Dr Melina Arnold: We know, for example, that in males in very highly developed countries, there's about 3-3.2 percent of all cancer cases that are related to obesity and being overweight. And in low-developed countries we see it's close to zero - it's about 0.3 percent - that was our estimate for the low human development index (HDI).
Where do you see the biggest problems? But also, where are the biggest problems developing - where do we have to watch out?
We estimated this new proportion of cancer cases linked to high body weight for every country in the world, and for males and females. And we see that for males, for example, there's a really high burden in Czech Republic, where 5.5 percent of the country's new cancer cases have been linked to high body weight. And in females this was very high in Barbados, and also in Czech Republic, where we have about 12 percent of all new cancer cases in females being due to overweight and obesity. So females have a higher proportion of cancer cases.
And what sort of cancers are we talking about? Is there a link between obesity and being overweight to particular types of cancer?
The underlying mechanism differs a lot by cancer type. We know for breast cancer, for example, that one of the pathways is related to hormones that are produced by fat tissue and that can lead to cancer development. But this is the hormonal pathway, which is true for several cancer sites. For others, there are other underlying mechanisms for how obesity is linked to cancer.
People talk about women as having had a lot of success in raising awareness about breast cancer - men, on the other hand, have not had a lot of success in raising awareness about male-specific cancers. And so I wonder whether, if we highlight in a study such as this that women are most affected, men may take away the message that they don't have to worry. Do you not see that as a risk?
It is true that women are more affected, but that doesn't mean that men are not affected. They are affected, and there's a substantial number of new cancer cases in men that are related to being overweight, and obesity. It's just that common cancer sites in women, such as breast cancer and also cancer of the womb, have been linked to excess body weight. And because those are frequent cancers in most parts of the world, the proportion of cases of excess body weight in women is higher than in men. So I think prevention needs to take place for both sexes, and the strategies need to take place on the three levels - at the individual level, at the societal level, and also at the industrial level. So we need to raise awareness for everyone.
Could you run through those prevention strategies in a little more detail? We know that on a personal level it means eating healthily and being active, but what about on the societal and industrial levels?
On the societal level, individual responsibility can only have its full effect when people have access to a healthy lifestyle, and so the societal level is important to support individuals in following the recommendations from the World Health Organization (WHO) - to limit energy intake through fat and sugar, to increase consumption of fruit and vegetables, and to engage in regular physical activity. We need to create the environment to enable people to actually follow these recommendations. And we need sustained political commitment and the collaboration of many public and private stakeholders to make regular physical activity and healthy dietary choices available, and affordable, and especially accessible for the poorest individuals in society.
Is there an economic link to obesity, and by extension to cancer?
Well, what we're talking about here is the so-called lag time, which is the time between having a high body weight and developing cancer. It wouldn't occur tomorrow if you start being overweight today. So we will only know the full extent of the obesity-related cancer burden 10-20 years from now. Even if the average body-mass index (BMI) is… leveling off in some high-income countries in recent years, it is steeply increasing in the developing world, so we expect increases in the cancer cases that are related to this only in the future. So this is only the beginning.
Dr. Melina Arnold is a postdoctoral fellow at the International Agency for Research on Cancer (IARC) in Lyon, France. She is a co-lead author of the study "Global burden of cancer attributable to high body-mass index in 2012: a population-based study" published in The Lancet Oncology.