Inhibition of intestinal carcinogenesis by dietary supplementation with calcium

Beneficial biological effects of miso with reference to radiation injury, cancer and hypertension

This review describes effects of miso with reference to prevention of radiation injury, cancer and hypertension with a twin focus on epidemiological and experimental evidence. Miso with a longer fermentation time increased crypt survival against radiation injury in mice. When evaluating different types of miso provided by different areas in Japan, miso fermented for a longer period increased the number of surviving crypts, and 180 days of fermentation was the most significant. Dietary administration of 180-day fermented miso inhibits the development of azoxymethane (AOM)-induced aberrant crypt foci (ACF) and rat colon cancers in F344 rats. Miso was also effective in suppression of lung tumors, breast tumors in rats and liver tumors in mice. The incidence of gastric tumors of groups of rats given NaCl was higher than those of the groups given miso fermented for longer periods. Moreover, the systolic blood pressure of the Dahl male rat on 2.3% NaCl was significantly increased but that of the SD rat was not. However, the blood pressures of the rats on a diet of miso or commercial control diet (MF) did not increase. Even though miso contains 2.3% NaCl, their blood pressures were as stable as those of rats fed commercial diet containing 0.3% salt. So we considered that sodium in miso might behave differently compared with NaCl alone. These biological effects might be caused by longer fermentation periods.

Evidence in favour of lifestyle intervention for cancer prevention with special reference to colorectal cancer

Randomized controlled trials are recognized as having the strongest type of study design for generating evidence on prevention of disease. They are, however, the most labor- and time-intensive and costly to conduct. Intervention studies on the recurrence of colorectal adenomas might serve as a model with relevance to the etiology of not only large bowel cancer but also other sites of neoplastic development. The results of intervention studies assessing the effect of calcium, antioxidants and fiber on the recurrence of colorectal adenomas have been conflicting, showing a beneficial effect in some cases but not others. There are methodological issues in intervention trials for colorectal cancer, regarding study subjects, end point, dose, interaction, duration and timing, and compliance, for example. Although relatively few trials have been conducted to investigate the effects of an explicit dietary change on the recurrence of adenoma, results obtained so far have demonstrated that modifying the lifestyle may reduce the risk of chronic diseases including cancer. Furthermore, recent progress in molecular epidemiology has allowed clarification of many of the molecular mechanisms underlying susceptibility. Eventually, it may be possible to target intervention programs to genetically susceptible individuals, including molecular targeting, for the prevention of cancer.

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.

Calcium, dietary, and lifestyle factors in the prevention of colorectal adenomas

BACKGROUND

Many studies have suggested a role for calcium in reducing the risk of colorectal adenomas and cancer but its effectiveness may be dependent on interactions with other dietary and/or lifestyle factors. We examined the association between calcium and prevalence of adenomas and assessed whether the association was stronger in biologically plausible subgroups.

METHODS

Cross-sectional data from 222 cases and 479 adenoma-free controls who underwent colonoscopies and completed food frequency and lifestyle questionnaires were used in the analyses. Multivariable logistic regression was used to estimate the association between calcium and prevalence of adenomas. Stratified analyses and the likelihood ratio test were used to examine effect modification by various demographic, lifestyle, and behavioral factors.

RESULTS

Overall, little association was observed comparing total calcium intake of > or = 900 mg/day to < 500 mg/day (adjusted odds ratio [OR] = 0.85, 95% confidence interval [CI]: 0.53-1.37). However, stronger associations were observed in patients with lower fat intake and in those who regularly (> or = 15 times/month) took nonsteroidal antiinflammatory drugs (NSAIDs). Specifically, total calcium intake of > or = 900 mg/day was associated with a lower prevalence of adenomas among patients with lower fat intake (OR = 0.47, 95% CI: 0.25-0.91) but not among those with higher fat intake (OR = 1.20, 95% CI: 0.61-2.35; P-value for interaction = .01). For NSAIDs, the associations were OR = 0.37 (95% CI: 0.16-0.86) for regular NSAID users and OR = 1.27 (95% CI: 0.73-2.22) with infrequent or nonuse of NSAIDs, respectively (P = .06).

CONCLUSIONS

The data suggest that a lower-fat diet and regular NSAID use may enhance calcium's effectiveness as a colorectal cancer preventive agent.

Prolonged Effect of Calcium Supplementation on Risk of Colorectal Adenomas in a Randomized Trial

BACKGROUND

Calcium supplementation has been shown to decrease the risk of recurrence of colorectal adenomas in randomized trials. However, the duration of this protective effect after cessation of active supplementation is not known.

METHODS

In the Calcium Polyp Prevention Study, 930 subjects with a previous colorectal adenoma were randomly assigned from November 1988 through April 1992 to receive placebo or 1200 mg of elemental calcium daily for 4 years. The Calcium Follow-up Study was an observational phase of the trial that tracked adenoma occurrence for an average of 7 years after the end of randomized treatment and gathered information regarding the use of medications, vitamins, and supplements during that time. We obtained follow-up information for 822 subjects, 597 of whom underwent at least one colonoscopy after the end of study treatment and are included in this analysis. Generalized linear models were used to compute relative risks (RRs) and 95% confidence intervals (CIs) for the effect of randomized calcium treatment on risk of adenoma recurrence during the first 5 years after study treatment ended and during the subsequent 5 years. Statistical tests were two-sided.

RESULTS

During the first 5 years after randomized treatment ended, subjects in the calcium group still had a substantially and statistically significantly lower risk of any adenoma than those in the placebo group (31.5% versus 43.2%; adjusted RR = 0.63, 95% CI = 0.46 to 0.87, P = .005) and a smaller and not statistically significant reduction in risk of advanced adenomas (adjusted RR = 0.85, 95% CI = 0.43 to 1.69, P = .65). However, the randomized treatment was not associated with the risk of any type of polyp during the next 5 years. The findings were broadly similar when the analysis was restricted to subjects who did not report use of any calcium supplements after the treatment phase of the trial ended.

CONCLUSION

The protective effect of calcium supplementation on risk of colorectal adenoma recurrence extends up to 5 years after cessation of active treatment, even in the absence of continued supplementation.

Effect of calcium supplementation on the risk of large bowel polyps

BACKGROUND

Clinical trials have shown that calcium supplementation modestly decreases the risk of colorectal adenomas. However, few studies have examined the effect of calcium on the risk of different types of colorectal lesions or dietary determinants of this effect.

