Calcium

 
WHAT  IS  CALCIUM?  

Calcium  is  a  mineral  that  is  stored  in  abundant  amounts  

throughout  the  human  body.  Over  99%  of  calcium  is  found  in  
bones  and  teeth  where  it’s  responsible  for  providing  strength  
to  hard  tissues1.  The  remaining  calcium  can  be  found  in  nerve  
cells,  body  tissues,  blood,  and  other  body  fluids2.    

Calcium  is  essential  for  the  formation  and  maintenance  of  

healthy  bones  and  teeth,  in  addition  to  many  other  critical  
bodily  functions.  Some  of  these  functions  include:  regulating  
vascular  contraction  and  vasodilation,  muscle  function,  nerve  transmission,  intracellular  
signaling,  and  hormonal  secretion1.  These  functions  are  supported  by  the  calcium  that  is  
released  from  bone    tissue  during  the  bone  remodeling  process1.  This  release  of  calcium  also  
supports  the  regulation  of  serum  calcium  levels  despite  any  changes  in  dietary  intake,  as  it  is  
used  to  maintain  constant  concentrations  in  blood,  muscle,  and  intercellular  fluids3.      

HOW  MUCH  CALCIUM  DO  WE  NEED?  

Dietary  Reference  Intakes  (DRIs)  for  both  calcium  and  vitamin  D  were  developed  based  on  the  
amounts  necessary  for  achieving  peak  bone  mass  during  growth  and  minimizing  bone  mineral  
loss  in  adulthood4,  9.  These  DRIs  include  Estimated  Average  Requirements  (EARs)  and  
Recommended  Dietary  Allowance  (RDAs).  EARs  are  defined  as  “the  average  daily  nutrient  
intake  levels  estimated  to  meet  the  requirement  of  half  the  healthy  individuals  in  a  particular  
life  stage  and  gender  group,”  and  RDAs  are  “the  average  daily  dietary  nutrient  intake  levels  
sufficient  to  meet  the  nutrient  requirement  of  nearly  all  (97-­‐98%)  healthy  individuals  in  a  
particular  life  stage  and  gender  group”5.    

An  Adequate  Intake  (AI),  defined  as  “the  recommended  average  daily  intake  level  based  on  
observed  or  experimentally  determined  approximations  of  nutrient  intake  by  a  group  of  
apparently  healthy  people  that  are  assumed  to  be  adequate,”5  has  been  developed  for  infants  
aged  0-­‐12  months.  There  is  currently  not  enough  evidence  concerning  bone  health  outcomes  in  
infants  to  determine  an  EAR  or  RDA4.    

The  amounts  listed  in  the  table  below  can  be  obtained  through  the  consumption  of  a  variety  of  
foods  as  well  as  through  supplementation.  However,  dietary  intake  of  calcium  is  preferred  over  
supplementation,  whenever  possible.  
Table  1:  Dietary  Reference  Intakes  for  Calcium  and  Vitamin  D6

