Are Calcium Supplements Safe? The Real Facts

Are Calcium Supplements Safe? The Real Facts
Are Calcium Supplements Safe? The Real Facts

Do calcium supplements really cause heart attacks? A recent randomized controlled trial published in the January edition of the British Medical Journal (15 January 2008) concludes that "Loading with high doses of calcium reduces bone loss but at a cost in heart health that is not justified."

According to researchers Dr. Ian Reid and his colleagues, the risk of a heart attack, stroke and sudden death is about 1.5 times greater for those who supplement with calcium.

How can this be true?  Like other nutrients, calcium is interdependent on numerous other factors including the levels of vitamins, other minerals, hormones, the health of the digestive system and the degree of physical activity.  To make a simple pronouncement based on one factor, namely calcium supplementation, without looking at the numerous other variables in calcium biochemistry and nutrition can only lead to erroneous conclusions.

Sure, it’s possible that calcium supplements without a proper diet, enough physical activity and in the presence of magnesium and vitamin D deficiency leads to heart disease.  But, does this mean that all middle-aged women should stop taking calcium supplements?  I think not.

Calcium Quick Facts

Get the latest information, tips & recipes for healthy living delivered directly to your inbox.
Your privacy is important to us.
  • Calcium is the most abundant mineral in the body.
  • Calcium is 1.5-2% of our body weight.
  • 98% of all calcium is found in our bones, 1% in our teeth and 1% in other tissues.
  • Calcium requires many other minerals for healthy bone formation: magnesium, boron, manganese, zinc, copper, silicon, strontium and phosphorus.
  • Calcium requires vitamins A, C, D and K for optimal metabolism.
  • Calcium absorption becomes less efficient with age.
  • Aside from osteoporosis, calcium deficiency can cause kidney stones and allows the body to accumulate lead.
  • High animal protein (very high in phosphorus) intakes may incrase calcium loss through the intestines and kidneys.
  • A very high fat intake also inhibits calcium absorption.
  • Hydrochloric acid helps calcium absorption in the duodenum where most calcium is absorbed.
  • Antacids and prescription acid supressing drugs all reduce calcium absorption.
  • Stress can lower calcium absorption.
  • Excess sugar and salt intake leads to calcium loss in the urine.
  • Phytic acid (phytates) found in whole grain foods or foods rich in fiber may reduce the absorption of calcium and other minerals as well.
  • Foods high in oxalic acid (spinach, rhubarb, chard, and chocolate) can interfere with calcium absorption by forming insoluble saltes in the gut.
  • 3–80% of all calcium consumed is not absorbed due to all the above factors.
  • Overactive thyroid function can cause calcium loss from bone.

Is Your Calcium In The Right Place?

When a person absorbs calcium, regardless of the amount, there is no guarantee that this same calcium will be deposited into the bones.

Calcium tends to gravitate towards areas of injury in the body. If the lining of the arteries is damaged, calcium deposits there and causes hardening of the arteries.This could make cardiovascular disease worse. If the kidneys are damaged, the result of calcium deposition could be kidney stones. Calcium also tends to deposit in other soft tissue injured areas like tendons and ligaments causing stiffness or other disability.

Several studies in the past decade have shown that EFAs (Essential Fatty Acids) when combined with calcium can ensure that calcium deposition will take place in bone and not in the arteries, the kidneys or other soft tissues. EFAs enhance the effects of vitamin D in the gut and improve calcium absorption from the small intestine, reduce the urinary excretion (loss) of calcium, increase calcium that is deposited in the bone and improve the strength of bone.

The dosage required for evening primrose (an omega-6 EFA) for both men and women is between 1500 – 6000 mg. daily to ensure calcium is deposited into the bone. Of course, calciumdeposition also depends to variable degrees to the frequency of weight bearing exercises as well as the presence of minerals such as magnesium, zinc, copper, strontium, silicon, manganese and boron.  If your calcium supplement does not contain evening primrose oil, make sure you take an extra 1500 – 6000 mg. of this omega-6 source of essential fatty acids each day to prevent or reverse osteoporosis with much greater assurance.

Calcium Toxicity

Calcium toxicity can be a very complex issue and is not simply a question of the dose that one consumes. Virtually any amount of calcium supplementation can be toxic (soft tissue calcification, hardening of the arteries and kidney stones) in the presence of parathyroid disease, magnesium and vitamin D deficiency.  In fact, given the proper conditions, calcium deposits can occur in the arteries or kidneys with daily calcium intakes below the RDA. It all depends on the individual’s nutritional and general health status at the time.

