“Pollution is making children fat, say experts”, reported The Independent on Sunday. It said that a new Spanish study found that exposure to a range of common chemicals while in the womb sets up a child to ‘grow up stout’. The newspaper suggests that this may be helping to drive the worldwide obesity epidemic. The study measured levels of hexachlorobenzene (HCB), a pesticide, in the umbilical cords of children and found that those with the highest levels were more than twice as likely to be obese six years later.

The study has some limitations and the researchers mention some of these, including that the children’s diet and activity levels were not considered; two important known determinants of BMI. To have a clearer idea of the effect of environmental pollutants, more research that considers these factors is needed. Obesity is a complex disorder with a number of contributing factors. Pollutants are unlikely to be the sole cause of the obesity epidemic – in fact, this study found no statistically significant link between HCB and obesity (only the link with ‘overweight’ was significant).

Where did the story come from?Dr Agnes Smink and colleagues from the Centre for Research in Environmental Epidemiology at the Institut Municipal Investigacio Medica in Barcelona and other academic institutions across Spain, carried out the research. The study was funded by the Spanish Ministry of Health, Instituto de Salud Carlos III, Fundacio La Caixa and the European Commission. The study was published in the (peer-reviewed) medical journal: Acta Paediatrica.

In this longitudinal study, the researchers aimed to investigate the effect of organochlorine compounds (OCs), chemicals used in agriculture and industry, on children in the womb. These chemicals are resistant to degrading naturally and can build up in the food chain. They were particularly interested in hexachlorobenzene (HCB), used as a pesticide to protect seeds against fungus. Previous research has found an association between OCs and body size, and they wanted to look at exposure to HCB in the womb and its effects on the child’s weight and BMI in later life.

To do this, the researchers looked at the concentration of HCB in the umbilical cord blood of 405 children born in Menorca from mid 1997 to mid 1998. Originally, 482 children had been recruited, but umbilical cord blood was only available from 405 of them. The researchers kept in contact with the remaining 77 for comparison. Preterm births were excluded. When mothers were recruited, questionnaires were used to collect data from mothers on their age, education, socio-economic status, number of children, whether or not they smoked during the first trimester, how much alcohol they drank, their pre-pregnancy weight and their diet during pregnancy. Infant height and weight was measured at birth and feeding practices were reported by mothers in interviews at six months and one year after birth. The children’s height and weight were measured when they were 6.5 years old.

The researchers then assessed the link between concentrations of HCB in cord blood and weight and BMI at age 6.5 years. There were three different statistical models that took into account different factors: one that took into account child age and sex, a second that took into account sex, maternal age, height, pre-pregnancy overweight or obesity, education and number of children and a third that also took into account the weight of the child at birth.

The researchers report that they detected OCs in all 405 cord blood samples. They found no differences in BMI at 6.5 years between the 405 children who had had their umbilical cord blood measured for OCs (BMI of 16.6) and the 77 who had not (BMI of 16.8).

Children with higher HCB levels in cord blood were heavier and had a higher BMI than children with low HCB levels. When they adjusted for various factors, they found a statistically significant increase in BMI ‘related to prenatal exposure to hexachlorobenzene’. Children in the highest exposure group of HCB were 2.5 times more likely to be overweight. The researchers also report that they were three times more likely to be obese, but this was not statistically significant.

The researchers report that prenatal exposure to HCB increased the risk of being overweight at age 6.5 years. This link is independent of socio-economic status, maternal education, and number of children, maternal obesity and weight at birth. This effect is stronger in children whose mothers smoked. Overall, they conclude that additional studies are needed to “assess directly whether HCB at current concentrations of exposure increases health risks on children such as obesity’”.

This study suggests that prenatal exposure to HCB is linked with height and weight at age 6.5 years. There are several points to highlight however:

• The researchers note that they interviewed mothers at six months and one year after birth when they asked about ‘feeding practices’. Importantly though, there was no assessment of diet during the children’s toddler years, and diet is probably one of the most important environmental factors affecting weight. The researchers add that ‘some now-known relevant variables were not included, like… improved diet variables’. The study also did not account for activity levels in childhood. Given the known contribution of diet and activity levels to being overweight and obese, studies that assess ‘causal’ links should consider these factors.
• The researchers also note that this was a small study cohort.

