Update of preclinical and human studies of calcium and colon cancer prevention

Links between Diet, Intestinal Anaerobes, Microbial Metabolites and Health

A dense microbial community resides in the human colon, with considerable inter-individual variability in composition, although some species are relatively dominant and widespread in healthy individuals. In disease conditions, there is often a reduction in microbial diversity and perturbations in the composition of the microbiota. Dietary complex carbohydrates that reach the large intestine are important modulators of the composition of the microbiota and their primary metabolic outputs. Specialist gut bacteria may also transform plant phenolics to form a spectrum of products possessing antioxidant and anti-inflammatory activities. Consumption of diets high in animal protein and fat may lead to the formation of potentially deleterious microbial products, including nitroso compounds, hydrogen sulphide, and trimethylamine. Gut anaerobes also form a range of secondary metabolites, including polyketides that may possess antimicrobial activity and thus contribute to microbe-microbe interactions within the colon. The overall metabolic outputs of colonic microbes are derived from an intricate network of microbial metabolic pathways and interactions; however, much still needs to be learnt about the subtleties of these complex networks. In this review we consider the multi-faceted relationships between inter-individual microbiota variation, diet, and health.

Calcium, vitamin D and colorectal cancer chemoprevention

Identifying modifiable risk factors, particularly dietary factors, which have been hypothesized to play an important role in colorectal carcinogenesis, remains crucial in developing primary prevention strategies. Calcium and vitamin D have been shown consistently in experimental studies to have anti-cancerous properties including but not limited to stimulating differentiation, reducing proliferation, and inducing apoptosis. The majority of epidemiologic studies consistently support an approximately 20-30% reduction in risk of colorectal cancer and adenomas comparing high to low intake categories of both calcium and vitamin D, although independent effects may not be adequately separated. Less consistency exists on the dose-response relation for both nutrients. Intake of calcium of not more than 1000 mg/d and intake of vitamin D of 1000-2000 IU/d, achieving a level of at least 30 ng/mL, appear important for colorectal cancer prevention. More study is warranted to determine the optimal intake levels and duration to reduce the colorectal cancer risk.

Specific interaction between Ca2+ and anionic lipids in cancer cells along with apoptosis

Markedly inhibitory effects of Ca(2+) on the growth of human tumor cells were attained through the induction of apoptosis in vitro. On the other hand, a good correlation between the growth inhibition effects of Ca(2+) and the amounts of phosphatidylserines (PS) in the cell membranes (plasma membranes) was obtained. Furthermore, the decrease of membrane fluidity and the localization of lipid microdomains "lipid rafts" in the cell membranes were observed in the presence of Ca(2+). The findings in this study suggest that Ca(2+) could induce apoptosis toward tumor cells through the localization of lipid rafts in plasma membranes by the specific interactions between extracellular Ca(2+) and PS.

Multiple sources of dietary calcium-some aspects of its essentiality

The increasing recognition of the important role of calcium in the myriad regulation of cellular processes in the health and well being throughout one's lifetime has focused on the need to ensure a sufficiency of its intake for nutritional, physiological, and medical reasons. Additionally, the recognition of the dynamic dietary changes and preferences of various populations in terms of their consumption of calcium-containing products coupled with large variations of food patterns and availability of calcium, highlights the need to consider and evaluate multiple sources of calcium (dairy, non-dairy, fortified foods, and supplemental). Aspects of the essentiality of calcium are thus considered via an initial consideration of: the salient aspects of absorption and bioavailability, changes in individual and societal dietary habits and preferences and the evaluation of various RDAs, AIs, and DRIs for calcium.

Associations of Adequate Intake of Calcium with Diet, Beverage Consumption, and Demographic Characteristics among Children and Adolescents

OBJECTIVE

The objective of this study is to examine various factors associated with total calcium intake and percent adequate intake (% AI) of calcium by children and adolescents, with respect to age, gender, race/ethnicity, and diet and beverage choices.

