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


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Institute of medication (US) Committee to review Dietary referral Intakes because that 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 also metabolism the bone. Over 99 percent of total body calcium is found as calcium hydroxyapatite (Ca1062) in bones and also teeth, whereby it provides hard tissue v its strength. Calcium in the circulatory system, extracellular fluid, muscle, and other tissues is critical for mediating vascular contraction and also vasodilatation, muscle function, nerve transmission, intracellular signaling, and also hormonal secretion. Bone organization serves together a reservoir for and resource of calcium because that these crucial metabolic requirements through the procedure of bone remodeling.

Calcium metabolism is regulated in big part by the parathyroid hormone (PTH)–vitamin D endocrine system, i m sorry is defined by a collection of homeostatic feedback loops. The rapid release the mineral native the bone is important to keep adequate level of ionized calcium in serum. During vitamin D deficiency states, bone line is significantly affected as a result of reduced energetic calcium absorption. This leader to increased PTH secretion together the calcium sensing receptor in the parathyroid gland senses transforms in circulating ionic calcium. Raised PTH levels induce enzyme task (1α-hydroxylase) in the kidney, i m sorry converts vitamin D come its energetic hormonal form, calcitriol. In turn, calcitriol stimulates enhanced calcium absorption from the gut. Not surprisingly, the interplay in between the dynamics that calcium and also vitamin D frequently complicates the interpretation of data family member to calcium requirements, deficiency states, and also excess intake.


SOURCES the CALCIUM

Ingested calcium originates from food sources and also dietary supplements. In this report dietary calcium refers to both food sources and also supplements linked (although part researchers make reservation the term diet calcium to average only food sources) and also is most regularly referred come as total calcium intake because that clarity. With much more than one-half that the U.S. Populace (Bailey et al., 2010)—and in between 24 and also 60 percent the Canadians (2004 Canadian neighborhood Health Survey, an individual communication, D. Brulé, health and wellness Canada, April 29, 2010)—reporting use of diet supplements of some type, diet supplements need to be taken right into account when considering the resources of calcium in the diet and, in turn, estimating total calcium intake. Current estimates indigenous 2003 to 2006 suggest that the median total intake the calcium from all resources for persons > 1 year of period ranges indigenous 918 to 1,296 mg/day, depending upon life phase (Bailey et al., 2010). Only little amounts that calcium are contributed by water, depending on geographic location. Chapter 7 of this report has an evaluate of quantitative calcium input in the U.S. And also Canadian populations.


Food

Calcium is classically associated with dairy products; milk, yogurt, and cheese space rich sources of calcium, offering the major share of calcium from foods items in the basic diet in the joined States and also Canada. In the united States, an estimated 72 percent of calcium originates from milk, cheese and also yogurt and from foods to i m sorry dairy products have been included (e.g., pizza, lasagna, dairy desserts). The remaining calcium originates from vegetables (7 percent); grains (5 percent); legumes (4 percent); fruit (3 percent); meat, poultry, and fish (3 percent); egg (2 percent); and miscellaneous foodstuffs (3 percent).1 comparable data indigenous Canada are not right now available.

Fortification with calcium for a variety of foods that execute not naturally add calcium—such together orange juice, various 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). This practices challenge the capability of nationwide food ingredient databases, such as those kept by U.S. Department of farming (USDA), to save abreast of these newer products and may result in some underestimation of yes, really calcium intake from food sources. However, for those persons who select such foods, complete calcium input is increased.


Dietary Supplements

Among the U.S. Population, about 43 percent of all persons—but nearly 70 percent of older women—reported calcium intake indigenous supplements, based on a national survey conducted in between 2003 and also 2006 (Bailey et al., 2010). Once calcium indigenous supplement usage is taken into account based upon these survey data, the median intake rises by about 7 percent because that males and also 14 percent because that females. However, this is not a meaningful picture of the impact of complement use, because non-users that supplements are averaged with users, definition that the result is much more skewed than can be reflect by a mean estimate. Similar data room not obtainable for Canada, however the frequency of usage data display that 48 to 82 percent of Canadians reported taking a calcium supplement within the previous 30 work (2004 Canadian ar Health Survey, an individual communication, D. Brulé, health Canada, April 29, 2010).

