So, why do we get cancer and more importantly, what can we do to prevent it?

In order for cancer to develop, at least three events need to occur:

  1. Damage to the genome affects one or more facets of cell replication, so growth becomes uncontrolled.
  2. The damage to the genome is not recognized or not repaired and the affected cell is allowed to propagate.
  3. The altered cancerous cell escapes detection by the immune system and is allowed to live and replicate.

The first event probably happens daily. Every day, we’re exposed to conditions and substances that cause DNA damage. Our bodies are equipped to deal with a low level of DNA damage, either by destroying the cell that has damaged DNA or by repairing the damage.

However, our capacity to deal with the genomic damage can be overwhelmed if the volume and frequency of damage is too great. Our goal then is to reduce our exposure to things that cause DNA damage as much as is practically possible.

What things should we avoid that cause DNA damage?

  • Tobacco is possibly the single leading cause of cancer in the world.
    • It’s implicated in cancers of the lung, bladder, throat, larynx, mouth, esophagus, bladder, kidney, liver, pancreas, colon, rectum, cervix and even leukemia.
    • Tobacco smoke has over 7,000 chemicals, most of which are probably bad for you and 70 of which have been definitively proven to cause DNA damage and cancer.
    • Chewing tobacco is similarly bad but concentrates the damage to the mouth and throat.
  • Alcohol is a causal agent in cancers of the head and neck, esophagus, liver, colon, rectum and breast.
    • Alcohol metabolizes in the body into acetylaldehyde and reactive oxygen species, which then causes DNA damage.
    • It also prevents your body from absorbing a wide range of micronutrients like vitamins A, B, C, D, E and folate among others that are important in processes like DNA repair.
    • It increases blood levels of estrogen which can drive breast cancer.
    • Use of alcohol and tobacco together greatly increases cancer risk.
  • Ionizing radiation causes direct DNA damage.
    • The most common sources of ionizing radiation are far UV light from sunlight, radon and medical imaging.
    • We are probably all aware the too much sunlight is a major cause of skin cancers. So it is important to use a hat and cover up when in the sun for prolonged periods of time.
    • Radon is a common radioactive gas found in soils and rocks and can be a factor in basements and first floors of many homes. Radon tests for your home are relatively inexpensive and steps can be taken to reduce or eliminate exposure if detected. Information about radon can be found here.
    • Finally, X-rays, CT scans, pet scans and many other medical tests expose patients to ionizing radiation. However, the amount of radiation is very low and physicians are well aware of the risks and usually only order these tests of the benefits outweigh risks.
  • Infectious agents can cause cancer through DNA damage via chronic inflammation, direct effects of cell growth or depression of the immune system.
    • The most important infectious agents are human papilloma virus (HPV), hepatitis B and C virus, and human immunodeficiency virus (HIV).
    • Risk from these infectious agents can be reduced by avoiding unprotected sex, sex with multiple partners, and IV drug use.
  • Meat.
    • Processed meats such as bacon, ham, hot dogs, deli meats have been recently classified as definite carcinogens in the same category as tobacco.
    • Red meats are classified as probable carcinogens1.
    • And all meat including fish and poultry are carcinogenic if cooked by frying, grilling, barbeque or broiling. Cooking meats under high heat produces heterocyclic amines and polycyclic aromatic hydrocarbons which causes DNA damage.
    • The best diet for cancer prevention as well as your overall health is a vegetarian or vegan diet that avoids meats altogether.
  • Obesity.
    • Obesity is linked to about 20% of all cancers2.
    • The mechanisms behind obesity and cancer risk are not well understood but the relationship between obesity and increased cancer incidence is clear.
    • Some proposed mechanisms are that obesity leads to chronic inflammation which can lead to DNA damage, hormonal effects of excess fat may drive some forms of cancer, obesity affects immune system efficiency which may lead to more cancers.

Why doesn’t everyone have a form of cancer? 

One of the reasons why we don’t all get a form of cancer every day is that our cells have a robust system of checks for DNA integrity. This system prevents almost all cells with DNA damage from propagating, as well as repair mechanisms to correct most genomic defects. Processes that disrupt these protective mechanisms will increase cancer incidence while improving DNA repair will decrease cancer incidence.

Most of the things that affect DNA repair are beyond our control. For example, some people are born with defective DNA repair mechanisms in diseases such as Fanconi anemia and xeroderma pigmentosum and these people develop multiple cancers very early on in life.

However, there are a few ways in which we may be able to enhance our DNA repair or prevent DNA damage.

