Mixed Findings in Study of Vegetables and Breast Cancer Risk

Laurie Barclay, MD

October 27, 2010

October 27, 2010 — High vegetable consumption is associated with a significantly lower risk for estrogen receptor-negative/progesterone receptor-negative (ER-/PR-) breast cancer in black women, according to results from the Black Women's Health Study reported online October 11 in the American Journal of Epidemiology. However, there was no association of total fruit/vegetable intake with overall breast cancer risk, and the investigators suggest that their significantly positive finding of a lower risk for ER-/PR- breast cancer could possibly be due to chance as a result of multiple comparisons.

"This is an important finding because if confirms what we had seen earlier in our cohort of registered nurses who are predominantly white, specifically that higher intake of vegetables is associated with lower risk of ER- breast cancer," Walter Willett, MD, DrPH, chair of the Department of Nutrition at Harvard School of Public Health in Boston, Massachusetts, told Medscape Medical News when asked for independent comment. "If this is seen in just one study, we can't be confident that the results are not due to chance, but this finding provides strong support that this is real."

Deborah A. Boggs, from Slone Epidemiology Center at Boston University in Boston, Massachusetts, and colleagues prospectively evaluated the association of fruit and vegetable intake with breast cancer risk in a cohort of 51,928 women aged 21 to 69 years in 1995 when they enrolled in the Black Women's Health Study. The investigators used a validated food frequency questionnaire to determine dietary intake and Cox proportional hazards models to estimate incidence rate ratios and 95% confidence intervals (CIs), which were adjusted for breast cancer risk factors.

There were 1268 incident cases of breast cancer during 12-year follow-up. Dietary consumption of total fruits, total vegetables, and total fruit and vegetables was not significantly associated with the overall risk for breast cancer. However, total vegetable intake was linked to a lower risk for ER-/PR- breast cancer. For at least 2 vegetable servings per day vs less than 4 servings per week, the incidence rate ratio for ER-/PR- breast cancer was 0.57 (95% CI, 0.38 - 0.85; P for trend = .02).

There was also some evidence of inverse associations with overall breast cancer risk for cruciferous vegetable intake (P for trend = .06) and for carrot intake (P for trend = .02). Therefore, the investigators suggest that frequent consumption of vegetables is inversely associated with the risk for ER-/PR- breast cancer, and that intake of specific vegetables may be associated with a reduced risk for breast cancer overall.

"So far, there has not been much identified that women could do to reduce their risk of ER negative breast cancer, but this provides evidence that regular consumption of vegetables is likely to help," Dr. Willett said. "It will be important to examine this relation in additional populations and to focus more detail on the specific types of vegetables that could be beneficial."

Limitations of this study include possible misclassification of long-term dietary intake, which would likely be random and would have attenuated true associations, and possible confounding by unknown lifestyle factors. However, the study authors noted that they were able to control for several established breast cancer risk factors, which did not appreciably affect the results.

"Because we examined a large number of associations in these analyses, it is more likely that a given significant finding may be due to chance, and our results need to be confirmed," the study authors write. "Future studies investigating the association between subclasses of vegetables and subtypes of breast cancer are warranted."

The National Cancer Institute supported this study. The content of the study article is solely the responsibility of the authors and does not necessarily reflect the official views of the National Cancer Institute or the National Institutes of Health. The study authors and Dr. Willett have disclosed no relevant financial relationships.

Am J Epidemiol. Published online October 11, 2010. Abstract

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