METHODS

Our analysis used patients from the Calcium Polyp Prevention Study, a randomized, double-blind, placebo-controlled chemoprevention trial among patients with a recent colorectal adenoma. Nine hundred thirty patients were randomly assigned to calcium carbonate (1200 mg/day) or placebo. Follow-up colonoscopies were conducted approximately 1 and 4 years after the qualifying examination. We used general estimating equation (GEE) and generalized linear regression analyses to compute risk ratios and 95% confidence intervals (CIs) to assess the effect of calcium treatment versus placebo on the risk of hyperplastic polyps, tubular adenomas, and more advanced lesions. Additionally, we used GEE analyses to compare the calcium treatment effects for various types of polyps with that for tubular adenomas. We also examined the interaction between calcium treatment and baseline intake of dietary calcium, fat, and fiber. All P values were obtained using Wald tests based on the corresponding models. All tests of statistical significance were two-sided.

RESULTS

The calcium risk ratio for hyperplastic polyps was 0.82 (95% CI = 0.67 to 1.00), that for tubular adenomas was 0.89 (95% CI = 0.77 to 1.03), and that for histologically advanced neoplasms was 0.65 (95% CI = 0.46 to 0.93) compared with patients assigned to placebo. There were no statistically significant differences between the risk ratio for tubular adenomas and that for other types of polyps. The effect of calcium supplementation on adenoma risk was most pronounced among individuals with high dietary intakes of calcium and fiber and with low intake of fat, but the interactions were not statistically significant.

CONCLUSION

Our results suggest that calcium supplementation may have a more pronounced antineoplastic effect on advanced colorectal lesions than on other types of polyps.

Intestinal polyp formation in the Apcmin mouse: effects of levels of dietary calcium and altered vitamin D homeostasis

This study evaluated the effects of various levels of dietary calcium on polyp formation, vitamin D homeostasis, and fecal bile acids in the Apcmin mouse. Female Apcmin mice were randomized to three groups and fed a purified diet with either half or double the level of calcium in control AIN-93G. Serum 25-OH-D and fecal bile acids were measured at weeks 0 and 12 of treatment. Mice were killed for polyp scoring by two observers blinded to treatment after 12 weeks. Results show there was no difference in polyp number or tumor load with dietary calcium in any treatment group. Serum 25-OH-D was reduced and total fecal bile acids were increased in animals that received the high calcium diet. We have previously shown that vitamin D supplementation diminishes polyp load; the lack of effect of an altered calcium diet seen here may be due to a disturbance in vitamin D homeostasis.

Dairy products and colorectal cancer. A review of possible mechanisms and epidemiological evidence

OBJECTIVES

This review provides an overview of the principal hypotheses and epidemiological evidence of the possible links between colorectal cancer and intake of milk and/or dairy products.

METHODS

The first section outlines the main hypotheses about the possible effect of calcium, vitamin D, fats and other milk components. The possible role of acid lactic bacteria in fermented products is also discussed. The second section is a summary of the published epidemiological evidence. The results on milk, cheese and yoghurt are summarized using a meta-analytical approach. The results of studies on calcium and vitamin D are briefly described.

RESULTS

Case-control studies are heterogeneous and, on average, do not provide evidence of association between total intake of total dairy products, milk, cheese or yoghurt and colorectal cancer risk. The average result from cohort studies support the hypothesis of a protective effect of total dairy products (odds ratio (OR): 0.62; 95% confidence interval (CI): 0.52-0.74; P heterogeneity test: 0.93) and for milk (OR: 0.80; 95% CI: 0.68-0.95; P heterogeneity: 0.77). No association was found between cheese (OR: 1.10; 95% CI: 0.88-1.36; P heterogeneity: 0.55) or yoghurt (OR: 1.03; 95% CI: 0.83-1.28; P heterogeneity: 0.69) in cohort studies.

CONCLUSIONS

Cohort studies consistently found a protective effect of total dairy products and milk intake, but the evidence is not supported by case-control studies. No relationship was found with cheese or yoghurt intake. As the number of cohort studies is still limited, their results need to be confirmed by other prospective studies.

Dietary calcium supplementation increases apoptosis in the distal murine colonic epithelium

BACKGROUND

Increased dietary calcium might reduce colorectal cancer risk, possibly by reduction of colonic epithelial hyperproliferation, but not all studies have demonstrated this. Little is known about the effects of calcium on colonic apoptosis.

AIM

To quantify the effects of increasing calcium on apoptosis and cell proliferation in normal murine colonic crypt epithelium.

METHODS

Twenty one day old male C57B1/6 mice were fed either control AIN-76 diet (0.5% calcium wt/wt; n = 10) or the same supplemented with calcium carbonate (1.0% calcium; n = 10) for 12 weeks. Apoptotic cells in proximal and distal segments were counted and expressed as an apoptotic index (AI: frequency of apoptosis/100 longitudinal crypts). The bromodeoxyuridine (BrdU) labelling index was also determined. Differences were analysed by the student's t test.

RESULTS

In control animals, the AI was significantly higher in the caecum/proximal colon (mean, 28.6; SEM, 2.0) compared with the distal colon (mean, 19.9; SEM, 1.8; p = 0.004). In the calcium treated group, the AI in the caecum/proximal colon (mean, 30.6; SEM, 1.7) was similar to controls (p = 0.71) but the AI in the distal colon was significantly greater (mean, 32.6; SEM, 1.8; p = 0.001) than in control mice and was raised to values similar to those in the proximal colon. Calcium was also associated with reduced crypt cellularity and, in the proximal colon, a downward shift in the crypt position at which apoptosis occurred. There were no significant differences in the BrdU labelling index between groups or between proximal and distal colonic segments in each group.

CONCLUSIONS

Increased dietary calcium is associated with the induction of apoptosis in normal mouse distal colonic epithelium without affecting cell proliferation. This might contribute to its putative chemopreventive role in colorectal carcinogenesis. Whether this effect is direct or indirect requires further study.

