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When we think about reducing cancer risk, the “big three” lifestyle factors are well established: smoking, obesity, and alcohol consumption. Genetics also play a role — some people carry inherited mutations such as BRCA1 gene mutation that significantly increase the likelihood of certain cancers. In those cases, additional medical strategies may be appropriate.

But once those major risk factors are accounted for, one of the most powerful — and most under-utilised — tools we can control is exercise.

The American Cancer Society estimates that roughly 40% of cancers could potentially be prevented through modifiable lifestyle behaviours including avoiding smoking, maintaining a healthy body weight, limiting alcohol, improving diet, and regular physical activity. Physical activity consistently sits near the top of that list.

And the evidence is no longer just observational.

A landmark 2025 study published in the New England Journal of Medicine demonstrated that a structured exercise programme after colon cancer treatment significantly improved disease-free survival and overall survival. Patients who exercised had lower rates of recurrence, new cancers, and death compared with those receiving standard health education alone.

This adds to an already substantial body of research linking regular exercise with lower rates of colon, breast, endometrial, oesophageal, stomach, liver, kidney and several other cancers.

Exercise and cancer risk: More is generally better

One of the most interesting findings in exercise oncology is what researchers call a dose-response relationship. In simple terms: the more exercise people do, the lower their cancer risk tends to be.

Benefits continue to rise with increasing activity levels, although gains appear to plateau somewhat beyond around 300 minutes per week of moderate activity (or the vigorous equivalent) in most studies.

Intensity matters too.

Higher-intensity exercise appears to provide additional protective effects compared with lighter movement alone.

Importantly, exercise reduces cancer risk independently of body weight. In other words, its protective effect is not simply because active people may be leaner. Exercise also appears protective even after adjusting for factors such as smoking status and body weight, although it cannot fully offset the risks associated with smoking.

Exercise likely reduces cancer risk through multiple pathways, including improved insulin sensitivity, reduced chronic inflammation, enhanced immune surveillance, lower visceral fat accumulation, improved sex hormone regulation, and favourable effects on the tumour microenvironment.

What you need to do

1. Vigorous Cardiovascular Exercise (75–150 minutes/week)

This is where the strongest evidence currently sits.

Vigorous exercise means working hard enough that conversation becomes difficult. On a 0–10 Rating of Perceived Exertion scale, this feels like about a 7–8/10. If you wear a heart rate monitor, it’s roughly 75–85% of maximum heart rate.

For a fit person, this might look like:

• Running
• Spin classes
• Road cycling or mountain biking
• Rowing
• Swimming
• High-intensity circuit classes

For someone newer to exercise, brisk uphill walking, light jogging, swimming, or stationary cycling may achieve the same intensity.

The key is sustained effort, enough to become properly “puffed”.

Research suggests vigorous exercise may offer a disproportionately large protective effect against cancer and other chronic diseases.

2. Moderate Exercise (150–300 minutes/week)

Moderate intensity sits at around 4–5/10 effort. You could still hold a conversation, but singing would be difficult.

Examples include:

• Brisk walking
• Steady cycling
• Swimming
• Dancing
• Hiking
• Continuous resistance circuits

This amount of activity is strongly associated with reduced cancer risk and improved overall longevity.

For most people, breaking this into 3–5 sessions per week is realistic and sustainable.

3. Resistance Training: The Often-Overlooked Piece

While aerobic exercise receives most of the attention in cancer prevention research, resistance training is emerging as a critical component of healthy ageing and cancer resilience.

Muscle mass matters.

Many cancers, and some cancer treatments can lead to cachexia, a complex wasting syndrome characterised by progressive muscle loss. Low muscle mass is increasingly associated with poorer treatment tolerance, higher recurrence rates, reduced function, and worse survival outcomes.

Strength training 2–3 times per week helps preserve and build muscle across the lifespan. 

And encouragingly, newer research suggests the exact rep range matters far less than previously believed. Rather than obsessing over the old “8–12 reps for hypertrophy” rule, we now know muscle growth can occur across a broad range, roughly 6 to 20 reps, provided the effort is challenging enough and sets are performed close to muscular fatigue.

Combined with adequate protein intake and good nutrition, resistance training becomes one of the most powerful longevity tools we have.

Exercise doesn’t just reduce risk, it improves outcomes

Perhaps even more compelling is the growing evidence that lifelong exercisers who do develop cancer may experience:

• Delayed onset of disease
• Better treatment tolerance
• Improved physical function during treatment
• Lower recurrence rates
• Higher survival rates

Exercise effectively acts as “prehabilitation”, building physiological reserve before illness occurs.

The recent colon cancer trial led by Kerry Courneya showed structured exercise after chemotherapy significantly improved long-term outcomes, providing some of the strongest evidence yet that exercise is not merely supportive care, it is biologically meaningful medicine.

But isn’t everyday activity enough?

Gardening, cleaning the house, wandering through Costco, and general incidental movement are all valuable. They absolutely contribute to overall health and reduce sedentary time.

However, even in people who exercise regularly, prolonged sedentary time is independently associated with poorer metabolic and cancer outcomes.

But incidental movement alone is probably not enough to meaningfully optimise cancer prevention.

The gold standard remains a structured exercise programme that combines:

• Cardiovascular training
• Resistance training
• Progressive overload
• Sufficient intensity
• Consistency over time

In short: moving more is good. Training intentionally is better.

The takeaway

Exercise is one of the rare interventions that simultaneously improves:

• Cancer risk
• Cardiovascular health
• Brain health
• Bone density
• Muscle mass
• Insulin sensitivity
• Mood
• Functional independence
• Longevity

And unlike many medical interventions, its side effects are overwhelmingly positive.

You do not need to become an elite athlete. But the evidence strongly suggests that deliberately training your body, particularly with a combination of aerobic fitness and strength work, is one of the smartest long-term investments you can make in your future health.

Exercise is not simply about weight control or fitness. It is a direct biological signal that influences metabolism, inflammation, immune function, muscle preservation and long-term disease risk. In many respects, it behaves more like medicine than recreation.