Due to these limitations, confidence in the results is limited. It would be best to see these results replicated in other studies that take into account diet and activity levels during childhood before coming to any conclusions. Such studies are helpful in adding pieces to the puzzle, but they must take into account other obvious factors to reliable quantify the link with a new exposure.

“Playing active computer games 'keeps children fit' and could turn the tide of obesity”, reports the Daily Mail. It said that research in children between six and 12 years of age found that the “physical effort of playing Nintendo Wii and similar virtual sports console” used up more than four times as many calories as computer games played sitting down. It said that just 35 minutes a day of playing such games burns 150 calories, enough to stop weight gain.

This was a small study looking at heart rate and energy expenditure in 18 children while they played sedentary and active computer games. It did not use the Nintendo Wii, or look at weight loss or obesity prevention. The finding that active gaming burns more calories than seated gaming or resting in the very short-term is not surprising. Children should exercise and active gaming could be a way to get those who spend a lot of time playing computer games to do more. However, it remains to be seen whether the health benefits of active gaming are as good as those from conventional exercise and play, which should still be encouraged.

Robin R. Mellecker and Alison M. McManus from the University of Hong Kong carried out the research. The study was funded by the University of Hong Kong Research Council Strategic Research Theme Public Health. The study was published in the peer-reviewed medical journal: Archives of Paediatric and Adolescent Medicine.

This was an experimental study carried out in the laboratory. It looked at children’s energy expenditure as they played active or seated computer games.

The researchers enrolled 18 healthy children between six and 12 years of age from local primary schools. The children were asked to visit the laboratory in the morning, having fasted and not exercised for the 12 hours leading up to the experiment. Their energy expenditure was estimated through their oxygen intake and carbon dioxide production during the experiment, which was measured by masks connected to a machine. They also wore heart rate monitors. To get their measurements at rest, the children were asked to lie down and relax as they watched a film of their choice for 20 minutes. Their energy expenditure and heart rate were then measured in the last 15 minutes of this period.

The researchers then got the children to play three different computer games. The first was a 10-pin bowling game that was played sitting down and operated by a computer mouse. The other two were active games that involved more movement. These were another bowling game (XaviX bowling) that required a bowling motion, and a game involving various actions including running, walking, squatting and jumping (XaviX J-Mat). The children played the games for five minutes to familiarise themselves with them. They then played a 25-minute set that included all three games and involved five minutes just sitting looking at the game, five minutes seated bowling, five minutes active bowling, five minutes rest, and five minutes of the J-Mat game. Their heart rates and energy expenditure were measured during each of these periods. The researchers then compared children’s heart rate and energy expenditure at rest and during each game.

The researchers found that both seated and active gaming increased energy expenditure and heart rate compared to being at rest. The seated bowling game increased kilocalories burnt per minute by 39%, the active bowling game by 98%, and the J-Mat game by 451%. Both active games increased children’s energy expenditure compared to the seated games. Only the J-Mat game increased heart rate compared to the seated game, and the heart rate in this game was reported to be similar to that seen with vigorous exercise.

The researchers concluded that playing active computer games leads to “meaningful increases in energy expenditure and heart rate” compared with seated games. They suggest that active computer games may provide “appealing activity alternatives” for children, and that development of more games that provide exercise and entertainment is needed.

This study does indicate that children will burn more calories with computer games that are active than games that are seated. There are a few points to consider when interpreting these results:

• This study was in only a small number of children; larger studies will be needed to confirm these findings.
• The children in this study were new to these games and only played them for a short period of time as they wore monitoring equipment. It is possible that the results may not have been the same if the children were familiar with the games, had played them for a longer period of time, or were not wearing the monitoring equipment.
• Five of the children included were overweight, but none was obese. Results may be different for children who are obese.
• The fact that children all performed the games in the same order, rather than in random order, may have an effect on their energy expenditure.
• Energy expenditure during gaming was compared to a period of rest. It is not clear whether gaming increases energy expenditure any more than normal levels of activity.

Active gaming may provide a way of getting children who normally play a lot of computer games to exercise more. However, it is unclear from this study whether this would have an effect on a child’s health or weight in the long term. Ideally, children should also be encouraged to engage in non-computer related exercise.