Through the actions of the parathyroid hormones PTH and calcitonin, the body attempts to keep blood levels of calcium within a certain normal range.  The adrenal glands, the thyroid, the small intestines, the liver and kidneys can all modify whether or not calcium absorbs, stays or comes out of the bones.

Calcium status is also strongly influenced by the levels of vitamin D, vitamin K, phosphorus, magnesium, boron, strontium, manganese, zinc, silicon and copper. High blood levels of calcium leading to soft tissue calcification will occur with both severe deficiency as well as excessive calcium intake.

Calcium deficiency or very low blood levels of calcium can cause a wide range of symptoms including anxiety, hyperactivity, headaches, irritability, muscle cramps or spasms, numbness and tingling in the hands or feet, palpitations, insomnia, confusion and even depression.  Drinking soft water (distilled, reverse osmosis or calcium deficient water) increases the risk of cardiovascular disease. This is something that has been documented for over 100 years.  In other words, a lack of dietary or supplemental calcium causes heart disease.

Adequate Intake (AI) for Calcium
Life Stage  Age  Males (mg/day)  Females (mg/day) 
Infants 0-6 months 210 210
Infants 7-12 months 270 270
Children 1-3 years 500 500
Children  4-8 years 800 800
Children 9-13 years 1,300 1,300
Adolescents 14-18 years 1,300 1,300
Adults 19-50 years 1,000 1,000
Adults 51 years and older 1,200 1,200
Pregnancy 18 years and younger 1,300
Pregnancy 19 years and older 1,000
Breast-feeding 18 years and younger 1,300
Breast-feeding 19 years and older 1,000
Tolerable Upper Intake Level (UL) for Calcium
Age Group   UL (mg/day)
Infants 0-12 months Not possible to establish*
Children 1-13 years 2,500
Adolescents 14-18 years 2,500
Adults 19 years and older 2,500


Dairy Dithering

While North Americans have the highest intake of dairy products in the world, they also have the highest incidence of osteoporosis.  Cow’s milk has been linked to numerous digestive disorders including constipation, lactose intolerance, casein (milk protein) allergy, irritable bowel syndrome, colitis, and a long list of allergic and autoimmune disorders including juvenile onset diabetes mellitus. The good news is that there are many healthy calcium alternatives to dairy products.  Although cow’s milk has the highest calcium content, many studies demonstrate that absorption is inferior to that seen with calcium from plant sources.

Dark green leafy vegetables have relatively high calcium concentrations. With the exception of spinach, due to the high oxalate content, the calcium from greens is very well absorbed.  Kale and other members of the same food family such as broccoli, turnip greens, brussels sprouts, collard greens and mustard greens are also excellent sources of magnesium, a trace mineral that is important for calcium utilization and which is found in only small amounts in cow’s milk.  In the past few years, a large number of excellent whole food supplements high in both calcium and magnesium have come out on the market.  These include spirulina, chlorella, barley green, green kamut, blue green algae and several others.  These all make ideal supplements for children because they are easy to mix with juices, are highly bioavailable, easily absorbed and have a very healthy balance of dozens of trace minerals, antioxidants, vitamins, amino acids and essential fatty acids.

Other natural sources of calcium include cooked beans and peas, seaweeds, soy products like tofu and soy milk, sprouts (e.g. alfalfa), seeds and nuts like sesame, pumpkin and hazelnuts as well as whole grains (e.g. corn tortillas, quinoa).

Food Serving Calcium (mg) Servings needed to equal the absorbable calcium in 8 oz of milk
Milk 8 ounces 300 1.0
Yogurt 8 ounces 300 1.0
Cheddar cheese 1.5 ounces 303 1.0
Pinto beans 1/2 cup, cooked 45 8.1
Red beans 1/2 cup, cooked 41 9.7
White beans 1/2 cup, cooked 113 3.9
Tofu, calcium set 1/2 cup 258 1.2
Bok choy 1/2 cup, cooked 79 2.3
Kale 1/2 cup, cooked 61 3.2
Chinese cabbage 1/2 cup, cooked 239 1.0
Broccoli 1/2 cup, cooked 35 4.5
Spinach 1/2 cup, cooked 115 16.3
Rhubarb 1/2 cup, cooked 174 9.5
Fruit punch with calcium citrate malate 8 ounces 300 0.62


Best and Worst Calcium Supplements

Whatever the calcium supplement, make sure it is balanced by at least half the amount of magnesium and that vitamin D levels in your system are adequate. Many health experts recommend a 1:1 ratio of calcium to magnesium in a supplement but this is not something cast in stone (or, dolomite, if you prefer).

