The Effects of Fruit and Vegetable Intake on Breast Cancer Risk

Abstract

Diet has long been suspected to affect breast cancer risk and development, yet evidence has been inconsistent. The possibility that high fruit and vegetable intake could lower the risk of cancer has been studied now for over 40 years (Key, 2011). Results over the years have shown protective effects, weak protective effects, and no effects, and are thus largely inconclusive. The purpose of this literature review is to assess the most current research studies available to see whether or not current research is finding an correlation between high fruit and vegetable intake and reduced risk of breast cancer development or recurrence. This paper analyzes one meta-analysis and nine original research studies published within the last 12 years. While some significant and some weak inverse associations are found, the majority of studies find no association, suggesting that either fruit and vegetable intake does not affect breast cancer risk, or other factors are involved, such as specific types of fruits and vegetables consumed, hormone receptor status type, and age and menopausal status when observed. Introduction

Breast cancer accounts for about 23% of cancer incidents and 14% of cancer deaths in women worldwide, making it the most common cause of cancer for women (Aune et al., 2011). Diet has long been suspected to affect breast cancer risk and development, yet evidence has been inconsistent. The possibility that high fruit and vegetable intake could lower the risk of cancer has been studied now for over 40 years (Key, 2011). While many studies have found a protective or weak protective effect of a high intake of fruits and vegetables, many other studies have found no association at all. 

It believed that fruits and vegetables could lower the risk of breast cancer for several reasons. They are high in fiber, which may bind to estrogens; they are good sources of antioxidants, which may improve the activity of detoxifying enzymes; and they can lower’s one’s risk of overweight or obesity, which may also lower the risk of developing cancer (Aune et al., 2011). The purpose of this literature review is to compare the most current research studies to see whether or not a relationship between fruit and vegetable intake and breast cancer risk exists. 

Results

For this literature review, the researcher used the search parameters “fruit and vegetable intake” AND “breast cancer” in ProQuest Central. The researcher limited the search to original research studies, meta-analyses, and systematic reviews published within the last 12 years that sought to determine whether or not a correlation existed between the risk of breast cancer development or recurrence and a high or low intake of fruits and vegetables. This review is including nine research studies and one meta-analysis. The purpose of the paper is to find the most recent studies available in scientific literature to determine whether or not fruit and vegetable intake affects the risk of breast development or recurrence.

In a meta-analysis and systematic review, Aune et al. (2011) used 14 cohort studies and one case-control study to determine if a relationship existed between fruit and vegetable intake and breast cancer risk. The researchers found that a high intake of fruits, and fruits and vegetables combined was associated with a weak reduction of breast cancer risk. They did not find the same correlation with a high vegetable intake. 

In a large cohort study in Sweden, Löf et al. (2011) followed 44,838 women who completed a food frequency questionnaire (FFQ) for an average of 14 years, to determine whether or not there was a correlation between fruit and vegetable intake and overall cancer risk. They found no significant association between fruit, vegetable, or fruit and vegetable intake and a reduced risk of cancer. The researchers recognize that there may be a significance to fruit and vegetable intake that occurs early in life; most studies follow older or postmenopausal women. This study followed women between ages 30-50.

Other studies have attempted to see if accounting for different estrogen receptor (ER) and progesterone receptor (PR) status could influence the effect of fruit and vegetable intake on breast cancer risk. Suzuki et al. (2013) studied 47,289 Japanese women who returned three FFQs over a 10 year period that analyzed intake of 138 food and beverage items, including 16 fruits and 30 vegetables. Over the course of the study, 452 cases of breast cancer were diagnosed and no major association was found. Cruciferous vegetable intake was associated with a statistically significant decrease in risk among premenopausal women, but there was no connection found for postmenopausal women. When considering ER and PR status, the researchers found that intake of Japanese radish was significantly correlated with a decreased risk of ER+ PR+ tumors; however, no association was found for any ER/PR tumor type for total fruit, vegetable, or fruit and vegetable intake. 

Similarly, Lissowska et al. (2007) conducted a large case-control study in Poland to determine if ER status affected the association between diet and breast cancer risk. They found a significant association between reduced breast cancer risk and high fruit intake that was stronger for ER+ than ER- tumors. They did not find a correlation between risk and vegetable intake. 

In another study that found slight differences between hormone receptor status, Fink et al. (2006) followed 1,235 women with invasive breast cancer to see if fruit, vegetable, or micronutrient intake one year prior to diagnosis was associated with a reduced risk of mortality. They found an insignificant association between higher intake of fruits, vegetables, and micronutrients and survival advantage, but only in post-menopausal women. Although there was little difference between hormone receptor status, these results were slightly more pronounced among women with ER+PR+ tumors. The results for pre-menopausal women were even less consistent, with only a slight reduction in mortality observed, and only for intake of leafy or cruciferous vegetables. 

