stopping cancer before it starts

by Dr. Donna Douglas

When I first began my oncology training a number of years ago, the most startling statistic I encountered was that only 5-8% of cancers have been linked to genetics, while more than 90% can be attributed to lifestyle and environmental influences. This means that lifestyle choices -- what you do for a living, where you live and work, and what you eat and drink -- are the main factors influencing the development of most cancers. Luckily, this also means that making small changes in your lifestyle can add up to big benefits in the future. But how can such simple choices impact such a complicated disease?

In the most basic terms, cancer is defined as the occurrence of heritable mutations in a cell's DNA that provide growth advantages to the affected cell. When we look at cancer this way, we can see that the first logical steps in cancer prevention are protecting our DNA from damage, and helping our bodies to repair the damage done. Factors that can damage DNA include reactive oxygen species (ROS) that are created during the body's normal metabolic processes, ultraviolet (UV) radiation, x-rays, and certain environmental chemicals such as vinyl chloride, hydrogen peroxide, and polycyclic hydrocarbons from tar and soot. The damage caused may occur as breaks, mutations or adducts to the DNA.

Much of the damage that occurs to DNA is quickly recognized and repaired in a healthy body. Normal p53, p21 and BRCA1 complexes play an integral role in detecting DNA damage, and inducing repair mechanisms. However, when the damage becomes too severe, or nutritional deficiencies weaken the body's repair systems, DNA mutations can lead to tumor formation. One study of middle-aged men suggested that blood selenium levels lower than 100 ng/ml were inadequate for surveillance or repair of oxidative (and other) DNA damage (Ferguson, LR).

Because damage can occur anywhere in the DNA sequence, the proteins and processes that are affected vary widely. Some cancers may result from mutations in surveillance proteins, while others may involve disrupted pathways for programmed cell death (apoptosis). Therefore, preventative approaches to cancer control must bring into play a wide range of complementary protective mechanisms.

Nutrition to Prevent Cancer

Epidemiologic studies consistently show a correlation between increased fruit and vegetable intake and reduction in the incidence of various cancer types. The EPIC study followed this association in more than 500,000 men and women (Gonzalez). This study demonstrated that regular intake of fiber, fruits and vegetables produced a protective effect against colon and rectal cancer, and regular fruit consumption reduced the incidence of lung cancer.

Many of the benefits of a diet rich in fruits and vegetables are attributed to the complex additive and synergistic effects of phytochemicals that are present in whole foods. In contrast, research has demonstrated substantial risks in the use of mega-dose, isolated nutrient/vitamin supplements. Allium and cruciferous vegetables are especially beneficial, with broccoli sprouts providing the densest source of sulforophane. Protective elements included in a cancer prevention diet should include selenium, folic acid, vitamin B-12, vitamin D, chlorophyll, and antioxidants such as the carotenoids (alpha-carotene, beta-carotene, lycopene, lutein, cryptoxanthin). Dietary fiber provided by fruit and vegetable intake also plays a crucial role in processing potentially harmful compounds. For example, estrogen is a potent growth signal for some cancer cells, and in the lumen of the intestines, it is bound by dietary fiber for removal from the body (Goldin).

Anti-cancer nutrients exert their influence through induction of programmed cell death, competition for estrogen receptors, antioxidant/free radical scavenging, proteasome and aromatase inhibition, anti HIF-1 alpha activity, proliferation/cell cycle inhibition, angiogenesis inhibition, etc. Certain nutrients can benefit specific organs; for example, the effect of the red pigment lycopene, found in foods such as tomatoes and watermelon, is localized to the prostate gland (Heber). Recent data clearly demonstrates that specific nutrients can produce effects even at the genetic level. Indole-3-carbinol is a phytochemical from cruciferous vegetables that has been shown to induce BRCA1 expression, and thereby to inhibit estrogen activity in human cells (Fan).

Calorie Restriction to Prevent Cancer

Calorie restriction with adequate nutrient intake contributes to reduction of cancer risk through nutrient sensing pathways and decreased metabolic rate (Heilbronn 2006). Though the details of these processes have yet to be discovered, the behavior of many genes involved in DNA repair seems to be altered during caloric restriction. A decrease in metabolic rate reduces the frequency of biochemical reactions in general, and thus the opportunities for DNA damage to occur.