The most common forms of supplemental calcium room calcium carbonate and also calcium citrate.2 The bioavailability of the calcium in these forms is discussed below in the section titled “Other determinants Related come Calcium Nutriture.” typically fewer tablet computers of calcium carbonate are forced to achieve given dose of element calcium because calcium carbonate generally provides 40 percent elemental calcium, compared with 21 percent for calcium citrate. Thus, prices tend come be reduced with calcium lead carbonate (Heaney et al., 2001; Keller et al., 2002) than v calcium citrate, and compliance might be higher among patients who execute not desire to take it (or have an obstacle swallowing) many pills. Chewable calcium lead carbonate supplements are additionally available. However, contrasted with calcium citrate, calcium lead carbonate is much more often linked with gastrointestinal side effects, consisting of constipation, flatulence, and also bloating (Straub, 2007). Calcium citrate is less dependent 보다 calcium carbonate on stomach acid for absorption (Hunt and also Johnson, 1983; Recker, 1985; Straub, 2007) and thus can be taken there is no food. It is helpful for individuals with achlorhydria, inflammatory bowel disease, or absorption obstacle or who room taking histamine-2 receptor blockers or proton pump inhibitors; for occupants of long-term treatment facilities whereby calcium supplements space not offered with meals; and also for others who schedules preclude acquisition supplements through food (Bo-Linn et al., 1984; Carr and Shangraw, 1987; Straub, 2007). Calcium can complete or interfere through the absorb of iron, zinc, and magnesium. For this reason, people with known deficiencies that these other minerals who require calcium supplementation normally take calcium supplements between meals (Straub, 2007).


Absorption

Calcium is absorbed by energetic transport (transcellularly) and by passive diffusion (paracellularly) throughout the minister mucosa. Energetic transport the calcium is dependence on the activity of calcitriol and the minister vitamin D receptor (VDR). This transcellular device is caused by calcitriol and accounts for many of the absorb of calcium at low and also moderate intake levels. Transcellular deliver occurs mainly in the duodenum wherein the VDR is to express in the highest concentration, and also is dependency on up-regulation the the responsive genes including the calcium deliver protein called transient receptor potential cation channel, vanilloid household member 6 or TRPV6 (Li et al., 1993; Xue and Fleet, 2009). This features—up-regulation that VDR and TRPV6—are most evident during states in which a high efficiency of calcium absorption is required.

Passive diffusion or paracellular uptake entails the motion of calcium in between mucosal cells and is dependence on luminal:serosal electrochemical gradients. Passive diffusion occurs an ext readily during higher calcium join (i.e., as soon as luminal concentrations are high) and can take place throughout the size of the intestine (Ireland and also Fordtran, 1973). However, the permeability of each intestinal segment determines passive diffusion rates. The greatest diffusion of calcium occurs in the duodenum, jejunum, and also ileum (Weaver and Heaney, 2006b).

From a recent series of controlled metabolic studies undertaken by the USDA, average calcium absorption (also described as “fractional calcium absorption,” which is the portion of a provided dose of calcium that is absorbed) in men and non-pregnant women—across a large age range— has been demonstrated to be about 25 percent the calcium entry (Hunt and Johnson, 2007). Mean urinary ns averages 22 percent and fecal loss 75 percent of total calcium intake, through minor losses indigenous sweat, skin, hair, etc. In general, mean calcium absorption and also calcium input are directly related (Heaney et al., 1975; Gallagher et al., 1980; Hunt and also Johnson, 2007). However, fractional calcium absorption different inversely through calcium intake as soon as the entry is very low (Malm, 1958; Spencer et al., 1969; Ireland and also Fordtran, 1973). For example, once calcium intake was lowered indigenous 2,000 to 300 mg, healthy and balanced women raised their fractional totality body retention the ingested calcium, an table of contents of calcium absorption, native 27 percent to about 37 percent (Dawson-Hughes et al., 1993). This type of adaptation occurs within 1 to 2 weeks and also is attach by a decline in serum calcium concentration and a climb in serum PTH and also calcitriol concentration (see section listed below titled “Homeostatic Regulation of Calcium”). The fraction of calcium absorbed rises adaptively together intake is lowered. However, this rise is not adequate to offset the lose in soaked up calcium that occurs as a result of the lower intake the calcium—however modest that decrease may be—and for this reason net calcium absorption is reduced.