If a calcium supplement is giving you constipation, just up the dose of the magnesium you take with it to where your bowels are moving well enough to your liking.  Ideally, get biochemical tests for the levels of all these nutrients before engaging in any aggressive supplementation.

Since many people are unable to follow a diet with an acceptable calcium intake, have digestive problems, food allergies that prevent calcium absorption and a long list of other special situations already enumerated, calcium supplements can become a necessity.

Studies indicate that calcium carbonate, the most widely used calcium supplement, is suitable for most people.  While other forms of calcium like calcium citrate, fumarate, gluconate, lactate, malate, orotate, succinate and aspartate may be better absorbed, the disadvantages of using the carbonate forms can be overcome by taking the supplement with food or something that acidifies the duodenal contents (e.g. betaine hydrochloride, apple cider vinegar or citrus juice).  The big advantage of calcium carbonate is that it is inexpensive and requires fewer capsules or tablets to obtain equivalent amounts of elemental (pure) calcium.

Microcrystalline calcium hydroxyapatite, a hyper-hyped form of calcium supplementation provides no advantage over calcium carbonate, is more expensive and is the poorest absorbed of all the supplemental forms of calcium.

Coral calcium, another of the over-hyped calcium supplements, has been found to contain traces of lead and other toxic impurities.  Like oyster shell calcium, dolomite and bone meal, coral calcium is nothing more than calcium carbonate plus lead and other poisons.  None of these are recommended.

Calcium bound to Krebs Cycle intermediates (citrate, lactate, aspartate, gluconate, malate, etc.) have the decided advantage of being better absorbed from the gastrointestinal tract than calcium carbonate, even in the absence of adequate stomach and duodenal acidity.  The problem with all of them is the expense and the fact that they are all bulkier molecules requiring more capsules or tablets to achieve the same dosage as calcium carbonate.

Some supplements contain calcium phosphate, which is very poorly absorbed and can block the absorption of iron and other trace minerals.  Calcium phosphate is the most constipating of all the calcium supplements and should be avoided.

Dumb and Dumber Studies

Every year, without exception, we see counter-intuitive studies concluding nonsense like “calcium supplements cause heart attacks” or “vitamin C causes DNA damage” or “beta carotene causes cancer” or “vitamin E causes phlebitis”.  The public panics, throws the vitamin and mineral supplements into the garbage and heads for the Aspirin and Lipitor bottles.

Examine any of these not so brilliant studies closely enough and you discover that the research was conducted in a test tube as opposed to a human or that smokers taking prescription cholesterol lowering drugs were used in the study or that synthetic inactive forms of a vitamin were used.  If a study sounds too weird to be true, it’s probably not true.

In this study on calcium supplements there was no mention of magnesium or vitamin D blood levels, dietary animal protein intakes or any of at least a dozen factors influencing calcium metabolism. There is therefore no evidence that calcium supplements taken as part of a balanced nutritional program of diet and vitamin and mineral supplements leads to heart attacks.  If you are still not convinced, see a natural health care practitioner who can sort out what’s high or low in your body so that the appropriate adjustments can be made to get you into balance.

Calcium is the mineral that has always had the most media attention as well as the overwhelming approval of the medical profession as a supplement that women should be taking.  That in itself may be enough to arouse suspicion.  As you might suspect, there are other more important minerals to consider for optimal health.   For example, despite a great deal of published medical and biochemical research, there is little, if any, attention paid to calcium’s neglected cousin, magnesium and most certainly no medical pronouncements that anyone should be supplementing this mineral in any serious way.  Its under-utilization in clinical medicine is nothing short of scandalous, especially in its use as a life-saving cardiovascular tonic.

Magnesium Facts and Figures

Magnesium appears by many names.  Below is a list of how you might see it in health food stores and pharmacies:

Chelated Magnesium, Dolomite, Epsom Salts, Magnesia, Magnesium Aspartate, Magnesium Carbonate, Magnesium Chloride, Magnesium Citrate, Magnesium Disuccinate Hydrate, Magnesium Gluconate, Magnesium Glycerophosphate, Magnesium Glycinate, Magnesium Hydroxide, Magnesium Lactate, Magnesium Malate, Magnesium Murakab, Magnesium Orotate, Magnesium Oxide, Magnesium Phosphate, Magnesium Sulfate, Magnesium Trisilicate, Milk of Magnesia.

