Colorectal cancer is the third most common cancer in men and the second in women worldwide and it accounts for 8% of all cancer deaths, making it the fourth most common cause of death from cancer (WHO, 2008). In the Philippines, colorectal cancer is the third most common cancer and, next to lung cancer and breast cancer, the third leading cause of cancer deaths (DOH, 2008). According to the World Health Organization (2008), the Philippines ranks low in terms of age standardized survival rates for colorectal Cancer in both sexes.
It ranks 27% for women, 29% for men, falling behind countries like the United States, West Europe, Japan, Thailand and India. The risk of having colorectal cancer increases sharply after age 40 with 90% of cases occurring in people over age 50 (Fauci, 2008). Of all cancers, colorectal cancer seems most connected to diet ,as a result, the past decade has produced many studies looking at colorectal cancer in relation to single nutrients or foods, including dietary fats, red meat, ? ber, vegetables and fruits, calcium, vitamin D, and antioxidants (Kornaroff, 2005).
Vitamin B6, because of its role in the synthesis of nucleic acid and DNA, it has also been proposed to affect colorectal carcinogenesis (Kim, 2004). Vitamin B6 is a water-soluble vitamin that is naturally present in many foods, added to others, and available as a dietary supplement. It is the generic name for six compounds (vitamers) with vitamin B6 activity: pyridoxine, an alcohol; pyridoxal, an aldehyde; and pyridoxamine, which contains an amino group; and their respective 5′-phosphate esters. Pyridoxal 5′ phosphate (PLP) and pyridoxamine 5′ phosphate (PMP) are the active coenzyme forms of vitamin B6 (McCormick, 2006).
Vitamin B6 in coenzyme forms performs a wide variety of functions in the body and is extremely versatile, with involvement in more than 100 enzyme reactions, mostly concerned with protein metabolism (McCormick, 2006). Both PLP and PMP are involved in amino acid metabolism, and PLP is also involved in the metabolism of one-carbon units, carbohydrates, and lipids (Macky et. al. , 2005). One-carbongroups are important for DNA synthesis and DNA methylation; hence, low vitamin B6 may increase colorectal cancer risk through aberrations in DNA synthesis, repair, and methylation (Larsson, et. al. , 2010).
The richest dietary sources of vitamin B6 include fish, beef, liver and other organ meats, potatoes and other starchy vegetables, and non-citrus fruits (Mackey et. al. , 2005) While previous studies have supported the inverse association between vitamin B6 and colorectal cancer, the findings of a cohort of studies involving both men and women by de Vogel et. al. in 2008 suggested that vitamin B6 has a protective property for men but not on women against colorectal cancer. Thus, the aim of this meta-analysis is to examine further the effect of dietary intake of vitamin B6 in women regarding the risk of colorectal cancer.
METHODOLOGY Literature Search The researcher comprehensively performed literature search through electronic databases such as PUBMED, MEDLINE, EBSCO and Google Scholar for relevant medical literatures published in English-language journals from 2000 to the present. Keywords such as vitamin B6, pyridoxine, colorectal cancer, colon and rectal cancer where used. Reference lists from all relevant articles were also reviewed to identify additional studies. Inclusion and Exclusion Criteria Prospective cohort studies of the relationship of dietary intake of vitamin B6 and colorectal cancer in women of age 40 and above were included.
Non-cohort studies, studies utilizing supplemental intake of vitamin B6, studies involving male participants or women who are aged lower than 40 where excluded. RESULTS and DISCUSSION The researcher was able to retrieve 19 fully accessible researches relevant to the study. Only three of these studies met the inclusion criteria. The three studies reported on the association of vitamin B6 and colorectal cancer involving women 40 years of age and above. The results of the three studies are summarized in the table below: Table 1.
