Studies of calcium in food supplements in humans

Dietary calcium supplementation enhances efficacy but also toxicity of EGFR inhibitor therapy for colon cancer

The inverse correlation between levels of dietary calcium and colorectal cancer (CRC) incidence has been extensively investigated. However, the impact of supplemental calcium on cancer therapy remains unknown. We used four models of CRC, Caco-2 and HCT116 human cancer cell lines and Apc (Min/+) and azoxymethane carcinogen-induced mouse models, to investigate the impact of a western-style diet low in calcium (0.05%) vs. a similar diet but supplemented with calcium (5%) on therapeutic targeting of the epidermal growth factor receptor (EGFR). We found that calcium supplementation combined with pharmacologic blockade of EGFR results in an additive effect on tumor growth inhibition in all models. Unexpectedly, the combined use of dietary calcium supplementation and EGFR inhibitors also resulted in elevated toxicity suggesting that careful consideration be given when combining dietary supplements with prescribed cancer therapies.

Extracellular calcium sensing receptor stimulation in human colonic epithelial cells induces intracellular calcium oscillations and proliferation inhibition

The extracellular Ca(2+)-sensing receptor (CaR) is increasingly implicated in the regulation of multiple cellular functions in the gastrointestinal tract, including secretion, proliferation and differentiation of intestinal epithelial cells. However, the signaling mechanisms involved remain poorly defined. Here we examined signaling pathways activated by the CaR, including Ca(2+) oscillations, in individual human colon epithelial cells. Single cell imaging of colon-derived cells expressing the CaR, including SW-480, HT-29, and NCM-460 cells, shows that stimulation of this receptor by addition of aromatic amino acids or by an elevation of the extracellular Ca(2+) concentration promoted striking intracellular Ca(2+) oscillations. The intracellular calcium oscillations in response to extracellular Ca(2+) were of sinusoidal pattern and mediated by the phospholipase C/diacylglycerol/inositol 1,4,5-trisphosphate pathway as revealed by a biosensor that detects the accumulation of diacylglycerol in the plasma membrane. The intracellular calcium oscillations in response to aromatic amino acids were of transient type, that is, Ca(2+) spikes that returned to baseline levels, and required an intact actin cytoskeleton, a functional Rho, Filamin A and the ion channel TRPC1. Further analysis showed that re-expression and stimulation of the CaR in human epithelial cells derived from normal colon and from colorectal adenocarcinoma inhibits their proliferation. This inhibition was associated with the activation of the signaling pathway that mediates the generation of sinusoidal, but not transient, intracellular Ca(2+) oscillations. Thus, these results indicate that the CaR can function in two signaling modes in human colonic epithelial cells offering a potential link between gastrointestinal responses and food/nutrients uptake and metabolism.

Review Paper: Cancer Chemopreventive Compounds and Canine Cancer

Canine cancer has become more prevalent in recent years because of increased life expectancy and greater attention to the health of pets. The range of cancers seen in dogs is as diverse as that in human patients, and despite more intensive therapeutic interventions, fatality rates remain unacceptably high in both species. Chemoprevention is therefore an important means of confronting this disease. Because domestic pets share our environment, greater cross-application and study of the protumorigenic and antitumorigenic factors in our shared environment will benefit all species, leading to the development of new families of less toxic antitumorigenic compounds based on novel and established molecular targets. Currently, the most interesting cancer preventive agents are nonsteroidal anti-inflammatory drugs, peroxisome proliferator-activated receptor-γ ligands, and dietary compounds. This article provides an overview of what is known about how these agents affect molecular signaling in neoplastic disease, with reference to reported application and/or study in dogs where available.

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.

Mortalidade por câncer de cólon e reto e consumo alimentar em capitais brasileiras selecionadas

As taxas de mortalidade por câncer de cólon e reto mostram uma variação regional no Brasil e a heterogeneidade do padrão alimentar nas suas regiões geográficas poderia possivelmente explicar, pelo menos em parte, essas diferenças. Um estudo ecológico foi realizado com o objetivo de identificar possíveis associações entre padrões de consumo alimentar e taxas de mortalidade padronizadas por idade em capitais brasileiras selecionadas. O padrão de consumo alimentar em cada capital foi caracterizado com base no consumo de grupos de alimentos associados a essa neoplasia na literatura. Os dados de consumo de alimentos foram obtidos no ENDEF (Estudo Nacional de Despesas Familiares). A regressão linear múltipla foi utilizada para analisar as correlações entre as taxas de mortalidade e as variáveis alimentares. Essas taxas mostraram uma correlação positiva com o consumo de calorias, cereais, carnes, ovos/leite e legumes/frutas. Quando ajustado por consumo calórico total, carne e legumes/frutas foram as únicas variáveis que mantiveram uma correlação positiva. O modelo multivariado final com essas variáveis foi capaz de explicar 92% da variação das taxas de mortalidade nas capitais selecionadas. Esses resultados sugerem que diferenças no consumo calórico total e no consumo de carne e legumes/frutas poderiam explicar, parcialmente, os diferentes padrões de distribuição da mortalidade por câncer de cólon e reto no Brasil.

