Alcohol followed by cigarettes are the next things that also appear to affect hormone levels.
The Cancer Research UK funded study examined how levels of sex hormones* – known to affect breast cancer risk – varied among post menopausal women. Some types of breast cancer are fuelled by the female sex hormone oestrogen. The analysis combined the records of nearly 6,300 post menopausal women from 13 different studies.
Age, type of menopause (natural or caused by surgery to remove ovaries), body mass index (BMI – the measure indicating normal weight, overweight or obesity), smoking, alcohol and reproductive factors were all examined by the researchers based at the University of Oxford.
They found the biggest influence on sex hormone levels was BMI scores. The biggest increases were for oestrogens, and this increase in oestrogen may explain why post menopausal, obese women are at higher risk for breast cancer.
Women who drank 20g of alcohol or more per day (around two and a half units) had higher levels of all hormones. One alcohol unit is measured as 10ml or 8g of pure alcohol. A large 250ml glass of wine (12 per cent) is 3 units of alcohol. The higher oestrogen levels may contribute to the increased risk of breast cancer in regular drinkers.
Women who smoked 15 cigarettes a day also had moderately higher levels of all hormones than non-smokers, with the largest difference for testosterone.
Dr Gillian Reeves, a co-author of the study and based at the University of Oxford, said: “Our study shows that changes in hormone levels might explain the association of established risk factors such as obesity with breast cancer risk. Other studies have found that weight and alcohol can affect hormone levels and this research confirms and adds to these findings and provides more information about how breast cancer develops.”
Dr Julie Sharp, Cancer Research UK’s senior science information manager, said: “There’s already strong evidence that drinking alcohol and being overweight can increase the risk of breast cancer but it’s important to understand why these links exist. This is an important study as it helps to show how alcohol and weight can influence hormone levels. Understanding their role in breast cancer is vital and this analysis sheds light on how they could affect breast cancer risk.
“We know that the risk of the disease can be affected by family history and getting older, 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.”
For media enquiries contact the Cancer Research UK press office on 020 3469 8300 or, out of hours, on 07950 264 059.
Notes to editors
* Sex hormones examined in this study included: Oestradiol, Free oestradiol, Oestrone, Androstenedione, Testosterone, Free testosterone. Levels of dehydroepiandrosterone sulphate (DHEAS), sex hormone-binding globulin (SHBG) were also examined.
Sex steroids in women are made generally by the ovaries, by adrenal glands or in fat tissue.
BMI is calculated by dividing weight by height.
- Under 18.5 is underweight
- 18.5-25 is healthy weight
- 25-30 is overweight
- 30-35 is obese
- Over 35 is very obese.