Children of mothers who smoke while breast feeding are more likely to develop serious health problems such as obesity, hypothyroidism, diabetes and cardiovascular disease later in life, according to new research done in rats. Scientists are calling for better information for new mothers on the long-term effects of nicotine exposure on their children's health.

The study, published in the Society for Endocrinology's Journal of Endocrinology, was carried out on rats that were fitted with nicotine-producing implants to model the effect of smoking during breastfeeding. The rats nursed their offspring as normal and the health of the offspring was monitored into adulthood. The adult offspring developed obesity and hypothyroidism while rats raised by mothers lacking the nicotine implant remained healthy.

Previous research has already shown a link between obesity and nicotine exposure during breastfeeding in humans. This study was carried out on rats so that the link could be studied at the molecular level.

The research team, based at the State University of Rio de Janeiro, looked further into the way in which nicotine has such long-lasting effects on the health of offspring. They found that the nicotine exposure caused decreased thyroid hormone levels and resistance to the hormone leptin, which tells us when it's time to stop eating. It is thought that smoking in human mothers affects the health of children in the same way.

Dr Patricia Lisboa, who led the study said, "We have shown that even a small period of nicotine exposure during breastfeeding can permanently damage the future health of a child. Future work on this project will investigate the addiction potential of nicotine and the neurological effects of smoking while breastfeeding on offspring."

She is lobbying for changes in advice to new mothers stating that "smoking during breastfeeding can be as dangerous to offspring as smoking during pregnancy".