INDULGENT grandparents threaten the health of children with sweets and second hand smoke, scientists claim.

Dr Stephanie Chambers said the group should be the target of public health messages in a bid to protect youngsters from increased cancer risks.

Chambers, of Glasgow University, led a review of research on the influence grandparents have on lifestyle factors that can lead to cancer in later life.

She said: “While the results of this review are clear that behaviour such as exposure to smoking and regularly treating children increases cancer risks as children grow into adulthood, it is also clear from the evidence that these risks are unintentional.

“Currently grandparents are not the focus of public health messaging targeted at parents and in light of the evidence from this study, perhaps this is something that needs to change given the prominent role grandparents play in the lives of children.”

While research has previously examined the way parents can affect their children’s susceptibility to cancer and other diseases, less attention has been paid to the role of part-time carers such as grandparents, according to the Glasgow team.

It analysed data from almost 60 studies and nearly 20 countries that included information about the influence of grandparents on youngsters.

Overall, grans and grandads were found to have an adverse effect, putting children’s health at risk by measures such as rewarding good behaviour with sweets.

“Excessive feeding” of children was found to be a significant problem, as was providing meals that may be made from scratch but with unhealthy ingredients. Evidence was also said to suggest that the poverty and hunger some elders experienced during their own childhoods led them to believe extra weight was a sign of good health.

Meanwhile, grandparents smoking in the home was identified as having a negative impact, both by setting a bad example and exposing children to second hand tobacco smoke.

However, the negative impact on diet and weight was said to be balanced by a more positive finding with respect to physical activity. Grandparents tended to be supportive of children engaging in active pursuits, often providing them with access to the necessary space.

Chambers said: “It appears that parents often find it difficult to discuss the issues of passive smoking and over treating grandchildren.

“Given that many parents now rely on grandparents for care, the mixed messages about health that children might be getting is perhaps an important discussion that needs to be had.”

The findings are published in the online journal Public Library of Science ONE.

Professor Linda Bauld of Cancer Research UK, which co-funded the study, said: “Children’s health can be affected by a range of factors, and this study reinforces the importance of the broader family picture.

“With both smoking and obesity being the two biggest preventable causes of cancer in the UK, it’s important for the whole family to work together.

“In today’s busy world it’s often the wider family who have a role to play in keeping youngsters healthy. If healthy habits begin early in life, it’s much easier to continue them as an adult.”

Tam Fry, chairman of the National Obesity Forum, said: “Finding a doting grandparent who is confident enough to follow rules laid down by mum and to the letter is frequently a rarity.

“Both nan and grandpa can leave themselves wide open to manipulative and increasingly savvy grandchildren in their desire to please the little darlings. They bring out the biscuits at the slightest hint of a tantrum and, as the researchers report, they are also often too protective in loco parentis. The thought of losing children when out in the park may result in the kids being under house arrest – sweeties on demand and woefully short on exercise.

“Unfortunately, despite the researchers’ suggested messaging, it may ever be so, as parents increasingly need to rely on this free form of childminding.”