Children whose mothers work are less likely to lead healthy lives than those with "stay at home" mums, a study says.

Professor Catherine Law, from the Institute of Child Health at University College London, has done the research. She said the findings cut across social status.

"We were able to take into account other factors which might influence diet and physical activity, such as whether a family had a very well educated mother and father or whether they hadn't had the benefit of such education", she said.

"But these findings were independent of that and in particular it didn't seem to be dependent on income, so going out to work might lead to better opportunities because of increased income, but that didn't seem to be the case in this study."