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Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium; Ross AC, Taylor CL, Yaktine AL, et al., editors. Dietary Reference Intakes for Calcium and Vitamin D. Washington (DC): National Academies Press (US); 2011.

Dietary Reference Intakes for Calcium and Vitamin D.

INTRODUCTION

Calcium as a nutrient is maximum generally related to the formation and metabolism of bone. Over ninety nine percent of total body calcium is observed as calcium hydroxyapatite (Ca10[PO4]6[OH]2) in bones and tooth, wherein it provides tough tissue with its strength. Calcium inside the circulatory system, extracellular fluid, muscle, and other tissues is important for mediating vascular contraction and vasodilatation, muscle characteristic, nerve transmission, intracellular signaling, and hormonal secretion. Bone tissue serves as a reservoir for and supply of calcium for those essential metabolic needs thru the procedure of bone reworking.

Calcium metabolism is regulated in huge part by using the parathyroid hormone (PTH)–nutrition D endocrine device, that's characterised by a sequence of homeostatic comments loops. The fast launch of mineral from the bone is vital to preserve adequate tiers of ionized calcium in serum. During nutrition D deficiency states, bone metabolism is significantly affected due to decreased energetic calcium absorption. This leads to elevated PTH secretion because the calcium sensing receptor within the parathyroid gland senses modifications in circulating ionic calcium. Increased PTH tiers set off enzyme activity (1α-hydroxylase) within the kidney, which converts nutrition D to its active hormonal form, calcitriol. In turn, calcitriol stimulates more advantageous calcium absorption from the gut. Not incredibly, the interplay among the dynamics of calcium and diet D often complicates the translation of facts relative to calcium necessities, deficiency states, and extra consumption.

SOURCES OF ALCIUM

Ingested calcium comes from food sources and nutritional dietary supplements. In this document nutritional calcium refers to both food sources and dietary supplements blended (even though a few researchers reserve the term dietary calcium to mean only meals sources) and is most customarily known as total calcium consumption for clarity. With more than one-half of of the U.S. Population (Bailey et al., 2010)—and between 24 and 60 percent of Canadians (2004 Canadian Community Health Survey, personal communique, D. Brulé, Health Canada, April 29, 2010)—reporting use of dietary supplements of some kind, dietary dietary supplements should be taken under consideration whilst considering the sources of calcium within the diet and, in turn, estimating total calcium intake. Current estimates from 2003 to 2006 imply that the median total consumption of calcium from all resources for humans > 1 yr of age ranges from 918 to 1,296 mg/day, relying upon life level (Bailey et al., 2010). Only small quantities of calcium are contributed by way of water, depending upon geographic vicinity. Chapter 7 of this report contains an assessment of quantitative calcium consumption in the U.S. And Canadian populations.

Food

Calcium is classically related to dairy merchandise; milk, yogurt, and cheese are wealthy resources of calcium, imparting the foremost proportion of calcium from meals within the widespread food plan inside the United States and Canada. In the United States, an expected seventy two percent of calcium comes from milk, cheese and yogurt and from meals to which dairy products have been brought (e.G., pizza, lasagna, dairy cakes). The ultimate calcium comes from veggies (7 percentage); grains (5 percent); legumes (four percent); fruit (3 percentage); meat, fowl, and fish (three percent); eggs (2 percent); and miscellaneus meals (three percentage).1 Similar facts from Canada aren't presently to be had.

Fortification with calcium for a number of meals that don't certainly make a contribution calcium—which include orange juice, other beverages, and geared up-to-devour cereals—is turning into not unusual in the United States (Calvo et al., 2004; Rafferty et al., 2007; Poliquin et al., 2009). These practices challenge the capability of national meals composition databases, such as the ones maintained through U.S. Department of Agriculture (USDA), to preserve abreast of these more recent products and may bring about some underestimation of actual calcium consumption from meals assets. However, for the ones persons who pick out such ingredients, general calcium consumption is elevated.

Dietary Supplements

Among the U.S. Population, about forty three percent of all individuals—but nearly 70 percent of older girls—stated calcium consumption from dietary supplements, primarily based on a national survey conducted between 2003 and 2006 (Bailey et al., 2010). When calcium from complement use is taken into account based totally on these survey facts, the average consumption increases by using approximately 7 percentage for males and 14 percentage for girls. However, this is not a meaningful picture of the effect of supplement use, because non-customers of supplements are averaged with customers, which means that the effect is a lot more skewed than may be reflected by way of an average estimate. Similar statistics are not to be had for Canada, however the frequency of use records show that 48 to 82 percentage of Canadians pronounced taking a calcium complement within the preceding 30 days (2004 Canadian Community Health Survey, private conversation, D. Brulé, Health Canada, April 29, 2010).

