Obesity a growing risk factor for cancer, study finds

Obesity is associated with an increased risk of cancer, but the risk varies depending on a person's sex and the type, researcher tells The National

New study reveals that obesity-related cancer risks vary by sex, type of cancer, and fat distribution. Ryan Carter / The National

Obesity is linked to an increased risk of cancer, with the risk varying by sex and type of illness, a new study found.

People with obesity were more likely to develop cancer and the risk was highest for women according to researchers.

The study, published in the journal Cancer Cell, reveals new insights into the relationship between obesity and cancer, highlighting the differences between male and female patients.

The researchers reported that both overall fat accumulation and the distribution of fat in different parts of the body can result in varying cancer risks depending on sex.

The risks were also found to differ across various types of the disease such as colorectal, esophageal, and liver cancer.

“Obesity's role in increasing cancer risk is generally understood in the medical and scientific community, but the public is less familiar with this connection,” explains lead author Dr Mathias Rask-Andersen, a researcher at Uppsala University in Sweden.

“The primary importance of this study is the comprehensive overview it provides of adiposity-related cancer risk,” Dr Rask-Andersen told The National.

“We found that the risks differ depending on biological sex, type of cancer, as well as both the accumulation and distribution of body fat throughout the human body.”

“These observations play a crucial role in risk assessment and deepening our understanding of adiposity-related disease risks.”

Senior author Asa Johansson emphasised that the distribution of fat in different compartments of the body is an important aspect of obesity-associated disease risk.

“Abdominal fat is considered more pathogenic compared to subcutaneous fat. Furthermore, fat distribution and the rates of most cancers differ between females and males.

“This inspired us to carefully analyse the relationship between adiposity and cancer risk based on sex.”

The team utilised data from the UK Biobank, a cross-sectional cohort of 500,000 UK residents aged between 37 and 73.

Those recruited between 2006 and 2010 were followed for an average of 13.4 years.

Information collected from participants included the distribution of fat in their bodies and any cancer diagnoses.

Using Cox proportional hazards modelling, the researchers identified the associations between the levels and distribution of fat in the participants' bodies at the time of the initial assessment and their subsequent rates of cancer.

They discovered that all cancer types, except brain, cervical, and testicular cancers, are associated with at least one obesity-related trait.

The results also showed gender-specific associations.

In female patients, the strongest links between overall fat accumulation and cancer were in gallbladder cancer, endometrial cancer, and oesophageal adenocarcinoma, Dr Rask-Andersen explained.

For males, the strongest links were in breast cancer, hepatocellular carcinoma, and renal cell carcinoma.

Fat accumulation and distribution also varied between sexes for colorectal, oesophageal, and liver cancer.

Prof Johansson provided insight into the unexpected differences observed in the effects of obesity on cancer risk. “There appeared to be a difference in the effect of obesity on cancer risk, not only between males and females but also between post- and pre-menopausal females.

“It's notable that obesity only becomes a risk factor for breast cancer after menopause, likely due to changes in oestrogen production.”

The study, however, does have limitations.

The fact that it mainly included British white participants, who represent almost 95 per cent of the UK Biobank, means that the findings might not apply to other ethnicities.

Additionally, given that the participants were older, the results may not be directly transferable to younger populations.

Further studies are planned to help understand the molecular mechanisms underlying these findings and to focus on genetic and environmental risk factors for cancer, which differ across a person's lifespan.

This includes looking closely at the effects of obesity before and after menopause.

“Considering the rapidly increasing rates of obesity globally, obesity is now the fastest-growing risk factor for overall cancer risk,” Dr Rask-Andersen told The National.

“Prevention and reduction measures for obesity and overweight conditions are highly motivated. However, it's crucial to remember that weight reduction does not completely eradicate the risk of cancer.

“There are many other individual risk factors, such as smoking for lung cancer and sun exposure for skin cancer, that can have a larger impact on specific types of cancer.”

Dr Rask-Andersen highlighted that while studies have shown weight loss can reduce the risks for obesity-associated cancer, the disease is caused by genetic mutations that lead to uncontrolled cell growth.

These mutations can be triggered by various factors, such as smoking, exposure to UV radiation from sunlight, and even chance.

Therefore, weight loss cannot eliminate cancer risk but is an important modifiable risk factor.

Dr Rask-Andersen concluded: “For some individual cancers there are specific risk factors that have more pronounced effects, e.g., smoking and lung cancer, sun and skin cancer.

“However, given that obesity is associated with several types of cancer and the rate of obesity is increasing globally, obesity is one of the largest and fastest-growing risk factors for cancer.”