Immaterial of their menopausal and hormone receptor status, Indian women who have a high waist-to-hip ratio (central obesity) of over 0.95 have three times higher risk of breast cancer than those who have waist-to-hip ratio of less than 0.84, according to a study published on August 30 in the European Journal of Cancer. The association was found even after body mass index (BMI) effect was adjusted.

Studies have already found that BMI is consistently associated with increased risk of breast cancer in postmenopausal women but decreased risk for premenopausal in Caucasians and Asian population. And central obesity or abdominal obesity — excessive abdominal fat around the stomach and abdomen — has also been associated with increased risk of breast cancer in postmenopausal women but its effect on premenopausal women varies in different ethnic groups.

“Breast cancer is a heterogenous disease but in our study we found that abdominal obesity was responsible for all types of breast cancer in both premenopausal and postmenopausal women. In fact, there is nearly three times increased breast cancer risk in women who have high central obesity,” says Dr. Rajesh Dikshit, the corresponding author of the paper from Tata Memorial Centre, Mumbai, India.

Higher abdominal obesity might be the reason for increasing trend in breast cancer cases in urban areas.The second important finding of the study was that even in those with normal BMI but high abdominal obesity, the risk of breast cancer was three times higher. “In India, it is common to see people with normal BMI having high central obesity.  So BMI is not a sensitive marker for obesity in the Indian ethnic population,” he says. This has been seen in several diabetes-related studies as well.

Another interesting finding of the study was the association of low BMI but higher abdominal obesity and increased risk of breast cancer irrespective of the menopausal status. It is well known that Indians with even low BMI have high abdominal obesity.  In the study, nearly 18 per cent of controls had low BMI but a high wait-to-hip ratio.

“Most Indian women have low birth weight and higher weight at age 20 years. An increase in body size from age 10 to 20 years is thus indicative of accelerated growth in childhood which may result in increased adiposity and insulin resistance influencing breast cancer risk,” they write.

“Obesity is associated with inflammatory response, and inflammatory response, in turn, starts the cell proliferation process,” Dr. Dikshit says. The greater the cell proliferation, the greater the chances of something going wrong and cancer setting in.

The number of women with breast cancer in urban areas is twice that of rural areas. “Breast cancer trend is increasing in the urban areas.  Central obesity could be the reason,” Dr. Dikshit says. The good news is that abdominal obesity can be controlled thereby reducing the risk of breast cancer.

The study was carried out in 1,633 breast cancer patients and 1,504 controls who visited Mumbai’s Tata Memorial Centre between 2009 and 2013. The researchers measured BMI, waist-to-hip ratio and other anthropometric measurement at the time of enrolment. The participants were then shown a pictogram for body size at different ages and asked to recall their body size and chose the pictogram that best depicted their size. Pictograms were used to understand the increase in body size at two stages — from age 10 to 20 and from age 20 to age at the time of enrolment.

“We found very good correlation between pictogram and current BMI. So if we see a sudden increase in weight between age 10 and 20 then there is higher breast cancer risk,” he says, explaining how the pictogram was used in the study.

“Our study is suggestive as it relies on recall. But that’s the only way to carry out the study as otherwise we must wait for 40 years to complete it,” he adds.

Published in The Hindu on September 5, 2016