Tuesday October 9 2007
Are hormones in the womb to blame?
The width of your mother’s hips can influence your risk of developing breast cancer, reported the Daily Mail today. Research has shown that “women whose mothers have wide hips could be seven times more likely to develop breast cancer,” it said.
Daughters have a 60% increased risk of developing breast cancer if their mother has wide hips, and if they are a younger sibling and were carried to full term, they may be seven times more likely to develop the disease, the newspaper said. Apparently, this may be accounted for by women with wider hips who have higher levels of sex hormones, to which the developing baby is exposed. This may affect developing breast tissue. Professor Barker, the lead researcher on this study is reported as saying that these results “could lead to the development of a drug that prevents breast cancer in just three years”.
This is the latest in a series of links that have recently been made between breast cancer and other factors. This study has several limitations and the idea that breast cancer is linked to the levels of hormone exposure during pregnancy, and whether these levels are directly reflected by the mother’s hip measurements, is only tentative. There is not enough evidence to suggest to women with wide hips that they could be a risk factor for their daughter developing breast cancer. It is also difficult to establish how these findings might suggest a way of preventing breast cancer.
Where did the story come from?
David J.P. Barker of Oregon Health and Science University, Oregon, USA, and colleagues from Britain’s University of Southampton, National Public Health Institute, Helsinki and University of Helsinki, Finland, carried out this research. Funding was provided by Academy of Finland, British Heart Foundation, and several other Finnish research foundations and institutes and it was published in the peer-reviewed medical journal American Journal of Human Biology.
What kind of scientific study was this?
This was a study that was designed to investigate the idea that the risk of breast cancer develops through a baby’s exposure to the mother’s circulating hormones while in the womb. They suggest that a larger pelvic width in the mother is a result of higher amounts of sex hormones being present at puberty and that these higher levels of hormones persist throughout life.
The researchers used data from the large Helsinki Birth Cohort Study, which followed 6,370 women who were born in Helsinki between 1934 and 1944; babies’ birth measurements were recorded in addition to gestational age (calculated from the date of the mother’s last period). Of all the women in the original study, 4,102 of the records included the mother’s hip measurements. The authors report that as these measurements were taken to assess the risk of obstruction during labour, these were more likely to be younger women who were having their first baby.
The researchers then looked to see how many of the adult daughters were hospitalised or died from breast cancer, as recorded by the national hospital discharge register and national mortality register in Finland between 1971 and 2003. The authors used statistical methods to assess the risk of developing breast cancer depending on variables of the mother’s characteristics, the baby’s birth measurements and length of gestation.
What were the results of the study?
The authors report that of the women for whom the mother’s hip measurements were available, 206 of these developed breast cancer.
They also report that when the difference between two hip measurements (the width of the lower part of the hips, and the width of the uppermost part of the hips, between the crests of the hip bones) was increased to more than 2cm (1in), then there was a two times increased risk of breast cancer.
When they looked at the link between length of gestation and breast cancer, they found that the risk increased slightly when the gestation fell below 36 weeks and increased slightly again when gestation rose above 41 weeks. When the breast cancer cases were grouped into whether the baby was born at less than or more than 40 weeks and according to the measurement between hip crests, they found that the risk was increased to nearly four times if the baby was born at above 40 weeks and the distance between hip crests was more than 30cm (12in). When they excluded the women who were first-born babies and only looked at those with elder siblings, the risk increased to seven times.
What interpretations did the researchers draw from these results?
The authors conclude that a wider distance between the hip crests and a greater difference between the two hip measurements taken (indicating the roundness of the hip crests), “predicted increased risk of breast cancer among the daughters”. They say that this is a result of growth during puberty, which is directly under hormonal control, and that “high levels of sex hormone production in puberty persist after puberty and adversely affect the mammary development of the daughters in early gestation”.
What does the NHS Knowledge Service make of this study?
The findings of this study are not reliable enough to suggest that the pelvic width of the mother, or the exposure to circulating female hormones while they were in the womb, can increase a woman’s risk of breast cancer. There are many limitations to this study.
- The researchers looked at a relatively small number of women with breast cancer, for whom they had the mothers’ hip measurements available, and then carried out various statistical risk calculations in groups. Initially, according to different hip measurements, gestational age, and then in combinations of gestational age, hip measurements and whether the mother had had previous children, to try to find significant links. Performing multiple statistical tests increases the likelihood that a link will be found, but not necessarily a reliable one. Also, the numbers of women who fell into some of the groups used in the analysis were relatively small, and smaller numbers in groups also increase the likelihood that differences can be found by chance.
- In the course of this 10-year study of births, hip measurements would have been taken by a large number of midwives with varying levels of experience. The consistency and accuracy of these measurements is likely to be questionable. In addition, the reliance upon the last period as the only method of determining the baby’s gestational age is also likely to lead to considerable inaccuracy.
- Potential risk factors for breast cancer in the affected women have not been considered by the researchers, such as family history, hormone therapy, or breast-feeding history. If these factors were imbalanced between the groups of women with different hip measurements, they could explain the apparent differences in risk.
- Hormone levels are known to alter during pregnancy: taking hip measurements as a rough indicator of the level of hormones present when the mother was in puberty is not a reliable indicator of her hormone levels as an adult during pregnancy.
- The birth cohort was taken from a period when there were higher degrees of malnourishment and food shortages than there are today, both amongst the daughters and the mothers when they were growing up. This may have affected pubertal growth, amongst other things, and may affect the general overview of these results to women today.
Sir Muir Gray adds...
Breast cancers, like all cancers, result from the interplay of genetic and environmental factors and the levels of hormones of the pregnant women’s blood are part of the environment of the foetus. The relationship between hormone levels throughout the life of the foetus, child and woman and the probability of breast cancer is becoming clearer and is already leading to treatment options. However, the female children of women with large hips do not have any specific action that they can take; they should consider the offer of screening seriously because that is one proven means of reducing risk.