Heather Bedard, C.H.E.
People usually talk about calcium when they are referring to bone health, but there are so many other important functions that it plays in the body. Calcium also plays an important role in releasing essential enzymes for digestion[1], chemical processes in the body, organ function, and allowing muscles to contract – including the heart.[2] We can get even more in depth when we realize that there is a small pool of calcium in the circulatory system, extracellular fluid, and various tissues that also helps to control blood vessel contraction and dilation, blood clotting, nerve transmission, and hormonal secretion. Wow!
If you were to listen to the going opinion out there, you may think that you are at risk for not getting enough calcium. This idea is perpetrated by a misunderstanding of calcium, how it is stored in the body, and how and why it is released. So let’s dive into it a little bit and see if we can make sense of this topic.
How does Calcium work?
We ingest calcium through the food that we eat. At least that’s the way nature intended it. Once you’ve taken it in, most of it is taken through passive transport as your body absorbs it through the intestinal mucosa and stored in the bones. About 98% of your body’s calcium is stored there for you to use when you need it! Here in the gut, however, vitamin D (which is not a vitamin, it’s a hormone) is used if calcium needs are higher and active transport is needed to get it where it needs to go and to maintain correct calcium levels in the blood.
Some people recommend testing blood plasma to help determine calcium levels in the body, but this is not an accurate picture as blood levels of calcium are tightly controlled. When calcium is needed in the body, your amazing body releases calcium from the bones, into your blood, in a process known as bone remodeling. This is the process by which bone is constantly broken down and rebuilt. This is a way for the body to make repairs, grow, and become stronger.
How much calcium do you need?
If you’re an adult, you’ve probably heard by now that you need 1,000mg per day as a man or woman and 1200mg per day if you’re over 50. You may be surprised to know that the RDA for calcium is much lower in other countries. For example, the UK sets the goal at 700mg and the World Health Organization sets the limit at 500mg per day. But how did we get the numbers we use here in America?
In the 1970’s researchers conducted a few brief studies that seemed to point to postmenopausal women needing 1200mg per day to achieve calcium balance. However, these studies were flawed in that you need more than a few weeks to determine calcium balance. Researchers in 1997 also hypothesized that taking in more calcium would raise serum (blood) levels of calcium.[3] But remember, we learned earlier that it doesn’t.
They also thought that higher calcium levels would keep the body from releasing calcium from the bones to buffer acidity. They failed to take into account several things, including the fact that blood calcium levels are tightly controlled, nutrient absorption relies on the health of the gut microbiota, the food being consumed, and the overall dietary pattern. When calcium intake is too high the body actually restricts calcium absorption to prevent that excess from being deposited in the arteries and soft tissues of the body![4] Based on flawed studies and flawed thinking, the Institute of Medicine Panel raised the RDA of calcium for women over 50, from 800mg to 1,200mg.
Bone density is affected when bone breaks down faster than it is formed. Rather than chalking that up a deficiency of calcium, it is more likely that there are other things going on in the body that are causing the calcium to be taken from the bones. One of the most startling reasons that this could be is a high protein diet. Because as protein is digested it increases the acidity of the blood and the body pulls calcium to neutralize it.
Risk of calcium supplementation
Despite the fact, that the evidence points to massive risk from calcium supplementation, sales in the U.S. in 2020 hit 2.9 billion.[5] Vitamin D supplementation is forecasted to hit 1.6 billion by 2025. [6] Many people take them in conjunction with each because vitamin D helps calcium to absorb and is beneficial for strong bones as well. There are a few other reasons that people turn to supplementation at this point. One is that they are legitimately concerned about osteoporosis through diagnosis, and another is that they have been told they can never get enough. While the evidence is minimal that supplementing with calcium can be helpful, the preponderance of evidence is heavily in the other direction.
A big risk of calcium supplementation is the risk of kidney stones. It is thought that high levels of dietary calcium can offer protection from developing kidney stones. However, high levels of calcium from supplementation may promote stone formation because they increase the amount of calcium that is excreted in the urine. Women who participated in the Woman's Health Initiative, and who took the calcium–vitamin D combination, had a 17% increase in kidney stones than those who got the placebo. These participants took 1000mg of calcium and 765 IU of vitamin D daily.[7]
There is also an increased risk of heart attack with calcium supplementation. In 2010, calcium supplements were linked with an increased risk of heart attack in an analysis of 15 randomized controlled trials.[8] Researchers believed that the higher risk was due to blood coagulation and calcium buildup in the walls of the arteries. From this study, they concluded that if 1,000 people took calcium for 5 years, 26 fractures might be prevented but 14 additional heart attacks would occur.
Another randomized study of 1,471 postmenopausal women found that 21 of 732 women who took 1,000 mg of calcium a day had heart attacks, compared with 10 of 736 who received a placebo.[9] Still another group of researchers found that women who consume more than 1400mg per day of calcium had twice the risk of dying from cardiovascular disease, ischemic heart disease, and stroke than women who consumed 660-999mg per day. In this instance, high dietary intake of calcium plus calcium supplements increased the risk by a lot.[10]
One of the limitations of clinical trial data on supplementation is that they, for the most part, are not structured to show all adverse events, but only the most acute toxicity reports. But let’s keep diving in. There’s more!
