If you’re an overweight adult, you are at increased risk of a load of health problems you don’t want, including cardiovascular diseases (CVD). These affect the heart and blood vessels and include coronary heart disease and stroke. As for children, evidence for a similar association is building up but the link is less well understood, including the age at which risk factors for CVD start to be affected and how big the effect might be.
Researchers at Oxford University have explored this topic by combining the results from studies on healthy school-aged children from developed countries, which reported an objective measure of weight and one or more risk factors for CVD. The results of their systematic review have now been published in the BMJ. After an extensive search for studies of a wide range of designs and published after 1990, they were able to include 63 studies with almost 50,000 children aged 5 to 15 years in 23 developed countries.
They found that risk factors for CVD were worse in overweight and obese children compared with normal weight children. Specifically:
- blood pressure (BP): systolic BP was higher by 4.54 mm Hg in overweight children and by 7.49 mm Hg in obese children. Similar associations were found for diastolic BP and 24 hours ambulatory systolic BP
- blood lipids: total cholesterol and triglycerides were 0.15mmol/L and 0.26 mmol/L higher in obese children respectively
- fasting insulin and insulin-resistance were significantly higher in obese but not overweight children
- obese children had a significant increase in left ventricular mass of 19.12g compared with normal weight children
How big are these effects?
The reviewers describe the effect sizes as ‘substantial and concerning’, particularly for obese children. For example, the difference in systolic blood pressure between normal weight and obese children was about 40% higher than the difference bewteen normal weight and overweight children, with total cholesterol nine times higher for the same comparison.
How good is the evidence?
This was a well-conducted review but, as is so often the case, there were some problems with the studies it included. Some limitations to bear in mind:
- quality assessments were made by rating the studies on five categories of risk of bias; 57 were judged to be moderate risk, 2 low risk and 4 high risk
- 39 studies did not provide data that could be combined in a meta-analysis and these were included in a descriptive analysis
- too few studies provided data to enable the reviewers to assess the influence of age or puberty
- the review provides a snapshot of CVD risk at one point in time, with no data on individuals’ weight changes or how risk progresses into adulthood
- there was variety between studies in a number of factors including age and ethnicity of participants
- the findings may not be generalisable to children in developing countries
The authors concluded:
Having a body mass index outside the normal range significantly worsens risk parameters for cardiovascular disease in school aged children. This effect, already substantial in overweight children, increases in obesity and could be larger than previously thought.
Next time here at the Lifestyle Elf, we’ll be looking at whether lifestyle interventions for preventing weight gain in young adults seem to work.
Friedemann C; Heneghan C; Mahtani K; Thompson M; Perera R; Ward AM. Cardiovascular disease risk in healthy children and its association with body mass index: systematic review and meta-analysis. BMJ2012;345:e4759 (Published 25 September 2012) Full text available.