High oestrogen levels among well-fed and largely inactive women in Western countries may be largely responsible for the epidemic of breast cancer. Tests show that oestrogen is far more prevalent in modern Western women than in those from less developed societies.
Far from being normal, the amounts of oestrogen found in women in Britain and other developed countries are, in historical terms, highly abnormal.
Dr Tessa Pollard, a lecturer in biological anthropology at the University of Durham, told the British Association for the Advancement of Science conference in Manchester, north west England, that it was probably only in the past 50 years that the levels had increased so much.
Dr Tessa Pollard suggests that affluent lifestyles and rich Western diets during pregnancy could be responsible for producing high levels of oestrogen in girls, who go on to keep those high hormonal levels for the rest of their lives.
Studies in Mali and the Congo had shown that African women in subsistence economies are exposed to much less oestrogen during their lifetime than are Western women. Among the Dogon people of Mali, women typically experience about 110 menstrual cycles in a lifetime. British women have about 400.
The difference is that Dogon women typically have eight or nine children and breastfeed them all. Breastfeeding halts the menstrual cycle and reduces production of oestrogen, so there are long spells when Dogon women are not exposed to it. British women have one or two children on average and breastfeed for shorter periods. In addition, women in rich countries start their periods sooner and end them later. A good diet and leisure also increase oestrogen. One in nine women in Britain can expect to suffer breast cancer.
Dr Pollard said her work was looking at whether a woman’s early environment in the womb and early childhood helped set her oestrogen levels for life.
Dr Pollard is carrying out a study in Newcastle upon Tyne, focusing on women from Pakistan, to prove her theory. She is also working with another researcher, in London to focus on Bangladeshi immigrant women.
Dr Pollard said: “In today’s world women’s environments are much more likely to change dramatically than in our evolutionary past.”