Excess calcium supplementation is not recommended and can cause soft tissue deposits and potential increases in arterial calcification.
Non-dairy food sources of calcium
- Nondairy sources include vegetables, such as Chinese cabbage, kale, and broccoli. Spinach provides calcium, but its bioavailability is poor.
- Most grains do not have high amounts of calcium unless they are fortified; however, they contribute calcium to the diet because they contain small amounts of calcium and people consume them frequently.
- Foods fortified with calcium include many fruit juices and drinks, tofu, and cereals
- The Adult RDA for calcium (non-pregnant) is 1000-1200 mg/day 1
Some foods have higher calcium bioavailability than others. 2
- The bioavailability of dairy foods is ~30%, therefore ~100 mg of calcium will be absorbed from a 300 mg dose of calcium in a cup of cow’s milk.
- Some plant foods such as bok choy have higher bioavailability at 50%, so 80 mg of calcium will be absorbed from 60 mg of calcium in a cup of cooked bok choy.
- Calcium in almonds is ~20% bioavailable
- Calcium in fortified orange juice or calcium-set tofu is similar to that of cow’s milk at ~30%
- Some plant foods contain “anti-nutrients’ such as phytates and oxalates that can bind calcium and make it less bioavailable.
- Spinach is high in oxalates which reduce calcium availability in spinach to ~5% even though it contains 260 mg of calcium per cup cooked.
- There is no need to avoid spinach, of course, just be sure to consume adequate calcium from other sources in a separate meal.
However, It is important to consume adequate calcium at meals containing oxalates as the calcium will bind the oxalate and prevent free oxalate from forming kidney stones. 3
Coronary artery calcification (CAC) scores
Vascular calcification reflects the presence of atherosclerotic plaque and is strongly associated with cardiovascular morbidity and mortality.
CAC scores evaluate calcification.
In apparently low-risk patients with a family history of CHD, CAC>100 were associated with increased risk of all-cause and CHD events and mortality 4
“…At high calcium score concentration (>300) lipoproteins are directly proportional with calcium score in contrast with high-density lipoprotein which is inversely proportional with calcium Score. 5
Excess calcium supplementation appears to increase risk of atherosclerosis and cardiovascular death and all-cause mortality, particularly among men supplementing with 1000 mg or more per day. However, in women, calcium supplementation was inversely associated with all-cause mortality.
Research suggests that: 6
- “calcium supplement use was associated with a 22% increase in the risk of incident CAC”
- “after 10 years of follow- up, calcium supplement use was associated with increased risk for
Dietary calcium intake alone does not appear to contribute to cardiovascular disease risk and may protect from atherosclerosis.
It is important to note that CAC assessment uses CT scans which expose the patient to excess ionizing radiation and increased risk of cancer and ischemic heart disease 7
So, perhaps consider biomarkers to assess risk or presence of atherosclerosis:
“Recently, several biomarkers, including osteopontin, fetuin-A, matrix-carboxyglutamic acid protein, pyrophosphates, bone morphogenetic proteins, leptin, osteoprotegerin have emerged as surrogate markers of coronary calcification. 8
- Lp-PLA2 activity
- Oxidized LDL
- Blood glucose regulation biomarkers
- NIH Calcium Factsheet for Healthcare Professionals https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/
- Harvard Scool of Public Health - The Nutrition Source "Calcium" https://www.hsph.harvard.edu/nutritionsource/calcium/
- National Kidney Foundation "Calcium Oxalate Stones" https://www.kidney.org/atoz/content/calcium-oxalate-stone
- Dudum R, Dzaye O, Mirbolouk M, et al. Coronary artery calcium scoring in low risk patients with family history of coronary heart disease: Validation of the SCCT guideline approach in the coronary artery calcium consortium. J Cardiovasc Comput Tomogr. 2019;13(3):21-25.
- Anmar Zaki Saleh, Emad AL-Mashat, et al. The Evaluation of Calcium Score Validity in the Diagnosis of Patients with Coronary Artery Disease by Using CT Angiography. Diyala Journal of Medicine. 2015; Volume 9, Issue 1, Pages 62-69
- Tankeu AT, Ndip Agbor V, Noubiap JJ. Calcium supplementation and cardiovascular risk: A rising concern. J Clin Hypertens (Greenwich). 2017 Jun;19(6):640-646. doi: 10.1111/jch.13010. Epub 2017 May 2. PMID: 28466573.
- Kim KP, Einstein AJ, Berrington de González A. Coronary Artery Calcification Screening: Estimated Radiation Dose and Cancer Risk. Arch Intern Med. 2009;169(13):1188–1194.
- Tousoulis D, Siasos G, Maniatis K, Oikonomou E, Vlasis K, Papavassiliou AG, Stefanadis C. Novel biomarkers assessing the calcium deposition in coronary artery disease. Curr Med Chem. 2012;19(6):901-20. doi: 10.2174/092986712799034833. PMID: 22229416.