Poor diet during teens, early adulthood may raise breast cancer risk

The risk of developing premenopausal breast cancer may be higher for women who have a poor diet during adolescence and early adulthood, new research finds.

Previous studies have associated an unhealthful diet - particularly one that is low in vegetables, high in refined sugar and carbohydrates, and high in red and processed meats - with chronic inflammation, which may raise the risk of certain cancers.

According to the new study, it is this diet-induced inflammation that may increase a woman's risk of breast cancer prior to menopause.

Study co-author Karin B. Michels, Ph.D. - professor and chair of the Department of Epidemiology at the Fielding School of Public Health at the University of California-Los Angeles - and colleagues recently reported their findings in the journal Cancer Epidemiology, Biomarkers & Prevention.

After skin cancer, breast cancer is the most common cancer among women in the United States. This year, around 252,710 new cases of invasive breast cancer will be diagnosed, and more than 40,000 women will die from the disease.

"About 12 percent of women in the U.S. develop breast cancer in their lifetimes," notes Michels. "However, each woman's breast cancer risk is different based on numerous factors, including genetic predisposition, demographics, and lifestyle."

For this latest study, Michels and colleagues set out to determine how a pro-inflammatory diet during adolescence or early adulthood might influence women's risk of breast cancer in later life.

Up to 41 percent greater breast cancer risk with pro-inflammatory diet

The researchers analyzed the data of 45,204 women who were part of the Nurses' Health Study II.

Some of the women completed a food frequency questionnaire in 1991, when they were aged between 27 and 44 years, which disclosed details of their diet in early adulthood. The questionnaire was completed again every 4 years thereafter.

In 1998 - when aged between 33 and 52 - some women completed a food frequency questionnaire that detailed their diet during high school.

Using a technique that associates food intake with markers of inflammation in the blood, the researchers allocated an inflammatory score to each woman's diet. The women were then divided into five groups based on their inflammatory score.

Compared with women who had the lowest inflammatory diet score during adolescence, those who had the highest score were found to be at a 35 percent higher risk of developing premenopausal breast cancer.

Women with the highest inflammatory diet score during early adulthood were found to have a 41 percent increased risk of premenopausal breast cancer, compared with those who had the lowest inflammatory diet score.

A pro-inflammatory diet was not associated with the overall incidence of breast cancer or the risk of postmenopausal breast cancer, the team reports.

Although the study cannot prove cause and effect between a pro-inflammatory diet during adolescence or early adulthood and premenopausal breast cancer, the team believes that the results further highlight the importance of a healthful diet.

"Our study suggests that a habitual adolescent/early adulthood diet that promotes chronic inflammation may be another factor that impacts an individual woman's risk.

During adolescence and early adulthood, when the mammary gland is rapidly developing and is therefore particularly susceptible to lifestyle factors, it is important to consume a diet rich in vegetables, fruit, whole grains, nuts, seeds, and legumes and to avoid soda consumption and a high intake of sugar, refined carbohydrates, and red and processed meats."

Karin B. Michels, Ph.D.

There are a number of limitations to the study. For example, participants reported their adolescent diet years later, so their recollections could be subject to error. Additionally, the researchers did not have access to subjects' measurements of inflammatory blood markers during adolescence or early adulthood.

Learn how exercise is the best lifestyle change for reducing breast cancer recurrence.