Calcium, Vitamin D, and Prevention of Colon Cancer

Martin Lipkin

• Publisher: CRC Press
• Year: 2018
• Print ISBN:
  9781315891286
• eBook ISBN:
  9781351087285
• Topic: Medicine
• Subtopic: Nutrition, Dietics & Bariatrics

These proceedings were published as a result of a workshop sponsored by the Chemoprevention Branch of the National Cancer Institute. The workshop covered a range of topics including calcium and vitamin D in human nutrition; epidemiologic relationships betweencalcium, vitamin D, and colon cancer; the biology of calium and vitamin D at the tissue and cellular level; and enimal and human studies investigating the potential for prevention of colon cancer with calcium and vitamin D.

Session V
Human Studies: Potential for Prevention of Colon Cancer with Calcium and Vitamin D

SHORT-TERM CALCIUM INTERVENTION STUDIES, IN ANIMALS AND HUMANS, USING EPITHELIAL PROLIFERATION AS BIOMARKER OF RESPONSE. THE INITIATION OF A CALCIUM INTERVENTION TRIAL IN ADENOMA PATIENTS

Paul Rozen

Department of Gastroenterology Tel Aviv Medical Center and Sackler Faculty of Medicine Tel Aviv University, 6 Weizman Street Tel Aviv, Israel

I. INTRODUCTION

Large bowel cancer is one of the most common internal malignancies found in countries having a westernized lifestyle and is a major cause of cancer mortality.¹ Its secondary prevention, by screening, is the subject of many large-scale trials. However, the effectiveness of this approach remains to be confirmed.¹

II. DIETARY ETIOLOGY

Over the past decades, there has been marked progress in the understanding of colorectal neoplasia etiology and pathogenesis. A sequence of events in the bowel mucosa, beginning with hyperproliferation -> adenoma -> dysplasia -> cancer has been recognized. Stepwise genetic changes are being mapped out, and nutritional studies have broadly delineated the role of diet in large bowel cancer etiology.¹ These have made the primary prevention of colorectal cancer a feasible goal in the not too distant future.²

In general, human nutritional studies have indicated a dietary pattern related to large bowel neoplasia rather than any one specific dietary factor. Inconsistencies in human studies are to be expected considering that we are trying to relate retrospectively dietary habits of tens of years to the onset of neoplasia.¹ Overall, it can be said that most studies indicate a relationship to total caloric and fat (especially saturated fat) intake and an inverse relationship to fiber, calcium, and vitamin consumption. Physical activity and obesity have also been partially associated with large bowel neoplasia. The inconsistencies of the various epidemiologic nutritional studies in colorectal cancer might also be explained by the fact that nutritional factors associated with its etiology act in opposite directions. Additional modulating effects of micronutrients, vitamins, and minerals are more difficult to evaluate in reported diets.³

III. CALCIUM AND COLORECTAL NEOPLASIA

One decade ago, Garland and Garland⁴ suggested that calcium might have a protective role in the etiology of large bowel neoplasia. Further epidemiological studies from the same group have continued to support this hypothesis.^5,6 However, only a few international or population correlation studies have provided confirmatory epidemiologic evidence.^7,8 This could be due to the lack of marked difference in calcium intake between the countries or populations at high risk for colorectal cancer.⁷ Another recent suggestion has been that it only has a site - specific protective effect, namely on the sigmoid colon.⁹

Stronger but indirect evidence for the protective role of dietary calcium came from animal studies. Diets high in bile acids and/or fat resulted in large bowel mucosal damage and, therefore, increased epithelial proliferation. This could be reduced by adding calcium or vitamin D to the diet, even in the presence of a carcinogen.^{10, 11, 12, 13}

These epidemiologic and experimental studies support the hypothesis by Newmark et al.¹⁴ that the western diet is calcium deficient relative to the high-fat intake. They suggested that dietary calcium, binding to intraluminal fat and bile salts and forming insoluble complexes, was probably the protective mechanism.

IV. EXPERIMENTAL STUDIES EVALUATING THESE MECHANISMS

To further elucidate the calcium protective mechanism, we designed a study in which rats were fed a low-calcium and low vitamin D, reduced-fat, and high-residue diet (Table 1).¹⁵ It should be noted that the amount of Ca²⁺ and vitamin D in the basal experimental diet is equivalent to a daily human intake of 300-400 mg Ca²⁺ and 400 IU vitamin D.

TABLE 1
Standard and Modified (Experimental) AIN-76 Formula Feed^a

	Standard	Modified
Fat %	5.0	3.50
Ca^2+ %	0.5	0.05
Phosphate %	0.4	0.40
Vitamin D IU/g	1.0	0.40
Cellulose %	5.0	16.50

^a Derived from reference 15.

