Weighing Evidence: Obesity and Breast Cancer Risk Across Life

by Hank Dart

In a paper published yesterday in the journal Science Translational Medicine, Cancer News in Context's Graham Colditz and Washington University researcher, Kelle Moley, detail the important role that overweight and obesity play in the development of breast cancer.

Looking at wide-ranging evidence at all periods of life -- from gestation to the years after menopause -- Colditz and Moley show that despite some targeted times in youth, excess weight increases breast cancer risk over the course of a woman's life.

In the womb.  Though there is still a great deal to learn about the impact of mother's weight on her daughter's adult risk of breast cancer, larger weight gain during pregnancy has been linked with a higher risk of breast cancer in daughters.  The more a daughter weighs at birth has also been found to increase risk.   

Infancy and childhood.  Overweight in this period of life likely has a mixed impact on adult breast cancer risk.  It can lower breast density as well as slow the rate that girls grow to their maximum height -- each of which can reduce breast cancer risk.  At the same time, being overweight in childhood can lead to earlier first periods (menarche), which is an important breast cancer risk factor. 

Adolescence.  The lower risks linked to childhood overweight likely continue through the adolescent years.  

Premenopause.  While the protection against breast cancer from youth overweight likely persist, adult weight gain in the years before menopause can increase risk, offsetting and likely surpassing protection from youth. 

Postmenopause.  Evidence has long-shown that overweight and weight gain after menopause increases the risk of breast cancer.  

Though there are a number of possible reasons why overweight influences breast cancer risk, it's impact on hormone levels and related responses at various stages of life is a major part.

Despite some periods in life where overweight may have a beneficial effect on breast cancer risk, its overall impact is certainly negative.  And the best approach is to maintain a healthy weight throughout life - from childhood on.   Weight often tracks children and adults throughout life.  Overweight youth are more likely to become overweight adults, and overweight young adults are more likely to be overweight in later life.

For adults who are overweight, though, there is good evidence that losing weight and keeping it off can significantly lower breast cancer risk as well as the risk of other important diseases, like heart disease and diabetes.

Here in Cancer News in Context, we've previously highlighted some straightforward -- and a few off-kilter -- tips for keeping weight in check, most recently during our series, 9 Days of Practical Steps to Prevent Breast Cancer. Perhaps less familiar for many is knowing how best to approach weight and breast health issues of their children.  The focus should be on helping children be active, eat a largely plant-based diet, and avoid tobacco and alcohol.  Hardest for many parents is simply recognizing if their child has a weight issue -- so making an effort to understand where their child falls on growth charts can be really important in helping them maintain a healthy weight in their youth, and beyond. A good place to start for questions about childhood weight is the CDC’s BMI Calculator for Child and Teen. For more on breast health approaches for youth, see The Power of Youth: Beginning Breast Cancer Prevention in Childhood.

Study Finds Periods Start Earlier in Girls Who Drink a Lot of Sugary Drinks. What Does This Mean for Breast Cancer Risk?

Creative Commons photo (cropped): Flickr/zingersbs

by Hank Dart

A new study released last week in the journal Human Reproduction has found that regularly drinking sugar-sweetened beverages - like sodas and fruit drinks - may cause girls to start their menstrual periods at earlier ages.  

The study, a spin off of the long-running Nurses' Health Study at Harvard University, followed around 5,000 9 - 14 year old girls for up to five years - tracking their food, beverage intake, and menstrual status along the way.  Researchers found a distinct link between regularly drinking sugary beverages and the age periods started (technically called, menarche).  Those girls who drank more than 1.5 servings of soda or fruit drink each day started their period on average at 12.8 years, about three months earlier than girls drinking 2 or fewer servings each week. Even after taking body mass index (BMI) into account, which is linked to age at menarche,  the same general association remained.

So, what does this have to do with cancer?

There's increasingly good data that early life plays a particularly important role in later adult breast cancer risk, something we've certainly written about here on CNiC.  This new study provides further evidence that the choices our children make - and that we help them make - can have implications later in life.  The earlier menarche begins, the greater the lifetime exposure to estrogen and other reproductive hormones, which is a key risk factor for breast cancer.

And while the age differences at menarche weren't huge in this new study - meaning the impact of sugary drinks on overall breast cancer risk would likely be modest - cutting back on sodas and fruit drinks still provides an easy way to help lower risk, which when combined with other healthy choices in youth - like choosing plant-based foods and getting regular exercise - can have an important overall impact on later breast health.

A healthy lifestyle started in mid-life - when most women are likely to actually start thinking in earnest about their breast health - can cut the risk of breast cancer by 50 percent.  Starting healthy behaviors in childhood and continuing them throughout adulthood can cut risk by close to 70 percent (see figure). And the steps are surprisingly simple, with one of the easiest being substituting water for sugary sodas and fruit drinks.

[Small text edit, Feb 5, 2015]