While most studies have followed adult and/or postmenopausal women, Farvid et al. (2016) conducted a cohort study to see if fruit and vegetable intake in adolescence could influence breast cancer development in adulthood. They analyzed the diets of 44,223 pre-menopausal women who completed a FFQ during adolescence in 1998. They found no association between risk and fruit intake in early adulthood, or for vegetable intake in either adolescence or early adulthood. They did, however, find an association between high fruit and high fruit and vegetable intake in adolescence and a reduced risk of breast cancer. An increased consumption of fruit during adolescence (e.g. apple, banana, and grapes) was shown to lower breast cancer risk. Furthermore, a high intake of fruits and vegetables rich in α-carotene during early adulthood (e.g. oranges and kale) was found to associate with a significantly reduced risk. 

Wang et al. (2014) also found a connection between α-carotene consumption and breast cancer risk. The researchers created a case-control study that investigated the association between plasma carotenoids with postmenopausal breast cancer risk in 496 invasive breast cancer cases. Carotenoids, found largely in fruits and vegetables, have been reported to inversely affect oxidative stress and inflammation, and thus may help protect against cancer. The researchers found that higher concentrations of plasma α-carotene were associated with a statistically significant lower risk of invasive breast cancer in postmenopausal women. 

In a similar attempt to identify a specific catalyst within fruits and vegetables that could prevent breast cancer, Hutchinson et al. (2012) used the food diaries of 2,851 women in five UK cohorts to see whether or not a relationship existed between vitamin C intake and reduced breast cancer risk. They found no significant association, neither beneficial or detrimental, regardless of whether vitamin C came from food sources or supplements. Food diaries are a significantly different method for collecting data than the more commonly used FFQs; they tend to get very accurate information over a short period of time (usually a few days), whereas FFQs ask participants to summarize eating habits over an extended period of time (usually 12 months). Repeated short-term diary collections over a longer period of time would reduce the limitations of such a study. 

Another aspect of breast cancer prevention involves the behavior and knowledge of survivors and how that affects their fruit and vegetable consumption. O’Neill et al. (2013) defined health behaviors that could reduce the chance of breast cancer recurrence as (1) maintaining a healthy body weight, (2) eating fruits and vegetables regularly, and (3) being physically active. The researchers found that most women were aware that these three health behaviors could influence cancer recurrence, however awareness did not translate into high rates of engaging in the behaviors, even for women at high risk of recurrence. Only a small percentage of the sample reported engaging in these behaviors specifically to reduce cancer risk. 

Similarly, Weiner, Jordan, Thompson, and Fink (2010) studied the attitudes towards fruit and vegetable intake and exercise in a cohort of breast cancer survivors in northwest Ohio. According to their findings, many breast cancer survivors are not aware of the benefits of diet and exercise to lower breast cancer risk, and many of those who are aware do not adapt their behaviors accordingly. 46.5% of participants were unsure or in disagreement with the statement: “Eating at least 5 servings of fruits and/or vegetables per day will reduce the risk of breast cancer recurrence.” Only 46.8% of those in agreement with the statement actually reported eating at least five servings of fruits and vegetables each day. Furthermore, only 68.5% of those in agreement with this statement reported engaging in any physical activity in the previous 30 days. The researchers believe that there is an education gap that would be best filled by breast cancer survivors’ physicians. 

Discussion 

Of these research studies that were analyzed, all of them began with a description of the anticipated benefits of fruit and vegetable intake that could reduce the risk of breast cancer development and recurrence. However, there is little evidence as of yet to support these claims. This association is generally assumed to exist due to the antioxidants, fiber, and vitamins in fruits and vegetables. Most studies that did not find a correlation contemplated that it could be due to specific types of fruits and vegetables consumed, differences in hormone receptor (ER or PR) status, sample size, or limitations of the FFQ.  

Two of the research studies that were analyzed mentioned the fact that fruit and vegetable intake that occurs early in life could have an impact on breast cancer development. As most studies follow adult women both pre- and post-menopausal, and women already diagnosed with breast cancer, the evidence of how fruit and vegetable consumption in childhood and adolescence affects cancer risk is not yet clear. However, the only study analyzed here that focuses on intake in adolescence found a significant reduction in breast cancer risk for high fruit and high fruit and vegetable intake if consumed during adolescence. 

The two studies that addressed behaviors and attitudes of breast cancer survivors suggests that a discrepancy exists between perceived and actual knowledge, and how people act on it. O’Neill et al. (2013) and Weiner et al. (2010) both came to the conclusion that survivors had either a lack of knowledge or a lack of drive to change their behaviors because they weren’t sure or didn’t believe that a relationship existed between fruit and vegetable intake and cancer recurrence. However, the current research does not show conclusive evidence that changing these behaviors will reduce the risk of breast cancer. This discrepancy shows what a conflicting topic this has become for researchers and survivors alike.

