Should You Take A Calcium Supplement?

Getting adequate calcium daily is critical for skeletal health, and calcium also plays a role in nerve transmission, muscle contraction, and the cardiovascular system. A prior blog ("Is It Possible to Get All the Calcium You Need from Diet Alone?", Nov 18, 2020) discussed getting enough calcium from diet alone — the strategy widely supported by research. This post covers considerations when supplementation is needed.

Recommended TOTAL Daily Intake (combined food + 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.

A calcium supplement should be regarded as a bridge for a possible dietary gap — some days may need none, and multivitamin calcium content must be included in the daily calculation. More is NOT better.

Safety. Excess calcium may carry risks: constipation, kidney stones, and possibly excess heart calcification.

• Constipation: calcium carbonate supplements are more likely to cause GI side effects (bloating, gas, constipation); trying different brands, or a calcium-magnesium combination (magnesium has laxative effects), may help.
• Kidney Stones: large doses of supplemental calcium (especially taken apart from meals) can lead to stone formation; per the Mayo Clinic, calcium should ideally come from food for best stone prevention.
• Heart Disease: the US Preventive Services Task Force found no association between calcium supplementation and cardiovascular disease risk, corroborated by the Multi-ethnic Study of Atherosclerosis (MESA); however, a more recent study points to a possible relationship between calcium supplements (not dietary calcium) and adverse cardiovascular events. Thomson and colleagues followed 36,282 postmenopausal women for ~20 years and found calcium and vitamin D supplements seemed to reduce cancer mortality and increase CVD mortality after 20+ years, with no effect on all-cause mortality. Because the effect is supplement-specific, it may relate to the higher, all-at-once concentration versus slower dietary absorption; combining with vitamin D (which enhances calcium absorption) may potentiate the effect, getting calcium into bone but potentially also into coronary arteries.

Possible Drug Interactions. Calcium can interfere with levothyroxine (Synthroid, Levoxyl) absorption if taken within 4 hours; quinolone antibiotics (Cipro, Levaquin) are not absorbed well within 2 hours of any calcium supplement. Bisphosphonates (Fosamax, Actonel, Boniva) require calcium supplements to be taken at other times of day due to absorption interference. Always tell your doctor/pharmacist about supplements you take.

Does the Type of Calcium Matter?

• Calcium carbonate: higher elemental calcium by weight; requires stomach acid, must take with food; can cause constipation/bloating; less well absorbed with low stomach acid; least expensive.
• Calcium citrate: less calcium per pill; readily absorbed, can take without food any time; less GI side effects; preferred for age-related low stomach acid and PPI/antacid users.
• Algae-derived calcium (e.g., AlgaeCal): company claims "pre-digested," more bio-accessible calcium from seawater-derived algae, but it's still just calcium carbonate; typically bundled with magnesium, vitamins D/K, boron, strontium; company effectiveness studies compare to calcium carbonate/citrate alone rather than to equivalent combinations, skewing the evidence; safe, but studies don't justify the higher cost versus less expensive OTC calcium.

For optimal absorption, calcium doses should not exceed 500 mg per dose regardless of type; split doses above 500 mg/day.

A Few Words About Strontium. Similar structural elements to calcium but heavier molecular weight, causing falsely increased apparent bone mineral density on DXA; half-life of 7–10 years after the last dose means inaccurate results persist a long time. Generally not recommended (see also the dedicated strontium blog post above).

Quality Concerns. Check labels for quality seals (USP, NSF, ConsumerLab) — independent companies manufacturers pay to verify quality, purity, and potency; only a tiny fraction of supplements carry these. "GMP" claims are considered by some to be largely worthless.

Calcium Supplements and DXA Scans. Avoid calcium supplements 24–48 hours before a DXA test, since undissolved supplement can be misread by the DEXA instrument as extra bone, producing an inaccurate reading.

Other resources: Bone Health and Osteoporosis Foundation (bonehealthandosteoporosis.org, merged with American Bone Health in 2023); Osteoporosis Canada (osteoporosis.ca); NIH calcium fact sheet (ods.od.nih.gov/factsheets/Calcium-Consumer).

References

1. 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.
2. Mayo Clinic Q&A: Kidney Stones and Calcium.
3. 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.
4. Thomson CA, et al. Long-Term Effect of Randomization to Calcium and Vitamin D Supplementation on Health in Older Women. Annals of Internal Medicine 2024 Mar;177(4).
5. 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.
6. Bartl R & Bartl C. The Osteoporosis Manual: Prevention, Diagnosis and Management. Springer, 2019.