Study: Thin Girls Have Higher Breast Cancer Risk

Doctors have known for years that gaining weight can increase a woman's risk of getting breast cancer. But a new Swedish study indicates being thin in childhood may also be a risk factor.

CBS News Medical Correspondent Dr. Jennifer Ashton observed that the study is counterintuitive.

She explained researchers looked at almost 3,000 breast cancer patients and control subjects. What they found was the thinner a woman thought she was at age 7, the higher the risk for breast cancer later in life. Body size at 7 was also found to point to tumor types, specifically estrogen-sensitive types of breast cancer.

Special Section: Dr. Jennifer Ashton

Ashton said Karolinska Institutet researchers showed nine numbered figure drawings ranging from skinny to very heavy to the study's participants. The women assessed their own body type at present, then how they remembered themselves being when they were 7 years old. Relying on the women's memory may be a weakness of this study, Ashton noted.

"Early Show" co-anchor Maggie Rodriguez said this study seems to contradict other studies which say being heavier may increase your risk for breast cancer.

Ashton agreed, saying having a high birth weight and a high adult Body Mass Index have been shown to increase breast cancer risk.

She said, "Studies have shown both the increased risk of developing breast cancer and dying from it after menopause are believed to be due to increased levels of estrogen in obese women which can fuel breast cancer. Estrogen is also produced in fat tissue and, after menopause, when the ovaries stop producing hormones, fat tissue becomes the most important estrogen source."

Ashton continued, "Weight gain during adulthood has been found to be the most consistent and strongest predictor of breast cancer risk in studies in which it has been examined."

But this study's results may be explained, Ashton said, through the high levels of sex hormones overweight girls produce. Ashton said the hormones may have a protective effect on the breast tissue.

"One thought is the timing of exposure to estrogens and other hormones that may determine their effects on breast tissue," she said. "Higher levels of estrogens may be protective in the breasts of young girls, which are less likely to contain malignant cells, but harmful in older women, whose breasts are more likely to have acquired transformed cells."

However, Ashton said this should not make obesity among children OK.
"Breast cancer is an incredibly complex disease. Not one factor is wholly responsible for a woman's development of breast cancer. … This is a complicated issue and the researchers are certainly are not trying to imply that we should advocate overweight children as a protection against later breast cancer.
In fact, Ashton said other factors, such as alcohol consumption, may also affect a woman's risk of breast cancer.

Ashton said drinking may increase young women's chances of developing non-cancerous breast disease in their 20s and possibly breast cancer later in life.

She added, "A study just this week in Pediatrics says that young women who drank the most alcohol during their teen years were five times more likely to develop benign breast disease as young adults than girls who didn't drink alcohol, or drank less frequently."

To lower your risk of breast cancer, Ashton suggests these tips:
• Maintain healthy weight - Weight gain of 20 pounds or more after your teens (the age of 18) may increase your risk of breast cancer.

• Exercise - Exercise keeps weight down but also can reduce the level of circulating hormones that are associated with breast cancer-primarily estrogen and insulin. Doctors recommend exercising 45-60 minutes a day.

It's estimated that up to 30% of breast cancer cases could be decreased if women weighed less and exercised more frequently.

• Healthy diet - Eat more fruits and vegetables. Strive to eat at least five servings per day. Eat fewer high fat foods and sweets. Get plenty of calcium. Your body needs at least 1000 mg each day. You can get it from low-fat milk or yogurt, fortified fruit juices, spinach, kale or calcium tablets.
• Limit alcohol - The more you drink, the more you increase your risks of breast cancer. Try to keep your drinking in moderation - try to limit yourself to one drink per day. Those who have two to five drinks daily have about one and a half times the risk of women who drink no alcohol.

• Breastfeed - Breastfeeding does appear to protect against breast cancer, probably by affecting levels of estrogen in a woman's body. Some studies have shown that breast-feeding slightly lowers the risk, especially if the breastfeeding lasts one and a half to two years. This could be because breast-feeding lowers a woman's total number of menstrual periods, as does pregnancy.