Friday December 19 2008
“Childhood obesity is determined before the age of five,” says The Daily Telegraph. The newspaper says a new study has found that the majority of seriously overweight children gained much of their excess weight before they started school.
This study is part of ongoing diabetes research investigating a range of health indicators in children including changes in weight. Researchers looked at the weight of 223 children at birth, then at ages five and nine. Today’s children had birth weights similar to babies born 25 years ago, but were found to gain far more weight by the time they started school.
The research also found that at puberty, most of a child’s excess weight had been gained before they started school. Over 90% of girls’ excess weight and 70% of boys', was found to have been 'carried over' from age five. The researchers say this provides a good reason for dealing with obesity early.
This study provides an early indication that programmes for managing the weight of pre-school children might be successful in preventing obesity in older children.
Where did the story come from?
This research was conducted by Dr Daphne Gardner and colleagues from the department of Endocrinology and Metabolism at the Peninsula Medical School in Plymouth. It is not clear from the available draft report what sources of funding where used for this research.
The study has been peer-reviewed and is awaiting full official publication in the medical journal Pediatrics.
What kind of scientific study was this?
This is the 36th publication from a prospective cohort study known as the EarlyBird Diabetes Study. This ongoing study is investigating the factors relating to the emergence of insulin resistance in a group of over 300 healthy children from school entry (four or five years old) to 16 years.
The study also has access to the weight data (retrospective data) collected at birth on these children, who by 2008 were approaching puberty. For this study (EarlyBird36), the researchers wanted to find out when the children who put on excess weight began to do so. They also looked at how this weight gain affected body composition and insulin resistance later in life.
Insulin resistance (IR) is a metabolic condition in which normal amounts of insulin are inadequate to produce the normal responses from fat, muscle and liver cells in the body. In healthy people, the release of insulin will cause these cells to act in different ways to reduce blood glucose levels, e.g. muscle cells will take in glucose and store it. This leads to a fall in the overall level of glucose in the blood as the level of insulin rises.
However, in children and adults who are insulin resistant, a rise in insulin leads to less glucose take-up by muscles and the liver increases its glucose production. Together these lead to an unhealthy rise in the level of glucose, despite the higher levels of the hormone insulin.
Excess weight gain contributes to IR and the metabolic link is thought to be one of the main factors underlying diabetes and cardiovascular disease. Early weight gain, from birth to five years is thought to be an important contributor to diabetic risk.
Between 2000 and 2001, 307 healthy, mostly Caucasian children (170 boys, 137 girls) were recruited from randomly selected schools around Plymouth. The children were an average of 4.9 years old at this time. They were weighed at ages five and nine and their birth weights were obtained from birth records.
As children continually grow throughout childhood, it was necessary to use a method called a weight standard deviation score (SDS), to get an idea of how different each child was from the expected weight for their age. The researchers also calculated the weight change between weighings, relative to that expected for their age (the change in SDS). They called this the excess weight.
They then used a recognised technique called the HOMA2-IR to measure insulin resistance and scanned the children to measure fat mass and calculate the fat mass index (FMI) by adjusting for height. The lean mass index is calculated from the lean mass in the same way.
In all, 31 children left the study before age nine. Of the remaining children, 126 boys and 97 girls had the required birth data and measurements, including insulin resistance, measured at five and nine years and had their fat and lean mass measured at age nine. It is the data for these 223 children that are presented.
The researchers used complex statistics (known as multiple regression modelling) to see if it was the current weight, or the weight gain (change in SDS) that was associated most strongly with IR at nine years.
What were the results of the study?
Excess weight gain (the change in weight SDS) was substantial from birth to five years but smaller from five to nine years. While weight SDS at five years correlated poorly with weight SDS at birth, it strongly predicted weight SDS at nine years.
When assessing how well their models predicted IR the researchers say that, “importantly, predictive strength was little different, whether the change in weight SDS over the time period (excess weight gain) was used in the analysis, or simply the weight SDS recorded at the end of the time period (current weight).” This means that the single measures of current weight are as strongly predictive of IR as weight gain, and supports their claim that future policy could be based on a school entry weight at about five years of age.
What interpretations did the researchers draw from these results?
The researchers claim these findings are important because a single measure of weight (or BMI) on school entry at five years provides both a record of the long term trends in the population (prevention), and an accurate pointer to future risk for the child (treatment).
They go on to say that the data implies that the successful prevention of excess weight gain early in childhood will be maintained, at least into puberty. They say that diabetes prevention strategies might better focus on pre-school children rather than older children, as “the die appears to be cast by five years”.
What does the NHS Knowledge Service make of this study?
The researchers claim that the current UK Department of Health guidelines are correct in proposing the routine measurement of children’s weight and height at school entry, around the age of five years. They say this is important for monitoring what is happening in the population, and for alerting parents, schools or healthcare professionals about the children that need more intensive treatments. They also say that taking action at even earlier ages would be better.
The researchers do note some limitations to the study:
- The analysis did not include weights for the children when they were younger than five, other than birth weights, as the records were not available. These records would have been useful for confirming the link.
- The children were from schools in the Plymouth area only. As none of the children were from other geographical areas and few were from black or minority ethnic groups, it is not certain that the findings would apply to all children.
- The measure of insulin resistance using HOMA-IR is not the preferred measure of IR for some researchers. Other, more uncomfortable tests, are used as the gold standard and may not be appropriate in children.
- The numbers of children examined are relatively small, and a larger study might mean that the researchers could be more certain of their findings.
The researchers do not say what the strategies in pre-school children are that might prevent diabetes in later life. They will no doubt involve attention to diet and increasing physical activity, as these are known proven to reduce insulin resistance.
It may be easier for parents to modify preschool diets than the diets of older children. If weight gain and insulin resistance can be prevented from developing at young ages this may play an important role in reducing the record levels of obesity and the current epidemic of diabetes and heart disease that threaten health the developed world.