A large-scale study of nearly 19,000 school students from 46 schools in Ernakulam district in Kerala has provided reference values for blood pressure in girls and boys in the 5-16 years age group.
The paper to be published in the journal Indian Pediatrics studied only children who had normal weight. Those who were overweight were excluded from the study. Three BP readings were taken on the same day with a two-minute interval between readings and the mean of the three was taken into consideration.
Blood pressure is generally positively correlated to body size. Greater the body size, the higher the blood pressure. And boys have generally been found to have higher blood pressure compared with girls.
But this study found the systolic blood pressure to be similar in both and boys and girls up to 8 years of age. But girls were found to have higher values thereafter till the age of 15, when boys tend to catch up.
This was true of mean diastolic blood pressure, as well. The study found BP of boys of age 16 to be higher than that of girls of the age.
The relative increase in systolic pressure was found to peak in girls compared with boys during 11 to 13 years of age. In the case of diastolic pressure, the relative increase happened during 12 to 15 years in girls compared with boys.
Linked to puberty?
“We think that the higher blood pressure must be linked to early puberty in girls,” said Dr. Manu Raj, “previous studies have found a link between sexual maturity and blood pressure levels in children.”
Though the study was adjusted for height, age and sex, no such correction was done for physical activity and nutrition.
Dr. Raj is the first author of the paper and is a Clinical Assistant Professor at the Division of Pediatric Cardiology, Amrita Institute of Medical Sciences and Research Centre, Kochi.
According to him, both boys and girls had higher diastolic pressure compared to American children. The differences show from the age of five and persist even at 16 years.
In the case of systolic pressure, the difference is seen only between Indian girls and their counterparts.
“It’s a relatively new phenomenon to see higher blood pressure in children who are smaller in size,” he said.
Dr. Raj also feels that apart from other factors such as poor diet, lack of physical activity and higher intake of salt, low birth weight, which is a reflection of poor in-vitro nutrition, would be partly responsible for higher blood pressure in Indian children.
According to the Barker hypothesis, a link exists between babies who are underweight at birth due to lack of nutrition in-vitro and susceptibility to many chronic conditions such as cardiovascular disease and diabetes.
According to him, unpublished data from the study show that children from higher socio-economic levels had comparatively lower blood pressure than children from lower socio-economic level.
Studies undertaken earlier in Mysore and Pune have found that children with low birth weight tend to have higher blood pressure.
He is however not sure if the higher BP levels in children are an early indication of cardiovascular problems.
The prevalence of cardiovascular aliments is high in India. The overall prevalence of high blood pressure in urban population is 24-30 per cent, and 12-14 per cent in rural areas.
This study, therefore, provides a compelling reason to undertake more investigations from across the country to get a more complete picture of BP status in children.