Calcium 🦴 and colon cancer risk

Could an additional 300mg of calcium in your diet lower our risk of colorectal cancer by 17%? March is Colon Cancer Awareness Month, and here are some tips to help you reduce your risk.

Colorectal cancer (CRC) is the second leading cause of cancer deaths in the USA, and 3rd most common cancer¹ worldwide.

Alarmingly, its incidence among younger adults has been rising in recent decades, with 20% of colon cancer now diagnosed in those under the age of 55 - it is now the leading cause of cancer death in men <50 years, because they are often diagnosed late - not a statistic that sits easily with moms of boys like me.²

While we don’t know for sure what is behind the increase, factors like diet, lifestyle, environmental pollutants, and genetics all play a role. But there is one simple dietary change—increasing calcium intake—that could offer some protection, according to a new report.

In January this year, the prestigious BMJ published findings from the Million Women Study, a large and comprehensive study funded by Cancer Research UK.³ This study found that higher calcium intake was associated with a lower risk of colorectal cancer, while alcohol consumption increased risk.

Then, just last month, another huge cohort study was published on this side of the pond in the prestigious JAMA and came to the same conclusion.⁴ They looked at both men AND women and found that higher calcium intake via either diet and/or supplements was associated with a lower risk of colorectal cancer.

So, how much calcium is needed? Does it matter where it comes from? And most importantly, how significant is this effect? Let’s break down the details.

The Million Women study

This is one of the largest prospective studies on women’s health in the world, conducted by the prestigious University of Oxford's Cancer Epidemiology Unit.

543,000 women were included in the study, with a mean age of 60 years, and these women were asked to fill out a survey every 3-5 years on their food intake over a typical week, including 130 quantitative or semi-quantitative questions on frequency of intake of specific foods and food groups, and then followed up for an average of 16 years. They didn’t just look at calcium, but a range of dietary variables.

This is what they found:

• Calcium intake: an increase of 300mg/day was linked to a 17% lower risk of colorectal cancer.

• Alcohol consumption: 20g/day (one large glass of wine) was associated with a 15% higher risk, consistent with prior research.

• Red & processed meat: Each additional 30g/day (e.g. one hot dog or 2 slices of bacon) increased the risk by 8%. This increased to 29% for every 100g of processed meat.

• Calcium sources: Both dairy and non-dairy calcium were protective. It is hypothesized that calcium can bind to secondary bile acids, reducing their carcinogenic effects.

Wait, what are secondary bile acids?

For the science nerds, there are two types of bile acids:

• Primary - these are produced by the liver to help us digest our food, particularly fat.

• Secondary - when the primary acids interact with our gut bacteria (which are normal residents in the gut, some friendly, some not) - secondary bile acids are formed. These have been found to damage cells and even cause DNA damage in mechanistic studies.⁵

How does calcium reduce colorectal cancer risk?

It is thought that calcium could bind to some of these secondary bile acids and ‘neutralize’ their damaging effects on colonic cells - more evidence is needed.

This is also thought to be one reason why dietary fiber is protective of CRC - it can bind to and reduce secondary bile acid, among other benefits like positively impacting the gut microbiome - which also has a huge role to play in CRC.⁶

What increases secondary bile acids? A high-fat diet⁷

Keto may be trendy, and you’ve probably seen people insisting that a diet loaded with red meat and butter is “healthy.” They’ll often point to mechanistic studies or low-quality research to support their claims - but the bulk of large, human studies tells a different story.

My job isn’t to follow trends—it’s to present the body of scientific evidence. If you’re skeptical of what I’m telling you, I encourage you to look it up on PubMed and let the overwhelming research speak for itself.

That said, let’s be responsible and acknowledge this study’s limitations. While large, it’s still a population study reliant on self-reported dietary surveys, which aren’t always perfect. Plus, it only followed women with a mean age of 60, so we can’t assume the same results apply to men or younger populations (keep reading for the study that did include men).

Other questions I had when I read the report:

Do calcium supplements offer the same protection?

The study above focused on dietary calcium, so we don’t know.

But are there other studies that have looked at calcium supplements and CRC? Yes.

