Effect of calcium carbonate and aluminum hydroxide on human intestinal function

National guidelines on nutrient reference values for the healthy adult population and for pregnant or lactating women are based on heterogeneous sources of evidence: review of guidelines

Many countries provide dietary guidelines for health practitioners and/or the general population. However, there is no general, international guideline serving as a template for national dietary guidelines, and there is little to no consensus regarding reference values for different nutrients. The present review compared 27 national dietary guidelines for healthy adults as well as for pregnant and/or breastfeeding women, and analysed their quality and the evidence behind their recommendations. The guidelines were evaluated for their quality using the instrument Agree II, and found to be heterogeneous (overall quality score 14%-100%) and often insufficient (quality score < 50%) due to missing information about their methodology and sources of evidence. We analysed the evidence (number of studies, study types and publication years) of reference values of a number of nutrients using the five guidelines that provided the highest scores in the Agree II assessment. The reference values varied among guidelines, were rarely based on up-to-date meta-analyses, and were often based on insufficiently reported evidence (22/27 guidelines with quality score < 50%). We recommend systematic reviews of high quality studies to formulate future guidelines, and to use guidelines on how to write guidelines.

Fatty Acids from Different Fat Sources and Dietary Calcium Concentration Differentially Affect Fecal Soap Formation in Growing Pigs

BACKGROUND

Calcium (Ca) can complex with free fatty acids in the gastrointestinal tract (GIT), leading to the formation of insoluble unabsorbable Ca-fatty acid soaps, contributing to the proposed effect of Ca on weight loss in humans.

OBJECTIVES

We determined the effect of dietary Ca concentration and the individual long-chain fatty acids on Ca-fatty acid soap formation and fatty acid digestibility.

METHODS

Nine-week-old crossbreed male pigs (n = 144; mean ± SD body weight: 21.7 ± 0.15 kg) were used as an animal model for digestion in the adult human. The animals received purified diets containing 4 Ca concentrations (0, 2, 4, and 6 g/kg diet) and 4 fat sources (tallow, palmolein oil, soybean oil, and olive oil) in a completely randomized design. Fatty acids, Ca, and Ca-fatty acid soaps were determined in feces (n = 9 per diet).

RESULTS

Increasing dietary Ca led to a 4-fold increase (P ≤ 0.05) in excreted palmitic and stearic acid when diets contained tallow or palmolein oil as the major fat source. More than 80% of these excreted fatty acids were present as soaps. For the tallow-based diets, increasing dietary Ca led to a decrease in stearic acid digestibility from 91% to 66% (P ≤ 0.01) and in palmitic acid digestibility from 96% to 83% (P ≤ 0.01). For the olive oil- and soybean oil-based diets dietary Ca did not (P > 0.05) influence fatty acid excretion.

CONCLUSIONS

Ca-fatty acid soap formation led to decreased fat absorption in the GIT of growing pigs, which supports the hypothesis that higher dietary Ca concentrations reduce fat absorption.

Vitamin D receptor polymorphism rs2228570 is significantly associated with risk of dyslipidemia and serum LDL levels in Chinese Han population

Background

The goal of this study was to determine if vitamin D receptor (VDR) gene polymorphisms underlie susceptibility to dyslipidemia in a Chinese Han population.

Methods

Three tag single nucleotide polymorphisms (SNPs) (rs11574129, rs2228570, and rs739837) were genotyped using TaqMan assays to determine VDR SNP associations with dyslipidemia. We genotyped 877 cases of dyslipidemia from a normotensive, non-diabetes mellitus population and 1822 non-dyslipidemia subjects in a stage I study. In a follow-up stage II study, we included a larger sample of 3124 controls and 1679 cases with dyslipidemia. Finally, we explored the potential molecular mechanism for the SNP associations using molecular modeling analysis.