While some studies analyzed in this literature review did find weak evidence of an inverse association between fruit and vegetable consumption and breast cancer risk, the evidence does not conclusively confirm or deny this idea. However, the studies analyzed did not find a positive association, in that fruit and vegetable intake does not appear to cause cancer development, and should certainly still be promoted for a healthy weight, nutrition, and lifestyle. 

Conclusion and Recommendations

At this time, it does not appear that there is enough conclusive evidence to confirm an association between fruit and vegetable intake and breast cancer risk, and more research is required. However, although an inverse association between fruit and vegetable intake and breast cancer risk has not yet conclusively been found, an increased consumption of fruits and vegetables has also been associated with a decreased risk of cardiovascular disease and diabetes (Farvid, 2016). High intake of fruit and vegetables can help maintain a healthy weight and in turn lower one’s risk of overweight or obesity, thus also lowering one’s risk of cancer.

Future research should study the effect of fruit and vegetable intake in childhood and adolescence, as this seems to be an area of study with promise that has been largely overlooked. It is possible that increased intake of fruits and vegetables in adolescence could lower the risk of breast cancer in adulthood. If this correlation exists, breast cancer could be prevented by increasing diet awareness early in life. This could potentially help to reduce the great number of men and women who suffer from breast cancer around the world.

References

Aune, D., Chan, D.S.M., Vieira, A.R., Navarro Rosenblatt, D.A., Vieira, R., Greenwood, D.C., & Norat, T. (2012). Fruits, vegetables and breast cancer risk: A systematic review and meta-analysis of prospective studies. Breast Cancer Research and Treatment. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/1030117908/1C0565340C214291PQ/2?accountid=158302

Farvid, M.S., Chen, W.Y., Michels, K.B., Cho, E., Willett, W.C., & Eliassen, A.H. (2016). Fruit and vegetable consumption in adolescence and early adulthood and risk of breast cancer: population based cohort study. British Medical Journal. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/1789196586/1C0565340C214291PQ/14?accountid=158302

Fink, B.N., Gaudet, M.M., Britton, J.A., Abrahamson, P.E., Teitelbaum, S.L., Jacobson, J…Gammon, M.D. (2006). Fruits, vegetables, and micronutrient intake in relation to breast cancer survival. Breast Cancer Research and Treatment. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/212445362/7511926AB8D04E85PQ/3?accountid=158302

Hutchinson, J. Lentjes, M.A.H., Greenwood, D.C., Burley, V.J., Cade, J.E., Cleghorn, C.L…Khaw, K.T. (2012). Vitamin C intake from diary recordings and risk of breast cancer in the UK Dietary Cohort Consortium. European Journal of Clinical Nutrition. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/1010511116/5C3E3E800F244EAEPQ/1?accountid=158302

Key, T.J. (2011). Fruit and vegetables and cancer risk. The British Journal of Cancer. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/822383915/95C77E77574644EBPQ/2?accountid=158302

Lissowska, J., Gaudet, M.M., Brinton, L.A., Peplonska, B., Sherman, M., Szeszenia-Dabrowska, N…Garcia-Closas, M. (2007). Intake of fruits, and vegetables in relation to breast cancer risk by hormone receptor status. Breast Cancer Research and Treatment. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/212471285/1C0565340C214291PQ/6?accountid=158302

Löf, M., Sandin, S., Lagiou, P., Trichopoulos, D., Adami, H.O., Weiderpass, E. (2011). Fruit and vegetable intake and risk of cancer in the Swedish women’s lifestyle and health cohort. Cancer Causes & Control. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/846758734/7511926AB8D04E85PQ/6?accountid=158302

O’Neill, S.C., DeFrank, J.T., Vegella, P., Richman, A.R., Henry, L.R., Carey, L.A., & Brewer, N.T. (2013). Engaging in health behaviors to lower risk for breast cancer recurrence. PLoS One. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/1289071309/1C0565340C214291PQ/3?accountid=158302

Suzuki, R., Iwasaki, M., Hara, A., Inoue, M., Sasazuki, S., Sawada, N…Tsugane, S. (2013). Fruit and vegetable intake and breast cancer risk defined by estrogen and progesterone receptor status: the Japan public health center-based prospective study. Cancer Causes & Control. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/1448800029/1C0565340C214291PQ/1?accountid=158302

Wang, Y., Gapstur, S., Gaudet, M.M., Furtado, J.D., Campos, H., & McCullough, M.L. (2014). Plasma carotenoids and breast cancer risk in the Cancer Prevention Study II Nutrition Cohort. Cancer Causes & Control. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/1704934064/1C0565340C214291PQ/10?accountid=158302

Weiner, J.G., Jordan, T.R., Thompson, A.J., & Fink, B.N. (2010). Analysis of the relationship between diet and exercise beliefs and actual behaviors among breast cancer survivors in northwest Ohio. Breast Cancer: Basic and Clinical Research. Retrieved from: https://search-proquest-com.ezp-02.lirn.net/central/docview/1034871513/C57A918CFF0541C0PQ/5?accountid=158302