Effects of miso and NaCl on the development of colonic aberrant crypt foci induced by azoxymethane in F344 rats

The present study was designed to investigate the effects of dietary miso and NaCl supplementation on the development of aberrant crypt foci (ACF) induced by azoxymethane (AOM) in male F344 rats. A total of 76 rats, six weeks of age, were divided into seven groups and given weekly subcutaneous injections of AOM (15 mg/kg body wt) for three weeks to induce ACF. The animals were placed on diets one week before the first AOM dosing. Group 1 was fed a normal diet as a control. Groups 2-4 were fed diets containing 5%, 10%, and 20% miso, respectively, and Groups 5 and 6 were fed diets containing 2.2% and 4.4% NaCl, respectively, for five weeks. Group 7 was fed a normal diet without carcinogen exposure. Dietary miso inhibited the development of ACF in a dose-dependent manner (y = -3.9x + 140, r = -0.94). Thus the mean numbers of ACF per colon were significantly lower in Groups 3 and 4 than in Group 1 (p < 0.01), and there were fewer aberrant crypts per colon in Group 4 than in Group 1. NaCl supplementation was associated with fewer ACF, but this was not statistically significant. 5-Bromo-2'-deoxyuridine labeling indexes in the colonic epithelium were significantly lower in Group 3 than in Group 1 (p < 0.05). The present results indicate that dietary miso could act as a chemopreventive agent for colon carcinogenesis.

Calcium inhibits colon carcinogenesis in an experimental model in the rat

Different dietary factors can affect colorectal cancer incidence. However, the effect of increased levels of dietary calcium on neoplasms is unclear. The present study was designed to examine the effect of a low calcium supplement on experimental colon carcinogenesis induced by parenteral administration of dimethylhydrazine (DMH). One hundred and twenty 10-week-old Sprague-Dawley rats were divided into five groups of equal sex distribution. The 10 rats in group A (control group) received no treatment; the 30 rats in group B (DMH group) were injected subcutaneously with 18 weekly doses of 21 mg/kg DMH; the 20 rats in group C (EDTA control group) received EDTA solution only; the 30 rats in group D (calcium group) received calcium at 3.2 g/l by adding calcium lactate to the drinking water from the start until the conclusion of the experiment; and the 30 rats in group E (DMH + calcium group) received oral calcium supplements at the same dose as the rats in group D (calcium group) and the same DMH injections as the rats in group B (DMH group). The rats were sacrificed at 25-34 weeks. In group E, we observed a significant diminution in the number of tumours (P = 0.01); an increase in the number of tumour-free animals (P = 0.006); a change in tumour location towards the distal colon (P < 0.025); more adenomas (P = 0.02); and a diminution of adenocarcinomas and mucinous carcinomas, although this was not significant. We conclude that a low dietary calcium supplement in rats inhibits colon cancer carcinogenesis induced by DMH, and changes tumour location towards the distal colon.

Experimental models of colorectal cancer

PURPOSE

A review of in vivo and in vitro models of colorectal cancer is presented.

METHODS

A retrospective literature review was performed with reference to CD-ROM Medline and Index Medicus.

RESULTS

A comparison of the advantages and disadvantages of the models is presented in addition to a summary of individual model methodology and applications.

CONCLUSIONS

Such models are a useful adjunct for surgical research in colorectal oncology.

Prospective randomized study of sulindac versus calcium and calciferol for upper gastrointestinal polyps in familial adenomatous polyposis

Eighteen patients with familial adenomatous polyposis (FAP) who had previously undergone colectomy but had upper gastrointestinal polyps were studied in a double-blind randomized crossover trial comparing sulindac with calcium and calciferol. Sulindac produced a reduction in the crypt proliferation index in the gastric epithelium of patients but did not significantly affect duodenal mucosa. Calcium with calciferol did not have any effects on crypt proliferation index in patients with FAP.

Calcium regulation of colonic crypt cell kinetics: evidence for a direct effect in mice

BACKGROUND & AIMS

Oral calcium supplementation is believed to decrease colonic hyperproliferation through neutralization of fatty acids and bile acids. In the present study, the effect of oral calcium, given with low-fat diets, in the early stages of colorectal carcinogenesis is evaluated.

METHODS

In experiment A, mice received normal or low-calcium diets and were killed at 25 weeks. In experiment B, mice were fed the same diets but were submitted to six weekly injections of dimethylhydrazine and were killed at 10, 16, and 21 weeks. Cell proliferation was evaluated using bromodeoxyuridine immunohistochemistry.

RESULTS

In experiment A, mice fed low-calcium diets showed a significant upward shift of the proliferative compartment (P = 0.04) (phase 2 defect) in the absence of hyperproliferation. In experiment B, besides a phase 2 defect, dimethylhydrazine-induced hyperproliferation was also significantly enhanced in animals fed low-calcium diets (phase 1 defect) as shown by an increased number of labeled cells per column and total labeling index (P = 0.01).

CONCLUSIONS

Low-calcium diets induce an upward shift of the main proliferative compartment, which reflects an increased risk for malignant transformation. This effect was observed with a low-fat diet, suggesting a direct mechanism, rather than the usual indirect one, documented with high-fat diets.

The effect of extracellular calcium on colonocytes: evidence for differential responsiveness based upon degree of cell differentiation

Calcium supplementation decreases the incidence of colon cancer in animal models and may prevent colon cancer in man. Potential mechanisms include binding of mitogens and direct effects of calcium on colonic epithelial cells. In this study, the effects of extracellular calcium on epithelial cell growth and differentiation were studied in three colon carcinoma and two colonic adenoma cell lines. The characteristics studied included morphology, cell cycle kinetics, [Ca2+]IC (intracellular calcium concentration), proliferation, and expression of differentiation markers such as carcinoembryonic antigen (CEA) and alkaline phosphatase (AP). Sodium butyrate (NaB) and 1,25-dihydroxyvitamin D3 were used as controls in the latter three assays as these two agents are known differentiating agents. Alteration of [Ca+2]EC (extracellular calcium concentration) did not affect carcinoembryonic antigen (CEA) or alkaline phosphatase (AP) expression. NaB enhanced the expression of AP three-fold and CEA five-fold. This effect was augmented by increasing [Ca2+]EC. The exposure of cells to 1,25-(OH)2-Vitamin D3 increased CEA but not AP. [Ca2+]IC increased in response to 1,25-(OH)2-vitamin D3 and NaB but not with variation in [Ca2+]EC. Increased [Ca2+]EC inhibited proliferation of well-differentiated cells, but had no effect on poorly-differentiated cells. Morphological studies showed that extracellular calcium was necessary for normal cell-cell interactions. These studies have demonstrated direct effects of calcium on colonic epithelial cells which may contribute to the protective effects of dietary calcium against colon cancer. Loss of responsiveness to the antiproliferative effects of [Ca2+]EC with de-differentiation suggests that calcium supplementation may be most beneficial prior to the development of neoplastic changes in colonic epithelium.