 
FOOD  SOURCES  

Dairy  products  and  milk  alternatives  are  most  commonly  

associated  with  calcium,  including  milk,  plant-­‐based  
beverages  and  cheese.  These  foods  are  rich  sources  of  
calcium  and  they  provide  a  major  portion  of  dietary  calcium  
intake  across  Canada  and  the  United  States1.  Other  high  
calcium  food  sources  include  dark  green  vegetables,  canned  
salmon  or  sardines,  legumes,  almonds  and  fortified  orange  
juice.  Health  Canada  recommends  2-­‐4  servings  of  milk  and  alternatives  (depending  on  the  age  
group)  per  day  to  encourage  consumption  of  calcium  for  optimal  bone  health6.    
Table  2:  Calcium  Content  of  Specific  Food  Sources  Based  on  Serving  Sizes7  
Food   Serving  Size   Calcium  (mg)  
MILK  &  ALTERNATIVES  
MILK  
Milk  (skim,  1%,  2%,  3.25%,  chocolate)   1  cup/250  mL   291-­‐322  
Buttermilk   1  cup/250  mL   300-­‐370  
Goat  milk   1  cup/250  mL   345  
Sheep  milk,  whole   1  cup/250  mL   500  
Soy  milk,  enriched   1  cup/250  mL   316  
Almond  milk,  rice  milk   1  cup/250  mL   123-­‐319  
Dry  milk  powder   24  g  (4  Tbsp)  to  make  250  mL  of  milk   302  
Condensed  milk   2  Tbsp   110  
YOGURT  
Fruit  flavoured  yogurt   ¾  cup/175  mL   178  
Plain  yogurt   ¾  cup/175  mL   191-­‐275  
Greek  yogurt   ¾  cup/175  mL   170-­‐389  
Soy  yogurt   ¾  cup/175  mL   ~124  
Kefir   100  g   95  
CHEESE  
Brie,  Camembert   50  g  (1  ½  oz)   92-­‐194  
Cheddar,  Colby,  Edam,  Fontina,   50  g  (1  ½  oz)   275-­‐373  
Gouda,  Monterey,  Mozzarella  
Processed  cheese  slices  (swiss,   50g  (1  ½  oz)   259-­‐303  
cheddar,  mozzarella)  
Parmesan,  grated   50  g  (1  ½  oz)   426-­‐554  
Goat,  soft   50  g  (1  ½  oz)   70  
Goat,  hard   50g  (1  ½  oz)   448  
  Ricotta     ½  cup/125  mL   271-­‐356  
Cottage  cheese   ½  cup/125  mL   ~133  
MEAT  &  ALTERNATIVES  
Salmon,  canned,  with  bones   75  g  (2  ½  oz)   161-­‐212  
Mackerel,  canned   75  g  (2  ½  oz)   181  
Anchovies,  canned  with  olive  oil   75  g  (2  ½  oz)   174  
Sardines,  Atlantic,  canned  in  oil,  with   75  g  (2  ½  oz)   286  
bones  
Sardines,  pacific,  canned  in  tomato   75  g  (2  ½  oz)   180  
sauce,  with  bones  
Beans  (white),  boiled/canned   ¾  cup   119-­‐141  
Tofu,  prepared  with  calcium  sulfate   ¾  cup/150  g   302  
Almonds,  dry  roasted  or  oil  roasted,   ¼  cup/60  g   94-­‐116  
unblanched  
VEGETABLES  
Collards,  frozen,  cooked   ½  cup/125  mL   189  
Spinach,  frozen,  cooked   ½  cup/125  mL   154  
Kale,  frozen,  cooked   ½  cup/125  mL   95  
Okra,  cooked   ½  cup/125  mL   65  
FRUIT  
Orange  juice,  fortified  with  calcium   ½  cup/125  mL   155  
Figs,  dried   ¼  cup/60  mL   64  
Navel  orange   1  fruit   60  
*  Based  on  Canadian  Nutrient  File  Database  
DIETARY  SUPPLEMENTS  

Calcium  supplements  can  contain  a  variety  of  calcium  salts,  

some  examples  include:  calcium  carbonate,  calcium  citrate,  or  
calcium  lactate.  Health  Canada  classifies  these  products  as  
natural  health  products.    

The  two  main  forms  of  calcium  found  in  supplements  are  
calcium  carbonate  and  calcium  citrate3.  Calcium  carbonate  is  
more  widely  available  and  is  less  expensive  than  calcium  citrate.  This  particular  type  of  calcium  
relies  on  stomach  acid  for  absorption,  thus  absorption  is  maximized  when  the  supplement  is  
taken  with  food3.  The  most  common  side  effects  of  calcium  supplementation  are  
gastrointestinal  symptoms  including  gas,  bloating,  constipation,  or  a  combination  of  each3.  
Calcium  carbonate  appears  to  be  associated  with  more  of  these  side  effects  than  calcium  
citrate3.  Calcium  citrate,  although  more  expensive,  is  associated  with  less  gastrointestinal  side  
effects  and  is  absorbed  equally  well  when  taken  with  or  without  food3.  These  supplements  are  
ideal  for  those  with  achlorhydria,  inflammatory  bowel  disease,  absorption  disorders,  or  those  
who  are  taking  proton  pump  inhibitors  or  histamine-­‐2  receptor  blockers1.  If  gastrointestinal  
side  effects  are  an  issue,  consider  spreading  out  the  calcium  dose  throughout  the  day  and/or  
taking  the  supplement  with  meals3.    

Additionally,  calcium  can  inhibit  the  absorption  of  other  essential  nutrients,  including  iron,  zinc  
and  magnesium1.  For  individuals  with  these  mineral  deficiencies  who  also  require  calcium  
supplementation,  it  is  important  to  take  these  supplements  at  different  times  throughout  the  
day1.  

Calcium  can  be  found  in  an  assortment  of  dietary  supplements.  It  can  be  taken  on  its  own  or  in  
varying  amounts  in  most  multivitamins.  Calcium  can  also  be  found  in  combination  with  select  
other  micronutrients,  including  Vitamin  D  and/or  magnesium.  For  maximal  absorption,  
consumption  of  ≤500  mg  at  a  time  is  recommended.  If  taking  1000  mg/day,  divide  into  two  
doses  of  500  mg  throughout  the  day3.  