  • Eat a diet rich in micronutrients
    • Many studies have shown that a diet rich in micronutrients can increase DNA repair efficiency or decrease DNA damage and decrease cancer incidence.
    • Micronutrients such as selenium, beta carotene, vitamin C, alpha tocopherol are found in plant based foods such as fruits, nuts, and vegetables and not found in the cuts of meats most often consumed in the U.S.
    • These are just the micronutrients we know about. There are likely many more micronutrients that aid in important cellular processes that we have not yet discovered and if the pattern holds true, these micronutrients will be found in plants and not in Twinkies, burgers or hot dogs3; 4;5; 6.
  • Exercise.
    • Beyond the myriad benefits of exercise on mood, strength, endurance, sleep, pain, stress, and disease prevention, exercise seems to actually improve DNA repair and reduce cancer incidence 7; 8; 9.
  • Eat a calorie poor diet.
    • The modern diet is one that is rich in macronutrients such as fats, protein and carbohydrates while being extremely poor in micronutrients.
    • The thought process with excess calories is that it encourages cell replication and doesn’t allow enough time for DNA repair mechanisms to repair or proofread the genome before allowing the cell cycle to progress. This can lead to genomic instability and cancer10.

How our immune system can help.

A kind of last line of defense against cancer is our immune system. If a cancer cell makes it past our DNA repair and proofreading mechanisms, a robust immune system may destroy it before it becomes a tumor in a process called cancer immunosurveillance.

It is possible that we are all developing cancer cells daily and that our immune system is keeping us from developing actual cancer by eliminating those as soon as they pop up. We know that organ transplant patients put on immunosuppressive regimens to prevent rejection of the transplanted organ have much higher rates of cancer than the rest of the population. AIDS patients also have increased rates of cancer.

It stands to reason that doing things to improve our immune system function will protect us from cancer

  • Reverse diabetes.
    • Diabetes induces a state of immunosuppression as well as chronic inflammation. Both of these processes encourage the development of cancer.
    • Diabetic patients have 25% higher risk of cancers in general and over twice the risk of liver, pancreatic and uterine cancer11; 12.
  • Get enough sleep.
    • Recent research demonstrates that sleep affect many aspects of immune function
    • Sleep activates T and NK cells and increases the function of antigen presenting cells which are the main components of cellular immunity that perform cancer immunosurveillance13.
    • And growing evidence points to a connection between poor sleep and cancer risk 14; 15.
  • Reduce stress.
    • There is strong evidence to support that role of chronic stress of immune system dysfunction and subsequent cancer initiation16.
    • The most effective methods of stress management are a strong collaborative relationship with God and aerobic exercise.
  • Make sure you’re getting enough Vitamin D.
    • Vitamin D is a potent regulator of immune function and deficiency causes impaired immune function.
    • A very active area of cancer research is exploring the relationship between vitamin D deficiency and increased cancer risk17; 18 ; 19; 20; 21.
    • Currently in the developed world, there is widespread vitamin D deficiency. This is probably a result of the shift of our lifestyles to indoor work and living as well as the vilification of sun exposure as a risk for skin cancer and skin aging leading to sun avoidance and use of sunscreens that impair vitamin D synthesis.
    • So what are we to believe? Is sun exposure bad for us or good for us? The truth is probably in between.
    • My belief is that most of us don’t get enough sunlight but when we do get it, we get it in concentrated prolonged doses rather than small amounts daily.
    • What is probably optimal for us is to get some sunlight daily rather than to get almost no sunlight for weeks and then spend 12 hours at the beach or outside all in one go.

So, let’s sum it up.  

Cancer is caused by damage to our DNA combined with a failure to detect and repair or destroy the damage.  All the recommendations above can be condensed into a few simple steps.

  1. Avoid alcohol and tobacco.
  2. Eat lots of beans, vegetables, nuts, fruits.  Avoid processed foods, especially sugar.  Avoid meats, especially processed and red meats.
  3. Get plenty of sleep and exercise outdoors.
  4. Nurture a vibrant spiritual life.

In Part 1 of this series on cancer, we started the journey to understanding what cancer really is. Stay tuned for Part 3, where Dr. Steve will discuss conventional treatment methods for cancer–namely radiation therapy and chemotherapy.

1 Bouvard, Véronique, Dana Dana Loomis, Kathryn Z. Guyton, Yann Grosse, Fatiha El Ghissassi, Lamia Benbrahim-Tallaa, Neela Guha, Heidi Mattock, and Kurt Straif. “Carcinogenicity of Consumption of Red and Processed Meat.” The Lancet Oncology 16.16 (2015): 1599-600. The Lancet. 26 Oct. 2015. Web. 18 Jan. 2017.

2 “Obesity and Cancer.” The Oncologist. U.S. National Library of Medicine, 27 May 2010. Web. 18 Jan. 2017.

