What can you do to lower your risk of cancer?

How much is preventable

In 2019, an estimated 40.0 percent of new US cancers and 44.0 percent of cancer deaths in adults 30 and older were attributable to modifiable factors. Cigarette smoking led (19.3 percent of cases, 28.5 percent of deaths), followed by excess body weight (7.6 and 7.3 percent) and alcohol (5.4 and 4.1 percent). Red and processed meat, low fruit, vegetable and fiber intake, inactivity, ultraviolet light and seven infections made up the rest¹. These are modeled estimates, not a promise about any one person.

What the major guidelines agree on

The American Cancer Society (ACS) and the World Cancer Research Fund (WCRF/AICR) recommend patterns rather than single foods^2,3:

• Keep a healthy weight and avoid weight gain in adult life.
• Be active: the ACS advises 150 to 300 minutes of moderate activity, or 75 to 150 of vigorous, each week².
• Eat plenty of vegetables, fruit, whole grains and beans. Limit red and processed meat, sugary drinks, and highly processed foods and refined grains.
• Both say it is best not to drink alcohol; if you do, the ACS caps it at one drink a day for women and two for men^2,3. See alcohol and health.

The numbers behind the big four

• Tobacco. Smokers lose at least a decade of life; quitting before 40 cut the added risk of death by about 90 percent⁸.
• Alcohol. Compared with non-drinkers and occasional drinkers, heavy drinkers had about five times the risk of oral, throat and oesophageal squamous cell cancers, 1.6 times the risk of breast cancer and 1.4 times that of colorectal cancer⁹.
• Activity. More leisure-time activity went with lower risk of 13 of 26 cancers, including lung, liver, kidney, colon and breast¹⁰.
• Meat. The International Agency for Research on Cancer classed processed meat as carcinogenic to humans and red meat as probably carcinogenic. The label reflects how sure the evidence is, not how big the risk is¹¹.

Vaccines, sun and screening

• HPV vaccine. Among 1.67 million Swedish girls and women, invasive cervical cancer was about 88 percent less common in those vaccinated before 17⁴.
• Sun. In a trial of 1,621 adults, daily sunscreen was followed by half as many new melanomas, a borderline result, and fewer invasive ones⁵.
• Screening. Colorectal screening is recommended for adults 45 to 75, and for some 76 to 85⁶.

Supplements and symptoms

Supplements do not replace food: in SELECT, vitamin E raised prostate cancer risk by 17 percent, and WCRF/AICR advises against supplements for prevention^7,3. And prevention is no substitute for checking symptoms: unexplained lumps, bleeding, weight loss or trouble swallowing deserve a visit¹².

Attribution and guidelines

Islami and colleagues combined national cancer and death counts, national surveys of risk-factor prevalence and relative risks from large published pooled analyses. For 2019 they attributed 713,340 of 1,781,649 cancers (40.0 percent) and 262,120 of 595,737 deaths (44.0 percent) to the factors studied; for 19 of 30 cancer types, more than half of cases and deaths were attributable¹. The ACS guideline and the WCRF/AICR Third Expert Report both summarize the evidence on diet, activity and weight and pair it with recommendations for communities as well as individuals^2,3. Attribution assumes the associations are causal and reversible, which is least certain for some dietary factors.

Alcohol and activity

A dose-response meta-analysis of 572 studies (486,538 cancer cases) found that heavy drinkers, compared with non-drinkers and occasional drinkers, had relative risks of 5.13 for oral and pharyngeal cancer, 4.95 for oesophageal squamous cell carcinoma, 2.65 for laryngeal, 2.07 for liver, 1.61 for breast and 1.44 for colorectal cancer, with a clear dose-risk relationship for these. Lymphoma risk ran the other way and was lower⁹. Moore and colleagues pooled 12 cohorts (1.44 million adults, 186,932 cancers). High versus low leisure-time activity went with lower risk of 13 cancers, for example esophageal adenocarcinoma (hazard ratio 0.58), liver (0.73), lung (0.74), kidney (0.77), colon (0.84) and breast (0.90). Activity was also linked to higher melanoma (1.27) and prostate cancer (1.05) risk¹⁰.

Vaccines, sun and screening

In a Swedish register study of 1,672,983 girls and women aged 10 to 30, cervical cancer was diagnosed in 19 vaccinated and 538 unvaccinated women. After adjustment, the incidence rate ratio was 0.12 (95% CI 0.00 to 0.34) for vaccination before 17 and 0.47 (0.27 to 0.75) at 17 to 30⁴. It is observational, so unmeasured differences between vaccinated and unvaccinated women remain possible. The Nambour trial randomized 1,621 Australian adults to daily or discretionary sunscreen on the head and arms until 1996. Ten years later there were 11 new primary melanomas in the daily group and 22 in the discretionary group (hazard ratio 0.50, 0.24 to 1.02, P=0.051), and 3 versus 11 invasive melanomas (0.27, 0.08 to 0.97)⁵. The US Preventive Services Task Force concluded with high certainty that colorectal screening at 50 to 75 has substantial net benefit, with moderate certainty of moderate benefit at 45 to 49 and small benefit at 76 to 85⁶.

Null and harmful results

The Selenium and Vitamin E Cancer Prevention Trial randomized 35,533 men (34,887 analyzed) to selenium, vitamin E 400 IU a day, both, or placebo. With extra follow-up, prostate cancer occurred in 620 men on vitamin E versus 529 on placebo (hazard ratio 1.17, 99% CI 1.004 to 1.36); selenium (1.09) and the combination (1.05) were not significantly different from placebo⁷. That is one cancer site and one supplement, but the WCRF/AICR recommendations advise against supplements for cancer prevention³.

Where the evidence is weaker

Most diet and activity links come from observational studies, which cannot fully separate one habit from another. Attribution percentages rest on assumptions. Alcohol and lymphoma, and activity and melanoma, went the opposite way from the general pattern, and the Nambour melanoma result only just missed conventional significance^5,9,10. Screening benefit shrinks with age⁶.

Bottom line

Confidence is fairly high (4 of 5). Smoking, weight, alcohol, activity, HPV vaccination and screening have strong, consistent support^1,4,6,9,10, while claims about individual foods are weaker and supplements have not shown protection⁷. Prevention lowers risk and never guarantees against cancer, so symptoms still need a doctor¹².