Just one year of being overweight lowers chances of cancer survival

The study, published in Cancer Epidemiology, Biomarkers and Prevention, found that not only is weight linked to an increased risk of cancer, but also that being overweight affects future survival rates.

Researchers found that for each year a person spends overweight in their twenties and thirties, their risk increases. The study looked at around 20 years of data from more than 47,000 Swedish women aged between 29 and 49. Of these, 1,500 went on to develop breast or bowel cancer.

The researchers found that those who were more overweight, with a BMI of over 25, early in adult life were up to 72% more likely to die from breast cancer than women with a BMI lower than 22. The risk of death also increased by 141% for women who had bowel cancer.

The longer that the women were overweight, the greater their risk of dying from these cancers. Women were found to increase their risk of dying by 3% and 4% respectively for breast and bowel cancer for each year that they were overweight. Women who had been overweight were also found to be more likely to be diagnosed later.

Although the study was observational and so could not prove that being overweight caused chances of survival to be lowered, the researchers suggest that the observed link may be connected to increased insulin resistance, DNA damage, effects on hormones and chronic inflammation, all of which can be linked to cancer and obesity.

In the UK, obesity and being overweight are common. In 2015, 58% of women and 68% of men were found to be overweight or obese. Cancer and various other chronic health conditions have been linked to weight by many studies.

This study is one of the first to look into how the amount of time spent overweight links to cancer survival, explained one of the researchers, Dr Isabelle Soerjomataram from the International Agency for Research on Cancer. "While previous studies have shown an association between being overweight and developing cancer, very little is known about how being overweight impacts your chances of surviving cancer. Our research shows that effective prevention of overweight and obesity must start at an early age."

The team encourage further research and especially studies into how weight in early adulthood affects men as this study only focused on women. They reflected that "these findings point towards a long-lasting effect of overweight and obesity during young adulthood, impacting not only the risk to develop but also the chance of dying after a cancer diagnosis. It also emphasises the need to understand and improve long-term outcomes in cancer patients with a history of obesity."

Dr Duane Mellor, Senior Teaching Fellow at Aston Medical School, encouraged people to use the results of this study to focus on leading a healthier lifestyle, rather than focusing just on weight.

"We need to make it easier to enjoy being healthy, by having tasty and healthy food accessible and acceptable to all and being able to be physically active as part of our daily lives. It is people's behaviours which really impact the risk of surviving after cancer. Being as healthy as possible throughout life is the best way of not only preventing many chronic diseases but also improving our chances of surviving them too. It is also important to remember that in people with cancer, sudden unexplained weight loss can be a bad sign, and perhaps we need to move away from a focus on weight to a focus on health - to being active to maintain muscle mass and eating healthily," explained Mellor.

Professor Justin Stebbing, NIHR Research Professor of Cancer Medicine and Medical Oncology at Imperial College London, echoed the need for healthier living to increase cancer survival rates. "These findings point towards a long-lasting effect of overweight and obesity during young adulthood, impacting not only the risk to develop but also the chance of dying after a cancer diagnosis later on. These results need confirmation in other studies but add to the growing evidence of an important relationship here, and is yet another reason to have a healthy lifestyle."

This study was published in Cancer Epidemiology, Biomarkers and Prevention.