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Institute of medicine (US) Committee to evaluation Dietary referral Intakes because that Vitamin D and also Calcium; Ross AC, Taylor CL, Yaktine AL, et al., editors. Dietary referral Intakes for Calcium and Vitamin D. Washington (DC): nationwide Academies push (US); 2011.


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Institute of medicine (US) Committee to evaluation Dietary recommendation Intakes for Vitamin D and Calcium; Ross AC, Taylor CL, Yaktine AL, et al., editors.

INTRODUCTION

Calcium as a nutrient is most commonly linked with the formation and metabolism of bone. Over 99 percent of full body calcium is found as calcium hydroxyapatite (Ca1062) in bones and also teeth, wherein it provides hard tissue with its strength. Calcium in the circulatory system, extracellular fluid, muscle, and also other organization is an essential for mediating vascular contraction and also vasodilatation, muscle function, nerve transmission, intracellular signaling, and hormonal secretion. Bone organization serves together a reservoir because that and resource of calcium for these an important metabolic needs through the process of bone remodeling.

Calcium line is regulation in large part by the parathyroid hormone (PTH)–vitamin D endocrine system, i beg your pardon is characterized by a series of homeostatic feedback loops. The fast release of mineral indigenous the bone is important to keep adequate levels of ionized calcium in serum. Throughout vitamin D deficiency states, bone management is significantly impacted as a an outcome of reduced energetic calcium absorption. This leads to increased PTH secretion as the calcium sensing receptor in the parathyroid gland senses changes in turn ionic calcium. Boosted PTH levels induce enzyme activity (1α-hydroxylase) in the kidney, i beg your pardon converts vitamin D come its active hormonal form, calcitriol. In turn, calcitriol stimulates magnified calcium absorption from the gut. No surprisingly, the interplay in between the dynamics the calcium and vitamin D often complicates the translate of data loved one to calcium requirements, deficiency states, and excess intake.


SOURCES of CALCIUM

Ingested calcium comes from food sources and dietary supplements. In this report diet calcium refers to both food sources and also supplements linked (although part researchers to make reservation the term diet calcium to average only food sources) and also is most regularly referred to as total calcium intake because that clarity. With an ext than one-half of the U.S. Population (Bailey et al., 2010)—and in between 24 and 60 percent that Canadians (2004 Canadian neighborhood Health Survey, an individual communication, D. Brulé, wellness Canada, April 29, 2010)—reporting usage of diet supplements of part type, dietary supplements need to be taken right into account once considering the resources of calcium in the diet and, in turn, estimating total calcium intake. Present estimates native 2003 to 2006 indicate that the median complete intake of calcium native all sources for persons > 1 year of age ranges indigenous 918 come 1,296 mg/day, relying on life stage (Bailey et al., 2010). Only little amounts of calcium are added by water, depending upon geographic location. Chapter 7 that this report includes an assessment of quantitative calcium intake in the U.S. And Canadian populations.


Food

Calcium is classically associated with dairy products; milk, yogurt, and cheese room rich sources of calcium, giving the major share of calcium from foods in the general diet in the unified States and Canada. In the united States, an approximated 72 percent that calcium originates from milk, cheese and also yogurt and also from foods to i beg your pardon dairy assets have been included (e.g., pizza, lasagna, dairy product desserts). The staying calcium comes from vegetables (7 percent); grains (5 percent); legumes (4 percent); fruit (3 percent); meat, poultry, and fish (3 percent); eggs (2 percent); and miscellaneous foods (3 percent).1 comparable data from Canada room not at this time available.

Fortification v calcium for a number of foods that execute not naturally add calcium—such as orange juice, other beverages, and also ready-to-eat cereals—is ending up being commonplace in the United says (Calvo et al., 2004; Rafferty et al., 2007; Poliquin et al., 2009). These practices an obstacle the ability of national food composition databases, such together those preserved by U.S. Room of farming (USDA), to save abreast the these newer products and may an outcome in part underestimation of actual calcium intake from food sources. However, for those people who choose such foods, complete calcium intake is increased.


