Cancer, risks and causes: here are the three commandments of prevention

IN BRIEF

• A significant proportion of cancers is linked to modifiable factors: tobacco, diet, excess weight, alcohol, and inactivity.
• Evidence is predominantly based on observational studies and meta-analyses: they indicate robust associations, but the causal strength varies by type of exposure and cancer.
• Three strategic lines emerge from the literature: avoid tobacco, maintain body weight within the recommended range, and engage in regular physical activity; limiting alcohol and moderating processed meat consumption are complementary.
• High-dose antioxidant supplements are not recommended for prevention and in some studies have shown adverse effects in smokers.

Abstract: what does science say?

"Cancer prevention" refers to interventions aimed at reducing the likelihood of a person developing cancer. The most solid epidemiological evidence indicates that some risk factors are modifiable: tobacco remains the most significant historical cause of cancer deaths, while diet, overweight/obesity, excessive alcohol consumption, and physical inactivity contribute measurably to the disease burden. Much research comes from observational studies (cohorts and case-control) and meta-analyses that show dose-response relationships for specific cancers (e.g., colorectal, breast, liver, uterine body). The effect depends on the intensity and duration of exposure, the context (age, smoking history, genetic makeup), and the form of consumption (e.g., processed meat versus unprocessed meat). Clinical trials on supplements have not confirmed generalized preventive benefits and in some cases have shown harm. Therefore, practical prevention is based on reducing exposure to known factors and on public health policies based on high-level evidence.

Historical foundations and what we know today

The modern concept that many forms of cancer are partially avoidable was formalized as early as the 1980s by historical works that grouped the main risk factors (tobacco, diet, occupational exposures, infectious agents, radiation, hormones). These initial estimates guided research and health policy on the avoidable causes of the disease [1]. More recent global risk assessment data show that behaviors and metabolic factors continue to determine a significant disease burden worldwide: among these, smoking, suboptimal diet, and increased body mass stand out, each with different impacts depending on the country and type of cancer [2][3].

The three commandments of prevention

The literature suggests three priority areas, presented here as practical "commandments": avoiding tobacco, maintaining an adequate body weight, and engaging in regular physical activity. These three guidelines summarize the measures with the strongest evidence of population-level benefit and are complemented by moderation in alcohol intake and informed food choices. It is important to consider that the effect of each measure depends on the dose, duration, and individual context: for example, the risk associated with alcohol consumption is dose-dependent, while the protective effect of physical activity varies by cancer type [5][6][7].

1. Avoid tobacco

Tobacco consumption is historically the factor with the broadest and strongest association with cancer mortality and with high percentages of attributable deaths from smoking in population analyses. Reducing smoking remains the preventive measure with the greatest individual and collective potential. Exposure to secondhand smoke also increases the risk for some cancers; therefore, tobacco control strategies (smoking cessation, environmental restrictions, pricing and marketing policies) are essential for primary prevention [3][1].

2. Body weight and diet

Excess weight is associated with an increased risk for various cancers (endometrial, colorectal, liver, pancreatic, kidney, among others); solid meta-analyses quantify risk increases as a function of BMI increase. Diet quality also plays a role: high consumption of processed meats is associated with a higher risk of colorectal carcinoma, while dietary patterns rich in vegetables, whole grains, legumes, and fish show favorable associations in observational studies [5][4][2].

3. Physical activity and alcohol limitation

Higher levels of physical activity have long been associated with a reduced risk for several cancer sites; analyses of large cohorts show significant reductions for about a dozen types of cancer in more active people compared to less active ones [6]. Alcohol consumption shows dose-dependent relationships with cancers of the esophagus, liver, breast, colon, and others: even small amounts increase the risk for some sites, so the strategy is limitation, not promotion of consumption [7].

Evidence on diet and individual foods

The relationship between diet and cancer risk is complex: much information comes from observational studies that measure dietary habits and follow populations over time. IARC has classified the consumption of processed meat as carcinogenic to humans, particularly for colorectal carcinoma, and has defined the consumption of red meat as probably carcinogenic based on a review of epidemiological evidence and plausible biological mechanisms [4].

Global analyses of the contribution of dietary risks to disease show that deficiencies or excesses of specific food components (high sodium intake, low intake of whole grains and fruit) contribute to a measurable disease burden at national and international levels [2]. However, the strength and specificity of associations vary greatly depending on the type of cancer and context: for example, the role of diet in breast cancer is also influenced by hormonal, reproductive factors, and menopausal age [2][5].

What this means in practice

For the individual citizen, the evidence suggests concrete but not prescriptive actions: quit smoking or don't start; adopt a diet rich in plant-based foods and limit highly processed foods and processed meats; maintain a body weight within the recommended range for age and height; engage in regular physical activity; limit alcohol consumption. These measures do not guarantee complete prevention of every cancer, but they reduce overall risk and improve general health. For cancer patients, the relationship between diet, physical activity, and outcomes is an active field of research, and recommendations must be discussed with the therapeutic team.