Results

We found a significant association between SNP rs2228570 and dyslipidemia in the additive (adjusted odds ratio (OR) = 1.255, 95% Confidence Interval (CI) = (1.118–1.409), P < 0.001), dominant (OR = 1.384, 95% CI = 1.384 (1.136–1.6), P = 0.001) and recessive models (OR = 1.356, 95%CI = 1.1–1.671, P = 0.004) in stage I. We further established that the rs2228570 variant was significantly associated with dyslipidemia in the additive (adjusted OR = 1.146, 95% CI = 1.053–1247, P = 0.002), dominant (OR = 1.184, 95%CI =1.018–1.376, P = 0.028) and recessive models (OR = 1.209, 95%CI = 1.064–1.374, P = 0.004) in stage II. The TT genotype was significantly higher (4.93 ± 0.75 mmol/L) compared to the TC (4.67 ± 0.47 mmol/L) or CC (4.66 ± 0.44 mmol/L) genotype (P = 0.01) in cases with elevated low-density lipoprotein cholesterol (LDL-C) levels. In contrast, the cases with the TT genotype had significantly lower serum 25(OH)D levels (18.43 ± 5.04 ng/ mL) compared to the TC (26.24 ± 4.16 ng/mL) and CC (36.76 ± 8.10 ng/ mL) genotypes (P < 0.001). Multivariable linear regression analysis indicated that the rs2228750 genotype significantly correlated with serum low-density lipoprotein-C (LDL-C) levels in cases with dyslipidemia. Using molecular modeling analysis, we further found that the rs2228570 variant changed the structure and the stability of VDR and altered the binding energy of its ligand.

Conclusions

The VDR rs2228570 variant may increase susceptibility to dyslipidemia in the Chinese Han population.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0819-0) contains supplementary material, which is available to authorized users.

Calcium Supplementation Does Not Contribute to Constipation in Healthy Women

PURPOSE

It is commonly suggested that calcium supplementation contributes to constipation; however, little research has explored the effects of calcium supplementation on gut motility.

METHODS

In an 8-week, randomized, double-blind, crossover pilot study, healthy females (n = 27, aged 43.0 ± 10.6 years) received a split dose of 500 mg/d of elemental calcium from calcium carbonate or calcium phosphate each for 2 weeks, after a 2-week baseline and separated by a 2-week washout. Participants completed daily questionnaires of stool frequency, Bristol Stool Form Scale (BSFS), and supplement intake compliance.

RESULTS

There were no differences among periods. Mean ± SE stool frequency averaged 1.3 ± 0.1 stools/d in each period. Participants reported 34%, 34%, 37%, and 29% of stools were indicative of slow transit or constipation (BSFS of 1 or 2) during baseline, calcium carbonate, calcium phosphate, and washout periods, respectively. Participants also reported from 6% to 10% of stools as fast transit or diarrhea (BSFS of 6 or 7) during the periods.

CONCLUSION

This study suggests that neither calcium carbonate nor calcium phosphate, providing 500 mg/d of calcium, affects stool frequency or form. Although stool frequency was normal, the healthy females participating in the study experienced stools indicating slow (constipation) and fast (diarrhea) transit.

Effects of vitamin D on plasma lipid profiles in statin-treated patients with hypercholesterolemia: A randomized placebo-controlled trial

BACKGROUND & AIMS

Lipid abnormalities are regarded as a risk factor for cardiovascular disease. Low vitamin D status has been shown to be associated with hyperlipidemia. We planned to research the effects of vitamin D supplementation as an adjuvant therapy for patients with hypercholesterolemia.

METHODS

Patients with hypercholesterolemia were enrolled in this single-center, double-blind, placebo-controlled trial in Beijing (39°54' N). Fifty-six patients were randomly assigned to receive vitamin D (n = 28, 2000 IU/d) or a placebo (n = 28) as an add-on to statin, by the method of permutated block randomization. Serum lipid levels were evaluated at baseline, 1, 3 and 6 months.

RESULTS

Vitamin D supplementation resulted in increased serum 25-hydroxyvitamin D concentrations compared with placebo (+16.3 ± 11.4 compared with +2.4 ± 7.1 ng/ml; p < 0.001). At 6 months, the primary end point, a difference in the fall of serum total cholesterol levels between the vitamin D and placebo groups after 6 months of treatment was significant -22.1 mg/dl (95% CI -32.3; -12.2) (p < 0.001). The difference between the groups in the fall of serum triglyceride levels after 6 months of treatment was -28.2 mg/dl (95% CI -48.8; -8.4) (p < 0.001). In patients with 25-hydroxyvitamin D level<30 ng/ml at baseline (n = 43), the serum total cholesterol and triglyceride levels were reduced by -28.5 ± 11.9 mg/dl (p < 0.001) and -37.1 ± 19.5 mg/dl (p < 0.001), respectively.

