The researchers show that obese children and adolescents have several risk factors for heart disease – including raised blood pressure, cholesterol and blood sugar levels, and a thickening of the heart muscle – compared with normal weight children.
‘We wanted to look at the relationship between the body mass index of school-age children and known risk factors for heart disease and stroke,’ explains Claire Friedemann, first author on the study and a DPhil student in the Department of Primary Care Health Sciences at Oxford University.
‘What we saw was really quite astounding. There were big effects,’ she says.
The size of the link between body mass index (BMI) and risk factors like blood pressure, cholesterol and regulation of blood sugar levels has not been fully established in children aged 5–16 before.
BMI is a way of seeing if your weight is appropriate for your height, and is calculated by dividing your weight in kg by the square of your height in metres. A BMI of 17 or less is classed as underweight; a value between 17 and 25 is normal weight; more than 25 is overweight; and over 30 is classed as obese.
The researchers identified 63 studies involving a total of 49,220 healthy children that addressed BMI and heart risk factors. Only studies conducted after 1990 in highly developed countries and published between 2000 and 2011 were included.
Their analysis of the studies showed that being obese as a child has a larger effect on blood pressure and other risk factors than may have previously been realised. Their findings are published in the medical journal the BMJ.
What we saw was really quite astounding. There were big effects
While the studies included in the analysis don’t show what happens as the children progress into adulthood, evidence from other studies suggests that the same patterns follow through.
As a result the researchers believe that these elevated risk factors could have a profound effect on the future health of obese children.
‘Healthy habits are much easier to begin as a child and then maintain into adulthood,’ says Claire Friedemann. ‘It is important that we don’t store up problems for the future.’
The findings are important as the number of children that are either overweight or obese continues to increase. In the school year 2010/11, figures from the National Child Measurement Programme show that the proportion of children in year 6 that were either overweight or obese was 33.4%, or one in three.
The researchers found that blood pressure was 7.49 mm Hg higher in obese children than in normal weight children. Children that were overweight also had raised blood pressure: 4.54 mm Hg higher than normal weight children.
As some comparison for the risk of similarly raised blood pressure as an adult, another study has found that adults who are able to lower their blood pressure by 10 mm Hg see a 30-40% reduction in their risk of dying from a stroke and a 30% lower risk of dying from ischaemic heart disease.
Other risk factors – total cholesterol, triglycerides, fasting insulin level and insulin resistance – were all raised in children that were obese.
The exact ages at which changes in a child’s risk factors begin need to be established, the researchers say, to help build a more accurate picture of the cardiovascular risk these young people are likely to face as adults.
‘If a child is overweight it could have wider consequences for their health that they may not be able to just grow out of, and so taking action early is important,’ says Claire Friedemann.
Dr Carl Heneghan of the University of Oxford and a co-author on the paper, says: ‘The relationship between obesity in children and cardiovascular risk factors such as blood pressure was much greater than we anticipated. The magnitude of the effect of obesity upon increasing cardiovascular risk in children is deeply worrying in terms of their future risks of heart disease.
‘Obesity is one of today’s most visible, yet highly preventable health problems. The good news is these risk factors can readily be reversed with exercise, good diet, and maintaining a healthy weight. Based on what we have found policy makers should make the epidemic of obesity in children as a priority for urgent public health action.’
Dr Matthew Thompson of the University of Oxford says: ‘Being overweight as a child is more than just about appearance – many children’s hearts and blood vessels are already getting damaged when they are overweight or obese.
‘Young people, their parents and doctors, and our politicians are in this together – we need to find better ways that we can put a stop to the obesity epidemic. New York’s banning of oversized sodas is exactly the type of public health intervention we need at this point.
‘Knowing that your heart and blood vessels are already damaged by being overweight or obese might help children and their parents put changes in place to change eating and lifestyle habits.’