Calcium 101

Recently, I was working with a client who was concerned that she might not be getting enough calcium in her diet. She doesn’t drink milk (dairy or otherwise) and she dislikes several of the non-dairy sources of calcium. I run across this question fairly regularly so I thought this might be a good time to review why calcium is so important, the variety of ways you can get it from your diet and when it might be a good idea to take a supplement. A “Calcium 101” course, if you will.


Why do I need calcium in my diet?

Calcium is the most abundant mineral in the body. 99% of the calcium in our body is stored in teeth and bones. Everybody knows that calcium is important for ensuring healthy bones and teeth but did you know that calcium is also necessary for several of the body’s critical functions such as blood clotting, nerve transmission, controlling your blood pressure and maintaining your heartbeat?


How much calcium do I need?

  • Adults aged 19-50 need 1000 mg per day; slightly higher after age 50 due to a decreased ability to absorb calcium; over 50 aim for 1200 mg per day.
  • Because so much skeletal growth happens during the adolescent years adolescents age 14-18 need 1300 mg per day.
  • During pregnancy and lactation the body has an increased ability to absorb calcium, so increased calcium intake is not required. If pregnant under age 19 aim for 1300 mg per day, 19 and over aim for 1000 mg per day.


Calcium 101: The best sources of calcium

Dairy, yogurt and cheese are all excellent sources of calcium.

How much calcium will I get?

  •  1 cup of 1% Milk provides 294 mg
  • 1/4 cup dry milk powder provides 292 mg
  • 1 cup of Low-fat Plain Yogurt provides 448 mg
  • ½ cup nonfat mozzarella cheese provides 543 mg


Don’t do Dairy?

Although dairy is a great source of calcium it is not the only place to get it! Non-dairy sources of calcium include: Soymilk, soy yogurt, canned sardines with bones, canned salmon with bones, fortified orange juice, tofu made with calcium sulfate, dark leafy greens such as kale and calcium fortified foods such as breakfast cereals.

Calcium 101 Tofu Package

How much calcium will I get?

  • 1 cup of unfortified soymilk provides ~ 8 mg
  • 1 cup fortified/enhanced soymilk provides 299-400 mg  depending on the product or brand
  • 3 oz canned sardines provides 325 mg
  • 1 cup fortified almond milk provides 451 mg
  • 3 oz canned salmon provides 183 mg 
  • 1 cup raw spinach provides ~ 30 mg
  • ½ cup tofu prepared with calcium sulfate provides 253 mg
  • 100 g (~3.5 oz or almost ½ cup) tightly packed raw kale leaves provides 150 mg
  • 1 cup cooked spinach provides 245 mg

But (yes, there is a but!) can the human body use all of the calcium that each of these foods provide?


Bioavailability Matters!

Bioavailability (which is just a fancy way of saying what amount your body can absorb) of calcium is decreased by the presence of tannins, fiber, phytates and oxalates. Cooking can improve the bioavailability of calcium in many foods but it varies. For information on the oxalate content of foods look here.


Some other factors that alter the way the human body uses calcium:

  • A High Sodium Diet can contribute to increased urinary excretion of calcium and can lead to bone loss.
  • Excess Dietary Protein can contribute to increased urinary excretion of calcium and can lead to bone loss.
  • Caffeine may interfere with absorption of calcium.
  • Alcohol and Smoking interferes with how your body uses vitamin D. Inadequate vitamin D can result in inadequate calcium and eventually lead to bone loss.
  • Lack of physical activity weakens bones and can put you at increased risk for osteoporosis. Exercise works bones much like muscles and helps the body to absorb calcium. Weight bearing exercises such as walking, jogging, hiking, tennis or stair climbing strengthens your bones and muscles. Consult your doctor for the type and duration of exercise that is right for you.


What helps with Calcium absorption?

More is not always better! The body is not able to absorb large doses of calcium. For example, much of a 1000 mg calcium tablet will not be absorbed. Likewise taking a 500 mg calcium tablet with a glass of calcium fortified orange juice is not likely to be helpful. It is better to spread calcium rich foods and supplements throughout the day optimize absorption.

