We all know that getting an adequate amount of calcium every day is critical for our skeletal health. You may also know that calcium plays an important role in nerve transmission, muscle contraction, and in our cardiovascular system. The question is whether calcium supplementation is necessary.
In a previous blog, (Is It Possible to Get All the Calcium You Need from Diet Alone? Nov 18, 2020), I discussed how to get enough calcium from our diet alone, and this is the strategy widely supported by research. But for a variety of reasons, a person may have trouble getting enough calcium from food, and in that case, there are very important considerations that I outline below.
Recommended TOTAL Daily Intake: (this is the combination of what you get from food and supplements)
Women:
Age 50 and younger: 1000 mg
Age 51 and older: 1200 mg
Men:
Age 70 and younger: 1000 mg
Age 71 and older: 1200 mg
It is very important that you regard your calcium supplement as what it is – a supplement to bridge the possible gap in your diet each day. There may be days when no supplementation is needed. More is NOT better. Please consider that if you also take a multi-vitamin, you must include those milligrams of calcium in your daily calculation.
Safety:
Excess calcium may carry risks such as constipation, kidney stones, and possibly excess heart calcification (1). Let’s look at these one by one:
Constipation: Calcium supplements can cause constipation in some people, and generally, calcium carbonate supplements are more likely to cause gastrointestinal side effects like bloating, gas, and constipation. You may need to try a few different brands or types of calcium supplements to find one that you tolerate best. You may also want to try a supplement that combines calcium with magnesium as the latter can have laxative effects that could counteract calcium-related constipation.
Kidney Stones: This can be such a painful experience, that one might be tempted to avoid calcium altogether to prevent future stone formation. But while large doses of supplemental calcium, (especially if taken separately from a meal), can lead to stone formation, managing your diet to ensure you get adequate calcium is a must. According to the Mayo Clinic, for the best stone prevention, calcium should come from food (2). There is a lot to consider here, and I would recommend reading the Mayo article I’ve cited below.
Heart Disease: Several years ago, the US Preventive Services Task Force investigated the reported connection between calcium supplementation and increased risk of cardiovascular disease and determined there is no association. This was corroborated by other large studies such as the Multi-ethnic Study of Atherosclerosis (MESA) (3). Unfortunately, there is still mixed data out there, and a more recent study points toward a relationship between calcium supplements and possible adverse cardiovascular events (4). Importantly, this finding only pertains to calcium supplements – there has been no relationship found between dietary calcium intake and cardiovascular adverse events.
Thomson and colleagues followed 36,282 postmenopausal women with no history of breast or colorectal cancer over a period of about twenty years. They found that “calcium and vitamin D supplements seemed to reduce cancer mortality and increase CVD mortality after more than 20 years of follow-up among postmenopausal women, with no effect on all-cause mortality” (4).
Because this relationship is only seen with supplements, the problematic effect may be due to the higher concentration of calcium coming in all at once, opposed to the slower absorption that occurs with food. In addition, since we know that vitamin D and calcium work synergistically, if the calcium supplement is taken simultaneously with D, there may be more of a potentiating effect that might exacerbate any potential risk. In other words, high levels of vitamin D on top of calcium supplementation, will help the calcium get absorbed better. It gets into the bone, but maybe also into the coronary arteries.
Possible Drug Interactions
Calcium dietary supplements can interfere with certain medicines. One of the most common examples is levothyroxine (Synthroid, Levoxyl, others) used to treat hypothyroidism. Levothyroxine is not absorbed well when taken within 4 hours of taking a calcium carbonate supplement.
Another example is antibiotics in the quinolone family such as Cipro or Levaquin. These are not absorbed well when taken within 2 hours of taking any calcium supplement. Always make sure to tell your doctor or pharmacist about the dietary supplements you take.
Bisphosphonates, (Fosamax, Actonel, Boniva, etc.), are the most common family of drugs used to treat osteoporosis and there are very specific instructions about how they must be taken. Because calcium interferes with the absorption of bisphosphonates, calcium supplements must be taken at other times of the day.
Does the Type of Calcium Matter?
