By Kathleen Doheny
WEDNESDAY, Sept. 24, 2014 (HealthDay News) -- If you want to minimize your chances of developing breast cancer, staying the same skirt size over the years might help, a new study suggests.
"Our study has shown that an increase of one size every 10 years between 25 and postmenopausal age [over 60] is associated with an increase of breast cancer [risk] in postmenopausal women by 33 percent," said lead researcher Dr. Usha Menon, head of the Gynecological Cancer Research Center at University College London.
The findings are based on information from nearly 93,000 women enrolled in a British database for cancer screening. When the women entered the study between 2005 and 2010, all were over age 50. None had a diagnosis of breast cancer.
At age 25, the women's average skirt size had been an 8. When they entered the study, at the average age of 64, the average size was a 10. Three out of four women reported increased skirt sizes.
The risk of breast cancer increased 77 percent if the skirt size went up two sizes every 10 years from 25 until women were past menopause, Menon said.
The study is published online Sept. 24 in BMJ Open.
The women provided information about their height and weight, so body mass index (BMI) could be calculated. They also gave details about other factors that could affect breast cancer risk. This information included fertility, family history of breast or ovarian cancers and reproductive information, along with use of hormonal birth control and hormone replacement therapy.
When they entered the study, the women told their current skirt size and what it had been in their 20s.
The researchers monitored the women for three to four years, asking more questions about general health and any cancer diagnosis. During that time, 1,090 women were diagnosed with breast cancer.
While risk factors such as family history and use of hormone replacement were linked with an increased risk, as expected, increases in skirt size emerged as the strongest predictor, Menon said.
"This is an observational study and no definitive conclusion can be drawn about cause and effect," Menon stressed. Changes in skirt sizing over the years also need to be taken into account, she added.
Skirt size served as a "proxy" for abdominal weight gain, Menon explained. The investigators found it was a better predictor of risk than BMI -- a ratio of weight to height -- alone.
Needing a bigger skirt size reflects an increase in abdominal fat, Menon said. The exact mechanism between increased abdominal fat and higher breast cancer risk needs more study, Menon said. But it is known that obesity increases the amount of estrogen in the body, which many breast cancers need to grow.
"Previous studies suggest that body fat around the waist is metabolically more active than fat tissue elsewhere in the body," she said.
Dr. Leslie Bernstein, director of cancer etiology at the City of Hope Cancer Center in Duarte, Calif., said the study findings make sense. She recalled a long-ago study that evaluated the uniform sizes of bus drivers and train conductors to see who gained the most weight and then evaluated their heart disease risks.
The conductors, who worked on their feet, didn't increase their uniform sizes as much as the bus drivers, who sat all day, she said, and the conductors were at lower risk of heart disease.
The skirt study uses the same sort of surrogate marker to measure weight gain, especially around the middle, Bernstein said. She, too, emphasized that the study only found an association, not a cause-and-effect link. "Of course we can't say this is the final answer," she added.
Also, sizing in the United States has become more generous in recent years, so accounting for that would likely make the association between increasing skirt sizes and breast cancer risk stronger, she said.
Using clothing size as a surrogate to study risk may produce more accurate data than asking people to measure their waists, as some studies have done, Bernstein noted.
"People are less likely to think about how to fudge it," she said. Also, most people remember what size they wore at specific ages, she added.