23: Calcium (Chapter 23a)
- Page ID
- 117181
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Calcium is known for being a major constituent of bones and teeth. About 99% of the body's calcium is found in these hard tissues. Calcium is also an extracellular divalent cation in the blood, where it exerts functional roles such as cell signaling and membrane transport. Its concentration in blood is tightly regulated by many hormones including parathyroid hormone (PTH), calcitriol, and calcitonin. Blood levels of calcium are not useful in determining the nutritional status of calcium because of these hormonal influences. Dietary requirements for calcium are derived using calcium balance, which is negative when calcium intake is too low to maintain normal bone density and zero in adults when calcium intake is sufficient or positive during growth and pregnancy. Calcium balance can be estimated using dual-absorptiometry (DXA) or measuring urine and fecal losses. A calcium intake above requirement does not stimulate further increases in bone mass; instead excess intake can lead to adverse effects such as soft tissue calcification and kidney stone formation. When calcium intakes are low, and/or when vitamin D is inadequate to permit sufficient calcium absorption, bone health is impaired leading to rickets in children and osteomalacia or osteoporosis in adults. Other health benefits of calcium are under investigation.
- 23.1: Calcium (23a.1)
- This page discusses the abundance and distribution of calcium, phosphorus, and magnesium in the human body. Calcium is the most prevalent mineral, mainly found in bones, while phosphorus and magnesium are more present in soft tissues. All three minerals play crucial roles as structural components of bones and regulatory agents in bodily fluids. A table illustrates their distribution in a 70 kg adult.
- 23.2: Functions of calcium (23a.2)
- This page discusses the importance of calcium for bone structure and health, noting that 99% is found in bones as calcium hydroxyapatite. It explains the mechanisms of bone remodeling by osteoblasts and osteoclasts, highlighting the shift in balance toward resorption with age. Additionally, it mentions that the remaining 1% of calcium aids metabolic functions in soft tissues and outlines how calcium blood levels are regulated by parathyroid hormone, vitamin D, calcitonin, and other hormones.
- 23.3: Absorption and metabolism of calcium (23a.3)
- This page summarizes the factors governing calcium balance, including dietary intake, absorption, excretion, and bone remodeling. Calcium absorption, influenced by age, vitamin D, and physiological conditions, is most efficient in infancy and adolescence. Urinary excretion is tightly regulated and dietary elements such as protein and phosphorus play a role.
- 23.4: Dietary sources and intakes of calcium (23a.4)
- This page discusses the uneven distribution of calcium in food sources, highlighting dairy as the most bioavailable option. Plant-based alternatives often need fortification, which may be ineffective. Foods like canned fish and leafy greens also offer calcium but can have low absorption rates. Certain preparation methods enhance calcium content.
- 23.5: Nutrient reference values for calcium (23a.5)
- This page discusses the 2011 calcium intake guidelines established by the Institute of Medicine, which include the Estimated Average Requirement (EAR), Recommended Dietary Allowance (RDA), and Upper Level (UL) based on age, sex, and special conditions like pregnancy. EAR ranges from 500mg for children to 800mg for adults.
- 23.6: Calcium deficiency (23a.6)
- This page discusses the regulation of calcium homeostasis via hormones like PTH and highlights the consequences of calcium deficiency, including osteoporosis and potential non-bone health issues. It notes calcium's broader health benefits, such as lowering pregnancy-related hypertensive disorders, blood pressure, and cholesterol levels. WHO recommends calcium supplementation for pregnant women with low intake to mitigate pre-eclampsia risk.
- 23.7: Effects of high intakes of calcium (23a.7)
- This page discusses the health risks associated with excessive calcium intake, including kidney stones, cardiovascular disease, and impaired iron absorption. The Tolerable Upper Intake Level for calcium has been reduced for adults over 50 due to increased kidney stone occurrences. While dietary calcium appears safe for cardiovascular health, supplements may heighten myocardial infarction risk.
- 23.8: Biochemical indices of calcium status (23a.8)
- This page discusses the complexity of calcium homeostasis, emphasizing the absence of a single test for calcium status. It highlights the roles of serum calcium, hormonal regulation, and the distinctions between hypo- and hypercalcemia. It covers the significance of ionized calcium in clinical settings, dietary intake, and calcium balance. Key biomarkers for bone health, including bone alkaline phosphatase, osteocalcin, and PINP, are mentioned for assessing bone formation and resorption.
- 23.9: Measurement of bone mineral content and bone mineral density (23a.9)
- This page reviews noninvasive techniques for assessing bone health, focusing on dual X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) for measuring bone mineral content (BMC) and density (BMD), essential for diagnosing osteoporosis. It emphasizes the importance of T-scores and the need for standardized procedures due to methodological variations.