Calcium and Colon Health: Can This Everyday Mineral Really Help Protect Our Gut?

One extra glass of milk a day. That's roughly how much additional calcium was linked to a 17% lower risk of bowel cancer in the largest study of diet and colorectal cancer ever carried out. It sounds almost too simple, and in some ways it is. But it's also a reminder that some of the most useful health habits are sitting quietly in our fridge.

Few people know the stakes of colon health better than American journalist Katie Couric. In 1998 she lost her husband, Jay Monahan, to colorectal cancer when he was just 42. Two years later she did something no TV host had done before: she had a colonoscopy live on NBC's Today show. Researchers later found that colonoscopy rates across the US rose by more than 20% in the months after the broadcast, a phenomenon now known as the "Katie Couric effect", documented in the Archives of Internal Medicine. She went on to co-found the National Colorectal Cancer Research Alliance and has written about her journey as a cancer advocate in The American Journal of Gastroenterology. Her message has always been the same: prevention and early checks save lives. Diet is one part of that picture, and calcium turns out to be a surprisingly interesting part of it.

Why this matters

When we talk about cancer, most people first think of something frightening and distant, something that happens to other people. Unfortunately, the numbers tell a different story. According to the World Health Organization (WHO), colorectal cancer is the third most common cancer in the world, with around 1.9 million new cases diagnosed in 2022 alone. At the same time, it is one of the cancers where healthy habits and timely screening can make a real difference.

We hear a lot about healthy eating, exercise, and avoiding alcohol and tobacco. We hear much less about one simple, almost everyday nutrient you probably already have at home: calcium. Yes, the same calcium you know as the building block of bones and teeth. Research suggests it may do something more, as adequate intake is associated with a lower risk of colorectal cancer.

What does the research say about calcium and colon health?

In January 2025, researchers from Oxford Population Health's Cancer Epidemiology Unit published a major study in Nature Communications. They followed more than 542,000 women from the UK Million Women Study for an average of about 16 years and looked at 97 different foods and nutrients. Of all the dietary factors, alcohol and calcium showed the strongest links to colorectal cancer risk: alcohol in the wrong direction, calcium in the right one.

Each additional 300 mg of calcium per day, about what you'd find in a large glass of milk, was associated with a 17% lower risk. Interestingly, calcium from dairy and calcium from non-dairy sources showed a similar effect, which suggests the mineral itself is doing much of the work. Milk and yogurt were also linked to lower risk. The study was funded by Cancer Research UK.

These findings fit well with the conclusions of the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR), whose expert panel concluded that dairy products, calcium, calcium supplements, whole grains and fiber-rich foods probably reduce the risk of colorectal cancer.

If you want to get more out of the calcium in your meals, it's worth reading our article Foods That Improve Nutrient Absorption, which explains why pairing calcium with vitamin D, such as a simple broccoli omelette, helps your body use it better.

Is the effect proven?

This is where science gets a little more complicated. An important point: the Oxford study is observational. It shows that people who consumed more calcium tended to have fewer cases of bowel cancer, but it can't prove that calcium alone caused the difference. Experts from the Science Media Centre also pointed out that a 17% reduction is a relative figure; for any single person, the absolute change in risk is much smaller.

Some studies have found weaker or no links. A 2013 meta-analysis led by researchers at the University of Auckland and published in the British Journal of Nutrition looked at randomized trials of calcium supplements taken without vitamin D. Over about four years, supplements did not change the risk of cancer overall, of colorectal cancer or of breast cancer. Interestingly, the researchers did see a lower rate of prostate cancer, the most common cancer in men, in the calcium groups, though they noted the trials were too short to detect effects that take longer to appear.

A large clinical trial published in the New England Journal of Medicine in 2015 also found that calcium and/or vitamin D supplements did not reduce the return of colorectal polyps in people who had had them removed.

When we take a step back, researchers agree on one thing: calcium has potential, but it is not a miracle cure. The effect seems to depend on the person, their overall diet, lifestyle, and even whether they have enough vitamin D, which helps the body absorb calcium properly.

How can you help yourself with everyday foods?

In folk medicine, calcium has long been used as something that strengthens the body. In the past, people drank water in which eggshells had been soaked for several days. Today we know that eggshells really are made up of roughly 95% calcium in the form of calcium carbonate. Experts don't recommend this trick for everyday use because of the risk of bacteria such as Salmonella on the shells, but it shows that people have been looking for natural ways to support their health for centuries.

If you want to get enough calcium in a safe and inexpensive way, you can reach for:

• dairy products – a glass of milk contains around 250–300 mg of calcium, and yogurt and hard cheeses are also excellent sources,


• leafy green vegetables – a cup of cooked broccoli has around 60 mg, and kale is another good choice,


• sardines – a can of sardines with bones contains more than 300 mg of calcium,


• almonds – a handful of almonds (30 g) has around 75 mg of calcium,


• fortified plant drinks and tofu – a good option for people who avoid dairy (check the label, as calcium content varies by brand).

For more ideas, the International Osteoporosis Foundation offers a handy list of the calcium content of common foods. And a small tip from our kitchen: if there's liquid on top of your yogurt, don't pour it away. That whey contains calcium, protein and other minerals, as we explain in Foods We Use Incorrectly.

Most nutrition experts, including oncology dietitians interviewed by Cancer Today, recommend a "food first" approach, because whole foods bring fiber, protein and other helpful compounds along with the calcium. Supplements are inexpensive and can be useful for people who can't get enough calcium from their diet, but they are best chosen together with a doctor or pharmacist.

Why might calcium help?

Scientists still aren't completely sure, but there are several theories. One is that calcium binds to bile acids and free fatty acids in the gut, substances that can irritate the lining of the colon, and helps carry them out of the body. Another suggests that calcium supports the normal renewal and maturation of cells in the intestinal lining, helping it stay healthy and intact.

To put it simply, calcium may act as a kind of "buffer" in the gut, helping to reduce how long irritating substances stay in contact with the delicate lining of the colon.

What about the risks?

As with everything, balance is key. Too much calcium can cause problems such as constipation and, especially with supplements, may raise the risk of kidney stones. According to the National Institutes of Health (NIH), adults should not exceed 2,500 mg of calcium per day up to age 50, or 2,000 mg per day after age 50, counting food and supplements together. Most adults need around 1,000–1,200 mg per day in total, and many people already get a good part of that from their diet.

If you are already taking other medicines, it's a good idea to talk to your doctor before starting a calcium supplement, as calcium can interact with some medications, including certain antibiotics and thyroid treatments. People with kidney problems or a history of kidney stones should be especially careful and seek personal advice.

How do science and folk wisdom fit together?

An old folk saying goes: what strengthens the bones also strengthens the inside. It fits surprisingly well with current research. Calcium is not just a "bone builder"; it plays a role in muscle function, nerve signaling and the healthy behavior of cells throughout the body, including in the gut.

In this case, folk wisdom and modern science seem to be pointing in the same direction. Calcium is affordable, widely available, and getting enough of it is one sensible part of a lifestyle that supports long-term health.

A small step with a big payoff

Cancer is a disease we all fear, but the good news is that there's a lot we can do ourselves to lower our risk. Calcium is not a miracle, but research suggests that getting enough of it, ideally from everyday foods like milk, yogurt, sardines and leafy greens, is linked to a lower risk of colorectal cancer. That's worth keeping in mind at your next shopping trip.

Combine that with a fiber-rich diet, regular movement, limiting alcohol and processed meat, and recommended screening from your doctor, and you give yourself a real head start toward a long, healthy life. Sometimes the answer is simpler than we think: it may start with one extra glass of milk or a bowl of yogurt a day.