Surekha Joshi, Sanjeev Gupta, Sonali Tank, Sushma Malik, D.S. Salgaonkar

From the Department of Pediatrics, T.N.M.C. & Nair Hospital, Mumbai-400 008, India.

Correspondence to: Dr. Surekha Joshi, Bld no 1, Flat no 35, Govt. Quarters, Haji Ali, Mahalaxmi, Mumbai  400034, India.

Manuscript received: December 24, 2001; Initial review completed: February 7, 2002;

Revision accepted: July 8, 2002.

 

A prospective study was conducted to determine the incidence of essential hypertension (EH) and identify markerss, if any, in children of essential hypertension families. The study group included 90 children (2-18 years) with a parent or grandparent with EH while the control group had 25 age matched children from non-hypertensive families. Around 30% children (n=27) from these families had a diastolic blood pressure of >95th centile and an additional 27% (n=24) had borderline hypertension. The serum cholesterol, serum triglycerides and 24 hour urinary sodium excretion were significantly higher in the study group ( p < 0.05) as compared to controls. The children from the study group also had a signifcant high salt (p< 0.001) and fat intake ( P < 0.05).

Key words: Children, Essential hypertension,

Essential Hypertension (EH), primarily a disease of adults is being increasingly encountered in the pediatric age group over the past few years. If left untreated EH would increase the risk of myocardial infarction, stroke and renal failure in these patients(1). EH is found with a greater frequency in children of parents with EH and that there is a "tracking" of blood pressure from childhood to adulthood(1,2). Several reports have also revealed significant association between certain physical, biochemical and dietary factors, which are pointers to the development of EH. It was with this in mind, that we conducted this prospective study to ascertain the presence of hypertension in children of familities with EH and to identify any markers in childhood that are predictive for the development of EH in adults.

This prospective study was carried out in a public hospital over one and a half year period. The study group comprised of 90 children aged 2-18 years with a parent or grandparent with EH while the control group included 25 age matched children of non-hypertensive families. The parents and grandparents (28 fathers, 25 mothers and 37 grandparents had EH) were taken from the hypertension OPD at our hospital.

The children in each group were subjected to a systematic evaluation of their anthropometric measurements (height, weight, triceps skin fold thickness), detailed dietary evaluation (daily calorie, protein, salt, and fat intake) and measurement of heart rate and blood pressure serially on four separate occasions one month apart. In all children fasting blood sample for serum cholesterol, triglycerides, high-density lipoprotein were estimated by enzyme assay and serum calcium was done by cresolpthalene complexon method. A 24-hour urinary electrolyte (sodium and potassium) estimation using a flame photometer was also done in all patients.

NCHS charts were used for charting the anthropometric percentiles. Weight was recorded using a standard floor weighing scale having an accuracy of upto 0.1 kg. Height was recorded against a standard vertical sliding scale with an accuracy of upto 0.5 cm. The triceps skinfold thickness was measured using the Ponderal skinfold measuring instrument in the left mid-triceps region with an accuracy of upto 1 mm. Body mass index (BMI) was calculated using the formula BMI = weight/height in m2. Detailed dietary evaluation included calorie, protein, salt (dietetic sodium, inclusive of high salt containing items such as pickles, papads, tinned foods, seafood etc.) and fat intake. Blood pressure recording was done after a half hour resting period on each occasion with two readings per sitting half hour apart and fourth phase of Korotkoff sound taken as the diastolic blood pressure. Hypertension was defined as a blood pressure above the 95th percentile for age and sex. A basal heart rate was also recorded at each setting and the mean was noted. The data was subjected to statistical evaluation using paired student’s ‘t’ test.

The study group comprised of 90 children (2-18 years) from families with hypertension, while 25 age matched children from non-hypertensive families formed the control group. Due to limitation of funds we had restricted the sample size in our study to a minimal number that permits statistical evaluation. The incidence of hypertension (>95th percentile) in children with hypertensive families was as high as 30% (n = 27) as against none of the children from the control group. An additional 27% (n = 24) in the study group had borderline hypertension i.e. their blood pressure was between the 90th-94th percentile as compared to none in controls. Among the parents, 31% of fathers and 28% of mothers had essential hypertension. None of the children had both parents with essential hypertension. Also, 36% grandmothers and 5% grandfathers had essential hypertension, and in 8 of these cases, the grandparents as well as the parents (father, in all cases) had hypertension.

Table I shows comparison between various parameters in the two groups. On comparison of the basal heart rates, there was no significant difference when taken as a whole. However, there was a significant fall in the heart rate from the highest to the lowest centiles of diastolic blood pressure in the subset of hypertensive children ( p < 0.05). There was no such difference noted for the daily average protein intake. A study of salt and fat intake revealed a significantly higher intake in the study group, though the nature of fat consumed was similar in the two groups.

