Hypertension in childhood usually carries over into adulthood 1. A huge variation in the prevalence of hypertension in Arab countries was found. In Egypt, the overall prevalence of hypertension was 26.7% 2. The prevalence of hypertension was 9.6% among school children in Tunisia 3, 5.1% in Kuwait 4, 3.6% in Jordan 5, and 20.4% in Saudi Arabia for systolic blood pressure (SBP) and 25.9% for diastolic blood pressure (DBP) among children younger than 18 years of age 6.
Poor eating patterns formed early in life [such as irregular consumption of meals, excessive snacking, eating away from home (fast foods and soft drink), dieting, and skipping meals] may lead to health problems such as cardiovascular disease, cancer, and osteoporosis in later years 7,8. These poor dietary habits are carried over to adolescence in Upper Egypt 9.
The transition in nutrition in Egypt over the last decades highlights the emergence of obesity and diet-related chronic diseases, and their relation to changes in dietary patterns. These changes such as an increase in the consumption of high fat such as fast foods and chips, and sugar foods and drinks such as soft drinks, and decrease in the consumption of protective foods such as fruits and vegetables have been implicated. Scientific and epidemiologic evidence supports the relation between dietary patterns and the development of chronic diseases including hypertension 10.
Hypertension is one of the leading causes of cardiovascular disease, end-stage renal disease, and cerebrovascular accidents. Although hypertension and associated end-organ damage occur more commonly in adults, hypertension and its resultant complications do occur in childhood 11.
According to the fourth report of the National High Blood Pressure Education Program Working Group) on High Blood Pressure in Children and Adolescents in USA 12, as hypertension is asymptomatic in most patients, the diagnosis can only be made through accurate measurements of blood pressure in the office clinic or in screening programs. Because the long-term health risks for hypertensive children and adolescents can be high, it is important that clinical measures be adopted to reduce these risks and optimize health outcomes.
It has been noted that intrauterine growth retardation leads to hypertension in childhood 13. Physical inactivity, smoking, obesity, stress and a family history of hypertension are well-known nondietary predictors of hypertension 14,15. The dietary factors associated with an increase in blood pressure are increased salt intake, decreased potassium intake, decreased intake of omega-3 polyunsaturated fatty acid (commonly termed ‘fish oil’), and high consumption of caffeine, 16 fructose, and soft drinks 17,18. An improvement in blood pressure control may be associated with increased consumption of calcium, fibers, and vitamins E and C 16.
Few studies have been carried out on hypertension among adolescents in Egypt 2,19,20, and they did have not investigated the effect of dietary patterns of this age group on the elevation in their blood pressure. The present study aimed to assess the relationship between dietary patterns and blood pressure levels of school age children, 12–18 years, in Sohag, an Egyptian city in Upper Egypt.
Participants and methods
Study design and sampling
A comparative cross-sectional study was carried out from February to July 2010 on a total of 300 adolescents of both sexes aged between 12 and 18 years. The sample size was calculated statistically assuming a 26.7% prevalence of hypertension in Egypt 2; using a 5% confidence level and a power of 80%, the estimated required sample size was 300 adolescents. The studied sample was selected using the stratified type of sampling as follows: one educational district was selected at random from a list containing all educational districts in Sohag (Egypt). Stratification of preparatory and secondary schools of the selected district into private and governmental sectors and each sector was stratified into boys and girls schools. From each stratum, one class was selected randomly from a list containing all classes in each school and about 35–40 students were selected randomly from each class.
A structured questionnaire was used by interviewing each adolescent to collect data on sociodemographic characteristics (sex, age, parents’ educational level, fathers’ occupation, working status of mothers, and place of residence), medical history (family history of hypertension, cardiovascular diseases, and obesity), and lifestyle practices including smoking and physical activity (physically active adolescents were those who reported practicing exercise or any type of sport >1 h ≥3 times/week). Data were also collected on dietary habits including eating snacks between meals, eating outside the home, consumption of fast foods, chips, salty foods (such as pickles and salted fish), fruits and vegetables, tea, coffee, and soft drinks (consumption daily and >3 times/week was considered high and less than that was considered low consumption), and the habit of using table salt.