The most common sorts of supplemental calcium are calcium carbonate and calcium citrate.2 The bioavailability of the calcium in those forms is mentioned under within the phase titled “Other Factors Related to Calcium Nutriture.” Generally fewer drugs of calcium carbonate are required to acquire given dose of elemental calcium because calcium carbonate generally affords 40 percent elemental calcium, in comparison with 21 percent for calcium citrate. Thus, expenses tend to be decrease with calcium carbonate (Heaney et al., 2001; Keller et al., 2002) than with calcium citrate, and compliance may be higher amongst patients who do no longer want to take (or have issue swallowing) more than one tablets. Chewable calcium carbonate dietary supplements are also available. However, in comparison with calcium citrate, calcium carbonate is extra regularly associated with gastrointestinal side effects, which includes constipation, flatulence, and bloating (Straub, 2007). Calcium citrate is less structured than calcium carbonate on stomach acid for absorption (Hunt and Johnson, 1983; Recker, 1985; Straub, 2007) and accordingly may be taken without food. It is useful for people with achlorhydria, inflammatory bowel ailment, or absorption issues or who're taking histamine-2 receptor blockers or proton pump inhibitors; for citizens of long-term care facilities wherein calcium dietary supplements aren't given with food; and for others whose schedules avert taking dietary supplements with meals (Bo-Linn et al., 1984; Carr and Shangraw, 1987; Straub, 2007). Calcium can compete or intrude with the absorption of iron, zinc, and magnesium. For this cause, persons with acknowledged deficiencies of those different minerals who require calcium supplementation normally take calcium dietary supplements among meals (Straub, 2007).

METABOLISM OF CALCIUM

Absorption

Calcium is absorbed by energetic transport (transcellularly) and through passive diffusion (paracellularly) throughout the intestinal mucosa. Active shipping of calcium is dependent on the motion of calcitriol and the intestinal nutrition D receptor (VDR). This transcellular mechanism is activated by way of calcitriol and money owed for maximum of the absorption of calcium at low and moderate intake tiers. Transcellular shipping takes place broadly speaking inside the duodenum in which the VDR is expressed in the highest awareness, and is depending on up-law of the responsive genes including the calcium transport protein known as transient receptor ability cation channel, vanilloid member of the family 6 or TRPV6 (Li et al., 1993; Xue and Fleet, 2009). These features—up-regulation of VDR and TRPV6—are maximum obvious throughout states wherein a excessive performance of calcium absorption is required.

Passive diffusion or paracellular uptake entails the movement of calcium among mucosal cells and is depending on luminal:serosal electrochemical gradients. Passive diffusion takes place extra comfortably throughout higher calcium intakes (i.E., while luminal concentrations are excessive) and can arise at some stage in the period of the gut (Ireland and Fordtran, 1973). However, the permeability of each intestinal segment determines passive diffusion quotes. The highest diffusion of calcium occurs inside the duodenum, jejunum, and ileum (Weaver and Heaney, 2006b).

From a latest collection of controlled metabolic studies undertaken through the USDA, imply calcium absorption (also called “fractional calcium absorption,” that is the share of a given dose of calcium that is absorbed) in men and non-pregnant women—throughout a huge age range— has been established to be about 25 percent of calcium intake (Hunt and Johnson, 2007). Mean urinary loss averages 22 percentage and fecal loss seventy five percentage of overall calcium intake, with minor losses from sweat, skin, hair, and many others. In general, mean calcium absorption and calcium consumption are immediately associated (Heaney et al., 1975; Gallagher et al., 1980; Hunt and Johnson, 2007). However, fractional calcium absorption varies inversely with calcium consumption whilst the intake is very low (Malm, 1958; Spencer et al., 1969; Ireland and Fordtran, 1973). For instance, while calcium intake changed into lowered from 2,000 to 300 mg, healthful girls expanded their fractional entire body retention of ingested calcium, an index of calcium absorption, from 27 percent to about 37 percent (Dawson-Hughes et al., 1993). This kind of model takes place inside 1 to two weeks and is followed by a decline in serum calcium attention and a rise in serum PTH and calcitriol concentrations (see phase below titled “Homeostatic Regulation of Calcium”). The fraction of calcium absorbed rises adaptively as intake is reduced. However, this upward push isn't sufficient to offset the loss in absorbed calcium that takes place because of the decrease consumption of calcium—but modest that decrease may be—and as a consequence net calcium absorption is decreased.@  Read More minisecond