DESIGN

Data from the U.S. Department of Agriculture's Continuing Survey of Food Intake by Individuals 1994-96, 98 were used in the analyses. Age groupings (2-3, 4-8, 9-13, and 14-18 year olds) were based on the National Academy of Sciences recommendations for AI of calcium-500, 800, 1,300, and 1,300 mg calcium per day, respectively.

RESULTS

Consumption of milk products was strongly and positively associated with calcium intake. Consumption of carbonated soft drinks and other non-dairy beverages was also positively associated with calcium intake, but this association was very weak. Beverage choices of African-American children and adolescents are significantly different than white and Hispanic children and adolescents. For example, African-American adolescent girls consume fewer milk products and more fruit drinks/ades. Average daily carbonated soft drink consumption is approximately 1.6 and 1.0 twelve ounce cans among 14-18 year old boys and girls, respectively.

CONCLUSION

Carbonated soft drink consumption among adolescent girls is modest and does not appear to be linked to decreased calcium intake. The analyses in this paper show that creative effective, efficient, and targeted policies should be considered to help adolescent girls increase calcium intake. Making low-fat milk products, flavored milks, calcium-fortified beverages and foods more attractive and available will help encourage girls to consume more of this important mineral. When adequate calcium intake is not achieved through foods, health professionals should consider recommending calcium supplements.

Meta analysis of risk factors for colorectal cancer

AIM: To study the risk factors for colorectal cancer in China.

METHODS: A meta-analysis of the risk factors of colorectal cancer was conducted for 14 case-control studies, and reviewed 14 reports within 13 years which included 5034 cases and 5205 controls. Dersimonian and Laird random effective models were used to process the results.

RESULTS: Meta analysis of the 14 studies demonstrated that proper physical activites and dietary fibers were protective factors (pooled OR < 0.8), while fecal mucohemorrhage, chronic diarrhea and polyposis were highly associated with colorectal cancer (all pooled OR > 4). The stratified results showed that different OR values of some factors were due to geographic factors or different resourses.

CONCLUSION: Risks of colorectal cancer are significantly associated with the histories of intestinal diseases or relative symptoms, high lipid diet, emotional trauma and family history of cancers. The suitable physical activities and dietary fibers are protective factors.

Variability of cell proliferation in the proximal and distal colon of normal rats and rats with dimethylhydrazine induced carcinogenesis

AIM: To investigate the patterns of cell proliferation in proximal and distal colons in normal rats and rats with 1,2-dimethylhydrazine (DMH) induced carcinogenesis using the thymidine analogue bromodeoxyuridine.

METHODS: Colonic crypt cell proliferation was immunohistochemically detected using the anti-bromodeoxyuridine Bu20a monoclonal antibody.

RESULTS: Marked regional differences were found in both groups. Total labelling index (LI) and proliferative zone size in both normal (8.65 ± 0.34 vs 7.2 ± 0.45, 27.74 ± 1.07 vs 16.75 ± 1.45) and DMH groups (13.13 ± 0.46 vs 11.55 ± 0.45, 39.60 ± 1.32 vs 35.52 ± 1.58) were significantly higher in distal than in proximal colon (P < 0.05), although the number of cells per proximal crypt was greater (31.45 ± 0.20 vs 34.45 ± 0.39, 42.68 ± 0.53 vs 49.09 ± 0.65, P < 0.0001). Crypt length, total LI and proliferative zone size all increased in both proximal and distal regions of DMH rats compared to normal controls (P < 0.0001). In DMH-treated rat colon a shift of labelled cells to higher crypt cell positions was demonstrated distally whilst a bi-directional shift was evident proximally (P < 0.05).

CONCLUSION: Our results show that changes in cell proliferation patterns, as assessed by bromodeoxyuridine uptake, can act as a reliable intermediate marker of colonic cancer formation. Observed differences between proliferation patterns in distal and proximal colon may be associated with the higher incidence of tumors in the distal colon.