23.4: Dietary sources and intakes of calcium (23a.4)
- Page ID
- 117185
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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 not widely distributed in all food groups, as shown in Table 23a.2.
| Food | Serving size |
Calcium Content (mg) |
Estimated Absorp- tion % |
Net Ca* Absor- bed (mg) |
|---|---|---|---|---|
| Cow milk (fluid) | 250mL | 310 | 32 | 100 |
| White beans (cooked) | 125mL | 85 | 22 | 18 |
| Red beans (cooked) | 125mL | 26 | 24 | 6 |
| Whole wheat bread | 35g slice | 26 | 82 | 21 |
| Broccoli (cooked) | 125mL | 33 | 20 | 20 |
| Spinach (cooked) | 125mL | 129 | 5 | 7 |
| Almonds (raw, roasted) | 60mL | 97 | 21 | 21 |
| Tofu (set with CaSO4) | 85g | 171 | 31 | 53 |
| Soy “milk” (unfortified) | 125mL | 5 | 31 | 2 |
Milk and milk products (e.g., cheeses, yoghurt) are excellent sources of readily available (bioavailable) calcium. Plant-based beverages made from soy, almonds, rice and oats are available as substitutes for milk, but must be fortified. The availability of the calcium from these beverages is unknown, except for fortified soymilk for which the calcium availability is similar to cow milk, but only if calcium carbonate is used as a fortificant (Weaver and Peacock, 2019). Unfortified plant-based beverages have little calcium. Canned fish with bones (e.g., salmon, sardines) are good sources of calcium. Leafy-green vegetables are also good sources, but absorption of calcium from some of these foods, especially spinach, may be low (Weaver and Plawecki, 1994). Ancient grains (e.g., teff, quinoa, amaranth) and nuts are good sources of calcium (Cormick and Belizan, 2019), but highly refined or modern cereal grains such as wheat and maize are not.
Preparation of foods may also be a factor influencing their calcium content. For example, in Guatemala, when corn (maize) tortillas are prepared according to the Mayan tradition of cooking corn with limestone and leaving it to soak overnight in hot water, the calcium content rises from about 10mg to about 200mg of calcium per 100g (Belizan and Villar, 1980). In Sub-Saharan Africa, dietary calcium intake may be increased by using powdered eggshell added to foods (Bartter et al., 2018).
Foods fortified with calcium are available in many countries. In the European Union, the following forms of calcium are authorized for addition to foods and for use in food supplements: carbonate, chloride, citrate malate, gluconate, glycerophosphate, lactate, hydroxide, oxide, acetate, L‑ascorbate, bisglycinate, salts of citric acid, pyruvate, salts of orthophosphoric acid, succinate, L‑lysinate, malate, L‑pidolate, L‑threonate, sulphate (EFSA, 2012). Most of these forms are allowable in other countries. The citrate malate calcium salt is an allowable fortificant for orange juice in the United States (ODS, 2020). The United Kingdom is the only country where calcium fortification is a mandatory addition to flour; 235–390mg of calcium carbonate are added per 100g of flour. This represents about 94–156mg of elemental calcium per 100g of flour (Cormick et al., 2020). Other countries permit calcium addition to certain foods, often proprietary packaged foods, a practice called discretionary fortification.
Supplemental sources of calcium are widely available in many dosages and in a variety of chemical forms in many countries. These pills, capsules and liquids are usually regulated by the government. For example, in the United States, the following forms of calcium are allowable as supplements: carbonate, phosphate, citrate, gluconate, and lactate (Weaver and Peacock, 2019; ODS, 2020). Some supplements that are derived from oyster shell, algae, and in chewable drugs labeled as antacid such as TUMSTM, are mainly in the form of calcium carbonate, the form of calcium naturally occurring in rocks such as chalk and limestone. This form of calcium is generally the cheapest to buy and has the highest amount of calcium by weight (40%). However, calcium carbonate is poorly absorbed unless stomach acid is available for dissociation. Also, calcium carbonate is the form of calcium that causes the most side-effects such as bloating and constipation (ODS, 2020).
Dietary calcium intakes vary across countries, ranging from 175–1233mg/d (Balk et al., 2017). Countries in Asia have average dietary calcium intakes less than 500mg/d while in countries in Africa and South America, calcium intakes vary from 400–700mg/d. Only Northern European countries have a national calcium intake greater than 1000mg/d, reflecting a high dairy consumption. The average calcium intake is generally lower in women than men, although across the 74 countries included in an analysis by the International Osteoporosis Foundation (IOF, 2020), no clear patterns regarding differences by age, sex, or socioeconomic status emerged.