Dietary Supplements

Among the U.S. Population, about 43 percent of all persons—but virtually 70 percent of enlarge women—reported calcium intake native supplements, based upon a national survey conducted between 2003 and 2006 (Bailey et al., 2010). When calcium from supplement use is taken right into account based on these survey data, the average intake boosts by about 7 percent because that males and also 14 percent for females. However, this is not a meaningful photo of the impact of complement use, because non-users the supplements space averaged with users, meaning that the result is much an ext skewed than deserve to be reflect by a mean estimate. Comparable data room not available for Canada, but the frequency of usage data present that 48 to 82 percent of Canadians reported taking a calcium complement within the ahead 30 days (2004 Canadian ar Health Survey, personal communication, D. Brulé, health and wellness Canada, April 29, 2010).

The most usual forms the supplemental calcium are calcium carbonate and calcium citrate.2 The bioavailability that the calcium in these develops is discussed below in the section titled “Other components Related come Calcium Nutriture.” usually fewer tablets of calcium carbonate are forced to attain given dose of elemental calcium because calcium carbonate typically provides 40 percent elemental calcium, contrasted with 21 percent for calcium citrate. Thus, costs tend come be lower with calcium lead carbonate (Heaney et al., 2001; Keller et al., 2002) than through calcium citrate, and compliance may be higher among patient who carry out not desire to take it (or have challenge swallowing) lot of pills. Chewable calcium lead carbonate supplements are likewise available. However, contrasted with calcium citrate, calcium carbonate is an ext often linked with gastrointestinal next effects, consisting of constipation, flatulence, and also bloating (Straub, 2007). Calcium citrate is much less dependent than calcium carbonate on stomach mountain for absorption (Hunt and also Johnson, 1983; Recker, 1985; Straub, 2007) and also thus deserve to be taken without food. It is useful for individuals with achlorhydria, inflammation bowel disease, or absorption disorders or who space taking histamine-2 receptor blockers or proton pump inhibitors; for inhabitants of long-term treatment facilities wherein calcium supplements room not offered with meals; and for others whose schedules preclude taking supplements with food (Bo-Linn et al., 1984; Carr and also Shangraw, 1987; Straub, 2007). Calcium can contend or interfere through the absorb of iron, zinc, and also magnesium. Because that this reason, people with known deficiencies the these various other minerals who require calcium supplementation commonly take calcium supplements between meals (Straub, 2007).


Absorption

Calcium is soaked up by active transport (transcellularly) and by passive diffusion (paracellularly) across the intestinal mucosa. Energetic transport the calcium is dependency on the action of calcitriol and also the intestinal vitamin D receptor (VDR). This transcellular device is triggered by calcitriol and also accounts for most of the absorption of calcium at low and moderate intake levels. Transcellular move occurs primarily in the duodenum whereby the VDR is express in the greatest concentration, and is dependent on up-regulation of the responsive genes including the calcium transport protein referred to as transient receptor potential cation channel, vanilloid family members member 6 or TRPV6 (Li et al., 1993; Xue and Fleet, 2009). These features—up-regulation of VDR and also TRPV6—are most obvious during states in i beg your pardon a high efficiency of calcium absorb is required.

Passive diffusion or paracellular uptake entails the movement of calcium between mucosal cells and is dependency on luminal:serosal electrochemical gradients. Passive diffusion occurs an ext readily during greater calcium intakes (i.e., when luminal concentrations room high) and can happen throughout the length of the intestine (Ireland and also Fordtran, 1973). However, the permeability of every intestinal segment determines passive diffusion rates. The highest possible diffusion the calcium occurs in the duodenum, jejunum, and ileum (Weaver and Heaney, 2006b).

From a recent series of controlled metabolic research studies undertaken by the USDA, typical calcium absorb (also described as “fractional calcium absorption,” i m sorry is the percent of a offered dose of calcium that is absorbed) in men and non-pregnant women—across a broad age range— has actually been prove to be about 25 percent that calcium entry (Hunt and Johnson, 2007). Average urinary lose averages 22 percent and also fecal ns 75 percent of complete calcium intake, v minor losses from sweat, skin, hair, etc. In general, average calcium absorption and also calcium intake are directly related (Heaney et al., 1975; Gallagher et al., 1980; Hunt and Johnson, 2007). However, fractional calcium absorption varies inversely through calcium intake once the entry is very low (Malm, 1958; Spencer et al., 1969; Ireland and Fordtran, 1973). Because that example, when calcium intake to be lowered indigenous 2,000 come 300 mg, healthy and balanced women boosted their fractional totality body retention that ingested calcium, an index of calcium absorption, native 27 percent to about 37 percent (Dawson-Hughes et al., 1993). This type of adaptation occurs in ~ 1 come 2 weeks and also is accompanied by a decrease in serum calcium concentration and a climb in serum PTH and calcitriol concentrations (see section below titled “Homeostatic Regulation the Calcium”). The fraction of calcium soaked up rises adaptively as intake is lowered. However, this rise is not sufficient to balance out the loss in soaked up calcium the occurs together a result of the lower intake that calcium—however modest the decrease might be—and for this reason net calcium absorption is reduced.