The effect of calcium supplements on rectal mucosal proliferation

Seventy-nine patients with colorectal adenomata were randomised to receive calcium carbonate (3,000 mg) or placebo in a double-blind randomised trial to assess the short- and long-term effects on rectal mucosal proliferation measured by the in vitro metaphase arrest technique crypt cell production rate (CCPR). There was no significant difference in mean CCPR between the groups before treatment or after 3 or 12 months. In those patients randomised to calcium, CCPR fell at both 3 months [9.0 (2.8) cc c-1 h-1, t = 3.15, d.f = 76, P = 0.002] and 12 months [9.2 (3.3) cc c-1 h-1 t = 2.7, d.f. = 74, P = 0.009] compared with pretreatment CCPR [12.2 (5.5) cc c-1 h-1]. We have demonstrated that calcium had no effect on mucosal proliferation compared with placebo. The results on adenoma formation are awaited.

Calcium phosphate supplementation results in lower rat fecal bile acid concentrations and a more quiescent colonic cell proliferation pattern than does calcium lactate

Although there is general agreement that dietary calcium is protective against colon carcinogenesis, considerable controversy exists on the relative efficacy of the counterion in calcium supplements. We therefore conducted a comparative study in rats of four forms of calcium supplementation (calcium phosphate, casein, lactate, and a 50:50 phosphate-carbonate combination). The relative effects of these supplements on measurements of colon physiology, in vivo pH, fecal fat, individual bile acids, and in vivo cell proliferation were measured in the same animals. In contrast to results when amounts of calcium are varied, there was no effect of form of supplement on total fecal output or output of fecal fat. Calcium phosphate resulted in the most acidified cecal contents. Calcium phosphate and calcium casein resulted in lower fecal concentrations of lithocholate and lower amounts of total fecal bile acids than supplementation with the calcium lactate or combination diets. In addition, rats fed calcium phosphate had lower concentrations of fecal beta-muricholate than rats provided with the calcium combination supplement. In the proximal colon, calcium phosphate resulted in a significantly lower number of cells per crypt column and a lower labeling index than the calcium lactate diet. The position of the highest labeled cell was lower with calcium phosphate supplementation than with supplementation from the calcium combination or the calcium lactate diet. There was a highly significant correlation between the pH of cecal contents and labeling index in the proximal colon (r = 0.98, p = 0.003). The results suggest that calcium phosphate may inhibit colon tumor incidence more effectively than calcium lactate, because the calcium phosphate group had a lower colonic proliferative status than the calcium lactate group. Changes in the proliferative status of colonocytes are known to precede and accompany neoplasia.

Effect of calcium supplementation on rectal epithelial hyperproliferation in intestinal bypass subjects

BACKGROUND/AIMS

Fatty acids and bile acids are tumor promoters of experimental colon cancer in rats. Calcium can inhibit their effects. After intestinal bypass (IB), fecal bile acid and lipid levels increase markedly. In rats, IB increases colonic cell proliferation and carcinogen-induced colon tumor incidence. Whether fecal bile acids and lipids influence rectal epithelial proliferation in humans is uncertain. This study compared rectal epithelial proliferation in IB subjects and in controls matched for age, sex, and body mass index and investigated the effects of calcium carbonate supplementation (2400 or 3600 mg Ca2+/day for 12 weeks) on proliferation indices in IB subjects.

METHODS

Epithelial proliferation was studied by in vitro incubation of rectal biopsy specimens with [3H] thymidine. Twenty-four-hour stool collections were assayed for bile acids, lipids, and calcium.

RESULTS

Whole crypt labeling index (LI) and upper crypt LI were increased in IB subjects compared with controls (P < 0.005). Calcium reduced whole crypt LI by 38% (P < 0.001) and upper crypt LI by 56% (P < 0.05). Levels of fecal bile acids (4.5 mmol/day) and lipids (131.9 g/day) were markedly elevated in IB subjects (P < 0.005).

CONCLUSIONS

IB induces rectal hyperproliferation and expansion of the proliferative zone in association with excessive output of fecal bile acids and lipids. Oral calcium reverses the proliferative changes.

Role of calcium in colon cancer prevention: experimental and clinical studies

Many dietary factors have been studied for their potential in the chemoprevention of human colorectal cancer. From an epidemiological standpoint, there have been many studies linking calcium intake to colon cancer risk. Significant reductions in risk have been shown for the consumption of milk, dietary calcium and dairy products in general. Additionally, there have been numerous studies of calcium and cell proliferation in experimental animals. Supplemental calcium in the diet or drinking water has been reported to decrease the colonic epithelial hyperproliferation induced by bile and fatty acids, enteric resection, a nutritional stress diet, and to suppress induction of the tumor-promotion enzyme ornithine decarboxylase. Calcium has also demonstrated an inhibitory effect on experimental colon carcinogenesis. Mechanisms of calcium inhibition are still speculative, but the "calcium soaps" hypothesis, fatty acid destabilization of cellular membranes, modulation of protein kinase C and K-ras mutations are under investigation. Additionally, numerous clinical studies of calcium modulation of human colonic hyperproliferation in high-risk groups as well as chemoprevention trials of calcium supplementation are currently ongoing. Although the question of whether dietary calcium can prevent human colorectal cancer remains to be answered, the data presently available appear promising.

Calcium intake and 28-year gastro-intestinal cancer mortality in Dutch civil servants

The association between calcium intake and gastrointestinal cancer mortality was investigated in a 28-year follow-up study. Data were obtained from a general health examination in 1953-1954 among Dutch civil servants and their spouses, aged 40 to 65 years. Information from 2,591 participants was used for this study. Risk analyses were performed using logistic regression models with the highest quintile of calcium intake as reference. No statistically significant relation between calcium intake and gastrointestinal cancer mortality is observed, although the risk estimate for women with the lowest calcium intake is substantial. Odds ratios (OR) were adjusted for age, energy intake and dietary fiber. After inclusion of other potential confounders to the models (body-mass index and smoking habits), the results hardly differed. Both men and women who died of colorectal cancer had a lower mean calcium intake compared to the rest of the population. For women this was statistically significant. Our results suggest that a low calcium intake may be related to gastrointestinal cancer mortality among women of this study population.

