cancer and exercise (pleasantly surprising data)

I found this great study on weightlifting and cancer. I was looking for why exercise was bad for cancer because that used to be common advice in the medical community but was surprised to find that it may actually be beneficial. I decided to dig deeper and wrote a summary of my findings.

Study summary — Weightlifting (resistance/strength training) and cancer

​Below is a concise, evidence-based summary that pulls together the best recent research on weightlifting (resistance/strength training) and cancer risk, outcomes, and survivorship. I’ve highlighted key findings, typical study designs, practical recommendations, and important limitations — with citations to the most relevant papers.
 
Background & why it matters 
Physical activity in general is associated with lower cancer incidence and mortality; muscle-strengthening activities (weightlifting/resistance training) are a distinct domain of activity with specific metabolic and functional benefits (improved insulin sensitivity, reduced adiposity, preserved lean mass) that may affect cancer risk and outcomes. (PMC, Cancer.gov)

Representative high-quality studies1) Prospective cohort: Resistance training and total & site-specific cancer risk (Br J Cancer / Nature family, 2020)

• Design: Prospective cohort analyses linking self-reported weight training to later cancer incidence across multiple sites.
• Major finding: Weight training (muscle-strengthening activities) was associated with lower risk for some cancers (notably colon in some cohorts) and suggested trends for lower risk at other sites; effects varied by site and study. (Nature)

2) Pooled evidence / systematic reviews & meta-analyses (multiple, 2021–2025)

• A pooled/meta-analytic picture shows that muscle-strengthening activities are associated with a ~10–17% lower risk of total cancer incidence and cancer mortality in several large observational syntheses. Strength training combined with aerobic exercise often shows the best effect sizes for survivorship outcomes. (British Journal of Sports Medicine, MDPI)

3) Randomized controlled trials and trials in cancer survivors

• RCTs of supervised resistance training in cancer survivors (breast cancer is the most common study population) show consistent improvements in muscle strength, physical function, quality of life, and reductions in cancer-related fatigue. These trials support safety and benefit of RT during and after treatment. (PMC, SpringerLink)

4) Large recent analyses linking fitness/strength to mortality in cancer patients

• Observational analyses have found that higher muscle strength and better cardiorespiratory fitness are associated with substantially lower all-cause mortality among people with cancer (risk reductions often in the 30–45% range in high vs low strength/fitness groups). These are mostly observational but large and adjusted for many confounders. (The Guardian, Oxford Academic)

Typical methods used in this literature

• Exposure: Self-reported frequency of muscle-strengthening activities (times/week), performance tests (handgrip strength), or structured exercise interventions (supervised RT programs).
• Outcomes: Incident cancer (site-specific and total), cancer mortality, all-cause mortality, treatment side-effects (fatigue, QoL), physical function, and sarcopenia/cachexia.
• Designs: Prospective cohorts for incidence/mortality; randomized controlled trials for survivorship/rehab outcomes; meta-analyses synthesizing both.

Key results — short summary (evidence grade)

• Prevention (incidence): Observational data suggest muscle-strengthening activity is associated with a modestly lower risk of some cancers and lower total cancer incidence in pooled analyses (suggestive evidence). Causality not proven because most data are observational. (British Journal of Sports Medicine, Nature)
• Mortality (in people with cancer): Better strength/fitness correlates with substantially lower mortality in large cohorts (observational). (The Guardian, Oxford Academic)
• Survivorship & treatment side-effects: RCTs show resistance training improves muscle strength, reduces cancer-related fatigue, and improves quality of life in patients undergoing or after treatment — and is generally safe when supervised/adapted. (PMC, SpringerLink)

Practical exercise prescription (what trials used / what appears safe)

• Frequency: 2–3 sessions per week of resistance training is commonly used. Some benefits seen with as little as 1 session/week (in specific trials), but 2×/week is typical. (SpringerLink, PMC)
• Intensity: Moderate intensity (e.g., 6–12 RM for hypertrophy/strength) tailored to the individual; start lighter during treatment and progress. Supervision improves adherence and outcomes. (PMC)
• Mode: Multi-joint exercises (squats/leg press, rows, presses), free weights or machines, plus aerobic activity when possible. Combine RT with aerobic training for additive benefits. (MDPI)
• Safety: Screen for treatment-related contraindications (e.g., bone metastases, lymphedema risk in breast cancer — which can still often be safely managed with adapted RT), and start supervised if frail or undergoing active treatment. (PMC, SpringerLink)

Biological plausibility / mechanisms

• Resistance training improves insulin sensitivity, reduces visceral fat, increases lean mass, lowers systemic inflammation markers, and improves immune and metabolic profiles — all mechanisms plausibly linked to lowered cancer risk/progression. Exercise may also counteract treatment-related muscle wasting (cachexia) and functional decline. (PMC, ScienceDirect)

Limitations & open questions

• Much of the data on cancer incidence are observational and rely on self-reported activity — confounding and reverse causation are possible (healthier people both exercise more and have lower cancer risk). (Nature)
• Heterogeneity by cancer site: benefits are clearer for some cancers (e.g., colon) than others. Site-specific evidence is mixed. (Nature)
• Optimal dose (intensity/duration), timing across the life course, and interactions with body composition and diet remain active research areas. (Cancer.gov)

Bottom line (practical takeaway)

• For prevention: incorporate regular muscle-strengthening activities (e.g., weightlifting or resistance training) as part of an overall active lifestyle — observational evidence suggests a modestly lower cancer risk and stronger reductions in cancer mortality when combined with aerobic fitness. (British Journal of Sports Medicine, PMC)
• For people with cancer: supervised, tailored resistance training is safe and effective for improving strength, reducing fatigue, and improving quality of life during and after treatment; higher strength/fitness is associated with better survival in observational analyses. Clinicians should consider referring patients to oncology-trained exercise physiologists when possible. (PMC, The Guardian)

If you want one concrete paper to read now

• Rezende LFM, et al. — “Resistance training and total and site-specific cancer risk” (Br J Cancer / Nature family, 2020). Good, fairly large prospective cohort analysis on weight training and cancer incidence; useful as a starting point for prevention evidence. (Nature)