Having a large body size in childhood is associated with an increased risk of coronary artery disease and type 2 diabetes, particularly when it persists into adult life, finds a study published by The BMJ today.
The results also suggest that a larger early life body size may help protect women against breast cancer in later life.
Obesity in children is widely recognised as a global public health crisis, yet levels continue to rise.
Having a high body mass index (BMI) in early life is thought to increase the risk of various health conditions in later life. But it is unclear whether an individual can reverse the impact of childhood obesity through lifestyle changes, particularly as those who are obese in early life tend to remain obese as adults.
So researchers at the University of Bristol used a technique called Mendelian randomisation to examine the genetic influence of body size in early life on risk of four diseases in later life - coronary artery disease, type 2 diabetes, breast and prostate cancer.
Their findings are based on more than 450,000 people from the UK Biobank database using measures of BMI in adulthood (average age 57) and self-reported perceived body size at age 10 and over 700,000 individuals from four large scale genome-wide association studies.
Analysing genetic information in this way avoids some of the problems that may hinder traditional observational studies, making the results less prone to unmeasured (confounding) factors, and therefore more likely to be reliable. An association that is observed using Mendelian randomisation therefore strengthens the inference of a causal relationship.
The researchers found that early life body size is associated with an increased risk of coronary artery disease and type 2 diabetes. However, when early life body size was analysed together with adult body size, the effects were considerably reduced, suggesting that the increased risk is most likely in those with a large body size in childhood that persists into later life.
They also found strong evidence that larger early life body size has a protective effect on risk of breast cancer, although they say timing of puberty might play an important role here and this requires further investigation before firm conclusions can be made.
However, no strong evidence was found of a causal effect of either early or later life measures on prostate cancer.
The authors point to some study limitations, such as relying on self reported early life body size which may have affected the accuracy of their estimates. However, strengths include the large number of participants and the sophisticated analytical methods used.
As such, they say their findings suggest that the positive association between body size in childhood and risk of coronary artery disease and type 2 diabetes in adulthood can be attributed to individuals remaining large into later life.
"Our approach therefore yields insight into the pathway between early life risk factors such as BMI and disease outcomes," they conclude.
This study suggests that the effect of self-reported adiposity at age 10 on coronary artery disease and type 2 diabetes "can be obviated by achieving and maintaining a normal body mass index (BMI) in adulthood," writes Professor Mary Schooling in a linked editorial.
The study used sophisticated and up-to-date mendelian randomization methods. Nevertheless, she says its findings "need careful interpretation and contextualization before they can be applied to population health."
She points to adolescence - the transition from childhood to adulthood - as a key point of intervention, and suggests that "puberty might be a key time to reduce adiposity."
Peer-reviewed? Yes (research), No (linked editorial)
Type of evidence: Mendelian randomisation; Opinion