Oral calcium inhibits rectal epithelial proliferation in familial adenomatous polyposis

Calcium reduces colorectal cell turnover and might therefore protect against neoplasia. The inhibitory effects of dietary calcium were tested in a double-blind controlled trial in patients with familial adenomatous polyposis who had undergone previous abdominal colectomy and ileorectal anastomosis. Patients received supplemental calcium carbonate (1500 mg/day) or placebo tablets for 6 months; sigmoidoscopy was performed before and after treatment. Rectal biopsies were maintained in short-term organ culture, and crypt cell production rate (CCPR) was measured stathmokinetically. A total of 25 patients completed the trial; polyp counts were obtained before and after treatment in all and CCPR values in 16. Calcium treatment reduced the mean (s.e.m.) CCPR from 4.72 (0.48) to 2.42 (0.48) cells per crypt per h (P < 0.05), while values for placebo were unchanged (5.46 (1.21) versus 5.08 (1.17) cells per crypt per h). Calcium had no demonstrable effect on the number, size or distribution of rectal polyps. The ability of oral calcium supplementation to suppress rectal epithelial proliferation supports its potential to prevent development of colorectal carcinoma in high-risk individuals.

Effects of dietary calcium and phosphate on the intestinal interactions between calcium, phosphate, fatty acids, and bile acids

Luminal free fatty acids and bile acids may damage the colonic epithelium and stimulate proliferation, which may increase the risk of colon cancer. It has been suggested that only soluble calcium ions (Ca2+) precipitate fatty acids and bile acids, thus reducing their lytic activity. Consequently, precipitation of luminal Ca2+ by dietary phosphate should inhibit these effects. To evaluate the proposed antagonistic effects of dietary calcium and phosphate, we studied the intestinal interactions between calcium, phosphate, fatty acids, and bile acids in rats fed purified diets that differed only in the concentrations of calcium and phosphate. Increased dietary calcium drastically decreased the solubility of fatty acids in the ileum, colon, and faeces, as well as the solubility of bile acids in the colon and faeces. Although dietary calcium strongly increased the total faecal fatty acid concentration and hardly affected the total faecal bile acid concentration, the fatty acid and bile acid concentrations in faecal water were drastically decreased by dietary calcium. Consequently, the lytic activity of faecal water was decreased. Dietary phosphate did not interfere with these intestinal effects of calcium. These results indicate that dietary phosphate does not inhibit the protective effects of dietary calcium on luminal solubility and the lytic activity of fatty and bile acids.

Preventive effect of magnesium hydroxide on carcinogen-induced large bowel carcinogenesis in rats

Preventive effect of magnesium hydroxide on carcinogen-induced, large bowel carcinogenesis was examined in three experiments using F344 rats. Experiment I: Rats received dietary administration of magnesium hydroxide at concentrations of 500 or 1,000 ppm after treatment with methylazoxymethanol (MAM) acetate (25 mg/kg, 3 times). These rats had a lower incidence of large bowel neoplasms than animals given MAM acetate alone. Reduction of the tumor incidence was especially significant at a dose of 500 ppm. Experiment II: Rats given magnesium hydroxide (250, 500, or 1,000 ppm) together with 1,2-dimethylhydrazine (DMH) (20 mg/kg, 10 times) showed a lower multiplicity of large bowel tumors than those given DMH alone. Experiment III: The labeling indices of the cryptal cells of the large bowel (cecum or proximal colon or distal colon) or rates given magnesium hydroxide for 4, 6, or 8 weeks after treatment with MAM acetate (25 mg/kg, 3 times) were smaller than those of animals given MAM acetate alone, indicating that magnesium hydroxide suppressed, carcinogen-induced epithelial cell (large bowel) proliferation. The results of the three experiments suggest that magnesium, one of the essential metals, is a promising chemopreventive agent in humans.

Protective mechanisms of dietary fibers in nutritional carcinogenesis

Fibers in foods are complex carbohydrates. There are several types of fiber, but, for the purpose of mechanistic insight into their mode of protective action in carcinogenesis, classification into two broad types, soluble and insoluble fibers, is warranted. Soluble fibers are present in fruits, vegetables, and certain grains like oats. This type of fiber undergoes metabolism in the small intestine and especially in the large intestine through bacterial enzymes, converting it to products that increase stool size only moderately. But, they have appreciable effects in modifying the metabolism of colon carcinogens like azoxymethane to yield detoxified products and, thus, reducing colon carcinogenesis. In contrast, insoluble fibers present in sizeable amounts in bran cereals, like wheat or rice, are not significantly metabolized by enzymes in the intestinal flora. Such fibers increase stool size substantially through several mechanisms, including higher water retention. The larger bulk dilutes carcinogens, especially tumor promoters such as secondary bile acids, resulting in lower risk of colon cancer in animals and in humans. Evidence in animal models and in humans also indicates that fiber may lower the risk of breast cancer, possibly via an endocrine mechanism. Based on these concepts, increased intake of total fiber, but especially of wheat bran cereal fiber, to yield a daily stool in adults of about 200 grams can significantly reduce the risk of colon cancer and, to a lesser but definite extent, of breast cancer. Thus, adequate fiber intake from cereals, fruits, and vegetables can help prevent important types of human cancer.

Vitamin D and its metabolites inhibit cell proliferation in human rectal mucosa and a colon cancer cell line

Like calcium, vitamin D may protect against colorectal neoplasia as it reduces epithelial cell proliferation and induces differentiation. Although its therapeutic use is limited by its effects on calcium metabolism, analogues such as calcipotriol produce little hypercalcaemia. Stathmokinetic and immunohistochemical techniques were used to study the effect of 1,25 (OH)2 D3 and its analogues on cell proliferation in human rectal mucosa and a colon cancer cell line. Paired sigmoidoscopic biopsy specimens were obtained from 17 control patients and five patients with familial adenomatous polyposis. Explants were established in organ culture, with or without the addition of vitamin D. Proliferation was assessed using (1) metaphase arrest to determine the crypt cell production rate (CCPR) and (2) Ki-67 monoclonal antibody directed against an antigen present in proliferating cells. 1,25 (OH)2 D3 in concentrations of 1 microM-100 pM (10(-6)-10(-10) M) reduced the CCPR (cells/crypt/hour) from 4.74 to 2.15-2.67 (p < 0.001), and the Ki-67 labelling index from 7.28-3.74 (p < 0.01). Likewise, vitamin D2, 10 nM (10(-8) M) reduced the CCPR from 4.74-2.74 (p < 0.05) and calcipotriol from 4.86-2.38 (p < 0.05). In familial adenomatous polyposis patients 1,25 (OH)2 D3 100 pM (10(-10) M) halved the CCPR from 8.75-4.22. Calcipotriol (10(-5) M to 10(-9) M) produced a clearcut dose response inhibition of HT-29 cell growth. Thus, vitamin D and its metabolites inhibit proliferation in normal and premalignant rectal epithelium and suppress growth in a colorectal cancer cell line.

