Further evidence of a link between obesity and breast cancer has been uncovered in a new study examining the protective effects of a hormone.

A study in the US into mice and breast cancer cells has shown that low levels of a protein hormone called adiponectin or Acrp30 may help to trigger the disease.

Crucially, it has been shown in the past that levels of the hormone, found in body fat, increase when people lose weight.

The research by scientists at the Hormel Institute, the University of Minnesota, and published in the British Journal of Cancer, examined the role played by two different forms of Acrp30 - full length - Acrp30 - and globular - gAcrp30 - in tumour growth.

The research found the hormone may protect against oestrogen receptor positive tumour development when levels are high. It is also likely that a balance between the growth factor leptin and Acrp30 determines whether a tumour increases or decreases in size. High levels of leptin and the hormone oestrogen can encourage breast cancer growth, according to past research.

Postmenopausal women who are overweight are at greater risk of developing breast cancer, as large amounts of body fat secrete much higher levels of oestrogen and leptin.

Lead researcher Professor Margot Cleary said: “In the developed world, as the average body mass index climbs, it’s vital that we understand the interaction of adiponectin with other growth factors such as leptin in breast cancer spread.

“Our findings indicate that adiponectin, which is released from fat tissue, may protect against oestrogen receptor positive tumour development when levels are high. It’s also likely that a balance between leptin and Acrp30 determines whether a tumour increases or decreases in size.”

Dr Lesley Walker, director of cancer information at Cancer Research UK, said: “We’ve known for some time that the overproduction of oestrogen in women who are overweight can play a part in the development of different types of breast cancer.

“This study, which examines how obesity-linked proteins interact, adds to the compelling evidence that maintaining a healthy body weight can help prevent disease.”