Table  3:  Types  of  Calcium  Supplements9  

Calcium  Salts   Dosage   Amount  of  Elemental   Cost  

Form   Calcium  
Carbonate   Tablets   300  mg,  500  mg,  600  mg   $  
  Powder   200  mg/1.25  mL   -­‐  
Citrate   Tablets   200  mg,  300  mg,  500  mg,   $$  
600  mg  
Hydroxyapatite   Tablet   250  mg   -­‐  
Lactate   Tablet   84  mg,  650  mg   -­‐  
 Lactate-­‐gluconate   Liquid   20  mg/mL   -­‐  
Combination  (carbonate,   Tablet,   333  mg,  650  mg   $    
citrate,  malate,  fumarate,   Soft  chews  
succinate)  
Combination  (tricalcium   Liquid   1000  mg   $  
phosphate,  calcium  citrate)  
Combination  (carbonate,   Tablet   500  mg,  1000  mg   -­‐  
lactate,  gluconate)  
It  is  important  to  note  that  many  calcium  supplements  contain  various  amounts  of  lead,  with  
those  developed  from  dolomite,  bone  meal,  fossil  or  oyster  shell  sources  containing  the  highest  
amounts9.  Calcium  carbonate,  calcium  gluconate  and  calcium  lactate  all  contain  lower  amounts  
of  lead9.    
 
SUPPLEMENT  PRECAUTIONS  

At  this  time,  high  doses  of  calcium  supplementation  are  not  recommended  for  individuals  who  
do  not  need  extra  calcium.  There  have  been  multiple  research  studies  and  systematic  reviews  
with  conflicting  evidence  concerning  an  association  between  increased  calcium  
supplementation  and  the  risk  of  myocardial  infarctions9.  Further  research  is  needed  in  order  to  
determine  the  safety  of  high  doses  of  calcium  supplements.  Increasing  dietary  intake  of  calcium  
should  be  considered  as  the  primary  course  of  action.  Health  Canada  recommends  no  more  
than  1500  mg/day  from  supplements  alone10,  while  some  experts  recommend  no  more  than  
500  mg/day9.    

High  total  calcium  intake  may  be  associated  with  a  slightly  higher  risk  of  prostate  cancer.  More  
research  is  needed  to  determine  if  the  source  of  calcium  affects  the  development  of  this  
disease9.  Additionally,  high  calcium  intake    from  supplements  may  increase  the  risk  of  
developing  kidney  stones  in  certain  individuals9.  

CONTRAINDICATIONS  FOR  DIETARY  SUPPLEMENTS  

Dietary  supplements  containing  calcium  are  not  recommended  for  individuals  with  
hypercalcemia  or  hypercalciuria,  which  may  occur  in  vitamin  D  overdosage,  
hyperparathyroidism,  decalcifying  tumors  or  bone  metastases.  They  are  also  contraindicated  in  
individuals  with  severe  cardiac  disease,  ventricular  fibrillation,  and  calcium  loss  due  to  
immobilization9.    
 
CALCIUM  STATUS  IN  CANADA  

In  2004,  information  concerning  the  dietary  intakes  of  Canadians  was  collected  through  the  
Canadian  Community  Health  Survey  (CCHS)8.  Results  indicated  that  inadequate  calcium  intake  
tends  to  increase  with  age  and  is  more  common  among  women  than  men8.  As  many  as  46-­‐87%  
of  adult  women  reported  inadequate  intakes,  compared  to  27-­‐80%  of  adult  men,  depending  on  
the  age  group8.  When  both  dietary  calcium  and  supplement  sources  were  taken  into  account,  
results  showed  that  supplements  did  not  significantly  affect  the  prevalence  of  inadequate  
calcium  intake,  except  for  women  over  the  age  of  508.  

ABSORPTION  OF  CALCIUM  

Humans  absorb  around  30%  of  the  calcium  in  foods,  but  this  amount  can  vary  depending  on  the  
type  of  food1.  Certain  compounds  found  in  food  can  inhibit  the  absorption  of  calcium,  including  
phytic  acid  and  oxalic  acid.  Phytic  acid  is  found  in  high-­‐fibre  whole-­‐grain  products,  wheat  bran,  
beans,  seeds,  nuts,  and  soy  isolates1.  High  levels  of  oxalic  acid  are  found  in  foods  such  as:  
spinach,  collard  greens,  sweet  potatoes,  rhubarb  and  beans1.  The  degree  to  which  these  
compounds  inhibit  calcium  absorption  varies  depending  on  the  combination  of  foods  
consumed1.  On  the  other  hand,  intake  of  vitamin  D,  through  sun  exposure  or  fortified  foods,  
actually  aids  in  increasing  the  absorption  of  calcium  in  the  body.      

The  table  below  lists  some  important  factors  to  keep  in  mind  when  determining  an  individual’s  
calcium  intake  in  terms  of  absorption  and  those  individuals  more  likely  to  have  a  decreased  
intake.      

