Advising Patients About Calcium Supplements
The primary reason practitioners recommend calcium supplements is to support bone health.* However, calcium also helps support the function of nerves, muscles, and the heart.* While it’s important to recommend calcium for certain patients, it’s also important to talk to them about how much calcium they get from their daily diet, the type of calcium they should take and how to take calcium supplements for optimal results.
The Recommended Dietary Allowance (RDA) for adults age 19 to 50 years old is 1,000 mg daily and 1,200 mg daily for adults over age 51. Foods that are high in calcium include:
• Dairy products
• Dark green leafy vegetables
• Dried figs
• Fortified foods, such as nut milks, cereals, soy products
It can be difficult getting all of the calcium needed from diet alone especially among certain patient populations including:
• Those following a vegan diet
• People who are lactose intolerant or allergic to dairy products
• Patients on a high protein diet
• People who consume too much sodium
• Patients with digestive or malabsorption issues
In these and many other cases, calcium supplementation is often indicated. Common forms of calcium include:
• Calcium carbonate = 40% elemental calcium
• Calcium citrate = 21% elemental calcium
• Calcium lactate = 13% elemental calcium
• Calcium gluconate = 9% elemental calcium
• MCHA (microcrystalline hydroxyapatite) = 20-25% elemental calcium
Not all calcium consumed is actually absorbed in the gut. Absorption is as high as 60% in infants and young children, who need substantial amounts of the mineral to build bone, and absorption decreases to 15%–20% in adulthood. Absorption continues to decrease as people age, so recommended intakes are higher for adults over 50. Calcium carbonate requires stomach acid to be absorbed and must be taken with meals for best effect. People with low stomach acid or taking medications to reduce stomach acid, should avoid calcium carbonate. The other forms are well absorbed, and can be taken with or without meals. However, taking a high dose of calcium with a meal (500 mg or more) will actually decrease the overall absorption of calcium from both the meal and the supplement. It is believed the body can absorb only about 500 mg at a time, but it may in fact be even less.
So, there are some very important things to remember about calcium supplements, to maximize absorption
1. The efficiency of absorption decreases as calcium intake increases. The higher the amount of calcium in the gut, the lower the absorption rate. That’s why it’s so important to take more frequent lower doses (250-400 mg) for best absorption and utilization.
2. Other components in food: phytic acid and oxalic acid, found naturally in some plant foods, bind to calcium and can inhibit its absorption. Foods with high levels of oxalic acid include spinach, collard greens, sweet potatoes, rhubarb, and beans. Among the foods high in phytic acid are fiber-containing beans, seeds, nuts, and soy. The extent to which these compounds affect calcium absorption varies. Research shows, for example, that eating spinach and milk at the same time reduces absorption of the calcium in milk. However, these nutrient interactions are accounted for in the overall calcium DRIs, which factor in differences in absorption of calcium in varied diets. Patients should consider their diet, and avoid taking calcium supplements with high calcium or high phytate meals, for example, a breakfast of milk and granola or oatmeal would reduce the overall absorption of calcium due to the nature of the meal, high in phytates and calcium.
3. Iron and zinc supplements interfere with calcium absorption
It’s also important to advise patients that more is not necessarily better. Aside from poor absorption of high dose supplements, in the case of calcium, taking too much can have a detrimental effect on bones and heart health. That’s why dietary intake assessment is important. Also, identifying any medications the patient is taking is key as calcium supplements interact with some prescriptions such as blood pressure medicines, certain hormone replacements (like thyroid), bisphosphonates, antibiotics, and calcium channel blockers.
To maximize absorption of total daily calcium, assuming your patient is getting some calcium from each meal, best practice is recommending 250 mg of a well absorbed calcium 4 times a day, to be taken with meals and at bedtime. This supplemental amount of 1000 mg of calcium in addition to dietary intake of at least 200 mg will meet the daily RDI, for almost everyone. Again, the AVERAGE adult consumes approximately 600-700 mg of calcium from diet every day. Knowing the approximate contribution of calcium from your patients diet, can inform your supplement recommendation.
And a note about magnesium, which is extremely important, and required for many physiological functions, some of which also require calcium. It’s still a common belief that calcium and magnesium should always be taken together. This is not exactly true. Studies have shown that what IS true, is maintaining an overall daily intake ratio of approximately 2:1 calcium to magnesium may be best for optimal for health.
Beto JA. Clinical Nutrition Research. 2015;4(1):1-8.
Ciria-Recasens M, Blach-Rubio J, Coll-Batet M, et al. Clinical Drug Investigation. 2011;31(12):817-24.
Shin CS, Kim KM. Endocrinology and Metabolism. 2015;30(1):27-34.
Tai V, Leung W, Grey A. BMJ. 2015;351.