Bioavailabilities of calcium, phosphorus and magnesium from whey mineral complex in growing male rats

The bioavailabilities of Ca, P and Mg from whey mineral complex (WMC) were studied from the viewpoint of the mineral balance and bone properties in growing male rats and compared with bovine bone ash (BBA) and CaCO3. Ca source showed no significant effect on feed intake, body weight gain or feed efficiency (p < 0.05). When the dietary Ca level was 0.3%, the dry weight of the femur in rats fed WMC was significantly higher than that in rats fed BBA. The femur P content of rats fed 0.3% Ca as WMC was significantly higher than that of rats fed BBA or CaCo3. The breaking energy of the femur from rats fed WMC was significantly higher than that from rats fed BBA at a Ca level of 0.2% or 0.3%. There was the same tendency in bone densities as was observed in breaking properties. There was no significant difference in quantitative values for Ca balance among three groups of rats, whereas those rats fed WMC had a significantly higher P retention than other groups. Ca bioavailability from WMC and the effect on the utilization of P and Mg were discussed.

Dietary calcium does not reduce experimental colorectal carcinogenesis after small bowel resection despite reducing cellular proliferation

It has been proposed that colorectal carcinogenesis is accompanied by increased mucosal cell proliferation and that the converse may also apply. To examine this thesis, the crypt cell production rate (CCPR) was measured in eight groups of rats (n = 187) that had received 1,2 dimethylhydrazine, 70% small bowel resection, supplemental dietary calcium, or a combination of these. Analysis of variance showed the following: (1) the CCPR decreased between the ileum and distal colon; (2) the CCPR decreased between 16 and 32 weeks; (3) 1,2 dimethylhydrazine and small bowel resection increased the CCPR and calcium decreased the CCPR independently of one another; (4) the CCPR interacted with 1,2 dimethylhydrazine x small bowel resection, calcium x 1,2 dimethylhydrazine and interacted between the site of bowel and calcium, 1,2 dimethylhydrazine, small bowel resection, and 1,2 dimethylhydrazine x small bowel resection (p = 0.014 to p < 0.001). The tumour yield was reduced by calcium in 1,2 dimethylhydrazine treated animals (chi 2 = 14.1, df = 3, p < 0.01) but was unaffected by calcium in 1,2 dimethylhydrazine and small bowel resection treated animals despite significant differences in the CCPR. An increase of the CCPR both preceded and accompanied colorectal carcinogenesis but reduction of the CCPR was not invariably accompanied by reduced carcinogenes.

Reduction of mucosal crypt cell proliferation in patients with colorectal adenomatous polyps by dietary calcium supplementation

The crypt cell production rate was measured in 14 patients with adenomatous colorectal polyps, 17 patients with colorectal cancer and 12 control subjects. The median (interquartile range) rate (cells per crypt per hour) was found to be significantly higher (P less than 0.001) in the polyp (2.45 (1.94-3.20)) and cancer (3.01 (2.35-3.68)) groups compared with controls (1.25 (0.70-1.85)). A double-blind cross-over study was performed in patients with adenomatous polyps consisting of 2 months' treatment, 2 weeks' washout, followed by 2 months' treatment with dietary calcium supplementation (1.25 g day-1) versus placebo. A significant reduction in the crypt cell production rate occurred with calcium treatment compared with the placebo (1.25 (0.6-2.25) versus 2.15 (1.58-3.08) cells per crypt per hour, P = 0.035). This study demonstrates a significant reduction in mucosal cell proliferation by dietary calcium supplementation in patients with adenomatous polyps. Such treatment may be worthy of further investigation in patients at high risk of developing colorectal polyps.

The effect of dietary calcium supplementation on intestinal lipid metabolism

Population studies in man and experimental animal work support the contention that dietary supplementation with calcium may prevent the development of colorectal cancer. The mechanism of action is postulated to be bile acid chelation in the small-bowed forming non-toxic calcium soap compounds but such substances have yet to be isolated and quantified. In this 2-part study faecal concentrations of acidic lipids and neutral sterols were measured in 93 Sprague-Dawley rats whose calcium intake was modulated by enriching the chow and adding calcium lactate (24 milligrams) to the drinking water. In study-1 (dietary calcium intake doubled from 0.4-0.8%) small bowel resection was used to manipulate colonic lipid concentration for comparison with control rats who had undergone transection with immediate restoration of bowel continuity at an equivalent point. Faecal concentrations of free bile acids were 53-67% less in animals receiving added calcium [1.76 +/- 1.33 vs 0.82 +/- 0.65 mg/g (transection); 2.74 +/- 3.73 vs 1.03 +/- 1.27 mg/g (small bowel resection): P less than 0.001]. In study-2 (dietary calcium intake trebled to 1.21%) faecal bile acid concentration was reduced by 32% (1.86 +/- 0.57 vs 1.27 +/- 0.34 mg/g: NS) whereas long chain fatty acid concentrations were increased by 117% (6.77 +/- 2.39 vs 14.67 +/- 4.82 mg/g: P less than 0.001) in animals receiving added calcium. Serum calcium levels remained unchanged in these animals. Calcium soaps of the bile acids were not detected in faeces and therefore contrary to popular theory these results indicate that conditions within the intestinal lumen favour calcium chelation of long chain fatty acids rather than bile acids.

Effect of magnesium hydroxide on methylazoxymethanol acetate-induced epithelial proliferation in the large bowels of rats

The effect of magnesium hydroxide on the epithelial proliferation of the large bowel was examined using rats given methylazoxymethanol (MAM) acetate. Dietary administration of magnesium hydroxide at 250, 500, 1000 or 2000 ppm. for 1, 3 or 5 weeks did not influence the cell cycle of the cryptal cells of the large bowel. However, the exposure to magnesium hydroxide under these conditions lowered the bromodeoxyuridine labeling index of the cells of the large bowel of the rats which had been initiated by MAM acetate (25 mg/kg, 3 times). The decrease in labeling index was more apparent in the proximal segment than in the distal segment. Such an inhibitory effect on the DNA synthesis of the epithelial cells by magnesium hydroxide may be related to the suppressive action of the trace element on the carcinogen-induced large bowel carcinogenesis.

