Trials using roughly 1,200 mg/day of calcium report modest reductions in the return of colorectal adenomas over about five years, with larger effects in some higher-risk lesions. Long-term protection against colorectal cancer is unproven. Calcium may be reasonable for patients who need it for bone health, but it should complement - not replace - colonoscopic surveillance and established lifestyle and clinical prevention measures.

Why adenomas (polyps) matter

Colorectal (large-intestine) tumors commonly begin as adenomas, commonly called polyps. Removing polyps found on colonoscopy remains the main way to prevent colorectal cancer. Chemoprevention - using a drug or supplement to lower future polyp or cancer risk - is an active area of research.

What trials of calcium found

Randomized trials in people with previously removed adenomas tested calcium supplements (the most common trial dose was about 1,200 mg daily). Those trials showed a modest reduction in the recurrence of new adenomas over the first five years - on the order of a single-digit to low-double-digit percentage reduction overall, with somewhat larger effects for advanced or higher-risk adenomas in some analyses.

Longer follow-up studies and pooled analyses show that the protective effect is modest and not consistently durable over extended follow-up. Trials have not shown a clear reduction in colorectal cancer incidence or mortality from calcium supplements alone.

How clinicians view calcium now

Because the benefit is modest and evidence on long-term protection against cancer is limited, calcium supplementation is not a universal, stand-alone recommendation for adenoma prevention. Many clinicians consider calcium supplementation reasonable for people who already need calcium for bone health, and they may discuss its modest potential to reduce adenoma recurrence with patients who have a history of polyps.

If you are considering supplements, discuss dose and timing with your clinician. Calcium supplements can cause side effects (constipation, bloating) and increase the risk of kidney stones in some people; studies of cardiovascular risk have produced mixed results. For most adults, getting calcium from diet is preferred when feasible.

Other proven prevention strategies

Colonoscopy and scheduled surveillance remain the most effective approach to prevent colorectal cancer after polyp detection. Lifestyle measures - a healthy diet, regular physical activity, maintaining a healthy weight, limiting alcohol, and avoiding tobacco - also lower colorectal cancer risk.

Aspirin and other anti-inflammatory agents reduce adenoma and colorectal cancer risk in some trials, but bleeding risks limit their routine use. Decisions about aspirin for cancer prevention are individualized and generally balanced against cardiovascular and bleeding risks.

Bottom line

Evidence supports a modest short-term reduction in adenoma recurrence with calcium supplements at doses used in trials (about 1,200 mg/day). However, calcium is not a substitute for colonoscopic surveillance. People with prior adenomas should discuss the risks and benefits of calcium, aspirin, and other prevention options with their clinician, and prioritize guideline-directed surveillance and healthy lifestyle measures.

FAQs about Treatments For Colon Cancer

Does calcium prevent colorectal cancer?
Clinical trials show a modest reduction in adenoma recurrence with calcium supplements, but they have not demonstrated a clear reduction in colorectal cancer incidence or death. Calcium is not a proven standalone cancer prevention strategy.
What dose of calcium was studied?
Many trials tested about 1,200 mg of elemental calcium per day. If you're considering supplements, review dose and needs with your clinician because dietary intake and individual risks vary.
Should everyone with polyps take calcium?
No. Because benefits are modest and potential harms exist, clinicians typically individualize recommendations. People who need calcium for bone health may view the modest adenoma benefit as an added advantage.
Are there safer or better ways to prevent colorectal cancer?
Yes. Timely colonoscopic surveillance and removal of polyps is the most effective prevention. Healthy lifestyle choices and, in selected patients, aspirin or other interventions may be considered under medical guidance.
Are calcium supplements safe?
Common side effects include constipation and bloating. Supplements can raise kidney-stone risk in some people, and studies of cardiovascular risk have mixed results. Discuss personal risk factors with your clinician.

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