Overweight women have a higher risk of delivering biologically older babies. This means they are more susceptible to age-related conditions such as heart disease and type 2 diabetes in later life, a new study shows.

Published in the journal BMC Medicine, the study found a strong association between a mother’s body mass index (BMI), even before she became pregnant, and a shorter telomere length in the baby’s chromosomes.

Telomeres are biological markers of accelerated ageing. They protect chromosomes – which carry genetic information in the form of DNA – by sitting at each end like shoe-lace caps.

Associate Professor Jeffrey Craig, an epigeneticist at the Murdoch Childrens Research Institute, said while high BMI in mothers is an established risk factor for chronic disease in the next generation, it has not previously been linked with telomere length in newborns.

“Telomeres stop our chromosomes degrading; they’re like the plastic ends on our shoelaces. From very early on in our development, our telomeres start to shorten. When we age, our telomeres shorten and when they get very short, our chromosomes start to fray and come apart, and then our cells die,” said Professor Craig, who was not involved in the study.

The BMC Medicine study was conducted by researchers from Hasselt University in Belgium. They measured the BMI of 743 mothers before conception and their baby’s telomere lengths. These were detected in cord blood and placental tissue at delivery.

“Telomere length in newborns was 5.5% lower in women with obesity, but this effect was continuous and also evident, though less pronounced, in the overweight mothers,” said co-author Professor Tim Nawrot, an environmental epidemiologist at Hasselt University.

Telomere length is measured by the number of DNA base pairs they occupy, which is directly linked to the number of times a cell can divide in its lifetime. Longer telomeres allow cells to divide more often, providing a link between telomere length and biological age.

The study found for each one-point increase in the mother’s BMI above a normal level, babies’ telomeres were 50 base pairs shorter; the equivalent of 1.1 to 1.6 years of adult life.

“Compared with newborns of mothers with a normal BMI, newborns of women with obesity are older on a molecular level, because shortened telomere lengths mean that their cells have shorter lifespans. So maintaining a healthy BMI during a woman’s reproductive age may promote molecular longevity in the offspring,” Professor Nawrot said.

The normal BMI range for adults is 18.5 to 24.9 and a BMI over 30 is considered obese.

Latest estimates from the Lancet Medical Journal suggest 20% of women will be obese by 2025 globally. In Australia those figures are even higher: more than half of Australian women were overweight or obese in 2011 to 2012.

“Our results add to the growing body of evidence that high maternal BMI impacts foetal programming, which could lead to altered foetal development and later-life diseases. The public health impact of our findings is considerable as in affluent societies about 30% of women of reproductive age are overweight,” Professor Nawrot said.

But this doesn’t mean the effects are irreversible. Dr Kyra Sim, a dietitian who specialises in early intervention in women and children, said while the foundations of health were built in early years, many factors accounted for disease progression.

“It doesn’t mean your health is set in concrete as there are many other factors that can effect longevity: your diet, whether you exercise, how well you deal with stress, social support in life, whether or not you smoke and other lifestyle factors are just as important, if not more important, in some cases than what actually happens in the developmental years,” said Dr Sim, who wasn’t involved in the study.

But Dr Sim also stressed the importance of being prepared for pregnancy.

“This study adds more support to the importance of making lifestyle changes, not just once we are pregnant but the importance of planning beforehand.”