Except for a control group that received intrarectal saline, colon cancer was induced with intrarectal N-methyl-N-nitro-N-nitrosoguanidine (MNNG). During this induction phase, the rats (other than controls) received solubilized calcium carbonate or lactate added to their drinking water. So, the mean intake for the control animals was 9 mg Ca²⁺/day, while the supplemented animals received about 8 times this amount. The rodents were sacrificed after 8, 16, 20, or 28 weeks of initiating MNNG or saline treatment. Large bowel epithelial proliferation was assessed by standard tritiated thymidine methodology. The labeling index (LI) rose significantly after 16 weeks of MNNG instillations and even more so after 28 weeks. Those rats receiving added Ca²⁺ had no significant change in their LI until after the 28th week when it was still only half that of those without added Ca²⁺ but triple the control values (Figure 1).

Figure 1. Bar graph demonstrating mean LI ± SD of rats killed 1 week after 8, 16, 20, or 28 weeks of i.r. MNNG or saline (first bar graph at 28 weeks).

Our conclusions from this study were: (1) Dietary Ca²⁺ supplements can reduce the hyperproliferation induced by MNNG. (2) This can occur when giving a low-fat and low vitamin D and high-cellulose diet. Because this diet is metabolically relatively inert in the rat colon, it would seem likely that the added Ca²⁺ effect was due to its property of maintaining intercellular stabilization and thereby reducing the need for cell replacement rather than an effect on intraluminal fat.

This hypothesis was supported by a recent review by Wargovich,¹⁶ who pointed out that calcium is required for stabilization of cellular membranes. Its loss could disrupt the intercellular tight junctions and stimulate proliferation. Calcium can also regulate the transition of nontumorous cells from the G to S phase during cell division but not influence proliferation of tumor cells. The Ca²⁺ effect might also be mediated via the calcium-binding protein, calmodulin, involved in initiation of DNA synthesis.¹⁷

In vitro human colonic epithelial studies have been made possible by the development of long-term culture techniques for normal epithelial cells. By altering, within physiological limits, the concentration of calcium in the medium, it was possible to demonstrate inhibition of proliferation as measured by [³H]- thymidine and autoradiography. This was true if the proliferation was abnormally high, as from persons at high familial risk for large bowel cancer, but not from most cases if cells came from adenomas and never if from carcinomas.¹⁸

There have been more recent experimental studies relevant to understanding the mechanism of the Ca²⁺ protective effect. Skraastad and Reichelt¹⁹ gave mice an endogenous colon mitosis inhibitor and a standard fat diet that was supplemented with cholic acid and various amounts of Ca²⁺. Those receiving the most Ca²⁺ had the lowest hyperproliferative response to cholic acid. In a further study by Welberg et al.,²⁰ adenoma patients were given 1.5 g Ca²⁺ daily, and their duodenal cholic acid was increased. The authors felt that this was a favorable response as the dihydroxy bile acids are the more cytotoxic. In a study by Sitrin et al.,²¹ rats receiving dimethylhydrazine (DMH) and a high Ca²⁺ diet had significantly fewer colon tumors. This protective effect was negated by a vitamin D-deficient diet but without increasing proliferation, as assessed by mucosal polyamine levels. The same group also studied K-ras mutations in the colon tumors and found that Ca²⁺ supplementation completely suppressed K-ras mutations but only partially in the presence of vitamin D deficiency.²²

These various studies again suggest that the protective effect of calcium could be at several sites at the cellular level, via effects on bile composition, and not only at the intraluminal level.

V. SHORT-TERM STUDIES IN HUMANS

Most of the studies in humans were clinical trials in which the effect of short-term calcium supplementation was studied. The germinal study, using proliferation of the colonic epithelium as a biomarker of response, was that of Lipkin and Newmark.²³ They demonstrated that hyperproliferative, asymptomatic persons at high risk for familial colon cancer had hyperproliferation suppressed by ...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• Introduction
• Presenters and Planning Committee Members
• SESSION I: CALCIUM AND VITAMIN D IN HUMAN NUTRITION
• SESSION II: EPIDEMIOLOGY: RELATIONSHIPS BETWEEN CALCIUM AND VITAMIN D INTAKE AND COLON CANCER
• SESSION III: BIOLOGY OF CALCIUM AND VITAMIN D AT THE CELLULAR AND TISSUE LEVEL
• SESSION IV: ANIMAL STUDIES: PREVENTION OF COLON CANCER WITH CALCIUM AND VITAMIN D
• SESSION V: HUMAN STUDIES: POTENTIAL FOR PREVENTION OF COLON CANCER WITH CALCIUM AND VITAMIN D
• INDEX