Can calcium protect you from radioactive strontium?

Nuclear ‘fallout’ from the Japan (Fukushima) nuclear power plant disaster contains radioactive iodine, radioactive strontium, and other radioisotopes. These same radioactive elements are also found in the fallout from nuclear bombs. In my previous post, I discuss the use of potassium iodide (KI) tablets to prevent the body from taking up radioactive iodine into the thyroid. This approach is well-established and is recommended by the U.S. FDA. The human body cannot distinguish between radioactive iodine and non-radioactive iodine. Taking KI tablets floods the body with non-radioactive iodine, in effect diluting the radioactive iodine (I-131) and substantially reducing the amount of I-131 taken up by the thyroid.

In this article, I suggest that calcium from food and/or from calcium supplements might have much the same effect with regard to radioactive strontium (Sr-90).

It is well-established that the human body cannot distinguish between strontium and calcium. Non-radioactive strontium is used in medicine to treat certain bone disorders; the strontium is incorporated into the bones in place of some of the calcium. Unfortunately, the body cannot distinguish between radioactive strontium, non-radioactive strontium, and calcium.

“Strontium-90 has a half-life of 29.1 years. It behaves chemically much like calcium, and therefore tends to concentrate in the bones and teeth…. When people ingest Sr-90, about 70-80% of it passes through the body. Virtually all of the remaining 20-30% that is absorbed is deposited in the bone.” [1]

Now it stands to reason that if you supply the body with plenty of calcium, the amount of strontium-90 deposited in the bones will be reduced, just as iodine supplements reduce the amount of iodine-131 deposited in the thyroid.

And it turns out that the U.S. Health and Human Services (HHS) has a webpage, on the National Library of Medicine website, under the title “Radiation Emergency Medical Management — Managing Internal Contamination” that recommends calcium carbonate as one treatment for internal contamination with radioactive strontium (and also radium). The calcium competes with strontium for “bone binding sites”. By competitive inhibition, the large amount of calcium in the supplement (calcium carbonate) prevents the uptake of strontium into the bones and teeth.

Calcium supplements are generally safe and inexpensive, and they provide calcium, which is an essential nutrient. The potential harm from the judicious and moderate use of a calcium supplement is small. But if there is strontium-90 in radioactive fallout in your area, the potential benefit from the use of calcium is great.

What kind of calcium supplement would work best? The ideal approach would be to obtain plenty of calcium from your diet, so that your system has ample calcium available. The calcium in food is absorbed well into your body, and can be included in every meal. Foods that are high in calcium include milk, soy milk, rice milk, almond milk, almonds, cheese, yogurt, calcium-fortified orange juice, and some forms of tofu (check the label).

If there is strontium-90 (radioactive strontium) in your body, and you are not dead from the radiation, then the amount of strontium is relatively small. The main concern is a long-term increase in the risk of bone cancer caused by strontium being incorporated into the bones in place of calcium. To dilute the strontium with calcium, so that strontium is much less likely to become part of your bones, does not require an amount of calcium that is dangerous. You do not need to take an excessive amount of calcium; doing so could cause serious short-term health problems or even death. Taking excessive amounts of calcium is not necessary and is harmful. So keep the amounts of calcium in your diet within recommended limits (discussed below). Please do not take excessive amounts of calcium out of fear. Keep the amounts of calcium within reasonable limits, and only use this approach if there is in fact radioactive fallout in your area.

According to the Food and Nutrition Board of the Institute of Medicine at the National Academies ( [2]

Recommended Dietary Allowances for Calcium
Age Male Female Pregnant Lactating
0-6 months* 200 mg 200 mg
7-12 months* 260 mg 260 mg
1-3 years 700 mg 700 mg
4-8 years 1000 mg 1000 mg
9-13 years 1300 mg 1300 mg
14-18 years 1300 mg 1300 mg 1300 mg 1300 mg
19-50 years 1000 mg 1000 mg 1000 mg 1000 mg
51-70 years 1000 mg 1200 mg
71+ years 1200 mg 1200 mg
* Adequate Intake (AI)

I think that children under 4 should receive their calcium from foods that are high in calcium, not from supplements.

For children ages 4 and up, all teens, and all adults, the RDA for calcium is between 1000 mg and 1300 mg. How much calcium each person should consume as a supplement depends in part on how much calcium they have in their diet. You can use the USDA Nutrient Database ( online to determine the calcium content of foods. Or, for a less precise determination, use the labeling on the package. If the USDA label for a product says each serving provides 30% of the RDA for calcium, then the product has approx. 300 mg of calcium per serving. The RDA for calcium — as it is used for labeling purposes — is 1000 mg of calcium per day. The full set of Recommended Daily Allowances for calcium varies by age and gender; a simplified number is used for labeling.