Here, across the pond, NIH has also been conducting one of the largest prospective studies examining the relationship between diet, lifestyle, and cancer risk.

In this study:

• They looked at 471,396 participants aged 50 to 71 years at baseline. Unlike the last study, this one looked at men as well 👏. 60% of the participants were male.

• Calcium intake was assessed through self-reported dietary questionnaires and supplement intake reports - i.e. they looked at both dietary and supplemental calcium intake.

• They divided the participants into:

  • Lowest calcium intake - around 400mg/day

  • Highest calcium intake - around 2000mg/day for women, 1700 mg/day for men

🚨 Compared to the lowest intake, those who had the highest intake had a 29% lower risk of colorectal cancer!

Did it matter where the calcium came from?

Yes, but there was a reduction in CRC risk regardless of whether the calcium came from food or supplements.

For every additional 300 mg/day of calcium intake from:

• Food AND supplement: 8% decrease in CRC risk

• Food: 10% decrease

• Supplement: 5% decrease

So, as you can see - the greatest benefit came from FOOD sources of calcium, although supplements seemed to have a small (but statistically significant) benefit too!

What do I do?

I am dairy-free because I am intolerant (not allergic, but I break out and become inflamed when I consume it), so I try to get enough calcium in my diet through food - My favorites? Collard greens, soy milk, okra, tofu, tahini, and ground sesame seeds.

Do I take a calcium supplement?

Yes.

It’s not always possible to get enough through diet alone, so I do take a calcium supplement every day now that I’m in my perimenopause, and my DEXA (bone) scan showed borderline osteopenia, so bone health is at the front of my mind.

After a lot of research, this is the one (up to 35% off + extra 10% off via my affiliate link) I’m happy with.

I take 2 capsules of Algecal Plus a day because I get a decent amount of calcium in my diet.

It is made from sustainably harvested marine algae and, unlike other calcium supplements, comes packaged with all the minerals that our bones need in an easy-to-absorb form.

*Note - Always check with your doctor before starting a new supplement, especially if you already take a vitamin D3/K2 supplement. Algecal has added D3, and Algecal Plus has D3 + K2.

I don’t take a separate vitamin D3/K2 anymore because my vitamin D is a solid 60ng/mL 💪 on just Algecal Plus alone.

Alcohol: A Significant Risk Factor

This likely won’t come as a surprise, especially with the Surgeon General’s recent push for cancer warnings on alcohol. Unlike calcium’s protective effects, alcohol consumption increases the risk of colorectal cancer (CRC).

Drinking just one large glass of wine (20g) was linked to a 15% higher CRC risk—a finding that aligns with the 2018 World Cancer Research Fund report, which showed a dose-response relationship between alcohol and CRC risk.⁸

And if you're in perimenopause, you may have already noticed alcohol’s increasingly negative effects on sleep, mood, and hormones.

Beyond Calcium: Other Key CRC Risk Factors

While calcium is promising, it’s just one piece of the puzzle. Other factors that impact CRC risk include:

• Processed & Red Meat: In addition to the Million Women study mentioned above, a meta-analysis published in PLOS ONE found that each 100g/day increase in red and processed meat consumption was associated with a 14% increase in CRC risk.⁹

• Fiber & Whole Grains: High-fiber diets lower CRC risk by improving gut health and reducing inflammation.

• Physical Activity: Regular exercise reduces CRC risk by 20-30% 😲 - one of the most powerful anti-cancer interventions.¹⁰

• Environmental toxins: You won’t hear many doctors talking about this yet, but studies suggest environmental toxicants like PM2.5 (air pollution) and phthalates may be associated with increased CRC risks. While more research is needed, strong evidence already links these exposures to hormone disruption, fertility issues, and other types of cancer.¹¹¹² I follow the precautionary principle—reducing exposure where I can - and you’ll find many practical, non-stressful tips by browsing my archive!

Last but not least, get your colonoscopies when recommended.

Screening guidelines vary by country, but in the U.S., routine screening starts at 45 for someone with an average risk of CRC. I had mine at that age, and because it was clear, I don’t need another for 10 years.