Influence of dietary calcium supplements on ileoanal pouch function and cytokinetics

A double-blind cross-over study was undertaken in 16 patients after panproctocolectomy and ileoanal pouch reconstruction to compare supplementary calcium (1.5 g/day) with placebo over 2 months with a 2-week washout period. Stool frequency was recorded and the effects on pouch mucosal crypt cellular proliferation were determined using an in vitro stathmokinetic technique which measures the crypt cell production rate (CCPR) and an immunohistochemical method using the Ki67 monoclonal antibody for proliferating nuclei. The median (interquartile range) diurnal stool frequency was reduced by calcium (4 (3-5) per day) compared with values obtained before treatment (7 (5-10) per day, P less than 0.002) and with placebo (7 (6-9) per day, P = 0.002). Similarly, calcium reduced nocturnal stool frequency (1 (0-1) per night) compared with pretreatment and placebo (both 2 (1-3) per night, P less than 0.05) values. Calcium reduced the mean(s.e.m.) CCPR to 1.88(0.41) cells per crypt per hour compared with pretreatment (3.63(0.53), P = 0.01) and placebo (3.24(0.43), P = 0.002) values. Median (interquartile range) Ki67 activity was also reduced by calcium (13.2 (9.7-16.7) per cent), compared with values obtained before treatment (27.3 (14.3-30.2) per cent, P = 0.001) and with placebo (26.0 (17.2-32.0) per cent, P = 0.001). Stool frequency was significantly correlated with the CCPR (diurnal: r = 0.37; nocturnal: r = 0.31, both P less than 0.05). Nine patients used antidiarrhoeal medication while receiving placebo compared with four patients receiving calcium (P = 0.032). This study has shown that supplementary oral calcium significantly reduced stool frequency in patients with pouches, a reduction that was associated with reduced cell proliferation. The mechanisms for this effect are not known.

Long-term toxicity/carcinogenicity study of calcium lactate in F344 rats

The long-term toxicity/carcinogenicity of calcium lactate, a food additive, was examined in F344 rats. Calcium lactate was given ad lib. in the drinking-water at levels of 0, 2.5 or 5% to groups of 50 male and 50 female rats for two years. No clear toxic lesion was specifically caused by long-term administration of calcium lactate. No significant dose-related increase was found in the incidences of tumours in any organ or tissue. The results indicated that calcium lactate had neither toxic nor carcinogenic activity in F344 rats.

Suture technique affects perianastomotic colonic crypt cell production and tumour formation

Suture line recurrence is an important cause of failure after potentially curative resection for colonic carcinoma. Our aim was to determine whether suture technique affected the incidence of perianastomotic tumours in experimentally induced colonic cancer. Sprague-Dawley rats were randomized into three groups. A 1 cm longitudinal colotomy was repaired with four interrupted 6/0 polypropylene monofilament sutures, using either a transmural technique (n = 18) or a seromuscular technique (n = 18). Control animals (n = 18) had a sham laparotomy. All animals received nine, weekly, subcutaneous injections of azoxymethane (total dose 90 mg/kg) starting 6 weeks after laparotomy. Surviving animals were killed 32 weeks after laparotomy. Five animals from each group were given intraperitoneal bromodeoxyuridine (100 mg/kg) 1 h before being killed. At death, perianastomotic tumours occurred more frequently in animals with transmural sutures than in either controls or those with seromuscular sutures. This difference was associated with a greater mucosal bromodeoxyuridine crypt cell labelling index in the transmural suture group. We conclude that a transmural anastomotic suture technique promotes the development of experimental perianastomotic colonic tumours.

Effects of dietary calcium and vitamin D3 on tumor promotion in mouse skin

The effects of low, adequate, and supplemental intake of calcium and vitamin D3 on 12-O-tetradecanoylphorbol-13-acetate (TPA) skin tumor promotion were examined. Administration of the experimental diets was started one week before the first TPA application to the 7,12-dimethylbenz[a]anthracene-initiated dorsal skin of female Sencar mice. Neither dietary calcium in a range from 0.15% to 2.0% of the diet as calcium carbonate nor vitamin D3 ranging from 200 to 4,000 IU/kg diet resulted in modulation of the skin papilloma response in terms of incidence, number per mouse, or size distribution of tumors. There were also no effects of the varied levels of calcium or vitamin D3 on mouse body weights, serum calcium, or TPA induction of epidermal ornithine decarboxylase activity. These results indicate that dietary administration of a wide range of doses of calcium or vitamin D does not alter the serum calcium levels and, therefore, does not appear capable of altering skin tumor promotion. These results are in contrast to reports that demonstrate antineoplastic activity for both calcium ion and active hormonal vitamin D, either in control of epidermal cell proliferation and/or differentiation or inhibition of carcinogenesis.

Intervention studies in adenoma patients

There is considerable evidence that most colorectal carcinomas arise in preexisting adenomas. It also appears that there may be a considerable influence of diet in the genesis and growth of adenomas. This evidence is discussed and the current dietary intervention studies in humans are reviewed.

Calcium and the prevention of colon cancer

Diet is a major determinant of colon cancer risk. Calcium may protect against colon cancer, presumably by binding cytotoxic bile acids and fatty acids. Numerous studies support this proposition. In subjects at risk for colon cancer oral calcium supplementation has been shown to reduce rectal epithelial proliferation rate, thereby supposedly decreasing cancer risk. In contrast to the original hypothesis that phosphate counteracts the effect of calcium, evidence has now been provided that phosphate is crucial for the intraluminal binding of bile acids in complexes of calcium, phosphate, and bile acids. Supplemental calcium has been shown to reduce the cytotoxic potential of fecal water, which is probably attributable to the profound effect of calcium on bile acid and fatty acid metabolism. However, some reservation with regard to the protective ability of calcium seems to be warranted as we found that oral calcium supplementation caused an increase in epithelial proliferation rate in the sigmoid of patients with adenomatous polyps. Further controlled studies evaluating the effects of calcium on the epithelium of different parts of the colon should now be performed.

