Cancer: risk factors

Cancer risk factors are similar worldwide. Smoking, low levels of physical activity, alcohol consumption, poor diet, overweight and obesity, and infections contribute to a high proportion of cancers globally, mirroring their impact in the UK. The prevalence of different risk factors varies by region and country, which partly explains the variations in overall cancer incidence rates and the most common types of cancer worldwide.

See the Global Burden of Disease (GBD) study for comparative data on a wide range of health outcomes and risk factors across 200+ countries and territories, including various cancers and cancer risk factors. View and download GBD data using the GBD Results tool from the Institute for Health Metrics and Evaluation (IHME), University of Washington.

The most common cancers in Scotland are lung, breast, colorectal (bowel) and prostate, accounting for over half of all malignancies (excluding non-melanoma skin cancers which are excluded from all cancers by convention). Summarised below are the main risk factors for each of these cancers.

Breast cancer

  • Reproductive history and oestrogen levels play significant roles:
    • Early age at menarche (first menstrual bleeding) and late menopause increase the risk, while early childbirth and breastfeeding reduce it.
    • Hormone replacement therapy (HRT) increases the risk, especially with prolonged use.
  • Lifestyle factors: A diet low in fat and high in vegetables may lower the risk, whereas overweight and obesity increase it. Alcohol consumption is associated with increased risk, while physical activity has a protective effect.
  • Other risk factors include ionizing radiation exposure, certain benign breast diseases, and inherited genetic factors such as mutations in BRCA1, BRCA2, and p53 genes.

Colorectal cancer

The main risk factors for colorectal cancer are:

  • Diet: Consuming foods rich in dietary fibre and relatively unprocessed cereals may decrease the risk. Similarly, intake of fruits and non-starchy vegetables may offer protection, although evidence is limited.
  • Lack of physical activity: Regular physical activity is convincingly associated with a decreased risk.
  • Obesity: Both general body fatness and abdominal fatness are established risk factors.
  • Long-term smoking: Studies suggest a heightened risk, with relative risks typically ranging from 1.5 to 3.0. Efforts to discourage smoking in Scotland should emphasize the decreased risk of colorectal cancer.
  • Alcohol consumption: Alcohol is a convincing risk factor for colorectal cancer in men and a probable risk factor in women.
  • Other risk factors include a history of inflammatory bowel disease and genetic factors such as familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC).

Lung cancer

The primary recognised risk factors for lung cancer include:

  • Tobacco smoking: Accounts for 80-90% of cases in developed countries.
  • Asbestos exposure: Interacts in a multiplicative way with smoking.
  • Ionizing radiation: Including domestic exposure to radon.
  • Various chemicals, typically encountered in occupational settings, such as: arsenic, chloromethyl ethers, polycyclic aromatic hydrocarbons, chromium products, and nickel.

Prostate cancer

The causes of prostate cancer are largely unknown, but established risk factors include:

  • Age: Risk increases steeply with age, particularly after 50.
  • Family history: A family history of prostate cancer, breast cancer, or other cancers, especially at a young age, is associated with increased risk.
  • Ethnic origin: Risk tends to be higher in men of African descent and lower in men of Asian descent.
  • Hormones: Testosterone may play a role in promoting prostate cancer, while oestrogen might have a protective effect.
  • Genetic factors: Mutations in genes such as BRCA2 and Lynch syndrome increase risk (Bancroft EK (2021)).
  • Diet: Risk may be influenced by dietary factors, such as high animal fat intake and low fruit and vegetable consumption. Lycopene, selenium, and vitamin E may offer protection.
  • Occupation: Some research suggests that occupational exposure to pesticides may increase the risk.