CONCLUSIONS

Vitamin D supplementation might improve serum lipid levels in statin-treated patients with hypercholesterolemia, it might be an adjuvant therapy for patients with hypercholesterolemia. Clinical Trials Registration Number - NCT02009787.

Effect of Low- and High-Calcium Dairy-Based Diets on Macronutrient Oxidation in Humans

OBJECTIVE

Higher calcium and dairy intakes may be associated with lower body weights, but a mechanism in humans has yet to be elucidated. We compared the effects of a dairy-based high-calcium diet and a low-calcium diet on macronutrient oxidation.

RESEARCH METHODS AND PROCEDURES

Subjects (10 men and nine women) consumed a low-dairy (LD, approximately one serving per day, approximately 500 mg Ca(2+)/d) or high-dairy (HD, approximately three to four servings per day, approximately 1400 mg Ca(2+)/d) energy balance diet for 1 week. Each diet condition was performed twice. On the 7th day, subjects were studied in a room calorimeter under one of four study conditions, applied in a randomized crossover design. Within each diet condition, subjects were studied under conditions of energy balance and acute energy deficit. The deficit (-600 kcal/d) was induced only for the 24 hours that subjects resided in the room and was achieved by a combination of caloric restriction and exercise.

RESULTS

Under energy balance conditions, there was no effect of diet treatment on respiratory quotient or 24-hour macronutrient oxidation. Under energy deficit conditions, 24-hour fat oxidation was significantly increased on the HD diet (HD with deficit = 136 +/- 13 g/d, LD with deficit = 106 +/- 7 g/d, p = 0.02).

DISCUSSION

Consumption of a dairy-based high-calcium diet increased 24-hour fat oxidation under conditions of acute energy deficit. We hypothesize that these effects are due to an increased fat oxidation during exercise.

Dairy beverages and energy balance

High dairy intakes have been associated with lower rates of obesity in observational studies, but mechanisms to explain the association are lacking. A high intake of dairy protein reduces spontaneous food intake and may be one important mechanism, but more specific effects of dairy calcium seem to exist. We have found that high versus low calcium intakes from dairy products had no effect on 24-h energy expenditure or substrate oxidation rates, but fecal fat excretion increased approximately 2.5-fold on the high-calcium diets. In a meta-analysis of intervention studies we found that increasing dairy calcium intake by 1200mg/day resulted in increased fecal fat excretion by 5.2 (1.6-8.8) g/day. Newer research shows that humans possess taste receptors for calcium in the gastrointestinal tract and that signaling may be linked to appetite regulation. A new line of evidence suggests that an inadequate calcium intake during an energy restricted weight loss program may trigger hunger and impair compliance to the diet. These mechanisms may be part of the explanation for the protective effects of dairy products with regard to obesity and metabolic syndrome.

Effect of calcium from dairy and dietary supplements on faecal fat excretion: a meta-analysis of randomized controlled trials

Observational studies have found that dietary calcium intake is inversely related to body weight and body fat mass. One explanatory mechanism is that dietary calcium increases faecal fat excretion. To examine the effect of calcium from dietary supplements or dairy products on quantitative faecal fat excretion, we performed a systematic review with meta-analysis. We included randomized, controlled trials of calcium (supplements or dairy) in healthy subjects, where faecal fat excretion was measured. Meta-analyses used random-effects models with changes in faecal fat excreted expressed as standardized mean differences, as the studies assessed the same outcome but measured in different ways. An increased calcium intake resulted in increased excretion of faecal fat by a standardized mean difference of 0.99 (95% confidence intervals: 0.63-1.34; P < 0.0001; expected to correspond to approximately 2g day(-1)) with moderate heterogeneity (I(2) = 49.5%) indicating some inconsistency in trial outcomes. However, the dairy trials showed homogeneous outcomes (I(2)=0%) indicating consistency among these trials. We estimated that increasing the dairy calcium intake by 1241 mg day(-1) resulted in an increase in faecal fat of 5.2 (1.6-8.8) g day(-1). In conclusion, dietary calcium has the potential to increase faecal fat excretion to an extent that could be relevant for prevention of weight (re-)gain. Long-term studies are required to establish its potential contribution.

