Research paper, 2013, 24 Pages
CITATION AND INTENDED AUDIENCE
LIST OF ABBREVIATIONS
CHAPTER 1: SUMMARY OF ARTICLE BY KEY ET AL. (2002)
CHAPTER 2: LITERATURE REVIEW
Raised Research Question
Significance of Topic
Vitamin D Synthesis
CHAPTER 3: RESEARCH HYPOTHESES
Research Hypothesis (Two-Tailed)
Research Hypothesis (One-Tailed)
CHAPTER 4: CONCLUSIONS
Please cite this publication as (APA style):
Akrawi. W. (2013). The association between vitamin D status and colon cancer risk: A review and synthesis. Germany: GRIN Publishing.
Professional and scholarly (e.g., doctors, educators, researchers);
College or higher education (e.g., master's and PhD students); and
General (e.g., anyone interested in medical research on cancer and its link to dietary habits).
Abbildung in dieser Leseprobe nicht enthalten
Several approaches have emerged to minimize the risk of developing cancer, including weight control, increased physical activity, smoking cessation, micronutrients intake, and changing dietary habits. With respect to the latter, thirty years of scientific research has confirmed some of the major dietary factors related to cancer development. The current knowledge on the relationship between diet and cancer shows that diets high in fruits, vegetables, and cereals may reduce the risk of developing several types of cancer. For instance, in the article "The Effect of Diet on Risk of Cancer," which appeared in The Lancet in September 2002, Timothy J. Key, Naomi E. Allen, Elizabeth A. Spencer, and Ruth C. Travis examine the prevalence of cancer risk behaviors, including dietary patterns, and obesity, in diverse parts of the globe (Key et al., 2002). Different dietary habits were observed in different countries. The observations suggested that a large number of food components in fruit and vegetables may reduce cancer risk, and it was documented that increased consumption of fruit and vegetables may be the most effective cancer prevention measure that can be implemented easily.
Accordingly, recommending dietary change offers a potential avenue for individuals to enhance their health, and quality of life. Yet, the progress towards achieving these goals has been slow, and the results reported in the literature have been limited or inconclusive, partly due to uncontrolled or unidentified confounding factors, and recall and selection biases. In addition, much more research is needed in this field to examine the roles of genetics and the environment in the regulation and development of cancers.
The research question discussed in this paper is: Is there an association between vitamin D status and colon cancer risk? The main objective is to explore the association observed between vitamin D blood levels and colon cancer risk. Since vitamin D promotes calcium absorption (Solomon et al., 1996), calcium supplementation has also been included in previous research for its possible role in decreasing the risk of cancer formation. Previous studies have indicated that measured vitamin D levels and the use of calcium supplements have a joint effect on colon cancer risk (Grau et al., 2003). However no definite answer has yet been given to the stated research question.
In the next sections, a summary of the above-mentioned article (Key et al., 2002) is presented, followed by the developed research question. A literature review is then provided, and previous analyses, results, and limitations are reviewed and synthesized. The final section of the paper offers the conclusions, and areas for future research. The following research hypothesis is proposed for testing: Having optimal vitamin D blood levels reduces the risk of colon cancer.
The article entitled The Effect of Diet on Risk of Cancer, published in The Lancet by Key et al. (2002), highlights the connection between diet and the risk of developing cancer. The authors examine the prevalence of cancer risk behaviors, including alcohol use, dietary patterns, obesity, and physical activity, in various groups of people. Key team indicates that some cancers are more common in women than in men. Whereas lung, prostate, and colorectal cancers are the three most common cancers in males in western countries, breast and colorectal cancers are the most common in females (see Figure 1 in Chapter 2).
Regardless of gender differences, different populations seem to have different dietary patterns that are partly linked to cancer formation. Cancers that are common in developed countries are relatively rare in developing countries. For example, while the number of cases of liver cancer is much higher in developing countries compared to industrialized countries, the risk of breast cancer is five times higher in developed countries than in developing countries (see Figure 1). The reason could be that the level of fruit and vegetable consumption in the western part of the world is insufficient. In addition, the fact that migrant groups adopt the host population's cancer rates underlines the importance of environmental factors in cancer etiology.