  • the second most plentiful cation (positive ion) in the intracellular (inside cells) fluid and the most plentiful cation in the body
  • involved with more than 300 enzyme systems; plays an essential role in more than 300 cellular reactions
  • the body contains about 25 grams of magnesium, divided equally between the skeleton and soft tissue
  • extracellular (outside cells) magnesium makes up only 1% of total body magnesium
  • absorbed throughout the gastrointestinal tract, although whether maximal absorption occurs in the duodenum or colon is unclear
  • about one third of dietary magnesium is absorbed with efficiency of absorption depending on magnesium stores in the body, among other factors.
  • average absorption of supplements is 38%, but varies from 65% in people with low magnesium stores to 11% with high magnesium stores
  • excreted mainly through the kidneys
  • is important for normal bone structure
  • required for the formation of cyclic AMP (cAMP) and is involved in ion movements across cell membranes
  • requires both parathyroid hormone and vitamin D for absorption

Sources and Bioavailability of Magnesium

Magnesium is well absorbed from food sources such as legumes, whole grains, vegetables (especially broccoli, squash, and green leafy vegetables), seeds, and nuts (especially almonds). Magnesium is the central element of chlorophyll, the substance that gives plants their green color.  Hence, if it’s green, consider the food as a potentially good magnesium source.

Water with a high mineral content, or "hard" water, is also a source of magnesium. So-called “soft water” (e.g. distilled or reverse osmosis water) is not only void of magnesium but may actually promote its loss from the body.

Absorption of magnesium from supplements (i.e. bioavailability) varies. Magnesium chloride, magnesium lactate and magnesium aspartate appear to be most bioavailable. Magnesium oxide and magnesium sulfate have bio-availability only of about 4%. Enteric coating of some magnesium products may reduce the absorption of magnesium.

Magnesium Deficiency Effects

Magnesium deficiency is not uncommon in North America, especially among African Americans and the elderly. Low intake and impaired absorption of magnesium are associated with osteoporosis, hypertension, atherosclerotic vascular disease, cardiomyopathy, diabetes, and stroke.

Serum magnesium levels are depressed only in cases of severe magnesium deficiency and it poorly correlates with body magnesium). The body preserves serum magnesium at the expense of magnesium in cells and bone, so serum levels may appear normal in magnesium deficiency. Red cell and urine magnesium levels are also poor indicators of body magnesium). The intravenous magnesium loading test is considered to be a more reliable test to measure magnesium status but the test is cumbersome and is known for poor patient compliance.

Free ionic magnesium levels have been shown to vary with many disorders such as cardiac disease, stroke, diabetes, and migraines but measurement of ionized magnesium may not be readily available in labs outside the research setting.

Since magnesium is an anti-spasmodic or relaxant, one expects and sees symptoms of severe magnesium deficiency to include convulsions, confusion, muscle weakness, abnormal muscle movements such as spasms, tremors, myoclonus, and tetany as well as arrhythmias including ventricular tachycardia, fibrillation, and something called torsades de pointes.

Magnesium is often referred to as nature’s calcium channel blocker.  When intracellular levels of magnesium are low, this causes an increase in intracellular calcium. In addition to contributing to insulin resistance, higher intracellular calcium levels enhance calcium-mediated vasoconstriction, and inhibit cardiac and smooth muscle relaxation. The increased vascular tone can cause increased blood pressure. The pharmaceutical industry makes use of calcium channel blocking drugs to reverse this.  Practitioners in the natural health care industry use magnesium to accomplish this with fewer side effects.

Low serum magnesium is related to low-grade chronic inflammation. Magnesium deficiency is associated with elevated serum concentrations of tumor necrosis factor-alpha and C-reactive protein (CRP). People with high dietary magnesium intake have lower levels of CRP, which may reduce cardiovascular disease risk. Consuming less that the recommended dietary allowance (RDA) for magnesium is associated with a 1.48 to 1.75 times higher risk of having an elevated CRP.