Make sure you are getting enough Vitamin D! The body needs it to use calcium.


Dietary sources of vitamin D include:

  • fatty fish ( salmon, tuna, mackerel)
  • mushrooms
  • fish liver oils
  • eggs
  • fortified cows milk as well as non-dairy milks
  • fortified cereals and other foods

Eat a varied diet to ensure you are getting the other nutrients thought to assist in calcium absorption!

Don’t forget Sunlight! Our bodies are able to make vitamin D when our skin is exposed to sunlight.


Are there signs of calcium deficiency I should look for?

Unfortunately, no. The calcium in your bones makes up your “bone bank”. Throughout your lifetime, the calcium from the foods you eat is “deposited” into and “withdrawn” from your bone bank, depending on your needs. When your calcium intake is too low to keep your blood calcium normal, your body will “withdraw” the calcium it needs from your bones.

Over time, if more calcium is taken out of your bones than is put in, the result may be thin, weak bones that may break more easily. I am sorry to report that unlike your cash bank who will definitely notify when funds are low, no such warning comes from the “bone bank”, they just take what is needed to keep the body functioning. There are no real signs of a calcium deficient diet until there is bone loss or fracture happens. If you are concerned that you might not be getting enough calcium in your diet it may be a good idea to keep track of the foods you eat for a few days. Go here  for a very helpful worksheet to help you keep tally of your calcium intake.


When to take a supplement?

If you are lactose intolerant, have milk allergy, follow a dairy free vegetarian diet, or for any reason are unable to eat enough calcium rich foods, a calcium supplement might be in order.

For best absorption, it is a good idea to take calcium supplements with food. Calcium citrate is an exception; it may be taken with or without food. It is best to spread out the calcium you consume from food and/or supplements throughout the day. Aim for 600mg of calcium or less at one time. If you take more than 600mg of calcium from supplements each day, the dose should be split to improve calcium absorption. It might be helpful to choose a calcium supplement with at least 400 IU of vitamin D to ensure you are getting enough of the sunshine vitamin as well.


Can I get too much Calcium?

Yes, excess calcium can lead to kidney stones and other kidney health issues. Chronic high calcium intakes, particularly from calcium supplements, may be harmful.


Anything else I should keep in mind while taking calcium supplements?

  • Calcium interferes with the function of some antibiotics. Speak with your doctor or pharmacist if you have questions.
  • If you take calcium and iron supplements, they should be separated by at least 2 hours to optimize absorption of each mineral.
  • Calcium supplements — or antacids containing calcium — can interfere with the absorption of levothyroxine (Synthroid, Unithroid, others), a synthetic form of thyroid hormone. So make sure you separate your calcium from this medication by at least 4 hours. 
  • Some people have constipation with calcium supplements. If you get enough fiber, drinking at least 6-8 glasses of water and engaging in physical activity each day and still have constipation, you may consider opting for a lower dose calcium supplement which might be better tolerated.


Tips for fitting in calcium:

  • Smoothies are a delicious and nutritious way to include calcium rich foods and beverages in your day! Consider using dairy or non dairy milk, dry milk powders, yogurt, tofu, fortified orange juice and /or kale in smoothies to get a calcium boost.
  • Opt for yogurt at snack time.
  • Make kale a go to green for salads.
  • Include tofu in a stir-fry.
  • Include a variety of cooked dark leafy greens at mealtime.


Calcium 101 References



I am a Registered Dietitian Nutritionist living in Greensboro, North Carolina. I help people overcome nutrition obstacles and help them meet their nutrition and wellness goals.

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Hi, I’m Mona. I have been living with Relapsing Remitting Multiple Sclerosis (RRMS) for over ten years. As a registered dietitian nutritionist (RDN) I help others with MS to navigate the nutrition superhighway and make sustainable progress toward their unique wellness goals.

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