The Association of Obesity with Non-Dipping Status and Laboratory Biomarkers in Hypertensive Children

Objective: To investigate the 24-h ambulatory blood pressure monitoring (ABPM) and laboratory markers associated with target organ damage and to evaluate the relationship between obesity and non-dipping status on ABPM in children with essential hypertension (HT). Methods: We conducted a study using a database of patients aged 5-18 years. Inclusion criteria were: subjects where records documented a blood pressure >95 th percentile for age, sex, and height by a referring physician had ABPM for diagnosis. The data of target organ damage, body mass index (BMI), and laboratory parameters were collected. Results: This study included 175 patients (48 lean, 127 overweight+obese). Thirty-seven patients had white coat hypertension (WCH), 29 patients had Pre- HT, and 109 patients had HT. There were no significant differences in mean age, gender or mean BMI of children between the groups (p>0.05). Non-dipper status and uric acid level were significantly higher in overweight+obese patients compared to normal weight patients (55.9% vs. 39.5%, p=0.04, 4.9±1.4 vs. 5.3±1.3, p=0.03). Nine patients had left ventricular hypertrophy (2 WCH, 7 HT) and 17 patients had retinopathy (4 WCH, 2 Pre-HT, 11 HT). Discussion: Obese patients should be screened for HT by ABPM. WCH and Pre-HT are also not innocent and cause significant morbidity. associated with an increase in blood viscosity (32, 33). Platelet aggregation and blood viscosity are increased in hypertensive patients regardless of BMI. In normotensive obese patients, there is a risk for platelet aggregation and increased viscosity which is correlated with the BMI values. This finding suggests that despite of normal BP measurements in obese patients, an essential need for careful follow-up for development of HT and endothelial dysfunction should be performed. Obese children have been shown to have higher total cholesterol and triglyceride levels have a higher prevalence of dyslipidemia and HT (34, 35). In our study, LDL and platelet levels were found to be significantly higher in the Pre-HT group than in the WCH group. Moreover overweight + obese patients were shown to have higher UA, Hb, Plt, total cholesterol, triglyceride and lower HDL compared to patients with normal weight. LVH retinopathy delayed detection HT Our findings revealed that overweight and obesity play an important role in the development of childhood HT. Since HT is an important complication of obesity, it has been shown that obese patients should be screened for HT by ABPM. Demonstration of target organ damage in WCH, Pre-HT and HT groups supported the fact that WCH and Pre-HT are also not innocent and cause significant morbidity and mortality for cardiovascular diseases as HT. Conflict of interest No conflict of interest was declared by the authors.


INTRODUCTION
The prevalence of hypertension (HT) shows a constant increase in children and adolescents in favor of primary HT. Obesity is the main inducer for the increment in the prevalence of HT in childhood as in adults (1,2). Hypertension is a leading risk factor for cardiovascular disease and mortality (3). Epidemiological studies have shown a strong relationship between obesity and cardiovascular diseases (4).
The mechanism of HT in obesity seems to be multifactorial, with hyperinsulinemia, hyperlipidemia, renal structural deformation, and endothelial dysfunction comprising major components of this mechanism. Although the relationship between hypertension and uric acid has been known for about half a century, this issue has been explained more detail recently. The association between uric acid and HT is confounded by numerous factors. For instance, elevated serum uric acid is also observed in obese subjects which in turn affects the development of HT (5)(6)(7).
Twenty-four-hour ambulatory blood pressure monitoring (ABPM) has been immensely helpful in diagnosing hypertension in children, allowing physicians to identify white coat hypertension (WCH), masked HT, and evaluate nocturnal dipping status. In adults, obesity is associated with nocturnal HT and abnormal dipping status on 24-hour ABPM. Nocturnal HT and abnormal dipping status have been shown to significantly affect prognosis and target organ damage in adults and children (8). The aim of this study is to investigate the ABPM and laboratory markers associated with target organ damage and to evaluate the relationship between obesity and non-dipping status on ABPM in children with essential HT which may eventually lead to better treatments and prevention methods.

METHODS
We conducted a cross-sectional study using a database of patients aged 5-18 years who had undergone a first time 24-hour ABPM at Gazi University Faculty of Medicine Pediatric Nephrology Outpatient Clinic between January 2008 and January 2013. The data was collected retrospectively. Inclusion criteria were: subjects where records documented a BP >95 th percentile for age, sex, and height by a referring physician on at least three separate occasions and were in turn confirmed in pediatric nephrology clinic by auscultation and had ABPM for initial diagnostic assessment. Patients who receiving antihypertensive, glucocorticoid, immunosuppressant, and stimulant treatment before or during the ABPM and who had any kidney, cardiac or neurological disorders were excluded.