The most common calcium supplements are calcium carbonate and calcium citrate. There are also other forms including calcium phosphate, and those from algae, coral, oyster shell, or bone meal. Let’s take a closer look at some of the most common forms:
Calcium carbonate:
-
- higher percentage by weight of elemental calcium
- requires stomach acid for absorption; must take with food
- can cause constipation and bloating
- people with low stomach acid may not absorb it as well (thus the direction to take it with meals)
- the least expensive option
Calcium Citrate:
-
- has less calcium per pill
- is readily absorbed; can take without food, any time of day
- less likely to cause gastrointestinal side effects
- is the preferred form with age-related conditions associated with low stomach acid, and people who use proton pump inhibitor or antacids (5)
Algae-derived calcium: AlgaeCal is a very popular brand, and the following refers specifically to this product
-
- the company claims that because the algae plant draws calcium and minerals from seawater, the calcium is “pre-digested” and is more bio-accessible
- calcium derived from algae is still just calcium carbonate, not a new calcium supplement form
- typically contains other supplements like magnesium, vitamins D, K, boron, strontium, others, which may increase its effectiveness
- the company’s studies of effectiveness compare AlgaeCal to calcium carbonate and calcium citrate alone, not with the combinations of these other vitamins and minerals, skewing the evidence
- AlgaeCal is safe, but the studies posted on the company website do not present compelling evidence to justify the higher cost compared to the less expensive, over-the-counter calcium supplements currently available
*Regardless of the type of calcium, for optimal absorption, calcium doses should not exceed 500 milligrams (mg) per dose. If you need more than 500 mg per day, you should split your dose.
A Few Words About Strontium
Strontium has many structural elements that are very similar to calcium. Due to the heavier molecular weight of strontium versus calcium, when strontium is taken up in bone, the bone mineral density appears to falsely increase. Therefore the DXA scan results are not accurate. It also has a very long half-life: 7 – 10 years after the last dose, so the inaccurate results can persist for a long time. This supplement is generally not recommended (6).
Quality Concerns:
For any supplement, I strongly recommend that you check the labels for quality seals such as USP, NSF, or ConsumerLab. These are independent companies that the manufacturers volunteer to pay to acquire the quality seal which attests that the product has been tested for the quality, purity, and potency of its raw ingredients or finished products. Only a tiny fraction of supplements have these seals.
Some supplements have a “GMP” (Good Manufacturing Practices) claim that some consider to be basically worthless.
Calcium Supplements and DXA Scans:
It is recommended that you should avoid taking calcium supplements for 24-48 hours before your test because it can sometimes interfere with the imaging of the lumbar spine. If the calcium supplement is not completely dissolved, it will be interpreted by the DEXA instrument as extra bone and may produce an inaccurate reading.
- Li K, et al. The Good, the Bad, and the Ugly of Calcium Supplementation: A Review of Calcium Intake on Human Health. Clinical Interventions in Aging. 2018 Nov 28;13:2443-2452.
- https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-kidney-stones-and-calcium/
- Raffield LM, et al. The Association of Calcium Supplementation and Incident Cardiovascular Events in the Multi-ethnic Study of Atherosclerosis (MESA). Nutrition Metabolism and Cardiovascular Diseases 2016 Oct;26(10):899-907.
- Thomson CA, et al. Long-Term Effect of Randomization to Calcium and Vitamin D Supplementation on Health in Older Women: Post Intervention Follow-up of a Randomized Clinical Trial. Annals of Internal Medicine 2024 Mar; 177 (4).
- Palermo A, et al. Calcium Citrate: From Biochemistry and Physiology to Clinical Applications. Reviews in Endocrine and Metabolic Disorders 2019 Sep;20(3):353-364.
- Bartl & Bartl, (2019) Bartl R & Bartl C. The Osteoporosis Manual: Prevention. Diagnosis and Management. Springer, 2019.
Other Resources:
Bone Health and Osteoporosis Foundation: bonehealthandosteoporosis.org (Merged with American Bone Health in 2023.)
Osteoporosis Canada: osteoporosis.ca
National Institutes of Health: https://ods.od.nih.gov/factsheets/Calcium-Consumer/
Examples of Calcium Calculator Sources:
https://osteoporosis.ca/calcium-calculator/
https://www.bonehealthandosteoporosis.org/patients/treatment/calciumvitamin-d/