Anthropometric and body fat composition measurements were taken from each adolescent at the time of interview. Weight, height, and circumferences of waist and hip were determined according to the criteria of Jelliffe et al.21. BMI was calculated using the formula: BMI=weight (kg)/height2 (m2). The 5th, 85th, and 95th percentiles were determined using WHO adolescents’ BMI percentile tables 22. Obesity status was presented as overweight/obese and nonobese. An obese adolescent was defined if BMI of at least 95th percentile for age and sex, overweight if BMI of more than 85th percentile, and less than 95th percentile for age and sex 22. Body fat percentage was determined by bioelectrical impedance analysis using a Beurer BF25 body fat analyzer (Beurer Company, Germany) for assessment of total body fat. The measurement was carried out with the child barefoot and still standing during the measurement.
Data on dietary intake were collected from each adolescent using the food frequency questionnaire at the time of interview to estimate the dietary intake of adolescents and the consumption pattern of different foods and beverages most commonly consumed, with a focus on particular foods predicted to affect blood pressure such as energy-dense foods [carbohydrate (CHO)-rich foods and fat-rich foods] and salty foods consumed a week before the interview 23. Quantities of foods and drinks consumed were estimated using common household utensils, for example cups, plates, and tea or table spoons. For items such as eggs, slices of bread, and pieces of fruits, a simple count was used. Then, the mean daily intake from each item was analyzed using Egyptian Food Composition tables of the National Nutrition Institute 24 to obtain the mean daily intake of energy, macronutrients, sodium, and potassium. It should be noted that only the natural sodium content of food was included, but salt added during cooking or table salt was difficult to determine. Percent of nutrient adequacy was calculated for energy, protein, sodium, and potassium using the formula: nutrient adequacy%=nutrient intake/dietary reference intake×100 25,26. Nutrient density was calculated for CHO, protein, and fat using the formula: nutrient density%=nutrient intake (g)×calories/g/total energy intake×100.
Blood pressure was measured with a manual mercury sphygmomanometer using the standard technique. Participants were asked to sit in a chair and rest quietly for 5 min before blood pressure measurement, and then blood pressure was measured on the exposed outstretched right arm. Blood pressure was measured twice during the same visit with a short rest in between and the mean of two readings was used 27. The blood pressure percentiles were determined using The International Pediatric Hypertension Association tables 28. Hypertension in children and adolescents is defined as SBP and/or DBP, that is, at least 95th percentile for age and sex on repeated measurements. Prehypertension is defined as SBP and/or DBP at least 90th and less than 95th percentile for age and sex. Normotensive is defined as SBP and/or DBP equals 50th percentile and less than 90th percentile for age and sex 12.
Data analysis was carried out using the statistical package for social science version ‘17’ software (SPSS Inc., Chicago, Illinois, USA) 29. Data were presented in tabular form, graphically, and mathematically using the mean and the SEM. For all analyses, a P-value 0.05 or less was used to indicate a statistically significant difference. Data were analyzed using the χ2-test for analysis of categorical data; one-way analysis of variance test was used to compare the data of at least three independent groups (means); and two models of stepwise linear regression analysis were used to identify the most significant risk factors associated with SBP and DBP as outcome variables, with P-value less than or equal to 0.05 in the models.
This study was carried out according to the guidelines for medical research involving human participants and was approved by the ethics committee of the High Institute of Public Health, Alexandria University (Egypt). All measurements were taken following all privacy procedures and all data collected were kept confidential. All students were informed about the purpose of the study and they had the right to participate or not in the study; then, their written consent was obtained.
A total of 300 adolescents participated in the present study; 23 of these adolescents (7.7%) were diagnosed as hypertensive and 102 adolescents (34%) were prehypertensive. Hypertension and prehypertension were observed to be higher among children from a high socioeconomic level, but this was not statistically significant. Elevated blood pressure was higher among adolescents in private schools, in urban areas, had university educated parents, and had working mothers and fathers professionals or employees.