Office BP measurements
The clinical BP measurement values were collected from hospital records. The routine procedure for BP measurement in our clinic is to measure in a quiet, noncrowded room. After five-minute resting, BP is measured in the appropriate position as the cubital fossa would remain at the heart level. The length of the inflated part of the cuff is approximately 40% of the distance between the acromion and the olecranon. The stethoscope is placed on the brachial artery at the lower edge of the sleeve. The systolic BP is measured when the first Korotkoff sound was heard and diastolic BP is measured when the Korotkoff sound was disappeared (5th Korotkoff sound). The mean of the measurements which are usually repeated 3 times were recorded as the office BP. SBP and DBP percentiles were calculated according to the normograms recommended by the National High Blood Pressure in Children and Adolescents institute. HT was defined in a child or adolescent if the mean SBP or DBP was above the 95 th percentile for gender, age and height on three or more occasions. For adolescents aged 16 or older, the definition of HT was based on the absolute cutoff used for adults as high-normal (130-139/85-89 mmHg) and HT (≥140/90 mmHg) (9).

ABPM
All ABPMs were performed using Spacelabs Monitor model 90207 (Spacelabs Medical, Redmond, WA). The monitor was placed by nursing staff in our office at the time of clinic visit. Appropriate cuff size was determined using guidelines from the report on diagnosis, evaluation, and treatment of pediatric HT . Readings were taken every 20 minutes while awake and every 60 minutes while asleep. Patients were asked to keep a diary showing sleep and wake times. At least 40 readings were considered satisfactory for analysis.
The data were analyzed by calculating 24-h mean SBP and DBP, daytime SBP and DBP, nighttime SBP and DBP as described in the American Heart Association (AHA) statements on ABP. Elevated BP load was defined as more than 25% of recordings of SBP or DBP measurements being ≥95 th percentile for gender and height respectively. In addition, the patients were classified as dippers if the mean SBP and/or DBP decreased by ≥10% during the sleep period, and this was calculated as follows: (mean daytime-mean nighttime/mean daytime) x100. Subjects with a nighttime drop of SBP or DBP of <10% of daytime values were considered to be non-dippers (10). Based on the recommendations of the AHA statement patients were classified into three groups: WCH, prehypertension (pre-HT) and HT. WCH was defined as office BP percentiles of >95 th percentile, 24-h mean SBP of <95 th percentile and SBP load of <25%; Pre-HT was defined as mean ambulatory BP less than the 95 th percentile, but with a BP load of ≥25%. Ambulatory HT was defined as office BP of >95 th percentile, 24-h mean SBP of >95 th percentile and SBP load of >25% (10,11).

Anthropometric measurements
As part of routine clinical care, height was measured with a stadiometer and weight was measured on a calibrated scale with the child wearing light clothing. Kilogram (kg) / height 2 (m 2 ) formula was used to calculate body mass index (BMI). After evaluating the BMI percentiles for the Turkish population based on age and gender, subjects were grouped into categories based on body mass index (BMI) as: lean and overweight+obese (lean:15 th -85 th BMI percentile, overweight: >85 th -95 th percentile and obese ≥95 th percentile) (12). Additionally, the data of target organ damage (echocardiography, ophthalmologic examination), and laboratory parameters were collected by querying our database. Blood samples were obtained from all study subjects after a 12-h fasting period. The data of complete blood count, uric acid, aspartate aminotransferase (AST), alanine aminotransferase (ALT), fasting lipid profile (cholesterol, triglyceride, high-density lipoprotein (HDL), low-density lipoprotein (LDL), very low-density lipoprotein (VLDL) were collected.

Statistical Analysis
SPSS (Statistical Package for Social Sciences) version 15 was used. Chi-Square (x 2 ) test and Fisher exact test were used for statistical evaluation of categorical variables. The quantitative variables in which the parametric test conditions were achieved were evaluated by student T test in the comparison of the two groups and one-way analysis of variance by more than two groups. Mann-Whitney U test was used for the two groups and Kruskal Wallis H test was used for the comparison of more than two groups. In the one-way analysis of variance, Tukey and Kruskal Wallis variance analysis were used as multiple comparison tests and the Mann-Whitney U test with Bonferroni correction was used. In all statistical analyzes, p<0.05 was accepted as the significance level.

Ethical statement
The study adhered to the principles of the Declaration of Helsinki and was approved by the local Ethics Committee (Date: 27 April 2013; Protocol Number: 213).