Calcium supplementation comes with a risk of hypercalcemia and hypercalciuria. Hypercalcemia is increased calcium in the blood and hypercalciuria is increased calcium in the urine. This is according to a new study that was looking at the risk of both hypercalcemia and hypercalciuria in people who take the recommended amount of calcium per day from the Institute of Medicine.[11] For ages 51 and up, this was 2000mg per day. The calcium was taken with the amount of vitamin D that is recommended by the Endocrine society which is 10,000 IU per day or the federal RDA which is 600-800 IU per day. This was a randomized, double-blind, placebo-controlled trial that last for 1 year. There were two groups – one was 10,000 IU of vitamin D and 1200mg of calcium (assuming that they were getting 800mg from their diet) and the other took 600 IU of vitamin D and 1200mg of calcium; also assuming they were getting 800mg from their diet.
Even at the lower dose, the study found that taking vitamin D with calcium supplements was associated with many episodes of hypercalciuria. We know from the Women’s Health Initiative that over time, this can result in an increase of kidney stones.
Interestingly enough, we know that both calcium and vitamin D supplementation lower parathyroid hormone production. This hormone regulates the calcium levels in the blood and the bones.
Furthermore, in an analysis of 33 randomized clinical trials, calcium and vitamin D supplements did not reduce the risk of fractures. It did not matter whether they are used alone or together. In other words, supplementation was useless.[12]
The United States Preventative Task Force agrees stating, in 2013 that there was insufficient evidence to support the use of these supplements in preventing fractures in healthy adults.[13]
Ironically, calcium supplementation can actually INCREASE the risk of fracture.[14]
So let’s quickly go through some facts about calcium supplementation in particular:
Taking calcium supplements can increase the risk of coronary artery calcification.[15]
The majority of studies do NOT show that taking more than 400-500mg of calcium per day increases bone density.[16]
Calcium intake higher than 778mg per day OR lower than 275 mg per day increases fracture risk for men. For women, this is slightly different with risk showing at intake higher than 651 mg per day or lower than 248mg.[17]
In my opinion, the literature does not support calcium or vitamin D supplementation for healthy adults. If you are currently taking a multi-vitamin, you will want to be aware that calcium and vitamin D are both typically included. Additionally, the fortification of calcium in many products can lead to too much calcium being ingested. This can lead to arterial calcification.
The best way to get calcium
So what’s the best way to get calcium? I bet you know what I’m going to say. The best way to get calcium is from natural sources in your diet. The calcium you get from dietary sources is absorbed into the body more efficiently than calcium supplements. Along with that, the plant foods that you eat are also full of other nutrients like iron, vitamin A, and vitamin C and the components needed to absorb calcium.
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[1] Xie R, Tang B, Yong X, Luo G, Yang SM. Roles of the calcium sensing receptor in digestive physiology and pathophysiology (review). Int J Oncol. 2014;45(4):1355-1362. doi: 10.3892/ijo.2014.2560
[2] Kuo IY, Ehrlich BE. Signaling in muscle contraction. Cold Spring Harb Perspect Biol. 2015;7(2):a006023. doi:10.1101/cshperspect.a006023
[3] https://www.ars.usda.gov/news-events/news/research-news/2007/calcium-requirements-may-be-overestimated/
[4] Heaney RP, Saville PD & Recker RR “Calcium absorption as a function of calcium intake” J Lab Clin Med 1975; 85:881-887.
[5] https://www.marketandresearch.biz/report/201409/global-calcium-supplement-market-growth-2021-2026
[6] https://www.marketsandmarkets.com/PressReleases/vitamin-d.asp
[7] Wallace RB, Wactawski-Wende J, O'Sullivan MJ, et al. Urinary tract stone occurrence in the Women's Health Initiative (WHI) randomized clinical trial of calcium and vitamin D supplements. Am J Clin Nutr. 2011;94(1):270-277. doi:10.3945/ajcn.110.003350
[8] Bolland MJ, Avenell A, Baron J et al. “Effect of calcium supplementation on risk of myocardial infarction and cardiovascular events: meta analysis.” BMJ 2010;341:c3691
[9] Bolland MJ, Barber PA, Doughty RN, et al. Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. BMJ. 2008;336(7638):262-266. doi:10.1136/bmj.39440.525752.BE
[10] Nathan Gray “Elevated calcium intakes double risk of heart disease death in women: BMJ Study.” www.nutraingredients-usa.com/content/view/print/741826 accessed 2.19.2013
[11] Aloia JF, Katamuluwa S, Stolberg A et al. “Safety of Calcium and Vitamin D Supplements; A Randomized Controlled Trial.” Clin Endocrinology 2018;89(6):742-749
[12] Zhao JG, Zeng XT, Wang J et al. “Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community Dwelling Older Adults. A Systematic Review and Meta-analysis.” JAMA 2017;318(24):2466-2482
[13] “Vitamin D and Calcium Supplementation to Prevent Fractures in Adults: U.S. Prevention Services Task Force Recommendation Statement.” Ann Intern Med 2013 May;159(9):691-696
[14] Reid I, Bolland M, Grey A. “Effect of calcium supplementation on hip fractures.” Osteoporos Int 2008 Aug;19(8):1119-1123
[15] Anderson J, Kruszka B, Delaney J, et al. “Calcium intake from diet and supplements and the risk of coronary artery calcification and its progression among older adults: 10-year follow-up of the Multi-Ethnic Study of Atherosclerosis (MESA).” J Am Heart Assoc 2016;5:e003815 DOI:10.1161/jaha.116.003815.
[16] Lanou, Berkow S, Barnard N. “Calcium, dairy products, and bone health in children and young adults: a reevaluation of the evidence” Pediatrics 2005 March;115:736-43.
[17] Fang A, Li K, Guo M et al. “Long-term Low Intake of Dietary Calcium and Fracture Risk in Older Adults with Plant-Based Diet: A Longitudinal Study from the China Health and Nutrition Survey.” J Bone Min Res published online ahead of print DOI: 10.1002/jbmr.2874