Fractional calcium absorption different during crucial periods of life. In infancy, it is high at roughly 60 percent, although the selection is large (Fomon and also Nelson, 1993; Abrams et al., 1997). Calcium absorb in newborns is greatly passive and facilitated by the lactose contents of breast milk (Kocian et al., 1973; Kobayashi et al., 1975). Together the neonate ages, passive absorption declines and also calcitriol-stimulated energetic intestinal calcium absorption becomes an ext important (Ghishan et al., 1980; Halloran and DeLuca, 1980; Ghishan et al., 1984).

A recent preliminary report on breast-fed infants in the first 2 months of life (Hicks et al., 2010) reported calcium absorption of around 33.7 ± 2.0 mg/100 kcal. In an previously study using stable isotopes (Abrams et al., 1997), calcium absorption to be measured in 14 breast milk–fed babies who were 5 v 7 months of age at the moment of the study. Mean absorption to be 61 ± 23 percent of intake when around 80 percent the the calcium intake to be from human being milk (IOM, 1997). There to be no far-ranging relationship in between calcium intake from solid foods and the fountain calcium absorb from human milk. This finding says that calcium from solid foodstuffs does no negatively influence the bioavailability of calcium from human milk (IOM, 1997). Making use of measured urinary calcium and estimates that endogenous excretion, network retention that calcium was calculated to it is in 68 ± 38 mg/day because that those infants. Abrams (2010) concluded that in infancy, based on calcium intakes that vary from together low together 200 mg/day in specifically breast-fed babies in the early on months of life come 900 mg/day in older formula-fed babies receiving part solids, calcium absorb depends primarily on the level of intake. The writer reported the the absorption fraction can variety from somewhat over 60 percent with lower intakes to about 30 percent with higher intakes. Together the child transitions right into childhood, fractional calcium absorption declines, only to increase again in early on puberty, a time once modeling that the skeleton is maximal. Abrams and also Stuff (1994) found fractional absorb in white girls through a mean calcium input of around 931 mg/day to typical 28 percent prior to puberty, 34 percent throughout early puberty (the age of the development spurt), and also 25 percent 2 year after early puberty. Fractional absorb remains about 25 percent in young adults. In 155 healthy and balanced men and also women between 20 and also 75 year of age, typical calcium absorption was 24.9 ± 12.4 percent of total intake (Hunt and also Johnson, 2007). During pregnancy, calcium absorb doubles (Kovacs and also Kronenberg, 1997; Kovacs, 2001). Metabolic status likewise influences calcium absorption such that severe excessive weight is linked with greater calcium absorption and also dieting reduce the spring calcium absorption by 5 percent (Cifuentes et al., 2002; Riedt et al., 2006).

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With aging and after menopause, fountain calcium absorption has been report to decrease on mean by 0.21 percent per year after ~ 40 years of age (Heaney et al., 1989). Nordin et al. (2004) and also Aloia et al. (2010) additionally reported reduced absorption v age. There are early on reports of an inverse correlation in between age and also calcium absorption in ladies (Avioli et al., 1965), and also several studies have indicated the despite an increase in circulating levels of calcitriol in older women, which would certainly be suspect to boost calcium uptake, fractional calcium absorption was unaffected (Bullamore et al., 1970; Alevizaki et al., 1973; Gallagher et al., 1979; Tsai et al., 1984; Eastell et al., 1991; Ebeling et al., 1992). Thus, although calcium absorb (active calcium transport) has actually been reported to decrease with age, the is daunting to take it this aspect into factor to consider given that calcium intake have to be an extremely high to have actually a significant effect top top calcium absorb via the passive absorption.