Table I	Comparison of Anthropometric and Dietary Parameters (mean ± SD)  Between The Study and Control Groups

Variable

Study Group

Control Group

Value

Heart rate

91.44 ± 8.12

90.68 ± 8.8

NS

Height (cm)

133.48 ± 14.92

127.72 ± 24.65

NS

Body Mass Index

16.64 ± 2.54

15.80 ± 2.54

NS

Skin fold thickness (cm)

9.13 ± 3.35

7.12 ± 1.69

<0.001

Calories/day

1700 ± 428.5

1608.8 ± 372.36

NS

Proteins/day (g)

34.08 ± 11.43

34.48 ± 11.08

NS

Salt/day (g)

11.50 ± 2.71

7.08 ± 1.35

<0.001

Fat/day (g)

17.87 ± 3.37

15.92 ± 2.89

< 0.05

NS: not significant

The lipid profile revealed a significantly higher serum cholesterol and serum triglyceride values in the study group (Table II). The serum HDL level and calcium was higher in the study group as compared to the controls but with no significance observed. The 24-hour urinary sodium excretion revealed a significantly higher level in the study group but the urinary potassium level was comparable in the two groups.

Table II_Comparison of Blood and Urinary Parameters (Mean ± SD) Between The Study and Control Groups

Variable

Study Group

Control Group

Value

Serum cholesterol (mg/dL)

198.98 ± 43.77

182.8 ± 35.01

< 0.05

Serum triglycerides (mg/dL)

171.68 ± 87.61

138.48 ± 31.0

< 0.05

Serum HDL (mg/dL)

53.12 ± 6.91

48.88 ± 6.59

NS

Serum calcium (mg/dL)

9.06 ± 1.02

8.93 ± 0.85

NS

24 h urinary sodium (meq/dL)

99.86 ± 23.42

86.72 ± 26.98

< 0.05

24 h urinary potassium (meq/L)

24.71 ± 15.65

20.92 ± 10.05

NS

NS: not significant

Children of hypertensive parents are not only more likely to develop hypertension, but also have their blood pressures tracking along the upper percentiles(1,2). Hence it is imperative to screen these children to identify markers to assist in prediction of development of essential hypertension (EH) in adulthood.

Hospital based studies from developing countries have documented an incidence of EH in the range of 1-45%(3,4). Screening studies for EH among school going children in India show a prevalence of 0.46-11.7%(5,6,7) whereas a study by Arar et al(8) found EH in 22.7% in children amongst the group with sustained HT. In our study the incidence of EH in families with essential hypertension was 30% (diastolic BP >95th centile).

High risk factors like obesity, high salt, fat and calorie intake, high cholesterol, low high density lipoprotein (HDL) and apolipoprotein are known to be associated with development of hypertension. Obesity is known to run in families and is closely related to hypertension(1,2,9,10,11). We found that children from hypertensive families had a significantly higher skin fold thickness as compared to normotensive families. BMI did not show any difference in the two groups, implying that children prone to develop essential hypertension have a greater fat proportion in their body.

Dietary factors associated with essential hypertension are salt, fat and caloric intake(1,2). We observed that the salt and fat intake in the hypertensive families was higher as compared to normotensive families. We also found that there was a significantly higher caloric intake among the subset of hypertensive children as compared to all other normotensive children. Thus, we can conclude, that, in children "at risk" for developing hypertension, a high fat and salt intake can become important predisposing factors. We did not document any correlation between the protein intake between the two groups.

The association of hypertension with obesity and altered lipid patterns including familial lipid abnormalities is also well known(1,9,11). Children of essential hypertensive families have their serum cholesterol values tracking on the upper side, along with their blood pressure readings, as was also seen in our study. Serum HDL is known to be a protective factor for hypertension and atherogenesis, however we did not find any difference in the serum HDL in the two groups. On comparing the 24-hour urinary electrolytes in two groups, our results are contrary to study done by Geleijnse et al.(12) who showed no significant association between urinary electrolytes and blood pressure.

A study by Strazzullo et al.(13) have revealed an increased urinary calcium excretion in children with higher blood pressure centiles and therefore are at a higher risk of hypertension in adults and have attributed this to a primary abnormality of calcium metabolism in essential hypertension. Though we did not estimate urinary calcium levels, we did not find a significant difference between the serum calcium levels in the two groups. The role of calcium has well been documented in the pathogenesis of EH, with a decrease in calcium intake being associated with an increase in blood pressure in epidemiologic studies and the same has been the basis for the role of calcium channel blockers in treating hypertension(15).

Current literature has stressed and focussed on low birth weight as a risk factor for hypertension(5,6). However, at the time when the patients were enrolled for the study, this factor was not well known and hence not specifically enquired into.

Doppler studies on arteries and veins would have given an additional dimension. However, Doppler studies were not routinely done at our institute during the study period.

Children belonging to hypertensive families should be targeted for primary prevention in a vigorous manner (blood pressure and weight monitoring) along with dietary and lifestyle modification. Diet should include supplement of high fibre diet to reduce serum cholesterol and increase serum HDL and restriction of salt and polyunsaturated fat. Encouragement of physical activity, discouraging smoking and alcohol abuse, beginning from childhood and continuing through adolescence to decrease the risk of development of EH and its associated complications especially in this target population.

Indian studies on long term follow up of children with EH is necessary along with evaluation of factors whose role is now being implicated in the pathogenesis such as serum calcium, low birth weight and catecholamines etc.

The authors wish to thank the Dean, Dr S. Dahanukar for her permission in allowing us to publish this article.

Contributors: The concept and design of the study was by SJ, SG and SM. SG. DS and SJ conducted the project; ST, SM and SJ drafted the manuscript. SJ will act as the guarantor of this study.

Funding: None

Competing interests: None stated.

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