Whilst studies into the link between obesity and cancer are rife, the quality of analysis has often been weak, say a team of researchers at Imperial College London.
In order to provide finer detail of those at most risk, an umbrella evaluation was carried out on 204 studies into adiposity and its link with 36 forms of cancer.
Of those evaluated, researchers found that strong evidence supports the link with only 11 types of cancer.
These were: oesophageal, multiple myeloma (cancer of white blood cells), cancers of the gastric cardia (stomach), colon, rectum, biliary tract system (bile duct), pancreas, breast, endometrium (uterus), ovary, and kidney.
Statistical analysis was carried out to reveal discrepancies and evidence of bias between studies.
The report concluded that besides the connections they found to be strong, ‘Other associations could be genuine but uncertainty remains’, and called for further research.
The report showed that increases of just several kilograms in body weight can significantly increase the chance of developing cancers.
Risk of postmenopausal breast cancer for example, was shown to increase by 11% for every 5kg gained. Similarly, the risk of colon cancer in men increases 36% for every 5kg increase in body mass index (BMI).
Maria Kyrgiou, a co-author of the study, told FoodNavigator: “Being overweight or obese causes disruption in many hormonal and metabolic pathways. Excess adiposity has been linked to higher oestrogen levels, higher insulin levels and increased inflammation, all of which can affect cell division and therefore cancer development. Reducing the obesity epidemic by tackling the factors that predispose to it, including eating, drinking and exercise habits to mention few, as early as possible would obviously be of utmost importance.”
Obesity is one of the principle health issues worldwide. World Health Organisation data shows that one in three children aged 11 in the European region are overweight or obese.
In the UK, 68% of men and 58% of women are obese. The burden on health, labour and care is thought to cost tens of billions.
The researchers advised that policy makers need to focus on obesity prevention programmes at young ages, as soon as possible.
Source: British Medical Journal
Published online ahead of print, DOI: https://doi.org/10.1136/bmj.j477
"Adiposity and cancer at major anatomical sites: umbrella review of the literature"
Authors: Maria Kyrgiou et al.