Breast Cancer: Teen Fruit Consumption Linked to Lower Risk

Diana Phillips

May 16, 2016

An apple a day may do more than keep the doctor away: A new study looking at fruit and vegetable consumption in teenagers and young adults links higher fruit intake with a lower risk for breast cancer.

In an analysis of prospective data from the Nurses' Health Study II cohort, the consumption of 2.9 servings of fruit per day during adolescence was associated with a 25% reduced risk for breast cancer compared with the consumption of 0.5 servings of fruit daily.

The finding, reported in article published online May 11 in the BMJ by Maryam S. Farvid, PhD, from the Department of Nutrition at the Harvard T.H. Chan School of Public Health in Boston, Massachusetts, and colleagues adds to a growing body of literature suggesting the importance of food choices during adolescence. Earlier this year, Dr Farvid and team reported that women in the highest quintile of fiber intake during early adulthood had a relative risk for breast cancer of 0.81 (95% confidence interval [CI], 0.72 - 0.91) compared with women in the lowest quintile of fiber intake.

That study also analyzed data from women in the Nurses' Health Study II cohort. Women who consumed high levels of fiber during adolescence had a 24% reduced risk of developing breast cancer before menopause compared with those who ate low levels of fiber, and the lifetime risk of developing breast cancer was reduced by 16% in the high-fiber group.

The current analysis reflects data from 90,476 premenopausal women aged 27 to 44 years from Nurses' Health Study II who completed a questionnaire on diet in 1991, 44,223 of whom completed an additional questionnaire in 1998 about their diet during adolescence. The investigators looked at total fruit and vegetable consumption during adolescence and early adulthood, and they also looked specifically at intake of fruits and vegetables rich in α carotene in the study population. In addition to breast cancer incidence in the study population, the investigators also considered tumor hormone receptor and menopausal status at diagnosis.

In total, 3235 women developed invasive breast cancer over the course of 22 years of follow-up, including 1347 women for whom adolescent dietary information was available. The researchers assessed fruit intake by quintile. The hazard ratio for breast cancer risk for the highest vs lowest quintile of fruit intake was 0.75, the authors report. "Although women in third and firth category seemed to have a similar lower risk compared with those with the lowest intake, a test for non-linearity was not significant," they write.

"If this apparent risk reduction is applied to lifetime risk of breast cancer, the absolute number of breast cancers that could potentially be prevented by higher intake of fruits would be substantial," the authors explain.

The association for fruit intake during adolescence was independent of fruit intake during adulthood, and there was no association between breast cancer risk and either total fruit intake in early adulthood or total vegetable intake in either adolescence or early adulthood, the authors report.

In the analyses by fruit and vegetable type, "higher intake of fruits and vegetables rich in α carotene during early adulthood was specifically associated with lower risk," the authors write. "The associations with breast cancer differed significantly among individual fruits and vegetables: greater consumption of apple, banana, and grapes during adolescence, as well as oranges and kale during early adulthood, was significantly associated with a reduced risk."

Looking at the association between fruit intake and tumor type, the investigators observed that the association between adolescent fruit intake and reduced breast cancer risk was stronger for both estrogen- and progesterone-receptor-negative cancers (hazard ratio [HR], 0.70; 95% CI, 0.57 - 0.86, per serving/day) compared with both estrogen- and progesterone-receptor-positive cancers (HR, 0.91; 95% CI, 0.83 - 1.00) and estrogen-receptor-positive and progesterone-receptor-negative cancers (HR, 1.03; 95% CI, 0.82 - 1.29).

Although the relationship between diet and breast cancer has been studied for decades, with inconsistent results, much of the research has relied on dietary assessments during midlife or later, the authors note.

In an accompanying editorial, Timothy J. Key, PhD, and Gillian K. Reeves, PhD, from the Cancer Epidemiology Unit of the Nuffield Department of Population Health at the University of Oxford in England, point to examples "of other factors measured at early ages" that affect lifetime breast cancer risk. "For example, early menarche increases breast cancer risk, and there is evidence that relative fatness during childhood and adolescence is associated with a reduction in lifetime risk of breast cancer."

The variation in the association between adolescent fruit intake and breast cancer risk by hormone receptor status is of particular interest, according to the editorialists, "because a few recent studies have raised the possibility that diet could influence the risk for specific subtypes of breast cancer."

Although more evidence is needed to draw conclusions about whether adolescent fruit intake protects against breast cancer, "these foods have well known beneficial effects on health, and efforts should continue to increase intake of both fruit and vegetables at all ages," the editorial authors write.

The study authors agree that further studies are warranted to examine the relationship between diet in early life and breast cancer risk.

"Our findings are in line with cancer prevention recommendations to consume more fruits and vegetables and support the adoption of these behaviors in early life," the authors write.

This study was supported by grants from the National Institutes of Health and from the Breast Cancer Research Foundation. Dr Farvid was supported by the Japan Pharmaceutical Manufacturers Association. The editorial authors are supported by Cancer Research UK.

BMJ. Published online May 11, 2016. Article full text, Editorial full text

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