Children from poorer families do not necessarily have worse health than those with more affluent and better educated parents, research shows.
The researchers believe junk food may be to blame
A British Medical Journal study looked at insulin resistance - which ups the risk of diabetes and heart disease - in relation to socioeconomic status.
Among Danish schoolchildren, those with highly educated and big earning parents were the least insulin resistant.
However, the opposite was true for children from Estonia and Portugal.
The findings by the international team, from the UK, Estonia, Denmark and Norway, challenge the widely held view that adverse social circumstances in childhood lead to unhealthy lifestyles and poor health.
The study involved 3,189 randomly selected schoolchildren from Denmark - one of the richest countries in Europe - and two poorer countries, Estonia and Portugal.
The researchers decided to look at insulin resistance as a marker of disease.
Insulin is a hormone that the body uses to unlock the energy from the sugar that we eat.
If someone is insulin resistant, their body continues to produce insulin but the insulin does not work effectively. This means that the body cells cannot take up enough glucose.
This results in rising blood sugar levels. If these levels rise too high the patient may develop Type 2 diabetes.
Insulin resistance is also linked to other conditions, such as high blood pressure and cholesterol problems, which can lead to heart and circulation problems.
Among the Danish children studied, insulin resistance was 24% lower in those whose fathers had the most education compared with those with the least education.
Yet insulin resistance was 15% higher for children in more educated families in Estonia, and 19% higher for Portugal.
The researchers said the higher levels seen in Estonia and Portugal might be because down to the children adopting unhealthier Western lifestyles - eating lots of junk food and doing less exercise.
These children were more overweight than their less affluent school mates.
However, their parents were more likely to be healthier than less affluent parents, which suggests they themselves might not be following the same unhealthy lifestyle as their children.
The children of better educated parents in Denmark, presumably, might also be leading healthier lifestyles.
However, Swedish experts on health patterns across populations warned in an accompanying editorial that the findings could be down to other factors not scrutinised.
Genes, environment while in the womb and early childhood factors other than socioeconomic status all play a role in insulin resistance, they said.
"Anomalies such as those reported for Estonia and Portugal may be of special significance, as they point towards gaps in our understanding and warn against too simplistic a view of health inequalities," they added.
Amanda Vezey, care advisor at Diabetes UK, said: "Insulin resistance, which is often a precursor to Type 2 diabetes, is linked to genetic and lifestyle factors such as being overweight, eating a poor diet and leading a sedentary lifestyle.
"This research is interesting and may help us to target people at higher risk. However, more research is needed before we can come to any firm conclusions."
Steve Shaffelberg of the British Heart Foundation said: "We have to put this study into perspective for kids in the UK. Robust research has clearly demonstrated a solid link between poverty and heart disease in this country.
"It would be misleading to suggest that findings from this study override existing evidence that shows social and economic factors are critical factors for heart health in this country.
"We know that kids from the poorer families have a worse diet and are doing less exercise, which is something we're working hard to combat."