Hypertension was higher among boys than girls (8.7 and 6.6%, respectively), in contrast to prehypertension, which was higher among girls than boys (34.4 and 33.6%, respectively) as shown in Fig. 1. Hypertension and prehypertension were highest among the age group 14–16 years, followed by the age group 16–18 years (Fig. 2). The mean age of hypertensive adolescents was 15.1±0.3 years and the mean age of prehypertensive adolescents was 14.8±0.1 years.
Table 1 shows the medical history and lifestyle practices of the sample studied. Overweight or obese adolescents were markedly hypertensive (34.7%) and prehypertensive (34.3%), with a high statistically significant difference between groups (P=0.004). A positive family history of hypertension was present among more than half of all adolescents, with no statistically significant difference between the three groups of adolescents. The difference between the groups studied was not significant also in terms of a family history of cardiovascular diseases and obesity. The majority of the adolescents in the three groups were nonsmokers and physically active (females usually preferred walking and males usually preferred playing football), with no statistically significant difference between groups, as shown in Table 1.
Table 2 shows that the higher percentages were among the prehypertensive group of adolescents in terms of habits of eating snacks between meals (86.3%), eating outside the home (75.5%), and high consumption of soft drinks (79.4%) compared with the other groups, with a statistically significant difference (P=0.034, 0.044, and 0.005, respectively). Most of the hypertensive and prehypertensive adolescents (91.3 and 75.5%, respectively) had a high consumption of salty foods, with a statistically significant difference (P=0.047). Table 2 also shows that the higher percentages of hypertensive and prehypertensive adolescents had a high consumption of fast foods and usually added table salt compared with normotensive adolescents. Higher number of prehypertensive adolescents reported high consumption of chips and tea compared with the other groups. High consumption of coffee, fruits, and vegetables was more common among normotensive adolescents than the other groups of the studied sample. The difference between groups was not statistically significant in consumption of fast foods, chips, coffee, tea, fruits, and vegetables.
Table 3 shows that the mean BMI was higher among hypertensive and prehypertensive adolescents than normotensive ones, with a statistically significant difference (P=0.015). The same observation was made for weight, circumferences of waist and hip, and percent of total body fat, but with no statistically significant difference.
As shown in Table 3, the entire sample of adolescents consumed energy, protein, and sodium that exceeded their requirements, whereas their intake of potassium was less than the requirements. The prehypertensive group consumed the highest amounts of the nutrients studied. Prehypertensive and hypertensive adolescents consumed higher intake of energy and CHO than normotensive ones, whereas prehypertensive adolescents consumed the highest daily intake of fat and protein. However, the daily intake of sodium and potassium among the three groups of adolescents was not significantly different. Nutrient density of fat and percent adequacy of energy, protein, and potassium were the highest among prehypertensives, whereas nutrient density of CHO and percent adequacy of sodium were the highest among hypertensive adolescents as shown in Table 3. No statistically significant difference was observed between groups in dietary intake.
Table 4 shows the results of two models (one for SBP and the second for DBP) of stepwise linear regression analysis for significant factors affecting the blood pressure levels. Both models were statistically significant (F=7.56, P=0.000 and F=3.62, P=0.014). The high BMI was a good predictor for elevated levels of both SBP and DBP. High consumption of fruits and vegetables was a good predictor for lower levels of both SBP and DBP. High consumption of chips was a good predictor for increased SBP level. High consumption of soft drinks was a good predictor for increased DBP level.
It is hypothesized that early adoption of healthy eating habits in adolescence may contribute toward a lower incidence of diseases in adulthood and improved quality of life later in life 30. This study investigated the potentially modifiable dietary factors associated with blood pressure in a representative sample of school adolescents in Sohag as a representative stratum for the Egyptian city in Upper Egypt governorates.
Hypertension is a public health problem especially in developing countries that requires the identification of risk factors such as obesity and other dietary risk factors to reduce the complications of hypertension and cardiovascular diseases. The results of the present study showed that the rate of hypertension and prehypertension was 7.7 and 34%, respectively, among the studied sample, which may be related to the high rate of overweight and obesity among hypertensive and prehypertensive adolescents. Many studies have firmly established the link between increased BMI and increased blood pressure in children and adolescents 20,31,32. This is consistent with the findings that increased SBP and DBP was significantly associated with increased mean BMI, which was the highest among hypertensive adolescents. This may be attributed to the highest daily intake and adequacy of energy among prehypertensive and hypertensive adolescents.