The absorption of stearic acid from triacylglycerols: an inquiry and analysis

Although stearic acid is a saturated fatty acid, its influence on plasma cholesterol acid other health variables is neutral; possibly owing in part to poor absorption. Reduced absorption of stearic acid from particular triacylglycerols, cocoa butter and novel fats formulated with short- and long-chain acid triacylglycerol molecules (Salatrims) has been attributed to high intakes. However, the circumstances and causes of poor stearic acid digestion from triacylglycerols are unclear; published data were therefore collected and analysed, with emphasis on human studies. Of twenty-eight studies conducted in adults, most are in men (>90%). The assertion that reduced absorption is due to a high intake of stearoyl groups is not supported: dietary intakes of stearoyl of 0·05–0·65 g stearic acid equivalent/kg body weight (cf typical intake of 0·2 g stearic acid equivalent/kg body weight in the Western diet) indicate that the ‘true’ digestibility of stearoyl is 0·98 (SE 0·01) g/g, with apparent digestibility less than this value at low intakes owing to endogenous stearic acid excretion and to inter-publication variation of unidentified cause. The neutral health impact of stearic acid must be due to factors other than availability. Exceptions include cocoa butter, Salatrims and tristearin, for which digestibility is an additional factor. The efficiency with which human subjects digest stearoyl from cocoa butter still remains uncertain, while the digestion of total long-chain fat from this source is 0·89–0·95 g/g, high in comparison with 0·33 g/g for Salatrim 23CA and 0·15 g/g for tristearin in their prepared states. Salatrims contain the highest proportion of long-chain fatty acids that are stearic acid-rich other than tristearin, which is the main component of fully-hydrogenated soyabean and rapeseed oil. Analysis shows that apparent digestibility of stearic acid is associated with stearoyl density within the triacylglycerol molecule and that, in Salatrims, the occurrence of short-chain fatty acids in place of long-chain fatty acids increases this density. Soap formation appears not to be a major factor in the reduced digestion of stearic acid from tristearin under regular dietary circumstances, but both microcrystallinity and reduced digestibility of tri-, di- and monostearoylglycerols appears to be important. Solubilisation of high-melting-point tristearin in low-melting-point oils improves the digestibility of its stearic acid, particularly when emulsified or liquidized at above melting point. However, without such artificial aids, the digestive tracts of the rat, dog and man have a low capacity for emulsifying and digesting stearic acid from tristearin. Reduced digestibility of stearic acid from Salatrim 23CA also appears to be attributable to reduced digestibility of di- and monostearoylglycerols and is particularly due to remnants with the 1- or 3-stearoylglycerol intact after initial hydrolytic cleavage. Short-chain organic acid in Salatrim 23CA, which is readily hydrolysed, leaves such remnants. Unlike tristearin, Salatrim 23CA melts at body temperature and mixing it with low-melting-point oils is not expected to cause further disruption of microcrystalline structures to aid digestibility of its stearoyl groups. The low digestibility of stearoyl in Salatrim 23CA, together with the occurrence of short-chain organic acids in this product, account for its relatively low nutritional energy value (about 20 kJ (5 kcal)/g) compared with traditional fats (37 kJ (9 kcal)/g) and low fat value (<20:37 kJ/kJ; <5:9 kcal/kcal) relative to traditional fats. In part these differences are because of minor effects of Salatrim 23CA on the excretion of other fat and protein, due to the bulking properties of this poorly-digestible fat.

Effects of calcium and plant sterols on serum lipids in obese Zucker rats on a low-fat diet

Ca may interfere with fat and cholesterol metabolism through formation of insoluble soaps with fatty and bile acids in the intestine. In the present study, we examined the effects of different dietary Ca levels on the serum lipid profile and cholesterol metabolism in obese Zucker rats fed a low-fat diet. We also tested whether dietary Ca interfered with the lipid-lowering effects of a pine oil-derived plant sterol mixture. Increase in dietary Ca intake from 0·2 to 0·8 %, and further to 2·1 % (w/w) dose-dependently decreased serum total cholesterol (r -0·565,P=0·002,n27), LDL-cholesterol (r -0·538,P=0·006,n25), and triacylglycerol (r -0·484,P=0·014,n25) concentrations, and increased HDL-cholesterol (r 0·478,P=0·016,n25) and HDL : LDL cholesterol (r 0·672,P<0·001,n25) in rats fed a 1 % cholesterol diet. Analysis of serum campesterol : cholesterol and sitosterol : cholesterol suggested that Ca dose-dependently increased intestinal cholesterol absorption (r 0·913,P<0·001,n18), whereas serum desmosterol : cholesterol and lathosterol : cholesterol indicated that Ca dose-dependently increased endogenous cholesterol synthesis (r 0·691,P=0·003,n18). Therefore, the decrease of serum LDL-cholesterol appeared to be due to Ca-induced increase in the conversion of cholesterol to bile acids. The increase in Ca intake did not interfere with the beneficial effects of plant sterols on serum total cholesterol, LDL-cholesterol and HDL-cholesterol concentrations. The high-Ca diet with plant sterol supplementation further increased the HDL-cholesterol concentration and HDL : LDL cholesterol. The present findings indicate that the beneficial effects of dietary Ca on the serum lipid profile during a low-fat diet are dose-dependent, and resemble those of bile acid sequestrants. Increased dietary Ca did not impede the lipid-lowering effects of natural plant sterols.

