Calcium supplementation and prevention of colorectal neoplasia: lessons from clinical trials

Calcium: magnesium intake ratio and colorectal carcinogenesis, results from the prostate, lung, colorectal, and ovarian cancer screening trial

Background

We aimed to evaluate the associations between calcium and various stages of colorectal carcinogenesis and whether these associations are modified by the calcium to magnesium (Ca:Mg) ratio.

Methods

We tested our hypotheses in the prostate lung, colorectal and ovarian cancer screening trial.

Results

Calcium intake did not show a dose–response association with incident adenoma of any size/stage (P-_trend = 0.17), but followed an inverse trend when restricted to synchronous/advanced adenoma cases (P-_trend = 0.05). This inverse trend was mainly in participants with Ca:Mg ratios between 1.7 and 2.5 (P-_trend = 0.05). No significant associations were observed for metachronous adenoma. Calcium intake was inversely associated with CRC (P-_trend = 0.03); the association was primarily present for distal CRC (P-_trend = 0.01). The inverse association between calcium and distal CRC was further modified by the Ca:Mg ratio (P-_interaction < 0.01); significant dose–response associations were found only in participants with a Ca:Mg ratio between 1.7 and 2.5 (P-_trend = 0.04). No associations for calcium were found in the Ca:Mg ratio above 2.5 or below 1.7.

Conclusion

Higher calcium intake may be related to reduced risks of incident advanced and/or synchronous adenoma and incident distal CRC among subjects with Ca:Mg intake ratios between 1.7 and 2.5.

The Role of Aspirin, Vitamin D, Exercise, Diet, Statins, and Metformin in the Prevention and Treatment of Colorectal Cancer

Colorectal cancer (CRC) is a worldwide health problem leading to significant morbidity and mortality. Several strategies based on either lifestyle modifications or pharmacological interventions have been developed in an attempt to reduce the risk of CRC. In this review article, we discuss these interventions including aspirin (and other non-steroidal anti-inflammatory drugs), vitamin D, exercise, diet, statins, and metformin. Depending upon the risk of developing CRC, the current evidence supports the beneficial role of aspirin, vitamin D, diet, and exercise especially in high-risk individuals (advanced adenoma or CRC). However, even with these established interventions, there are significant knowledge gaps such as doses of aspirin and 25-hydroxy vitamin D are not well established. Similarly, there is no convincing data from randomized controlled trials that a high fiber diet or a low animal fat diet reduces the risk of CRC. Some potential interventions, such as statins and metformin, do not have convincing data for clinical use even in high-risk individuals. However, these may have emerging roles in the prevention and treatment of CRC. Greater understanding of molecular mechanisms and the application of genomic tools to risk stratify an individual and tailor the interventions based on that individual's risk will help further advance the field. Some of this work is already underway and is a focus of this article.

Dietary supplements and cancer prevention: balancing potential benefits against proven harms

Nutritional supplementation is now a multibillion-dollar industry, and about half of all US adults take supplements. Supplement use is fueled in part by the belief that nutritional supplements can ward off chronic disease, including cancer, although several expert committees and organizations have concluded that there is little to no scientific evidence that supplements reduce cancer risk. To the contrary, there is now evidence that high doses of some supplements increase cancer risk. Despite this evidence, marketing claims by the supplement industry continue to imply anticancer benefits. Insufficient government regulation of the marketing of dietary supplement products may continue to result in unsound advice to consumers. Both the scientific community and government regulators need to provide clear guidance to the public about the use of dietary supplements to lower cancer risk.

Calcium, vitamin D, VDR genotypes, and epigenetic and genetic changes in rectal tumors

Calcium, vitamin D, exposure to sunshine, and vitamin D receptor (VDR) genotypes have been associated rectal cancer. We used data from 750 rectal tumors and 1,205 population-based controls examine associations with TP53, KRAS2, and CpG Island methylator phenotype (CIMP) markers. Rectal tumors were associated with high levels of calcium overall and with TP53 tumor mutations specifically (OR = 0.6, 95% CI = 0.42-0.84). High levels of sunshine exposure had a borderline protective effect for TP53 tumor mutations (OR = 0.78, 95% CI = 0.59-1.03). A mutation at codon 248 was significantly associated with dietary calcium intake (OR = 0.26, 95% CI = 0.09-0.77); having the Ff/ff genotypes of the FOK1 VDR polymorphism significantly increased the odds of a mutation at codon 245 (OR = 4.74, 95% CI = 1.05-21.39); high levels of dietary vitamin D (OR = 3.42, 95% CI = 1.15-10.17) and the Ff/ff genotypes of FOK1 (OR = 3.34, 95% CI = 1.11-10.02) and the GA/AA genotypes of the CDX2 VDR polymorphism (OR = 2.85, 95% CI = 1.23-6.58) increased the odds of a TP53 mutation at codon 273. These data support an association between calcium and rectal tumors overall as well as specifically with TP53 mutations. However, given the number of comparisons, findings need to be confirmed in other studies.

Epidemiological and clinical studies of nutrition

In this review, we briefly summarize some of the key developments in nutritional epidemiology and cancer over the past two decades with a focus on the strengths and limitations of study designs and dietary assessment methods. We present the evidence on dietary fat, meat, fiber, antioxidant nutrients, and calcium in relation to carcinogenesis from large cohort studies and randomized clinical trials (RCTs) and refer to the conclusions of the 2007 World Cancer Research Fund/American Institute for Cancer Research summary report. One prominent theme that emerged is the lack of concordance of results from RCTs and observational studies. There are multiple potential reasons for these discrepancies, including differences in study population, dose and timing of the exposure, adherence to an intervention, length of follow-up, and the primary endpoint. Therefore, null findings of RCTs do not necessarily indicate a lack of effect for the tested dietary factors on cancer risk, as some of these nutrients may have chemopreventive effects if given at the right time and in the right dose. It is likely that potential benefits from diet are due to a combination of food constituents rather than single components acting in isolation. Future efforts need to recognize the integrative nature of dietary exposures and attempt to study nutrients in the larger context of the foods and diets in which they are consumed.

Dietary calcium, vitamin D, and the risk of colorectal cancer

BACKGROUND

Calcium and vitamin D have a potential protective effect against colorectal cancer.

OBJECTIVE

We investigated the association of dietary intake of calcium and vitamin D with the risk of colorectal cancer in a large prospective cohort study of middle-aged Japanese men and women.

DESIGN

A total of 74 639 subjects (35 194 men and 39 445 women) who participated in the Japan Public Health Center-based Prospective Study were followed from 1995-1999 to the end of 2004, during which time 761 cases of colorectal cancer (464 men, 297 women) were newly identified. Dietary intake of nutrients was calculated with the use of a 138-item self-administered food-frequency questionnaire.

RESULTS

After adjusting for potential confounding factors, the multivariate hazard ratio in the highest quintile of dietary calcium intake compared with the lowest was 0.71 (95% CI: 0.52, 0.98) among men. The association appeared to decrease considerably among subjects in the second quintile without a clear further dose-response relation (P for trend: 0.09). No association was seen among women. No statistically significant association with dietary vitamin D intake was seen in either men or women, although men in the highest dietary intake group of both nutrients had a lower risk than did men in the lowest group.

CONCLUSIONS

These findings indicate a potential decrease in the risk of colorectal cancer with higher dietary intake of calcium among middle-aged Japanese men, who have a relatively low dietary intake of calcium. Although vitamin D and colorectal cancer risk were not associated, potential effect modification between calcium and vitamin D on the risk of colorectal cancer was indicated.