Table  4:  Factors  Affecting  Calcium  Absorption  and  Intake  

Increased  Absorption   Decreased  Intake   Decreased  Absorption  

3 3
Vitamin  D  intake  (through   Lactose  intolerance   Increased  intakes  of  calcium  
sun  exposure  and  dietary   3
Cow’s  milk  allergy   Age  –  absorption  decreases  as  age  
intake)   Vegans  
3 increases1  
Pregnancy1   Lack  of  balanced  diet  or  poor   Dietary  factors  (phytic  acid  and  oxalic  
Lactation9   intake   acid,  caffeine  intake)  1  
Parathyroid  hormone  deficiency8  
Vitamin  D  deficiency8  
Post-­‐menopause1  
Amenorrheic  women  and  the  female  
3
athlete  triad  
3
Vegetarians  
• Increased  intake  of  phytic  acid  
and  oxalic  acid  
Alcohol  intake  (amount  required  
currently  unknown)  1  
Phosphate  (potential  affect  on  
absorption  of  calcium)  1  
Diseases,  such  as:  
• Achlorhydria9  
• Renal  osteodystrophy  9  
• Steatorrhea9  
• Uremia9  
CALCIUM  DEFICIENCY  

Calcium  is  the  mineral  most  likely  to  be  consumed  in  inadequate  amounts  in  the  diet12.  In  the  
short  term,  this  does  not  result  in  any  obvious  symptoms,  because  calcium  is  so  tightly  
regulated  in  the  blood.  In  the  long  term,  inadequate  intake  of  calcium  can  lead  to  ostopenia,  
which  can  develop  into  osteoporosis3.    During  childhood,  calcium  deficiency  can  also  cause  
rickets,  though  it  is  more  often  associated  with  vitamin  D  deficiency3.  
 
Hypocalcemia,  a  severe  calcium  deficiency,  most  commonly  results  from  a  deficit  of  parathyroid  
hormone  or  abnormal  vitamin  D  metabolism,  which  is  seen  in  patients  with  renal  or  liver  
failure11.    It  is  also  seen  in  patients  who  have  had  their  stomachs  surgically  removed  and  those  
who  take  certain  medications,  such  as  diuretics3.  The  main  symptom  of  hypocalcemia  is  tetany,  
which  includes  numbness  and  tingling  around  the  mouth  and  fingertips  and  painful  muscle  
aches  and  spasms12.  Other  symptoms  may  include  lethargy,  poor  appetite,  and  abnormal  heart  
rhythms3.  If  left  untreated,  hypocalcemia  is  life  threatening11.  
 
EXCESS  CALCIUM  

Most  cases  of  hypercalcemia  are  a  result  of  hyperparathyroidism  or  from  a  malignant  tumour  
which  metastasizes  to  the  bone11.  Signs  and  symptoms  can  vary  depending  on  the  degree  of  
hypercalcemia  and  the  rate  of  onset,  but  may  include  fatigue,  weakness,  bone  pain,  confusion  
and  cardiac  dysrhythmias11.  Treatment  focuses  on  the  underlying  cause  of  hypercalcemia11.  

Resources  

1. Institute  of  Medicine.  Dietary  Reference  Intakes  for  Calcium  and  Vitamin  D,  Chapter  2:  
Overview  of  Calcium.  Washington,  DC:  The  National  Academies  Press,  2011.  
doi:10.17226/13050.  Retrieved  from  http://www.nap.edu/read/13050/chapter/4    
2. Calcium  in  diet.  (2013).  In  MedlinePlus.  Retrieved  from:  
https://www.nlm.nih.gov/medlineplus/ency/article/002412.htm    
3. National  Institutes  of  Health:  Office  of  Dietary  Supplements.  (2013).  Calcium.  Retrieved  
from  https://ods.od.nih.gov/factsheets/Calcium-­‐HealthProfessional/    
4. Institute  of  Medicine.  Dietary  Reference  Intakes  for  Calcium  and  Vitamin  D,  Chapter  5:  
Dietary  Reference  Intakes  of  Adequacy:  Calcium  and  Vitamin  D.  Washington,  DC:  The  
National  Academies  Press,  2011.  doi:10.17226/13050.  Retrieved  from  
http://www.nap.edu/read/13050/chapter/7    
5. United  States  Department  of  Agriculture.  (n.d.).  Interactive  DRI  glossary.  Retrieved  from  
https://fnic.nal.usda.gov/interactive-­‐dri-­‐glossary    
6. Institute  of  Medicine.  (2010).  DRIs  for  calcium  and  vitamin  d.  Retrieved  from  
http://iom.nationalacademies.org/Reports/2010/Dietary-­‐Reference-­‐Intakes-­‐for-­‐
Calcium-­‐and-­‐Vitamin-­‐D/DRI-­‐Values.aspx  
7. Dietitians  of  Canada.  (2014).  Food  sources  of  calcium.  Retrieved  from  
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Calcium.aspx    
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