Lipid absorption and intestinal tumour incidence in rats fed on varying levels of calcium and butterfat

The purpose of the 2 x 2 factorial study was to determine the effect of varying levels of dietary calcium (2.5 and 10 g/kg) and butterfat (50 and 200 g/kg) on lipid utilization and on development of colon tumours in animals initiated with 1,2-dimethylhydrazine dihydrochloride. Among rats fed on 200 g butterfat/kg, the fourfold increase in Ca intake induced more than a sevenfold increase in faecal excretion of total lipids and almost a fortyfold increase in faecal excretion of acid-extractable lipid. Among rats fed on 50 g butterfat/kg, the ingestion of supplemental Ca had a less dramatic effect and induced only a twofold increase in faecal excretion of total lipids and a threefold increase in acid-extractable lipid. The volume of intestinal adenocarcinomas was correlated with the excretion of acid-extractable lipid in faeces (R 0.369, P less than 0.02). Caecal enzymic activity was not correlated with tumour incidence or size or faecal lipid excretion. Overall, the fourfold increase in Ca intakes decreased total lipid absorption significantly but by less than 6%.

Effect of defunction on cytokinetics and cancer at colonic suture lines

An intestinal suture line potentiates experimental carcinogenesis in its vicinity, probably due to adaptive hyperplasia. By contrast, a defunctioning colostomy causes distal hypoplasia, and fewer tumours develop. Male Sprague-Dawley rats (n = 160) were used to study adaptation (assessed by a stathmokinetic technique) and carcinogenesis (induced by azoxymethane) at an end-to-end anastomosis that was raised in either functioning or defunctioned left colon. Controls had no procedure and other rats had proximal colostomy alone. Defunction had a profound antitropic effect on the colon, reducing bowel length and weight and crypt cell production rate (CCPR) by 22-56 per cent. Anastomotic CCPR was increased by a factor of 2.6 over controls: mean(s.e.m.) values of 12.71(2.85) versus 4.87(0.41) cells/crypt/h (P less than 0.01), but defunction reduced this by 76 per cent to a mean(s.e.m.) value of 3.00(0.52) cells/crypt/h below that in the intact colon. In the left colon, 39-50 per cent of tumours were sited at the anastomosis. Compared with controls there were 77 per cent fewer tumours in defunctioned colon, but they still favoured the site of anastomosis. Neoplasms at the colostomy site accounted for 74-77 per cent of all right-sided tumours. Anastomosis and defunction have powerful but contrasting effects on colonic adaptation and carcinogenesis; when combined they tend to cancel each other out.

Injury induced by fatty acids or bile acid in isolated human colonocytes prevented by calcium

Measurement of the modulation of the growth fraction of isolated normal colonocytes from adult subjects in primary monolayer culture was used as a sensitive quantitative assay to evaluate toxic effects of several endogenous compounds found within the colon. This assay was used to study the role of CaCl2 in blocking cell injury. When added simultaneously with the injurious agent, 5-10 mM CaCl2 blocked the toxicity of physiological concentrations of deoxycholic acid, oleic acid, palmitic acid and linoleic acid.

Dietary calcium and chronic diseases

The Agricultural Revolution was almost certainly associated with a substantial decrease in human calcium intake. Calcium intakes typical of contemporary humans may well be inadequate for many individuals. Various slowly developing chronic disorders such as osteoporosis, hypertension, hyperlipidemia, and colon cancer may be induced or exaggerated by the current low level of dietary calcium intake in Western societies. We propose two hypotheses relating calcium intake to diverse diseases: first, the adaptation required to adjust to low intakes is inadequate to maintain critical components of cellular calcium regulation; second, the constant, forced adaptive response to low intake itself produces untoward consequences.

Changes in intestinal function of rats initiated with DMH and fed varying levels of butterfat, calcium, and magnesium

The effects of dietary calcium, magnesium, and butterfat on intestinal function and flora in rats initiated with 1,2-dimethylhydrazine (DMH) were studied. Male weanling rats were assigned to six isocaloric diets that varied in their levels of calcium and magnesium (0.25% Ca with 0.05% Mg, 1.0% Ca with 0.05% Mg, or 0.625% Ca with 0.50% Mg) and butterfat (5% or 20%). One-half of the rats in each treatment were injected subcutaneously with DMH weekly for four weeks. This short-term exposure to DMH increased colonic ornithine decarboxylase (ODC) activity and the mass of cecal contents. Ingestion of the high levels of either calcium or magnesium depressed colonic ODC activity and depressed apparent absorption of organic matter, calcium, magnesium, and phosphorus. Ingestion of excess magnesium increased the mass of the cecal contents by twofold, caused hypertrophy of cecal walls, and increased the total amount of protein and total nitroreductase and beta-glucuronidase activity in the ceca of rats. Ingestion of supplemental calcium had less dramatic effects and increased the mass of cecal contents by only 28% and decreased the total amount of protein in the ceca. On the basis of their different effects on cecal microflora, magnesium appears to have less potential than does calcium as a protective agent against colon cancer.

Basic and clinical investigations of dietary calcium in the prevention of colorectal cancer

Long-standing investigations into the role of diet in colon cancer have generally supported the notion that some aspect of dietary fats acts to promote cancer at this site. Understanding of the chemical behavior of lipids in the colon led to a hypothesis suggesting that depletion of calcium could partly explain the tumor-promoting effects of dietary fat. Calcium levels may control critical intracellular events in the course of proliferation. Lack of availability or loss of calcium may result in abnormalities in the regulation of colonic proliferation. Basic and clinical studies suggest that calcium supplementation reduces colonic proliferation implying a potential reduction in cancer risk. The current evidence supporting calcium as a cancer chemoprevention agent is reviewed.

Heterogeneity in the response of familial polyposis epithelial cells and adenomas to increasing levels of calcium in vitro

A biomarker of increased risk for colon cancer is abnormally high proliferation of colonic epithelial cells. The authors developed an in vitro assay that measures the ability of human colonic epithelial cells that are in progressive stages of abnormal development to respond to direct application of calcium as the chloride in tissue culture medium. Incorporation of 3H-thymidine and autoradiography in situ was employed to measure the number of proliferating cells cultured at 0.1 mM CaCl2, the optimum level for growth, and 2.2 to 5 mM, both levels achievable in the colonic lumen. Abnormal cell proliferation was reduced in biopsies from 13 of 14 patients without familial polyposis but at increased risk for colon cancer because of previous colonic neoplasms or familial association; in cells from three of four asymptomatic individuals in familial polyposis families at risk for that disease; and in cells of three of ten patients symptomatic with familial polyposis. Growth of tubular adenoma cells from two of seven familial polyposis patients was also inhibited by calcium. Growth inhibition was not observed in more advanced colon tumors including eight adenomas, either villotubular or villous, and five carcinomas. These findings indicate heterogeneity within the familial polyposis phenotype for the normal cellular response to growth inhibition by calcium, and a further loss of response to calcium as these cells progress toward malignancy.