Anthocyanin-Rich Extracts Inhibit Multiple Biomarkers of Colon Cancer in Rats

The aim of the present study was to investigate the chemoprotective activity of anthocyanin-rich extracts (AREs) from bilberry (Vaccinium myrtillus L.), chokeberry (Aronia meloncarpa E.), and grape (Vitis vinifera) by assessing multiple biomarkers of colon cancer in male rats treated with a colon carcinogen, azoxymethane. Fischer 344 male rats were fed the AIN-93 diet (control) or AIN-93 diet supplemented with AREs for 14 wk. Biomarkers that were evaluated included the number and multiplicity of colonic aberrant crypt foci (ACF), colonic cell proliferation, urinary levels of oxidative DNA damage, and expression of cyclooxygenase (COX) genes. To assess the bioavailability, levels of anthocyanins in serum, urine, and feces were evaluated. Total ACF were reduced (P<0.05) in bilberry, chokeberry, and grape diet groups compared with the control group. The number of large ACF was also reduced (P<0.05) in bilberry and chokeberry ARE-fed rats. Colonic cellular proliferation was decreased in rats fed bilberry ARE and chokeberry ARE diets. Rats fed bilberry and grape ARE diets had lower COX-2 mRNA expression of gene. High levels of fecal anthocyanins and increased fecal mass and fecal moisture occurred in ARE-fed rats. There was also a significant reduction (P<0.05) in fecal bile acids in ARE-fed rats. The levels of urinary 8-hydroxyguanosine were similar among rats fed different diets. These results support our previous in vitro studies suggesting a protective role of AREs in colon carcinogenesis and indicate multiple mechanisms of action.

Calcium intake and colorectal adenoma in a US colorectal cancer early detection program

BACKGROUND

Calcium can reduce the risk of colorectal tumors by binding secondary bile and fatty acids, which leads to antiproliferative effects in the bowel, or by acting directly on the colonic epithelium, which affects differentiation and apoptosis.

OBJECTIVE

We investigated calcium intake and risk of colon adenoma to evaluate the association of calcium intake with early stages of colorectal tumor development.

DESIGN

We compared the supplemental and dietary calcium intakes of 3696 participants with histologically verified adenoma of the distal colon (ie, descending colon, sigmoid colon, or rectum) with the calcium intakes of 34 817 sigmoidoscopy-negative control participants in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Calcium intake was assessed at study entry with a 137-item food-frequency questionnaire and additional questions on the amount and duration of calcium supplement use.

RESULTS

After adjustment for known risk factors, adenoma risk was lower by 12% for participants in the highest quintile of total calcium intake (>1767 mg/d) than for participants in the lowest quintile (<731 mg/d) (odds ratio: 0.88; 95% CI: 0.76, 1.02; P for trend = 0.04). The protective association between total calcium and colorectal adenoma was largely due to calcium supplement use, with a 27% decrease in adenoma risk for participants taking >1200 mg/d than for nonusers of supplements (odds ratio: 0.73; 95% CI: 0.56, 0.91; P for trend = 0.005). The protective associations of total and supplemental calcium were strongest for colon adenoma (descending and sigmoid colon).

CONCLUSION

High calcium intake, particularly from supplements, is associated with a reduced risk of distal colorectal adenoma.

Multiple sources of dietary calcium-some aspects of its essentiality

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

Dietary minerals and modification of cardiovascular risk factors

High serum cholesterol, hypertension and obesity are major risk factors for cardiovascular diseases, and together with insulin resistance form a deadly disorder referred to as the metabolic syndrome. All the aspects of this syndrome are strongly related to dietary and lifestyle factors; therefore, it would be reasonable to look for dietary approaches to their modification. Mineral nutrients, such as calcium, potassium and magnesium, lower blood pressure, and especially calcium has beneficial effects also on serum lipids. Recent evidence suggests that increased intake of calcium may help in weight control as well. This review summarizes previous literature on the effects and use of dietary minerals on serum lipids, blood pressure and obesity, with specific focus on the effects of calcium. Calcium and magnesium as divalent cations can form insoluble soaps with fatty acids in the intestine and thus prevent the absorption of part of the dietary fat. Decreased absorption of saturated fat leads to reduction in serum cholesterol level via decreased production of VLDL and increased intake of LDL in the liver. Dietary calcium may also bind bile acids, which increases the conversion of cholesterol to bile acids in the liver. Furthermore, calcium appears to enhance the cholesterol-lowering effect of plant sterols. Thus, dietary combination of the mineral nutrients and plant sterols provides a promising novel approach to the modification of cardiovascular risk factors.

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.

High bioavailability of calcium in fortified Horlicks

OBJECTIVE

To compare the bioavailability of calcium carbonate-fortified Horlicks with calcium naturally present in milk.

DESIGN

Randomised crossover within-subject comparison using a double label stable isotope technique.

SETTING

Institute of Food Research, Human Nutrition Unit.

PARTICIPANTS

Sixteen pre-menopausal women aged 23-40 y, habituated to a high-calcium diet (mean 1240 mg/day).

RESULTS

Mean true fractional calcium absorption was 38.8% (s.d.+/-14.5) from Horlicks and 21.2% (s.d.+/-4.6) from milk. Significantly more calcium was absorbed from a serving of Horlicks than from the same quantity of calcium present in 420 g semi-skimmed milk (P<0.001).

CONCLUSIONS

Fortified Horlicks is a highly bioavailable source of calcium. A single serving, containing at least 500 mg calcium, provides half the reference nutrient intake for the population sub-group with the highest requirement (adolescent boys) and more than half for all others.

SPONSORSHIP

SmithKline Beecham funded this research project.