This study mainly evaluated the associations between obesity at baseline, and hypertension at follow-up among preadolescent school children in Karachi, Pakistan. In this paper we found that prevalence of hypertension and prehypertension was notably high, 19.8%, and 16.8%, respectively, with variations observed between boys and girls. A substantial proportion of preadolescents were identified as obese (12.8%), and central obesity was prevalent in 29.8% of the participants. After adjustments for covariates, including age, gender, PA, sedentary time, fruit, vegetable intake and hypertension at baseline, the study revealed an association between obesity and hypertension (OR 8.5, 95% CI 3.5, 20.4). Similarly, central obesity exhibited a statistically significant association with both hypertension (OR 2.7, 95% CI 1.9, 3.9) and prehypertension (OR 1.9, 95% CI 1.4, 2.8).
The existing body of literature consistently highlights a concerning upward trend in the prevalence of hypertension, particularly among younger age groups (27, 28). For instance, a study involving 22,224 students aged 10 to 17 from schools in the USA found that 16.3% met the criteria for prehypertension as per the new American Academy of Pediatrics (AAP) guidelines (29). Additionally, a study from Pakistan on children aged 5–14 years reported a prevalence of hypertension at 18.0%, with rates of 18.4% in boys and 17.6% in girls (30). These findings are consistent with our research. However, our study found a higher prevalence of prehypertension (16.8%) compared to a study conducted in Karachi, which reported a prevalence of 14.5% among children aged 8 to 12 years (1).
Genetic predispositions, lifestyle differences, and environmental factors unique to each study population could contribute to variations in the prevalence of hypertension (28). Also rising obesity among adolescents, increase sugar and beverage intake, reduced PA spaces could be contributory factor for obesity and hypertension (31).
Prehypertension and higher prevalence among girls could be attributed to the onset of puberty. Puberty represents a potentially crucial period in the development of prehypertension and may serve as an independent influencing factor. A research study focusing on school children aged between 7 to 12 years found that those who entered puberty or experienced early puberty exhibited increased odds of experiencing prehypertension. Notably, the study observed a more pronounced increase in blood pressure levels during puberty among girls and identified a stronger association between pubertal development and both hypertension and likelihood of prehypertension (32).
A substantial body of research emphasize the significant role of obesity as a key risk factor for hypertension, establishing a positive correlation between hypertension in children with high BMI (33). A systematic review including thirteen longitudinal studies up to June 2013 investigated the association between childhood obesity and adult morbidities. The findings suggests that overweight children are at a higher risk of developing diabetes and coronary heart disease in adulthood (34). A systematic review and meta-analysis, including 23 studies and 21 studies up to June 2015 respectively, provided additional insights. These analyses revealed that childhood obesity is significantly and positively associated with adult SBP and DBP (35). This highlights the importance of addressing childhood obesity as a preventive measure against hypertension and related cardiovascular complications in adulthood.
Van Emmerik et al., revealed that for every 10 kg increase in body weight, there was a corresponding increase of 3.0 mmHg in SBP and 2.3 mmHg in DBP (36). Our data analysis similarly indicated that obese children exhibited an OR of 8.5 for hypertension, aligning with findings from other studies that emphasized a strong association between high BMI and WC with hypertension in children (37–39).
The data in our study revealed that central obesity was associated with an increased risk of both hypertension (OR 2.7) and prehypertension (OR 1.9). An analysis of community-based data (n = 1,278) from the Control of Blood Pressure and Risk Attenuation (COBRA) trial in Karachi, focusing on children aged 5–14 years was conducted to explore the relationship between WC and BMI with the age-related increase in BP over a 2-year follow-up period. The findings revealed that increases in WC and BMI over time were linked to elevations in both SBP and DBP (30). In another study conducted in China, the OR for WC was reported as 3.75, demonstrating a significant association with the prevalence of hypertension among children aged 6–15 years (37).
The phenomenon of adiposity rebound in children within this age group may contribute to the high prevalence of prehypertension. Adiposity rebound refers to the natural increase in body fat that occurs after a period of decreasing adiposity, and it could be one of the contributing factors to the prehypertension identified in our research.
The present study has both strengths and limitations. A notable strength lies in the large sample size of preadolescent school children from lower to middle-income classes, Furthermore, the study employs a robust analytical approach, utilizing various statistical methods such as t-tests, chi-square tests, logistic regression, and specialized R packages.
Limitations of this study include, firstly, variations in criteria for determining hypertension and prehypertension in children and adolescents, including screening standards from the AAP, WHO, and National Heart, Lung, and Blood Institute. The different criteria might lead to discrepancies in directly comparing or generalizing the findings, as different standards may yield different prevalence rates of hypertension and prehypertension. Secondly, we did not measure Tanner stages as pubertal development may influence BP levels. Thirdly, the study was conducted in private schools within the city, which may not provide a comprehensive representation of government sector schools. Children in government institutions often come from relatively low-income families and may face challenges in maintaining a healthy lifestyle.
Future research endeavors should explore dietary patterns and consider additional risk factors such as puberty development and family history of obesity.