High calcium intake lowers apparent digestibility of energy in veal calves

Veal calves aged 8 weeks were fed iso-energetic amounts of milk replacers with either a low (7.1 g of calcium/kg of air-dry diet) or a high concentration of calcium (11.6 g of calcium/kg of air-dry diet) for a period of 10 weeks. The extra calcium was added in the form of calcium formiate. Final body weight of the two dietary groups was similar. Faeces were collected during the final week of the trial. The high calcium diet raised faecal dry matter output by 87% and faecal energy by 70%. The extra output of faecal dry matter was composed of 36% and 37% of crude fat and ash, respectively. The extra faecal energy output was for 75% in the form of crude fat. The high versus low calcium intake not only depressed apparent digestibility of total lipids but also that of crude protein, carbohydrates and ash. It is concluded that a high calcium intake by veal calves reduced energy availability without affecting body weight gain.

Antacids revisited: a review of their clinical pharmacology and recommended therapeutic use

Antacids are commonly used self-prescribed medications. They consist of calcium carbonate and magnesium and aluminum salts in various compounds or combinations. The effect of antacids on the stomach is due to partial neutralisation of gastric hydrochloric acid and inhibition of the proteolytic enzyme, pepsin. Each cation salt has its own pharmacological characteristics that are important for determination of which product can be used for certain indications. Antacids have been used for duodenal and gastric ulcers, stress gastritis, gastro-oesophageal reflux disease, pancreatic insufficiency, non-ulcer dyspepsia, bile acid mediated diarrhoea, biliary reflux, constipation, osteoporosis, urinary alkalinisation and chronic renal failure as a dietary phosphate binder. The development of histamine H2-receptor antagonists and proton pump inhibitors has significantly reduced usage for duodenal and gastric ulcers and gastro-oesophageal reflux disease. However, antacids can still be useful for stress gastritis and non-ulcer dyspepsia. The recent release of proprietary H2 antagonists has likely further reduced antacid use for non-ulcer dyspepsia. Other indications are still valid but represent minor uses. Antacid drug interactions are well noted, but can be avoided by rescheduling medication administration times. This can be inconvenient and discourage compliance with other medications. All antacids can produce drug interactions by changing gastric pH, thus altering drug dissolution of dosage forms, reduction of gastric acid hydrolysis of drugs, or alter drug elimination by changing urinary pH. Most antacids, except sodium bicarbonate, may decrease drug absorption by adsorption or chelation of other drugs. Most adverse effects from antacids are minor with periodic use of small amounts. However, when large doses are taken for long periods of time, significant adverse effects may occur especially patients with underlying diseases such as chronic renal failure. These adverse effects can be reduced by monitoring of electrolyte status and avoiding aluminum-containing antacids to bind dietary phosphate in chronic renal failure. Antacids, although effective for discussed indications of duodenal and gastric ulcer and gastro-oesophageal reflux disease, have been replaced by newer, more effective agents that are more palatable to patients. Antacids are likely to continue to be used for non-ulcer dyspepsia, minor episodes of heartburn (gastro-oesophageal reflux disease) and other clear indications. Although their wide-spread use may decline, these drugs will still be used, and clinicians should be aware of their potential drug interactions and adverse effects.