Comparison of Three Studies on the Association of Vitamin B6 and Colorectal Cancer Risk in Women. Title| Variables| Number of Participants| Type of Study| Duration of Study| Result| Relationship of Folate, Vitamin B-6, Vitamin B-12, and Methionine Intake to Incidence of Colorectal Cancer| Vitamin B6 and Colorectal Cancer| 35, 216 women| Prospective Cohort| December 1986 – January 1998(13 years)| There were no association of vitamin B6with colon cancer risk. Risk of rectal cancer increased progressively with increasing intake of vitamin B6 (this is more associated with supplemental intake rather than dietary intake).
| Folate, Vitamin B6, Multivitamin Supplements, and Colorectal Cancer Risk in Women| Vitamin B6 and Colorectal Cancer| 37, 916 women| Prospective Cohort| 1992-2004(12 years)| Dietary intake of vitamin B6 is significantly inversely associated with colorectal cancer among women. | Dietary Vitamin and Methionine Intakes and Plasma Folate are Not Associated With Colorectal Cancer Risk in Chinese Women| Vitamin B6 and Colorectal Cancer| 74, 942 women| Prospective Cohort| 1993-2006| No statistically significant association between dietary intake of vitamin B6 and colorectal cancer risk.
| Table 1 presents the results of 3 prospective cohort studies regarding the effect of dietary intake of vitamin B6 and colorectal cancer in women. Of the three studies, the study from the Woman’s Health Study involving 37,916 women reported an inverse association between vitamin B6 and colorectal cancer. On the other hand, the study involving 35, 216 women from the Iowa Woman’s Health Study found no direct relationship between vitamin B6 and colorectal cancer.
This result is similar to the study done in China, Shangai Women’s Health Study, involving 74, 942 except that the study in China reported that intake of vitamin B6 could increase the risk of rectal cancer. The result of this cohort study supports the result of the cohort study by de Vogel et. al. regarding the lack of protective properties of vitamin B6 for women against colorectal cancer. On the other hands it contradicts the results of other studies that reported an inverse association of dietary intake of vitamin B6 and colorectal cancer.
Larsson et.al. (2010) in a their meta-analysis of prospective studies concluded that vitamin B6 is inversely related to the risk of colorectal cancer for both men and women. CONCLUSION AND RECOMMENDATIONS The result of this cohort study strongly suggests that there is no significant or direct relationship between colorectal cancer and risks of colorectal cancer in women. However, the result of this study may be compromised by the method of which data regarding dietary intake of vitamin B6 were gathered which utilized food frequency questionnaires (FFQ).
Furthermore, the study was limited by the inaccessibility of other relevant studies. Thus, the researcher recommends that a higher level of study utilizing other methods such as random-control study with a larger population involving multiethnic groups be done to come up with a clearer and more reliable result. On the meantime, women who rely on an increased dietary intake of vitamin B6 to prevent colorectal cancer should be made aware such results as of this study. BIBLIOGRAPHY Fauci. (2008). Harrison’s Principle of Internal Medicine 17th Edtion.
McGraw-Hill Companies Inc. Harnack, L. , Jacobs, D. , et. al. (2002). Relationship of Folate, Vitamin B-6, Vitamin B-12, and Methionine Intake to Incidence of Colorectal Cancers. Nutrition and Cancer. 43(20, 152-158 Kim Y I. Folate and DNA methylation : a mechanistic link between folate de? ciency and colorectal cancer? Cancer Epidemiol Biomarker s P rev. 2004;13:511 –9 Kornaroff, A. (2005, July 11). Vitamin B6 May Help Prevent Colorectal Cancer in Women. Harvard Women’s Health Watch, pp. 1-2. Larsson, S. , Orsini, N. , & Wolk, A. (2010).
Vitamin B6 and Risk of Colorectal Cancer. Journal of American Medical Association. Macky, A. , David, S. , & Gregory, J. (2005). Vitamin B6. In: Modern Nutrition and Health Disease. 10th Edition. Philadelphia: Lippincott Williams & Wilkins. McCormick D. Vitamin B6. In: Bowman B, Russell R, eds.
Present Knowledge in Nutrition. 9th ed. Washington, DC: International Life Sciences Institute; 2006. Shrubsole, M. , Yang, G. , et. al. (2009). Dietary B Vitamin and Methionine Intakes and Plasma Folates are Not Associated with colorectal cancer risk in Chinese women. Cancer Epidemiology Biomarkers Prev.
Zhang, S. , Moore, S. , et. al. (2005). Folate, Vitamin B6, Multivitamin Supplements, and Colorectal Cancer Risk in Women. American Journal of Epidemiology. Vol. 163. No. 2 GLOBOCAN 2008, International Agency for Research on Cancer of the WHO (2008). in a glimpse.
Retrieved February 10, 2012 from, http://globocan. iarc. fr/factsheets/cancers/colorectal. asp World Health Organization. (October 2008). Key facts about cancer. Retrieved February 10, 2012 from, http://www. who. int/cancer/about/facts/en/.