There are other CRC screening options, but in my opinion, colonoscopy is the best choice—it’s the only method that can detect cancer AND remove precancerous polyps before they become a problem. It wasn’t exactly a walk through a field of roses 🤭 (more like gallops to the bathroom the night before 😬), but the peace of mind? 👉 Priceless.

How do you make sure you are getting enough calcium? Share and discuss your thoughts with our community below! ❤️👩🏻‍🏫

P.S. Wondering what other less toxic products I use in my home🛍️ you can find them here ❤️

1. https://www.who.int/news-room/fact-sheets

2. https://www.cancer.org/content/dam/cancer-org/research/cancer-facts-and-statistics/colorectal-cancer-facts-and-figures/colorectal-cancer-facts-and-figures-2023.pdf

3. Papier K, Bradbury KE, Balkwill A, Barnes I, Smith-Byrne K, Gunter MJ, Berndt SI, Le Marchand L, Wu AH, Peters U, Beral V, Key TJ, Reeves GK. Diet-wide analyses for risk of colorectal cancer: prospective study of 12,251 incident cases among 542,778 women in the UK. Nat Commun. 2025 Jan 8;16(1):375. doi: 10.1038/s41467-024-55219-5. PMID: 39779669; PMCID: PMC11711514.

4. Zouiouich S, Wahl D, Liao LM, Hong HG, Sinha R, Loftfield E. Calcium Intake and Risk of Colorectal Cancer in the NIH-AARP Diet and Health Study. JAMA Netw Open. 2025 Feb 3;8(2):e2460283. doi: 10.1001/jamanetworkopen.2024.60283. PMID: 39960668; PMCID: PMC11833519.

5. Ajouz, H., Mukherji, D. & Shamseddine, A. Secondary bile acids: an underrecognized cause of colon cancer. World J Surg Onc 12, 164 (2014). https://doi.org/10.1186/1477-7819-12-164

6. Alberts DS, Ritenbaugh C, Story JA, Aickin M, Rees-McGee S, Buller MK, Atwood J, Phelps J, Ramanujam PS, Bellapravalu S, Patel J, Bextinger L, Clark L. Randomized, double-blinded, placebo-controlled study of effect of wheat bran fiber and calcium on fecal bile acids in patients with resected adenomatous colon polyps. J Natl Cancer Inst. 1996 Jan 17;88(2):81-92. doi: 10.1093/jnci/88.2.81. PMID: 8537982.

7. Zeng H, Umar S, Rust B, Lazarova D, Bordonaro M. Secondary Bile Acids and Short Chain Fatty Acids in the Colon: A Focus on Colonic Microbiome, Cell Proliferation, Inflammation, and Cancer. Int J Mol Sci. 2019 Mar 11;20(5):1214. doi: 10.3390/ijms20051214. PMID: 30862015; PMCID: PMC6429521.

8. https://www.wcrf.org/wp-content/uploads/2024/10/Alcoholic-Drinks.pdf

9. Chan DS, Lau R, Aune D, Vieira R, Greenwood DC, Kampman E, Norat T. Red and processed meat and colorectal cancer incidence: meta-analysis of prospective studies. PLoS One. 2011;6(6):e20456. doi: 10.1371/journal.pone.0020456. Epub 2011 Jun 6. PMID: 21674008; PMCID: PMC3108955.

10. World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Report: Diet, Nutrition, Physical Activity and Colorectal Cancer. 2017.

11. Pritchett N, Spangler EC, Gray GM, Livinski AA, Sampson JN, Dawsey SM, Jones RR. Exposure to Outdoor Particulate Matter Air Pollution and Risk of Gastrointestinal Cancers in Adults: A Systematic Review and Meta-Analysis of Epidemiologic Evidence. Environ Health Perspect. 2022 Mar;130(3):36001. doi: 10.1289/EHP9620. Epub 2022 Mar 2. PMID: 35234536; PMCID: PMC8890324.

12. Su WC, Tsai YC, Chang TK, et al. Correlations between urinary monoethylhexyl phthalate concentration in healthy individuals, individuals with colorectal adenomas, and individuals with colorectal cancer. J Agric Food Chem. 2021;69(25):7127-7136