RESULTS
This retrospective study included 175 patients who were evaluated for HT. According to ABPM measurements, 37 patients had WCH, 29 patients had Pre-HT, and 109 patients had HT. There were no differences in mean age, gender or mean BMI of children between the groups. The comparative demographic, clinical, laboratory and ABPM parameters among 3 groups of patients are given in Table 1.
Original Investigation / Özgün Araştırma GMJ 2021; 32: 527-531 Öztürk et al.    Table 2 and 4. Non-dipping status was not significantly different between HT, Pre-HT and WCH groups. Of the 48 subjects in normal weight group, 19 were classified as non-dippers (39.5%). Of the 127 subjects in the obese+overweight group, 71 were classified as nondippers (55.9%). Non-dipper status was significantly higher in overweight + obese patients compared to normal weight patients (p=0.04). Uric acid, platelet, AST, ALT, cholesterol, triglyceride, and HDL levels were significantly higher in overweight + obese patients compared to normal weight patients (Table 3).
There was a positive correlation between UA level and 24-h SBP (r=0. 29

DISCUSSION
In this study, the patients referred for evaluation of suspected hypertension, obesity was significantly associated with non-dipping status. Overweight and obese children with HT were also found to have higher serum uric acid levels compared to normal weight children with HT.
A relationship between non-dipper status and cerebrovascular diseases was shown previously. The prevalence of non-dipping status increases with obesity in adults (13). In obese children, it is also reported that there is a change in circadian BP rhythm and an increase in non-dipper status (14). It is thought that the decrease of night fall in obese patients may be an early sign of changes in BP regulation and development of target organ damage (15). There are few available data on the prevalence of non-dipping status in the general pediatric population. Framme et al. found that pediatric obesity only had a significant effect on nocturnal dipping in females of a total of 80 subjects (25 in the lean group and 55 in the obese group) (15), whereas Macumber et al. found an association between pediatric obesity and non-dipping status in both genders as in our study (8).
In children and adolescents, the increase in the prevalence of hypertension is highly associated with obesity as the risk of HT is 3.5-fold higher in obese children (16,17). In many studies, even normotensive obese patients were found to have significantly higher blood pressure but in normal limits (6,16). A populationbased study in which individuals were accessed by house visits throught Turkey (3622 children, 5-18 years) revealed the prevalence of overweight, obesity and HT as 9.3, 8.9 and 6.1% and obese children had the highest rate of HT ( 11.4% vs. 5.6%) (17). Thus, the most important risk factor for the development of essential HT likely seems to be the presence of obesity.
In our study, we have found that one fourth of hypertensive patients have WCH. In childhood, WCH is more common compared to adults (18). In a study conducted on 90 patients diagnosed with HT by clinical BP measurement method, it was detected that 28% of children had WCH.
To rule out WCH, ABPM is generally recommended (19). White coat hypertension is considered as a pre-hypertensive condition and was associated with risk of developing HT and target organ damage in adulthood (20,21). In the studies employing data for children, it was shown that WCH was associated with increased left ventricular mass index and impaired arterial elasticity (22,23). In our study, we demonstrated that target organ damage (2 patients with left ventricular hypertrophy (LVH), 4 patients with retinopathy) were also observed among patients with WCH.
Previous studies have shown that uric acid elevation is strongly associated with HT and obesity in children and adolescents. Elevated uric acid levels have been reported that there is a 1.6-2-fold increase for development of HT (24). Each 1 mg/dl increase in uric acid levels was shown to increase the risk of Pre-HT and HT by at least 50% (25). A significant relationship between SBP-DBP and uric acid levels was also detected in a large cohort of children evaluated with ABPM (26). High levels of serum uric acid were observed in about 90% of adolescents with recent onset hypertension and the serum uric acid levels correlated with BP values (27). In another study indicated that a positive association between uric acid, and office, daytime and night-time SBP, insulin and triglycerides (28). Akcaboy et al. studied the effect of plasma NOx levels on cardiac function in hypertensive pediatric patients and reported a significant positive correlation between ABPM values and uric acid levels and a negative correlation between plasma NOx levels and uric acid, BMI, triglyceride and VLDL values (29). In our study, overweight-obese children were found to have higher serum uric acid levels compared to normal weight hypertensive children and uric acid level was positively correlated with ABPM values.
Blood viscosity is determined by four different parameters. They are hematocrit, erythrocyte deformability, erythrocyte aggregation and plasma viscosity (30,31). Hypertension, obesity, high serum LDL cholesterol levels, and low serum HDL cholesterol levels, as well as other cardiovascular disease risk factors have been found to be associated with an increase in blood viscosity (32,33). Platelet aggregation and blood viscosity are increased in hypertensive patients regardless of BMI. In normotensive obese patients, there is a risk for platelet aggregation and increased viscosity which is correlated with the BMI values. This finding suggests that despite of normal BP measurements in obese patients, an essential need for careful follow-up for development of HT and endothelial dysfunction should be performed. Obese children have been shown to have higher total cholesterol and triglyceride levels have a higher prevalence of dyslipidemia and HT (34,35). In our study, LDL and platelet levels were found to be significantly higher in the Pre-HT group than in the WCH group. Moreover overweight + obese patients were shown to have higher UA, Hb, Plt, total cholesterol, triglyceride and lower HDL compared to patients with normal weight.
Although LVH (9 patients) and retinopathy (17 patients) were found in very few patients in our study, still we can emphasize the importance of delayed detection of HT in terms of the development of target organ damage as the patients were included in the study at their first presentation.