Pediatric hypertension has undergone shift from secondary hypertension to essential hypertension (as the main cause of hypertension in childhood and adolescence) [12]. In the present study, age and BMI were the main predictors of SBP and age, BMI, higher intakes of fruit and fast foods were in positive association and higher intake of vegetables was in negative association with DBP. The univariate analysis showed a significant correlation among adiposity indicators and sedentary lifestyle with SBP and DBP, whereas, higher intake of fruit, also, associated with DBP. In accordance to our findings, some other studies reported that increased prevalence of hypertension is associated with higher body mass index [13, 14]. Higher concentrations of circulating inflammatory cytokines have also been shown to be associated with the atherosclerotic process, and CRP is one of the most susceptible indicators in obese Japanese children [15, 16, 17]. Some studies, also, have shown that increasing age and puberty, especially in adolescent girls, can cause HBP [14, 18, 19].
Barba et al reported that in the period close to the completion of puberty, the association between age and BP becomes more evident among girls [18]. In the study of Oliveros et al, the prevalence of prehypertension and stage 2 of hypertension was higher among younger compared with older children, while stage one of hypertension was more prevalent among older children [20]. Among the dietary factors, a positive correlation between hypertension and increased consumption of fruit groups and fast food /junk food consumption, and inverse correlation between hypertension and vegetable groups was observed. Increased fast food consumption containing high amounts of salt, sugar, and fat, is associated with increased obesity [21, 22]. Studies showed that high levels of fats, sugars, and salt intake of fast foods are one of the other possible reasons of increased BP in children and adolescents [23, 24]. Stamler et al. showed that in addition to sodium, several other nutrients including calcium, magnesium, potassium, and fiber are also involved in the pathogenesis of hypertension [25]. One meta-analysis showed that sodium restriction could be beneficial among elderly individuals with hypertension, however, its beneficial effects are low among people with normal BP [26].
The higher sodium and energy contents of fast and junk foods are possible underlying reason of the association between fast food consumption and hypertension. Numerous studies have shown that higher intakes of fruits, vegetables and dairy products could have an effective role in prevention of childhood hypertension due to several nutrients including potassium, magnesium, calcium and fiber [27, 28]. The positive association between fruits intake and hypertension in our study in contrast with several previous studies, could be attributed to the difference in study design, target group characteristics such as age or gender distribution [27], or taken fruit and vegetables as a one group with no separation of them [28]; while we analyzed fruits and vegetables separately in two independent groups.
Consumption of 100% fruit juice may be associated with high blood pressure, possibly due to high fructose as well as increased energy consumption, weight gain, and increased uric acid production [29]. Also, consuming whole fruits in high amounts can increase weight due to increased energy intake. Therefore, it could be suggested to study the effects of whole fruits and fruit juices separately in further researches. No significant correlation was found between BP and dairy products in the current study. Greater intakes of dairy products were associated with lower SBP in white but not black children and teens in Dellavalle et al. study, suggesting that greater dairy products intake alone might be not beneficial for all races [30]. There was no significant relationship between meals and hypertension. Some studies showed that the prevalence of obesity declined by increased number of meals [31]. Donin et al. showed that more snacks and meal consumption leads to obesity and cardiovascular problems in children [32]. Also, Toschke et al demonstrated that the prevalence of obesity declines by increasing the number of meals [31]. In the final regression model, we did not observe any significant correlation between BP and PA or watching TV/PC. Torrance et al demonstrated that 40 minutes of moderate to vigorous aerobic-based PA 3–5 days/week is required to reduce BP in obese children [33]. TV commercials, also, influence the food choices of children and encourage people to buy the advertised products [34]. A program comprising screening, early detection and health promotion through school health programs may help to prevent future complications of hypertension [35]. Although in the current study we observed a correlation between BP and television viewing and PA in the univariate regression, however these associations had been vanished by including several confounders into the model.
Limitations
Several factors are possible limitations of the current reports; the family history of hypertension, the effects of other food items including the amount of salt and fat intake and classification of adolescence maturity status, had not been considered.