TOKYO, Oct 29, 2007 (AFP) - Children whose mothers smoked even in the early stages of pregnancy are nearly three times more likely to struggle with obesity later in life, according to a Japanese study.

While the study did not state an exact correlation, one theory is that children whose mothers smoked were deprived of nutrition in the womb.

The same study also found children of mothers who had a habit of skipping breakfast during pregnancy were 2.4 times more likely to be obese.

The survey was done over a period of nearly two decades by a team led by Zentaro Yamagata, professor at Yamanashi University's School of Medicine.

It covered about 1,400 women in Japan who gave birth between April 1991 and March 1997. The researchers then collected data on about 1,000 of their children until they entered fourth grade at age nine or 10.

The risk of obesity was 2.9 times higher among children whose mothers smoked when they were three months pregnant or at an even earlier stage, as compared with children of non-smoking mothers, the study showed.

The results "indicate smoking during pregnancy, even in the early stages, can affect the health of children over a long period of time," Yamagata said.

Researchers can "speculate" that children who had been poorly fed in the womb would stock up on nutrition after they were born, he said.

"But we don't know the truth. What is important here is to stop smoking," he said.

There have been studies around the world about the linkage between smoking during pregnancy and child obesity, but continuous research on the same group of children until they turn 10 is very rare, according to Yamagata.

The results of the study were announced at a meeting of public health experts in Japan last week and will be carried in a North American magazine to be published in December.