Physical Activity to Prevent Cancer

Exercise appears to produce a dose-response reduction in the incidence of colon and breast cancer. The California Teachers Study showed that invasive breast cancer risk was inversely associated with long-term strenuous activity (>5 vs </=0.5 h/wk per year), as was in situ breast cancer risk (>5 vs </=0.5 h/wk per year) (Dallal, Holmes). A study published in the Archives of Internal Medicine showed that men over age 65 who engaged in at least three hours of vigorous physical activity (such as running, biking, or swimming) per week had a nearly 70% lower risk of developing advanced prostate cancer, and of dying from the disease (Giovannucci). Regular exercise causes a decrease in serum insulin-like growth factor (IGF-I), and is associated with apoptosis and reduced prostate cancer cell growth. Physical activity also produces demonstrable effects on estrogen levels in pre- and post-menopausal women. Estrogen and IGF-1 are well known activators of cancer cell growth.

Another important benefit of exercise is in combating the effects of stress. Excessive stress negatively influences resistance to tumor growth, and some stress-reducing hormones released during exercise, such as corticosteroids or catecholamines, can modulate the ability of immune cells to kill tumor cells.

Seven Steps Toward Cancer Prevention

The following simple lifestyle changes can help to protect you and your loved ones from cancer:

Avoid tobacco and side stream smoke.
Get regular sun exposure, but avoid excessive UV exposure and sunburn.
Consume a variety of phytonutrients/antioxidants from whole food sources.
Avoid cured meats with nitrate additives.
Be sure that your diet includes adequate amounts of folate and selenium.
Stay active, and maintain your proper body mass.
Enjoy at least 8 hours of sleep each night.

It is not possible for us to understand all the mechanisms by which lifestyle interventions function for cancer prevention and control. However, it is good to know that we can supplement our body's natural health maintenance processes to produce significant and lasting benefits in the years to come.

Posted June 2007

Additional Reading

Chen, S. Prevention and treatment of breast cancer by suppressing aromatase activity and expression.

Dallal, CM. Arch Intern Med. 2007 Feb 26;167(4):408-15. Long-term recreational physical activity and risk of invasive and in situ breast cancer: the California teachers study.

Donaldson, MS. Nutr J. 2004 Oct 20;3:19. Nutrition and cancer: a review of the evidence for an anti-cancer diet.

Douglas, D. Hope on the Horizon: Breakthrough Natural Solutions for Preventing and Reversing Chronic Disease. Chancellor Publishing, 2006.

Fan, S., et al. British Journal of Cancer (2006) 94, 407-426. BRCA1 and BRCA2 as molecular targets for phytochemicals indole-3-carbinol and genistein in breast and prostate cancer cells.

Feskanich, D. J Natl Cancer Inst. 2000 Nov 15;92(22):1812-23. Prospective study of fruit and vegetable consumption and risk of lung cancer among men and women.

Ferguson, LR. Toxicology. 2004 May 20;198(1-3):147-59. Dietary cancer and prevention using antimutagens.

Giovannucci, E. Archives of Internal Medicine. 2005 May 9: vol 165; pp 1005-1010.

Goldin, BR. Cancer Res. 1981 Sep;41(9 Pt 2):3771-3. Effect of diet on excretion of estrogens in pre- and postmenopausal women.

Goldin, BR. Cancer. 1994 Aug 1;74(3 Suppl):1125-31. The effect of dietary fat and fiber on serum estrogen concentrations in premenopausal women under controlled dietary conditions.

Gonzalez, CA. Nutr Cancer. 2006;56(2):225-31. Diet and cancer prevention: where we are, where we are going.

Heber, D. J Postgrad Med. 2004 Apr-Jun;50(2):145-9. Vegetables, fruits and phytoestrogens in the prevention of diseases.

Heilbronn, LK, et al. JAMA. 2006 Apr 5;295(13):1539-48. Effect of 6-month calorie restriction on biomarkers of longevity, metabolic adaptation, and oxidative stress in overweight individuals: a randomized controlled trial.

Holmes, M. Journal of the American Medical Association (Vol. 293, No. 20: 2479-2486).

Michaud, DS. J Natl Cancer Inst. 1999 Apr 7;91(7):605-13. Fruit and vegetable intake and incidence of bladder cancer in a male prospective cohort.