Calcium is an essential mineral that your body needs in relatively large quantities, in contrast, to trace minerals, like iron, that you only need in small amounts. You’re probably most familiar with the role calcium plays in bone health. In fact, 99% of calcium is stored in your bones and teeth and that portion is vital for keeping your bones structurally sound. The other 1% of calcium is in your bloodstream. This component is critically important for survival on a minute-by-minute basis, as calcium regulates blood clotting, muscle contractions, and the rhythmical beating of your heart.
As you can see, calcium plays a number of vital roles that help keep your body in balance and the only way to maintain adequate levels is to get this mineral through diet or supplements. Although we think of dairy sources as being the go-to source of calcium, many non-dairy sources have substantial quantities of calcium, particularly tofu and green, leafy vegetables. However, the calcium from non-dairy sources isn’t absorbed as efficiently as calcium from dairy products. Yet, a growing number of people don’t consume dairy because they have lactose intolerance or eat a vegan diet. To make up for shortfalls, calcium supplements have become popular. However, recent research raises the possibility that calcium supplements have risks. Let’s look at why.
Do Calcium Supplements Increase the Risk of Colon Polyps?
A recent study linked calcium supplements with a greater risk of developing colon polyps. This study found that people who took calcium supplements or calcium supplements with vitamin D were at higher risk of developing colon polyps 6 to 10 years down the line. In the study, those who took vitamin D alone were not at higher risk.
Although colon polyps aren’t malignant, certain types increase the risk of developing colon cancer. One reason we get a screening colonoscopy is to remove polyps before they become cancerous. However, dietary calcium is NOT linked with a greater risk of polyps. In fact, some studies show diets higher in calcium protect against colon cancer. So, dietary calcium seems to have a different impact on colon health than supplemental calcium. It’s too early to draw firm conclusions about a link between supplemental calcium and cancer but it’s something to consider if you’re on the fence about taking a supplement.
The Impact of Calcium on Heart Health
Another disturbing finding is a link between calcium supplements and greater build-up of plaque in the coronary arteries. Researchers at Johns Hopkins discovered this association after following more than 2,700 men and women. As Erin Michos, M.D., M.H.S., associate director of preventive cardiology and associate professor of medicine at the Ciccarone Center for the Prevention of Heart Disease at Johns Hopkins points out, “This study adds to the evidence that excess calcium in the form of supplements may harm the heart and vascular system. However, studies don’t show a link between dietary calcium and a greater risk of plaque build-up.
In addition, a study published in the journal Neurology found the risk of dementia was up to two times higher in women with cerebrovascular disease who took calcium supplements. This includes women who have had a stroke. So, supplemental calcium may build up in the lining of arteries that lead to the heart AND brain.
Why Do People Take Calcium Supplements?
One reason many people, especially women, take calcium supplements is for bone health and to reduce the risk of bone fractures. However, not all research shows calcium supplements lower the risk of fractures. In fact, a meta-analysis, an analysis of multiple studies, found no association between dietary calcium and fracture risk. Other research also shows little correlation between calcium intake, bone density, and the risk of breaking a bone. So, taking a calcium supplement may not offer the protection that most people believe it does.
Another Reason to Reconsider High-Dose Calcium Supplements
If you take a large dose of calcium at once, for example, a 1000 milligram supplement, it can overwhelm your body’s ability to absorb it and, also, trigger an increase in parathyroid hormone, a hormone that breaks down bone and releases calcium into the bloodstream. So, taking a high-dose calcium supplement may actually be detrimental to the health of your bones. When you get calcium naturally through diet, you get it in smaller amounts throughout the day. This seems to be more favorable for bone health as you don’t overwhelm the system that regulates calcium.
Dietary Sources of Calcium
The good news is most people can meet their body’s calcium requirements through diet, assuming they eat a varied diet. More than half of the calcium Americans get through diet is from dairy products, although some plant-based foods contain substantial quantities of calcium. That means vegans can still get sufficient calcium through diet alone, although it takes a bit more planning. For example, a cup of milk contains 300 milligrams of calcium while a half-cup of tofu has roughly half that amount, about 155 grams. Green, leafy vegetables also contain significant quantities of calcium. For example, a half-cup of collard greens contains 110 grams.
You might wonder whether you absorb the calcium from plant-based foods easily. One problem is some plant-based foods, like leafy greens, contain phytates and oxalates, compounds that bind to calcium in the intestinal tract and block its absorption. So, calcium from plant-based sources is typically not as bioavailable as it is from dairy foods. But, that doesn’t mean you can’t get enough calcium eating a plant-based diet. You’ll just need to plan more carefully and consume more calcium-rich plant-based foods, like leafy greens. Chia seeds are another surprising rich source of calcium, with a 100-gram serving packing over 600 milligrams of this vital mineral.
The Bottom Line
Calcium is a vitally important mineral that your body needs for bone health and for survival. But, recent research calls into question the safety of calcium supplements. If you can, get your calcium from dietary sources. But, if you’re at high risk of osteoporosis or already have it, talk to your physician about the best option for you.
BMJ. 2015 Sep 29;351:h4580. doi: 10.1136/bmj.h4580.
J Intern Med. 2015 Oct;278(4):354-68.
WebMD. “Calcium Supplements Up Odds of Colon Polyps”
Healio.com. “NHANES: Calcium supplement use declining”
National Institutes of Health. “Calcium”
Johns Hopkins Medicine. “Calcium Supplements May Damage the Heart”
American Academy of Neurology. “Calcium supplements linked to dementia risk in women with certain health conditions”
Neurology. “Calcium supplementation and risk of dementia in women with cerebrovascular disease” August 2016.