In this context, it has been shown that dietary factors contribute to approximately 30 percent of total cancer cases in western countries. Previous studies have demonstrated that diet and obesity can lead to different kinds of cancer, such as oesophagus, colorectum, breast, endometrium, and kidney, and that drinking excessive amounts of alcohol has been associated with oral, pharynx, larynx, oesophagus, liver, and breast cancers. Key and colleagues suggest that such studies will further enhance our future understanding of the dietary risk factors that influence the occurrence of cancer.
Another main point of the article is the possibility of preventing cancer by changing diet, and avoiding certain kinds of food. High intake of fruit and vegetables is thought to decrease cancer risk, probably because of their high concentrations in antioxidants, such as vitamin E and ascorbic acid. Experts suggest that reducing intake of high-fat and high-sugar foods, and increasing fruit and vegetable intake and physical activity are the key to a healthy lifestyle. Research on the role of genes in diet-related cancer has shown evidence of an intimate association between diet and gene expression, but it has not yet reached the stage where the related genetic and metabolic mechanisms are clear and cohesive.
In conclusion, this article reviews recent findings related to the association between dietary factors and cancer risk, with an emphasis on future research directions. It is not yet possible to provide accurate estimates about the effects of diet on cancer incidence; nevertheless, extensive research has revealed the need to explore all possible ways in which diet, supplements, lifestyle, genetic, and environmental factors may play a role in the development of cancer.
This research paper is guided by the following research question:
Is there an association between vitamin D status and colon cancer risk?
Worldwide, colorectal cancer, which refers to cancer of the colon and rectum, is the third most common cancer, leading to 639,000 deaths per year (Key et al., 2002; WHO, 2009). Its incidence is increasing, particularly in countries where the consumption of healthy food is low (Bingham, 1999; Key et al., 2002). Many researchers are in agreement that diet may affect the risk of developing cancer (Key et al., 2002). Several studies have reported that high intakes of vitamin D, calcium, or both have a direct impact on cancer risk, and that these supplements may reduce the recurrence of colorectal adenomas (Wu et al., 2002; Bonithon-Kopp et al., 2000; Baron et al., 1999; WCRF, 1997). Vitamin D is a fat-soluble micronutrient that is naturally present in fatty fish species, whole egg, mushrooms and fish liver oils. It promotes calcium absorption from digestive tract and supports healthy growth and maintenance of bone (Solomon et al., 1996).
Although some clinical studies have linked calcium supplementations and vitamin D status with lower colon cancer, no consensus has been reached as to whether such a relationship does in fact exist. In 2003, Grau et al. examined former colon cancer patients and reviewed the effect of calcium supplementation and vitamin D status in preventing the recurrence of colorectal adenomas (Grau et al., 2003). The 803 participants were randomly assigned to receive either calcium supplementation (1200 mg of elemental calcium per day) or a placebo. The study lasted for four years, during which time the serum levels of 25-hydroxy [25-(OH)] vitamin D and 1,25- dihydroxy [1,25-(OH)2] vitamin D were measured at the beginning and the end of the trial. After evaluating the risk of recurrence of colon cancer, a two-tailed statistical test was conducted (adjusted RR per 12 ng/mL increase of vitamin D = 0.88, 95% CI [0.77 to 0.99]). The researchers found that serum 25-(OH) vitamin D levels were related to a lower risk of colon cancer recurrence, but only among participants receiving calcium supplements (p for interaction = .006). The study concluded that a combination of higher vitamin D levels and calcium supplementation could reduce the risk of colon cancer recurrence.
Several other studies supported these findings. For instance, a study conducted by Kumangai and colleagues (2003) suggested that paricalcitol, the synthetic, biologically active form of vitamin D, has anti-cancer activity against colon cancer cells both in vitro and in vivo, displaying various effects on the cell cycle, differentiation, and apoptosis (Kumangai et al., 2003). Additionally, Lieberman et al. (2003) carried out a prospective, cross-sectional study of vitamin D intake in a population of 3,121 participants with and without colorectal neoplasia (Lieberman et al., 2003). In their multivariate analysis, an inverse association was observed for vitamin D intake (adjusted OR = 0.94, 95% CI [0.90 to 0.99]) (Lieberman et al., 2003).
On the other hand, other researchers have not found such an association. For example, a randomized, double-blind, placebo-controlled trial conducted by the Women's Health Initiative indicated that daily supplementation of vitamin D (400 IU of vitamin D3) and calcium (1000 mg of elemental calcium) had no association with colorectal cancer rates among postmenopausal women (Wactawski-Wende et al., 2006).
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