Cancer Prevention(11 expert discussions analyzed)

Prevention and screening are different. Prevention lowers the chance that cancer develops. Screening looks for cancer, or for changes that may become cancer, in people without symptoms. Bowel and cervical screening can prevent some cancers, because precancerous changes can be removed. Breast, lung and prostate screening mainly find cancer earlier, when treatment works better. Screening also has harms, including false alarms and treatment of cancers that would never have caused problems (overdiagnosis). That is why programmes target specific ages and risk groups.

The established causes (external guidance). Tobacco: the largest single preventable cause of cancer. Quitting at any age lowers risk. The European Code adds vaping products and second-hand smoke. Alcohol: the International Agency for Research on Cancer (IARC) classifies it as a Group 1 carcinogen. It causes cancers of the mouth, throat, voice box, oesophagus, liver, bowel and breast. For cancer, no safe level is known (WHO, 2023). National drinking guidelines, such as the UK's 14 units a week, describe low overall health risk, not a cancer-safe amount. See Alcohol & Health. Excess body fat: IARC found sufficient evidence that it contributes to at least 13 cancers, including bowel, womb, kidney, liver, pancreas and post-menopausal breast cancer (2016). Whether losing weight lowers the risk is less certain. Large observational studies, including people who had weight-loss surgery, link substantial weight loss with fewer obesity-related cancers, but there are no randomised trials with cancer as the outcome. UV light: from the sun and sunbeds, it causes skin cancer. In an Australian randomised trial, daily sunscreen use roughly halved new melanomas over the following ten years (Green et al., 2011). Infections: HPV causes almost all cervical cancers and many anal, throat and genital cancers. Hepatitis B and C cause liver cancer. Helicobacter pylori causes stomach cancer. Home, work and hormones: Radon: a radioactive gas that seeps from the ground into homes. WHO describes it as the second most important cause of lung cancer after smoking in many countries. Many countries publish radon maps, and high levels can be measured and reduced. Air pollution: IARC classifies outdoor air pollution as a cause of lung cancer (2013). The European Code advises choosing low-traffic routes and not burning coal or wood at home. Workplace: some jobs involve known causes of cancer, such as asbestos, silica dust and diesel exhaust. Follow workplace safety rules and ask your employer about protection. Menopausal hormone therapy (HRT): all types except vaginal oestrogen are linked to higher breast cancer risk, which grows with longer use and is greater for combined oestrogen and progestogen (Collaborative Group, 2019). HRT also relieves menopause symptoms. If you use it, agree with your doctor on the shortest suitable duration.

Vaccination (established). HPV vaccine: in Sweden, women vaccinated before 17 had about 88% fewer cervical cancers than unvaccinated women (Lei et al., 2020). Hepatitis B vaccine: after Taiwan's national programme began in 1984, childhood liver cancer fell (Chang et al., 1997). Recommended ages: both vaccines are recommended for children and young people at the ages set in each country. Adults who missed them can ask whether catch-up vaccination applies.

Activity and diet. Physical activity (strong evidence): higher activity is consistently linked to lower risk of seven cancers: bowel, breast, womb, kidney, bladder, stomach and oesophageal cancer. Risk is lower with more activity. The US Physical Activity Guidelines Advisory Committee (2018) rated this evidence strong. It is observational, so the size of the benefit for one person is uncertain. The European Code also advises limiting time spent sitting. Diet (likely): the European Code advises the following. Most of this evidence is observational. The pattern matters more than any single food. Make whole grains, vegetables, legumes and fruit a major part of the daily diet. Limit red meat and avoid processed meat. IARC classifies processed meat as Group 1 and red meat as Group 2A, "probably carcinogenic" (2015). Limit sugary drinks and ultra-processed foods. Breastfeeding: it lowers breast cancer risk for the mother.

Screening programmes (as of 20 October 2026). Follow your own country's programme. Breast: UK (NHS England): mammogram every 3 years for women aged 50 up to their 71st birthday. EU Council Recommendation (2022): ages 50 to 69, and 45 to 74 suggested. US (USPSTF, 2024): every 2 years, ages 40 to 74. Bowel: UK: home test (FIT) every 2 years, ages 50 to 74 in most of the UK. EU: FIT, ages 50 to 74. US (USPSTF, 2021): ages 45 to 75, with a choice of tests. Cervical: UK: HPV test, ages 25 to 64. EU: HPV test, ages 30 to 65, every 5 years or more. US: ages 21 to 65. Lung (for people who smoke or used to smoke): England: targeted lung screening, ages 55 to 74, being rolled out. US (USPSTF, 2021): yearly low-dose CT, ages 50 to 80, for people with a 20 pack-year history who smoke now or quit within the last 15 years. EU: countries are invited to evaluate it. Prostate: UK: the UK National Screening Committee's final recommendation (May 2026) is targeted screening only. It covers men aged 45 to 61 with a BRCA2 gene change and a family history of certain cancers, with a PSA test every 2 years. This is a committee recommendation, not a programme: there is no UK prostate screening programme yet, and each UK government must decide whether to introduce one. It does not recommend screening all men or Black men as a group. US (USPSTF, 2018): an individual decision at ages 55 to 69; the recommendation is being updated. EU: countries are invited to evaluate PSA-based programmes with MRI follow-up. Family history: a strong family history or a known gene change (such as BRCA1, BRCA2 or Lynch syndrome) can mean earlier or different screening. Ask your doctor. Individual risk and your national programme take priority over any general age.

Ideas that are not established for prevention. The metabolic theory of cancer. Prof Thomas Seyfried argues that cancer is mainly a disease of damaged mitochondria and fermenting cells, rather than of gene mutations. He appears in three linked episodes, but this is one researcher's view, not three independent ones. Cancer cells' shift towards fermentation (the Warburg effect) is accepted biology. The claim that it is the main cause, and the "press-pulse" treatment built on it, are not supported by randomised trials. For prevention, the practical advice it leads to (healthy weight and less ultra-processed food) is already part of mainstream guidance. Supplements. In the VITAL trial of 25,871 adults, 2,000 IU of vitamin D a day did not lower cancer incidence (Manson et al., 2019). Trial pooling suggests a possible small reduction in cancer deaths. No supplement is recommended for preventing cancer. Some interact with cancer treatment. Fasting and fasting-mimicking diets. Prof Valter Longo describes fasting-mimicking cycles that may protect normal cells and stress cancer cells. These are being studied alongside cancer treatment. There is no evidence that they prevent cancer in people. Claims in some episodes that prolonged water fasting prevents or reverses cancer are not supported. "Anti-angiogenic" foods. Some sources promote foods such as berries, green tea and tomatoes because laboratory studies show they can affect blood-vessel growth in tumours. Laboratory effects do not show that eating these foods lowers cancer rates in people. They are healthy foods for other reasons. Elective whole-body MRI. Companies now sell scans to people without symptoms. The American College of Radiology (2023) states there is not enough evidence to recommend them for people without symptoms, risk factors or relevant family history. The scans can find harmless changes that lead to more tests and worry.