Fractional calcium absorption varies during critical periods of life. In infancy, it is high at around 60 percent, return the selection is huge (Fomon and also Nelson, 1993; Abrams et al., 1997). Calcium absorb in newborns is largely passive and facilitated by the lactose contents of chest milk (Kocian et al., 1973; Kobayashi et al., 1975). As the neonate ages, passive absorb declines and calcitriol-stimulated energetic intestinal calcium absorption becomes much more important (Ghishan et al., 1980; Halloran and DeLuca, 1980; Ghishan et al., 1984).

A current preliminary report top top breast-fed infants in the very first 2 month of life (Hicks et al., 2010) report calcium absorb of approximately 33.7 ± 2.0 mg/100 kcal. In an earlier study using secure isotopes (Abrams et al., 1997), calcium absorption to be measured in 14 breast milk–fed babies who to be 5 through 7 month of period at the moment of the study. Median absorption was 61 ± 23 percent of input when approximately 80 percent of the calcium intake was from human being milk (IOM, 1997). There to be no far-ranging relationship in between calcium intake indigenous solid foods and also the fountain calcium absorption from human being milk. This finding says that calcium indigenous solid foods does not negatively influence the bioavailability of calcium from human being milk (IOM, 1997). Using measured urinary calcium and also estimates that endogenous excretion, net retention that calcium to be calculated to it is in 68 ± 38 mg/day for those infants. Abrams (2010) concluded the in infancy, based on calcium join that vary from as low as 200 mg/day in exclusively breast-fed infants in the early on months the life to 900 mg/day in older formula-fed babies receiving some solids, calcium absorb depends primarily on the level the intake. The writer reported that the absorption portion can selection from somewhat over 60 percent with reduced intakes to around 30 percent with higher intakes. Together the infant transitions into childhood, fractional calcium absorption declines, only to increase again in beforehand puberty, a time when modeling the the skeleton is maximal. Abrams and Stuff (1994) uncovered fractional absorption in white girls through a mean calcium input of around 931 mg/day to median 28 percent prior to puberty, 34 percent during early puberty (the age of the development spurt), and also 25 percent 2 years after at an early stage puberty. Fractional absorption remains around 25 percent in young adults. In 155 healthy men and women between 20 and also 75 year of age, typical calcium absorption to be 24.9 ± 12.4 percent of total intake (Hunt and also Johnson, 2007). During pregnancy, calcium absorption doubles (Kovacs and also Kronenberg, 1997; Kovacs, 2001). Metabolic status additionally influences calcium absorb such the severe obesity is associated with higher calcium absorption and dieting reduces the spring calcium absorb 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 every year ~ 40 years of age (Heaney et al., 1989). Nordin et al. (2004) and also Aloia et al. (2010) additionally reported lessened absorption through age. Over there are early on reports the an train station correlation between age and also calcium absorption in females (Avioli et al., 1965), and several studies have indicated the despite boost in circulating levels of calcitriol in larger women, which would be anticipated to boost calcium uptake, fountain 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 absorption (active calcium transport) has been report to decrease through age, it is daunting to take this element into factor to consider given the calcium intake should be very high to have actually a significant effect ~ above calcium uptake via the passive absorption.