Health Enhancing Uses of Magnesium

The following list includes many very well documented uses of magnesium in health promotion:

  • To correct magnesium deficiency
  • Laxative effects (constipation and to prepare bowel for colonoscopy or surgery)
  • Asthma
  • Allergic rhinitis
  • Cancer-associated neuropathic pain
  • Cardiovascular disease: angina, arrhythmias, hypertension, coronary heart disease and hyperlipidemia, low high-density lipoprotein (HDL) levels, mitral valve prolapse, vasospastic angina, myocardial infarction
  • Multiple sclerosis
  • As an antacid for symptoms of gastric hyperacidity
  • Attention deficit-hyperactivity disorder (ADHD)
  • Anxiety
  • Chronic fatigue syndrome (CFS) – in people with low red blood cell magnesium, there is some evidence that weekly intramuscular injections of 1 gram magnesium sulfate improves CFS symptoms
  • Lyme disease
  • Fibromyalgia
  • Pregnancy-induced leg cramps
  • Diabetes, insulin resistance and metabolic syndrome
  • Kidney stones; magnesium can prevent the recurrence of especially calcium oxalate stones
  • Migraine headaches and cluster headaches
  • Neuroprotective agent in patients diagnosed with acute stroke
  • Osteoporosis
  • Post-hysterectomy pain
  • Premenstrual syndrome
  • Altitude sickness
  • Urinary incontinence
  • Erythromelalgia
  • Restless leg syndrome
  • Preventing hearing loss
  • Paranoid schizophrenia treatment because levels appear to be lower in acute attacks of paranoid schizophrenia
  • By athletes to increase energy and endurance
  • Topically, used for treating infected skin ulcers, boils, and carbuncles; and for speeding wound healing
  • Stroke risk reduction in men
  • Topically as a cold compress in the treatment of erysipelas and as a hot compress for deep-seated skin infections
  • Intravenously (IV) or intramuscularly (IM)  used for acute hypomagnesemia occurring in conditions such as pancreatitis, malabsorption disorders, and cirrhosis, and for treating pre-eclampsia and eclampsia (toxemia of pregnancy); considered the agent of choice for pre-eclampsia and eclampsia
  • As an additive to total parenteral nutrition (TPN)
  • Controlling seizures (IV or IM) associated with epilepsy, glomerulonephritis, or hypothyroidism when low serum magnesium levels are present
  • IV or IM in the treatment of atrial and ventricular arrhythmias, for preventing arrhythmias after myocardial infarction and for cardiac arrest
  • IV for treating acute exacerbations of asthma and chronic obstructive pulmonary disease (COPD), for migraine headaches, neuropathic pain and postoperative pain, as an osmotic agent for cerebral edema, and for tetanus.
  • Both oral and IV forms reduce the need for numerous prescription drugs

Safety Issues

Used orally, magnesium is safe when used in doses below the tolerable upper intake level (UL) of 350 mg per day. Doses greater than that frequently cause gastrointestinal irritation, nausea, vomiting, loose stools and diarrhea. Prolonged diarrhea caused by excessive magnesium intake can even cause worsening magnesium deficiency.

Doses of 5000 mg daily have been used IV and IM without significant side effects. Intravenously, rapid infusion of magnesium can cause a flushing sensation, local pain and irritation, dizziness, bradycardia (a very slow heart rate), and low blood pressure. In children, magnesium is safe when used in doses below the tolerable upper intake level (UL) of 65 mg per day for children 1 to 3 years, 110 mg per day for children 4 to 8 years, and 350 mg per day for children older than 8 years. Higher doses can cause diarrhea and symptomatic hypermagnesemia (high blood magnesium) including hypotension, nausea, vomiting, and bradycardia (slow heart rate). Some research suggests intravenous magnesium at higher doses in pregnant women can increase fetal mortality and adversely affect neurological development.

Although extremely rare, death is possible from excess magnesium supplementation.  There are two reports of fatal hyperma

Leave a Comment

Dr. Zoltan Rona
Dr. Zoltan P. Rona is a graduate of McGill University Medical School (1977) and has a Master’s Degree in Biochemistry and Clinical Nutrition from the University of Bridgeport in Connecticut (1984). He is past president of The Canadian Holistic Medical Association (1987-88) and is the author of three Canadian bestsellers: The Joy of Health (1991), Return to the Joy of Health (1995) and Childhood Illness and The Allergy Connection (1997). He is co-author with Jeanne Marie Martin of The Complete Candida Yeast Guidebook (1996) and is the medical editor of the Benjamin Franklin Award winning Encyclopedia of Natural Healing (1998). He has had a private medical practice in Toronto for the past 35 years, has appeared on radio and TV as well as lectured extensively in Canada and the U.S. Dr. Rona currently writes regular articles for Reader’s Digest, Alive, Vitality magazine and for several web sites. His latest book “Vitamin D, the Sunshine Vitamin” was published in 2010. In 2011, Dr. Rona was named Chief Medical Advisor for NAKA Herbs and Vitamins and has developed a line of nutritional supplements (TriStar Naturals) which are sold in health food stores across Canada. He can be found at