Kinetics of aluminum disposition after ingestion of low to moderate pharmacological doses of aluminum

We assessed the kinetics of aluminum uptake and elimination by tissues of Sprague Dawley rats following a single gavage dose of 0, 0.25, 0.5, or 1 mmol Al/kg body weight (b.w.) in 1 ml of 16% citrate (equivalent to 0-650 mg Al to a 70-kg human). Serum, liver, kidney, and tibia aluminum concentrations were measured 15, 30, 60, 120, 270, and 360 min after dosing. Serum aluminum concentrations were proportional to dose in rats dosed with 0.25 or 0.5 mmol Al/kg b.w. but were not proportional to dose for rats dosed with 1 mmol Al/kg b.w. Elimination half-lives of serum aluminum were similar for all treatments (102-119 min) which suggests that the non-linear aluminum kinetics in serum reflected a difference in absorption of the highest dose. Although fasted rats dosed with 0.25 or 1 mmol Al/kg b.w. with citrate absorbed aluminum with similar efficiency (4.2% of dose), the length of the absorptive period was prolonged in the rats given the highest does. Total absorbed aluminum mass in rats dosed with 0.25 and 0.5 mmol vs. 1 mmol Al/kg b.w. reached a plateau at 120 vs. 270 min after dosing, respectively. The kinetics of aluminum in liver, bone, and kidney were generally dose-independent. Elimination half-lives of liver aluminum were similar for all aluminum treatments (267-465 min); elimination half-lives could not be estimated in bone and kidney because of turnover exceeded the 6 h collection period.

Hypocholesterolemic action of Lactobacillus acidophilus ATCC 43121 and calcium in swine with hypercholesterolemia induced by diet

Thirty-three Yorkshire barrows (92 kg), fed a high cholesterol diet for 14 d had mean concentrations of serum cholesterol of 294.6 +/- 7.8 mg/dl. Starting on d 15 and for an additional 15 d, crystalline cholesterol was removed from the diet and pigs were assigned to one of four treatments: including two levels of calcium (0.7% and 1.4%) with and without added viable Lactobacillus acidophilus ATCC 43121 (2.5 x 10(11) cells per feeding). Serum cholesterol levels decreased, as expected, for all groups. However, the declines were initiated sooner for the groups receiving L. acidophilus. and those receiving the high level of calcium than for the respective control groups. When averaged over days, pigs fed L. acidophilus had 11.8% lower total cholesterol than pigs fed a diet without L. acidophilus. Similarly, pigs fed 1.4% calcium had a significantly lower total cholesterol than pigs fed 0.7% calcium. The effects were greater on low density lipoprotein cholesterol than on high density lipoprotein cholesterol. In addition, during the overall 15-d experimental period, serum bile acids were reduced 23.9% by dietary L. acidophilus and by 21.4% by 1.4% dietary calcium compared with those of their controls. Total bile acid concentration was positively correlated with total cholesterol concentration for pigs fed L. acidophilus or 1.4% calcium. These data suggest that both L. acidophilus and calcium can enhance the reduction of serum cholesterol in pigs that had been fed a high cholesterol diet, probably through alteration in the enterohepatic circulation of bile acids.

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.

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.

Effects of supplemental dietary calcium on the intestinal association of calcium, phosphate, and bile acids

It has been suggested that supplemental dietary calcium decreases hyperproliferation of colonic epithelial cells because calcium precipitates and thus inactivates luminal bile acids. Therefore, 12 healthy men were studied before and after dietary calcium supplementation (35.5 mmol/day) to quantify intestinal associations of calcium, phosphate, and bile acids. The supplemental dietary calcium was almost completely (95%) recovered, mainly in feces. Calcium increased the fecal excretion of both phosphate (31%) and bile acids (53%) and decreased the ratio of dihydroxy to trihydroxy bile acids in duodenal bile almost twofold. In vitro studies showed that precipitation of glycodeoxycholic acid was caused by the formation of insoluble calcium phosphate. Water-soluble and calcium-associated amounts of phosphate and bile acids in feces were measured by resolubilization studies, using the calcium chelator ethylenediaminetetraacetate. In both the control and calcium periods, significant amounts of phosphate (80% and 90%) and bile acids (33% and 50%) were calcium-associated. Moreover, the calcium-induced increments in fecal phosphate and bile acids were completely calcium-associated. Calcium decreased the amount of water-soluble phosphate but not of bile acids. These results indicate that supplemental calcium stimulates formation of insoluble calcium phosphate in the intestinal lumen and thus increases binding of luminal bile acids.