Elevation in blood pressure in obese adolescents in the present study may be because of the high consumption of fast foods, chips, and soft drinks as snacks, which are energy-dense foods (CHO-rich and fat-rich foods). The mean CHO and fat density among the studied sample were within the normal range of the dietary guidelines. However, hypertensive and prehypertensive adolescents had the highest values compared with the normotensive ones, which can explain the relation between increased intake of CHO and fat, obesity, and hypertension.
Soft drinks, fast foods, and convenience foods consumed by adolescents are often high in added fats, sweeteners, and sodium but low in vitamins, minerals, and fibers 16–18. The consumption of chips and soft drinks was the highest among the prehypertensive group. High consumption of chips was a significant dietary factor associated with increased SBP and high consumption of soft drinks was a significant dietary factor associated with increased DBP.
The prevalence of hypertension could vary according to certain factors such as age, sex, and family history of hypertension 1. The present study found more males had hypertension than females in contrast to prehypertensives. There was a gradual increase in the rate of hypertension with age. This increase in blood pressure with age can be attributed to the increase in body size, sexual maturation, and increase in arterial stiffness, and this is in agreement with the results of another study carried out on school children and adolescents 1.
Dietary habits are complex in nature and many factors influence food practices. Adolescence is a transitional stage and many changes take place at physiologic and behavioral levels. High consumption of salty foods is predicted to affect blood pressure. The increase in blood pressure with higher salt intake was evident in many studies 11,16,33,34. Although only the natural sodium content of food was calculated, without added salt, because it was difficult to calculate, the daily intake of sodium was higher than the recommendations for the three groups of adolescents because of the high consumption of salty foods such as pickles, salted fish, Mish (a traditional type of cheese that is hard and salty and is consumed in high quantities in rural and Upper Egypt cities), and chips on a daily basis. However, the most frequent consumption of salty foods was observed among the hypertensive group. Hypertensive and prehypertensive adolescents added table salt more than normotensives. This is in agreement with the results of another study carried out by Dholpuria et al.35. Studies document a disproportionately high ratio of sodium to potassium intake among children 31–34. This is linked to a reduction in the consumption of potassium-rich, low-sodium foods, particularly fruits and vegetables. This imbalance is more pronounced in the adolescent population, where dietary sodium intake far exceeds the nutritional requirements and the intake of fruits and vegetables is markedly reduced 11,32,33. The results of the present study also indicated that the consumption of fruits and vegetables was low and this low consumption was associated with the increased levels of both SBP and DBP.
Conclusion and recommendations
Hypertension and prehypertension were detected among 7.7 and 34% of adolescents in Sohag city, respectively. The entire studied sample consumed energy, protein, and sodium that exceeded their daily requirements, whereas their intake of potassium was less, with no statistically significant difference. High BMI and low consumption of fruits and vegetables were associated with increased blood pressure levels. Unhealthy eating habits and dietary practices such as high consumption of soft drinks, chips, fast foods, and salty foods; low consumption of protective foods rich in potassium as fruits and vegetables; and regular addition of table salt can be implicated as risk factors of hypertension among adolescents.
Nutritional education programs should be implemented for adolescents and their families by nutritionists and health professionals to provide the primary prevention steps for decreasing the risk of hypertension in adolescents and through adulthood. Modification of unhealthy dietary habits and lifestyle practices need to be considered in designing the nutrition education programs to reduce blood pressure during adolescence by (a) choosing a diet that includes plenty of fruits and vegetables to increase the intake of potassium for protection against elevated blood pressure, (b) reducing the intake of sodium, sugars, and fats by reducing the consumption of soft drinks, chips, and salty foods, (c) providing information on the consequences of unhealthy eating habits on health, (d) controlling weight as one of the primary interventions for obesity-related hypertension, and (e) supporting adolescents in the adoption of healthy lifestyle practices.
Conflicts of interest
There are no conflicts of interest.
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Keywords:© 2013 Egyptian Public Health Association
adolescents; dietary factors; Egypt; hypertension