP and associated risk factors may delay the need for pharmacological intervention or successfully treat prehypertension.16,21Therefore, detecting children with prehypertension would help in identifying those to be targeted for early management. The importance of the observed childhood BP elevations progressing to hypertension in young adulthood is underscored by the fact that adverse anatomic cardiovascular changes characteristic of hypertension already occur in children with elevated BP.22
A limitation of this study is the use of the average of the 2 consecutive measurements of BP for classification. A classification that is based on a single clinical visit overestimates the prevalence of prehypertension and hypertension. Blood pressure tends to decrease in subsequent visits because of accommodation effects and regression to the mean.16,23
Repeated BP measurements are necessary for diagnosis of hypertension and ascertainment of risk in asymptomatic healthy children and adolescents. Hansen et al.24used electric medical records from well-child care visits for a cohort of 14,187 children and adolescents (age range, 3-18 years) to determine the prevalence rates of prehypertension and hypertension. With the criterion of elevated BP on 3 or more well-child visits, the prevalence of hypertension was 3.6% and the prevalence of prehypertension was 3.4%.
The association between hypertension and childhood overweight and obesity has been documented in several studies.12,14,15,21In children from a rural community in Canada, prehypertension and hypertension were detected in 7.6% and 7.4% of the population, respectively. Also, obesity was associated with both prehypertension and hypertension; similarly, overweight was associated with hypertension but not prehypertension.25Another study reported that in children from Fort Worth, Texas, 21% had high BP; notably, the prevalence was higher among the overweight and Hispanic group.1Moreover, in one sample of Mexican Children from Mexico City, the waist circumference was the main factor associated with systolic hypertension.19Our results show a good relationship between BP in the 95th percentile or higher and the measurements of body fat. Interestingly, a strong association was observed between the skinfold thickness and elevated BP. This indicates that subcutaneous adiposity may be an important predictor of hypertension in children.
On the other hand, Hansen et al.24found that several patient-related factors were associated with increased risk for hypertension or prehypertension. Specifically, older and taller children were more likely to have abnormal BP identified. The normal BP range for children increases with age and height. Therefore, older and taller children with high BP are more likely to have their BP higher than 120/80 mm Hg, which is higher than the normal BP value for adults.
Our study may be limited by the fact that we did not assess the stage of sexual maturation in the sample of children. The impact of not having these measures available for the current analysis is not known, but other investigators such as Kozinetz26,27have suggested (from cross-sectional analyses using self-assessment of maturation) that there is an association between stage of sexual maturation and BP in girls, and that observed racial differences in BP could be explained by racial differences in the level of pubertal development. Moreover, SBP also rises with pubertal stage independent of age, particularly in girls.28
Some studies suggest that central fat distribution is a better predictor for hypertension than overall fat mass.29We demonstrate that both waist and hip circumferences and waist-to-hip ratio were good predictors of high BP; we also observed a strong association between BP in the 95th percentile or higher and subcutaneous adiposity (skinfold thickness), this supports the use of these measurements as a tool to assess obesity and to predict the risk of hypertension in children.
In this sample of children studied, the prevalence of obesity was higher than overweight, and the prevalence of BP in the 95th percentile or higher was moderate in comparison with other populations. These results suggest that subcutaneous adiposity evaluated by skinfold thickness is a better predictor of hypertension in a sample of Mexican children.
ACKNOWLEDGMENTS
The authors thank Dr. Tomás Patiño-Castro, Regidor de Salud Pública del Municipio de Chilpancingo, Guerrero, México, for his help in recruiting children. The authors are also grateful to Jesse Haramati for the English language revision of the manuscript.