Causes of Cancer

Exogenous Factors:

• Tobacco use
• Infectious Agents (bacteria, parasites, viruses)
• Medications
• Radiation
• Chemical Exposure (polychlorinated biphenyls, organic compounds used in plastics, paints, adhesives)
• Carcinogenic components founds in foods and beverages (aflatoxins, heterocyclic amines, polycyclic aromatics hydrocarbons, N-nitroso compounds)

Endogenous Factors:

• Inherited germ-line mutations
• Oxidative Stress
• Inflammation
• Hormones

Most experts believe that the majority of cancers are not inherited but rather arise from alterations in gene expression that promote changes in DNA over many years.

Nutrients that have been shown to influence cell-cycle progression and proliferation:

• Vitamin A - can result in cell-cycle arrist
• Retinoids can inhibit cellular proliferation of initiated cells by inducing apoptosis or inducing differentiation of abnormal cells back to normal
• Heme Iron - found to promote cellular proliferation of colonocytes

It is difficult to determine the precise etiology of specific cancers.  Many factors interact with one another as modifiers or precursors.

Energy intake and physical activity have been noted to alter pathophysiology.

• Energy restriction has been found to prevent cancer to a significant extent.  Supression of tumor development and increase in lifespan in animal studies.  Energy restriction results in reduced circulating levels of insulin-like growth factor (IGF-1) and insulin, both of which serve as growth factors for many cancer cells.  Other inflammatory markers also decline with energy restriction.
• Physical activity found to improve insulin sensitivity and reduce insulin levels.  Also decreases serum estrogen and androgen levels in both premenopausal and postmenopausal women (protection against hormone related cancers)

Lifestyle Factors

Cessation of tobacco use is the most critical modifiable risk factor in preventing cancer.
Body weight, diet and physical activity also play prominent roles in both primary and tertiary prevention of breast, colorectal, ovarian, endometrial, and prostate cancers.

Populations are increasingly sedentary.  Increasing physical activity may reduce risk for colorectal and breast cancers.  May also be beneficial for reducing risk of recurrence in survivors.