How high a dose of calcium is safe to take on a daily basis? According to the National Institutes of Health, and the Food and Nutrition Board at the Institute of Medicine, the following limits apply by age and gender [3]

Tolerable Upper Intake Levels for Calcium
Age Male Female Pregnant Lactating
0-6 months 1000 mg 1000 mg
7-12 months 1500 mg 1500 mg
1-8 years 2500 mg 2500 mg
9-18 years 3000 mg 3000 mg 3000 mg 3000 mg
19-50 years 2500 mg 2500 mg 2500 mg 2500 mg
50+ years 2000 mg 2000 mg

Your total daily intake of calcium, from diet AND supplements combined, should be well below those upper levels.

Now let’s compare the Recommended Daily Allowance (RDA) to the Tolerable Upper Intake Level (TUIL) for calcium. The RDA is at 1000 to 1300 mg of calcium for persons ages 4 through adult. The TUIL is at 2000 to 3000 mg for persons ages 4 through adult. Even in cases of radiation emergency, you should not exceed the TUIL dosage; to do so may cause serious health problems, or in some cases even death. So the dose of calcium that you take in cases of radiation emergency should be substantially less than the Upper Limits listed above.

The safest approach would be to take only the RDA for calcium for your age group and to obtain that calcium entirely from your diet. If you are unable to obtain the RDA for calcium from diet alone, then you might decided to add the amount of calcium supplement needed to equal the RDA. When there is no actual fallout in your area, there is no need to exceed the RDA for calcium. Just as with iodine supplements, if there is in fact no radioactive fallout in your area, then you should only be taking approx. the amount of iodine and of calcium in the RDA.

If there is nuclear fallout in your area, only then should you exceed the RDA for calcium. But in all cases, your intake of calcium should remain well below the Tolerable Upper Limit. You should consult a variety of sources and use your own judgment. But I suggest increasing your daily total intake of calcium — from diet AND supplements combined — to 1600 mg of calcium per day if there is radioactive strontium in your area. This dosage level applies to persons from age 4 through adulthood, unless you have a medical condition, or a chronic ailment, or you are on medications (which might interact with the calcium) — in which case consult your physician. For children under 4, you should simply ensure that they have plenty of high calcium food, so that they meet, or modestly exceed, the U.S. RDA for calcium for their ages. But in ALL CASES, keep the calcium intake for persons of ALL AGES well below the Tolerable Upper Limit.

The above discussion concerns the amount of calcium in your diet. If you choose to supplement your diet with calcium, you must calculate the amount of calcium that the supplement provides. Calcium carbonate is 40% calcium. So a 500 mg tablet of calcium carbonate provides 200 mg of calcium (500 mg x 0.40 = 200 mg). A 750 mg tablet of calcium carbonate provides 300 mg of calcium. A 1000 mg tablet of calcium carbonate provides 400 mg of calcium.


Calcium supplements can produce an allergic reaction in persons who are allergic to shellfish, if the calcium is made from oyster shells (or even coral, as is sometimes the case). If you are allergic to shellfish, consult a physician concerning which calcium supplements are safe to take.

If you have any serious or chronic medical condition, or you are pregnant or nursing, consult a physician before taking any calcium supplement. Also, if you become pregnant while taking a calcium supplement, consult your OB/GYN doctor.

Antacids interfere with many medications. Consult with a physician if you are taking any medications, before using calcium supplements. Your physician may tell you to stagger the antacid away from medications (take them at different times, hours apart).

Consult your physician if you have infants or young children. If there is radioactive fallout in the area, for young children (under 4 years), try to give them sufficient calcium from the diet, rather than from supplements. If sufficient high calcium foods are not available, consult a physician before giving young children calcium supplements.

by Ronald L. Conte Jr.
17 March 2011
updated 8 May 2013

[1] U.S. Environmental Protection Agency, ‘Strontium,’

[2], ‘Dietary Guidance / Dietary Reference Intakes / DRI Tables,’ Recommended Dietary Allowances and Adequate Intakes; DRI Tables
See also:

[3] Ibid.

[4] USDA National Nutrient Database for Standard Reference SR23;

See also: A Layman’s Intro to Radiation

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