Important: dietary supplements are not equivalent to consuming foods rich in micronutrients. Clinical trials have shown that some antioxidant supplements do not reduce mortality and in some subgroups (e.g., heavy smokers) may increase the risk of lung cancer; therefore, the routine use of high doses of supplements to 'prevent cancer' is not supported by evidence [8][9][10].

Limitations of the evidence

Most available information comes from observational studies: prospective cohorts and case-control studies. These designs can highlight associations and dose-response relationships, but they are subject to potential measurement errors of exposure (e.g., dietary recall), residual confounding (socioeconomic factors, related lifestyle habits), and selection bias. For some relationships, it is difficult to establish definitive causality without direct experimental evidence; however, when multiple independent studies and consistent biological mechanisms converge, plausibility increases.

Randomized trials are rare for long-term dietary interventions and, when present, often evaluate single nutrients or supplements rather than complex dietary patterns. Some trials on supplements have even shown undesirable effects, reminding us that isolated nutrients do not always replicate the effect of whole foods [8][9][10]. Interpreting the evidence requires caution: associating does not automatically mean asserting a causal relationship without considering context, dose, duration, and heterogeneity among populations.

Key takeaways

• Smoking is still the leading preventable cause of cancer at the population level.
• Maintaining an adequate body weight is associated with a lower risk for several cancers.
• Regular physical activity reduces the risk of many cancers and improves overall health.
• Limiting alcohol and processed meats helps reduce the risk for specific cancers.
• High-dose supplements do not replace a healthy diet and are not recommended for mass prevention; in some contexts, they have shown adverse effects.

Editorial conclusion

Cancer prevention is multifactorial and requires an integrated public health approach: policies for reducing tobacco and alcohol, promoting environments that facilitate physical activity, and dietary strategies that favor minimally processed foods. For the individual, following healthy lifestyle principles (not smoking, being active, controlling weight, choosing plant-based foods, and limiting alcohol and processed meats) represents the most solid strategy available today to reduce overall risk. Interpreting and applying evidence always requires dialogue with healthcare professionals, especially in the presence of specific clinical conditions.

Editorial note

This update was drafted according to institutional editorial criteria: clear language, reference to available evidence, and transparency in sources. The article does not provide individual therapeutic indications. For diagnosis, personalized prevention, or therapeutic modifications, consult a doctor or a specialized center.

Scientific research

1. R Doll, R Peto. The Causes of Cancer: Quantitative Estimates of Avoidable Risks of Cancer in the United States Today. J Natl Cancer Inst. 1981;66(6):1192–1308. https://doi.org/10.1093/jnci/66.6.1192
2. Afshin A, Sur PJ, Fay KA, et al. Health effects of dietary risks in 195 countries, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet. 2019;393(10184):1958–1972. https://doi.org/10.1016/S0140-6736(19)30041-8
3. GBD 2017 Risk Factor Collaborators. Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet. 2018;392(10159):1923–1994. https://doi.org/10.1016/S0140-6736(18)32225-6
4. International Agency for Research on Cancer Monograph Working Group; Bouvard V, Loomis D, Guyton KZ, et al. Carcinogenicity of consumption of red and processed meat. Lancet Oncol. 2015;16(16):1599–1600. https://doi.org/10.1016/S1470-2045(15)00444-1
5. Renehan AG, Tyson M, Egger M, Heller RF, Zwahlen M. Body-mass index and incidence of cancer: a systematic review and meta-analysis of prospective observational studies. Lancet. 2008;371(9612):569–578. https://doi.org/10.1016/S0140-6736(08)60269-X
6. Moore SC, Lee IM, Weiderpass E, et al. Association of Leisure-Time Physical Activity With Risk of 26 Types of Cancer in 1.44 Million Adults. JAMA Intern Med. 2016;176(6):816–825. https://doi.org/10.1001/jamainternmed.2016.1548
7. Bagnardi V, Rota M, Botteri E, et al. Alcohol consumption and site-specific cancer risk: a comprehensive dose–response meta-analysis. Br J Cancer. 2015;112(3):580–593. https://doi.org/10.1038/bjc.2014.579
8. Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study Group. The effect of vitamin E and beta-carotene on the incidence of lung cancer and other cancers in male smokers. N Engl J Med. 1994;330(15):1029–1035. https://doi.org/10.1056/NEJM199404143301501
9. Omenn GS, Goodman GE, Thornquist MD, et al. The Beta-Carotene and Retinol Efficacy Trial (CARET): incidence of lung cancer and cardiovascular disease mortality during 6-year follow-up after stopping beta-carotene and retinol supplements. J Natl Cancer Inst. 1996;88(21):1550–1559. https://doi.org/10.1093/jnci/88.21.1550
10. Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis. JAMA. 2007;297(8):842–857. https://doi.org/10.1001/jama.297.8.842