02.01.2016
Healthy eating in early adulthood may have protective effects

by Molly Walker

Participants in the Nurses’ Health Study II who ate healthier as teenagers and young adults had a lower risk of breast cancer as they aged, researchers said.

The hazard ratio for highest quintile of fiber consumption as adolescents and in early adulthood, versus the lowest, was 0.75 (95% CI 0.62-0.91, P=0.04 for trend), reported Maryam S. Farvid, PhD, of the Harvard T.H. Chan School of Public Health in Boston, and colleagues.

Among premenopausal women, this association was somewhat strengthened (relative risk 0.67 for highest versus lowest quintile, 95% CI 0.50-0.89, P=0.001 for trend), the authors wrote in Pediatrics. There was not a significant difference among postmenopausal women.

Farvid said that while the current study showed, for the first time, the role of an early-life diet high in fiber in reducing breast cancer risk, the results were not surprising given what is known about fiber intake and cancer risk.

“There is some evidence that mammary glands seem to be more susceptible to carcinogenic exposure during childhood due to rapid proliferation of cells and lack of terminal differentiation,” she wrote in an email to MedPage Today. “When we think about the modifiable risk factors, the first thing that comes to mind is about the role of diet on risk of breast cancer.”

The authors further examined fiber intake, and found that insoluble fiber and soluble fiber intake in early adulthood were both associated with reduced risk of breast cancer for women as adults (RR 0.80, 95% CI 0.71-0.90, P<0.001 for trend; and RR 0.86, 95% CI 0.77-0.97, P=0.02 for trend, respectively).

An accompanying editorial by Kathleen Harnden, MD, and Kimberly Blackwell, MD, both of Duke University in Durham, N.C., said that several recent studies have suggested a protective effect of fiber in the risk of breast cancer.

“Soluble fibers are believed to decrease intestinal cholesterol absorption, and there is emerging evidence that cholesterol byproducts may have estrogenic effects,” they wrote. “There is longstanding evidence that dietary fibers may reduce circulating estrogen levels through changes in the gut microbiome and increased excretion of estrogens in the gastrointestinal tract.”

In fact, Farvid’s team found that each 10 g/day increase in fiber intake in early adulthood was linked to a 13% reduction in the risk of breast cancer risk among all women (RR 0.87, 95% CI 0.80-0.95).

Farvid said that these results suggested women should increase their fiber intake early on in life rather than later in life, and said that clinicians could play a role in making this happen.

“Pediatricians (and any other types of clinicians) and dietitians could encourage teens and their parents to make sure they eat plenty of foods rich in fiber such as fruits, vegetable and whole grains at a young age,” she said.

The authors examined a cohort of 44,263 women from the Nurses’ Health Study II who had completed a questionnaire about their diet during high school. Among those, 1,118 women were diagnosed with invasive breast cancer. Women with a higher fiber intake when they were younger were also less likely to be associated with smoking and more likely to have earlier age at menarche, to be nulliparous and to be older at first birth. Higher fiber intake was also linked to lower alcohol consumption, lower adult BMI, and slightly higher rates of mammography screening.

Limitations include that the cohort is not a representative sample of U.S. women, and that the women were ages 33 to 52 years when they reported their adolescent diets. The authors also acknowledged the possibility of residual confounding.

The authors concluded that higher fiber intake during adolescence and young adulthood may be particularly important, but Farvid says additional research is still required.

“This is the first prospective study that shows the inverse association between a diet-high in fiber during adolescence and early adulthood and risk of breast cancer in later life,” she said. “Further study of the relation between early life diet and risk of breast cancer is needed.”

• Reviewed by Henry A. Solomon, MD, FACP, FACC Clinical Associate Professor, Weill Cornell Medical College and Dorothy Caputo, MA, BSN, RN, Nurse Planner

LAST UPDATED 02.01.2016