3 Wright, Margaret E., Susan T. Mayne, Rachael Z. Stolzenberg-Solomon, Zhaohai Li, Pirjo Pietinen, Philip R. Taylor, Jarmo Virtamo, and Demetrius Albanes. “Development of a Comprehensive Dietary Antioxidant Index and Application to Lung Cancer Risk in a Cohort of Male Smokers.” American Journal of Epidemiology. Oxford University Press, 01 July 2004. Web. 18 Jan. 2017. <https://academic.oup.com/aje/article/160/1/68/107187/Development-of-a-Comprehensive-Dietary-Antioxidant>.

4 Croteau, Deborah L., Nadja C. De Souza-Pinto, Charlotte Harboe, Guido Keijzers, Yongqing Zhang, Kevin Becker, Shan Sheng, and Vilhelm16 A. Bohr. “DNA Repair and the Accumulation of Oxidatively Damaged DNA Are Affected by Fruit Intake in Mice.” The Journals of Gerontology Series A: Biological Sciences and Medical Sciences. Oxford University Press, 16 Sept. 2010. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3004740/>.

5 Longtin, Robert. “Selenium for Prevention: Eating Your Way to Better DNA Repair?”Selenium for Prevention: Eating Your Way to Better DNA Repair? Oxford Journals, 2003. Web. 18 Jan. 2017. <http://jnci.oxfordjournals.org/content/95/2/98.long>.

7 “Exercise-induced Biochemical Changes and Their Potential Influence on Cancer: A Scientific Review.” British Journal of Sports Medicine. U.S. National Library of Medicine, n.d. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/27993842>.

8 “Exercise as Gene Therapy: BDNF and DNA Damage Repair.” Asia-Pacific Journal of Ophthalmology. U.S. National Library of Medicine, 5 Aug. 2016. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/27488073>.

9 “Regular Exercise Reduces 8-oxodG in the Nuclear and Mitochondrial DNA and Modulates the DNA Repair Activity in the Liver of Old Rats.” Experimental Gerontology. U.S. National Library of Medicine, 3 Jan. 2007. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/17204389>.

10 “High Nutrient Levels and TORC1 Activity Reduce Cell Viability following Prolonged Telomere Dysfunction and Cell Cycle Arrest.” Cell Reports. U.S. National Library of Medicine, 26 Sept. 2014. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/25263563>.

11 “Diabetes and Cancer: A Review of Current Knowledge.” Experimental and Clinical Endocrinology & Diabetes : Official Journal, German Society of Endocrinology [and] German Diabetes Association. U.S. National Library of Medicine, 24 May 2014. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/27219686>.

12 “Insights into the Relationships between Diabetes, Prediabetes, and Cancer.” Endocrine. U.S. National Library of Medicine, 31 Dec. 2016. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/28040833>.

13 “Sleep and Immune Function.” Pflugers Archiv : European Journal of Physiology. U.S. National Library of Medicine, 10 Nov. 2011. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/22071480>.

14 “Sleep and Breathing … and Cancer?” Cancer Prevention Research (Philadelphia, Pa.). U.S. National Library of Medicine, 7 Sept. 2016. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/27604751>.

15 “Emerging Co-morbidities of Obstructive Sleep Apnea: Cognition, Kidney Disease, and Cancer.” Journal of Thoracic Disease. U.S. National Library of Medicine, 8 Sept. 2016. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/27747026>.

16 Reiche, Edna Maria Vissoci, Sandra Odebrecht Varga Nunes, and Helena Kaminami Morimoto. “Stress, Depression, the Immune System, and Cancer.” The Lancet Oncology5.10 (2004): 617-25. The Lancet. Oct. 2004. Web. 18 Jan. 2017. <http://www.sciencedirect.com/science/article/pii/S1470204504015979>.

17 “An Update on Vitamin D and Human Immunity.” Clinical Endocrinology. U.S. National Library of Medicine, Mar. 2012. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/21995874>.

18 “Vitamin D: Modulator of the Immune System.” Current Opinion in Pharmacology. U.S. National Library of Medicine, 27 Apr. 2010. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/20427238>.

19 “Association between Vitamin D and Risk of Colorectal Cancer: A Systematic Review of Prospective Studies.” Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology. U.S. National Library of Medicine, 29 Aug. 2011. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/21876081>.

20 “Vitamin D Signalling Pathways in Cancer: Potential for Anticancer Therapeutics.” Nature Reviews. Cancer. U.S. National Library of Medicine, Sept. 2007. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/17721433>.

21 “The Vitamin D Receptor in Cancer.” The Proceedings of the Nutrition Society. U.S. National Library of Medicine, May 2008. Web. 18 Jan. 2017. <https://www.ncbi.nlm.nih.gov/pubmed/18412986>.


About the Author

Steve Lee, MD, PhD

Dr. Lee is a surgical oncologist and associate professor at Loma Linda University School of Medicine and currently serves as Vice Chairman of the Head and Neck Surgery Department and co-director of the Center for Skull Base Surgery. He lives in Redlands, CA with his wife and two daughters and enjoys dragging them out into the great outdoors every chance he gets.

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