Weight has the strongest effect on the sex hormones that increase breast cancer risk in post menopausal women, according to new research published in the British Journal of Cancer this week.

Alcohol, followed by cigarettes, are the next factors that appear to have a strong effect on hormone levels, said co-author Dr Gillian Reeves from the University of Oxford in the UK, and colleagues, all members of the Endogenous Hormones and Breast Cancer Collaborative Group.

Reeves told the press that:

“Our study shows that changes in hormone levels might explain the association of established risk factors such as obesity with breast cancer risk.”

She explained that while other studies have already suggested weight and alcohol are strong influencers of hormone levels, this study confirms that is the case, and also reveals some insights into how breast cancer develops.

Women’s bodies make their sex hormones in the ovaries, the adrenal glands and also in fat tissue.

Women with the highest levels of oestrogen and related hormones have more than double the average risk of breast cancer, which is now the most common cancer in the UK, where over 100 women are diagnosed with the disease every day. Men also get breast cancer but it is very rare.

For this Cancer Research UK funded study, Reeves and colleagues pooled and analyzed data on nearly 6,300 post menopausal women who took part in 13 different studies, to examine how levels of sex hormones, known to affect the risk of developing breast cancer, varied among them.

Their analysis included the following hormones: Oestradiol, Free oestradiol, Oestrone, Androstenedione, Testosterone, Free testosterone. They also examined levels of dehydroepiandrosterone sulphate (DHEAS), sex hormone-binding globulin (SHBG).

The factors they analyzed as potential drivers of hormone levels were: age, whether menopause was brought on naturally or by surgery to remove ovaries, BMI (body mass index), smoking, alcohol and reproductive factors, such as age at menarche (when a woman starts having her periods) and age at first full term pregnancy.

They found BMI had the strongest influence on sex hormone levels, and on oestrogens in particular. They said this might be why post menopausal, obese women have the highest risk of developing breast cancer.

They also found that women who drank 20g or more of alcohol on a daily basis (that is about 2.5 units) had higher levels of all the hormones they examined. (A large 250 ml glass of wine at 12% strength contains 3 units, or 24g, of alcohol.)

This may explain why regular drinkers have a higher risk of breast cancer.

The results also showed that women who smoked 15 or more cigarettes a day had moderately higher levels of all hormones compared to non-smokers, with testosterone showing the biggest difference.

The researchers also found that:

“Hormone concentrations were not strongly related to age at menarche, parity, age at first full-term pregnancy or family history of breast cancer.”

They concluded that:

“Sex hormone concentrations were strongly associated with several established or suspected risk factors for breast cancer, and may mediate the effects of these factors on breast cancer risk.”

Dr Julie Sharp, senior science information manager at Cancer Research UK, said while there already was strong evidence of links between weight, alcohol and breast cancer risk, we also need to understand why they exist, and this study is important because it shows how alcohol and weight interact with hormone levels to influence the risk.

“Understanding their role in breast cancer is vital and this analysis sheds light on how they could affect breast cancer risk,” she added.

Sharp explained that we already know that family history and age are risk factors for breast cancer, and we can’t change those, but “there are also things women can do help reduce the risk of the disease”:

“Maintaining a healthy body weight and reducing alcohol consumption are key to reducing breast cancer risk,” she added.

“Circulating sex hormones and breast cancer risk factors in postmenopausal women: reanalysis of 13 studies.”
Endogenous Hormones and Breast Cancer Collaborative Group.
British Journal of Cancer, Advance online publication 19 July 2011; doi: 10.1038/bjc.2011.254
Link to Article.

You can calculate your BMI using our BMI Calculator.

Additional source: Cancer Research UK.

Written by: Catharine Paddock, PhD