Researchers link obesity to more cancers

Obesity can double the risk of several cancers, according to a study published on Friday that for the first time also links being overweight with a number of less common forms of the disease.

The analysis of 144 published studies incorporating some 282,000 men and women also showed that gender can make a difference in the relationship between obesity and some cancers, the researchers reported in the Lancet medical journal.

The findings come after a major report from the World Research Cancer Fund in October showed that excess body fat was likely to cause some cancers, said Andrew Renehan, a cancer specialist at the University of Manchester, who led the study.

"This study has extended that further and reported specifically on 20 different types of cancer," he said in a telephone interview. "We showed an association with less common cancers that had not been shown before."

These included blood cancers such as adult leukaemia, multiple myeloma and non-Hodgkin's lymphoma for both men and women, he said.

Obesity is a major issue worldwide and also raises the risk of diseases such as type 2 diabetes and heart problems. The World Health Organisation classifies around 400 million people as obese.

Renehan and his colleagues looked at what happened to people whose body mass index (BMI) increased from the normal range to overweight or from overweight to obese.

BMI is a calculation of height to weight, and the normal range is usually considered to be 18 to 25, with more than 25 overweight and above 30 obese.

For men, the risk of thyroid cancer rose by a third and went up 24 percent for colon and kidney cancers, the researchers said. In women who went from normal to overweight, the risk of gall bladder cancer rose 59 percent and kidney cancer went up 34 percent.

"Increased BMI is associated with increased risk of common and less common malignancies," the researchers wrote. "For some cancer types, associations differed between sexes and populations of different ethnic origins."

The association of cancer and obesity was largely similar across Asia, Europe and North America, though the link between higher body mass index and breast cancer was higher in Asia, the researchers said.

There were also strong differences between men and women for cancers like bowel and kidney cancers. Knowing this kind of information could help scientists focus research on what is exactly causing some of these cancers, Renehan said.

"We suspect there are differences in changes in hormones due to the amount of fat cells in our body, and whether a person is a man or a woman," he said.