Nutrition and Cancer

Question 1

True or false? Cancer is the first leading cause of death in developed countries.

Answer 1

False, it is the second leading cause of death in developing countries

Question 2

What factors contribute to cancer development?

Answer 2

Genetic background, endogenous milieu and exogenous exposures.

Question 3

Name the characteristics of cancerous cells.

Answer 3

Escape normal growth signals, can replicate indefinitely, can form tumors, can avoid apoptosis, can alter energy metabolism, can avoid immune surveillance, can invade other tissues (metastasis) and can develop a blood supply (angiogenesis).

Question 4

Where does the word “cancer” come from and what does it mean?

Answer 4

Latin word cancri = crab and greek carcinos = crawfish

Question 5

Describe the process of carcinogenesis.

Answer 5

A mutation inactivates the tumor suppressor gene (inhibit cell growth and survival), which causes cell proliferation. A series of mutation occurs, firstly causing inactivation of DNA repair gene, second causing a proto-oncogene (promote cell growth and division) creating an oncogene, and a last mutation inactivating several more tumor suppressor genes, which results in cancer cells.

Question 6

What are strategies to block carcinogenesis and which one is most targeted by anti-cancer drugs?

Answer 6

Scavenge ROS (reactive oxygen species), decrease inflammation, suppress proliferation, enhance apoptosis, enhance immunity and discourage angiogenesis. Angiogenesis is usually targeted by anti-cancer drugs.

Question 7

What is a gene mutation and what is an example of it?

Answer 7

It is a structural change in the base pair sequence of DNA. There are two types of mutations: inherited and due to exogenous factors. An example of an inherited mutation is the BRCA1 gene, which increases the risk of breast and ovarian cancer because of its high penetrance (power at which a gene is expressed).

Question 8

What is polymorphism of a gene?

Answer 8

t is when the structure of the gene varies among individuals. It is weaker (has less penetrance) but is more common than mutations. SNIPs are an example.

Question 9

What are epigenetic changes in genes?

Answer 9

They affect gene structure, function and expression. Examples are DNA methylation (hypermethylation of promoter region of tumor suppressor genes leads to silencing) and acetylation of histones (affecting chromatin folding).

Question 10

What are the possible causes of cancer?

Answer 10

Tobacco and diet & obesity are the most contributing causes at 30%. Then there is lack of exercise, genetic background, infections and professional exposure at 5%. Lastly, there is alcohol at 3%, UV rays and pollution at 2%. All these possible causes affect genetic variability. About 65% of the causes of cancer are modifiable causes, such as tobacco, diet, exercice, alcohol.

Question 11

What type of nutrients can affect gene functions?

Answer 11

Oxidative damage to DNA can be:
Increased by carcinogens found in foods, PUFAs, iron (free iron in tissue)
Decreased by antioxidants (vitamin C&E) or cofactors in antioxidant enzymes (selenium, copper)
Direct role of folate in DNA synthesis, repair and methylation
Vitamins A and D interact with promoter regions of many genes, and regulate cell proliferation and differentiation
A group of nuclear receptors (PPARalpha) is activated by oxidized fats
Catechins (found in green tea, apples and chocolate) and flavonoids affect gene expression in cell culture

Question 12

What are the possible effects of diet on carcinogenesis?

Answer 12

Bioactive food components can affect:
Cell growth cycle
DNA repair
Cell differentiation
Hormone regulation
Carcinogen metabolism
Inflammatory response
Apoptosis

Question 13

What is the difference between incidence and mortality?

Answer 13

Incidence is the number of new cases of cancer in a certain period of time.
Prevalence is the overall number of cases of a certain disease/condition.

Question 14

What are the most dominant forms of cancer related to new cancer cases by sex in Canada?

Answer 14

Prostate (21%) is most of new cases for males, breast (25.8%) for females.

Question 15

What is the most dominant cancer related to deaths by sex in Canada?

Answer 15

Lung and bronchus (26.1%) for males and females. This is higher than the deaths for the new cancer cases, prostate and breast.

Question 16

How does cancer incidence vary with age and population growth?

Answer 16

Cancer incidence increases as age increases because cancers develop with time and because the older you get, the more chances that you develop cancer. The cancer incidence has not increased, but the number of cases has because of the aging population.

Question 17

What are the 4 different designs of studies that address diet and cancer?

Answer 17

Descriptive: cancer rates in populations having different diets are compared
Case-control: earlier diets reported by patients with a specific type of cancer are compared with matched controls without cancer
Prospective cohort: incidence of cancer is compared in persons whose diets (and other factors) are determined before follow-up begins
Interventional: incidence of cancer in 2 groups randomized to specific interventions is compared
Interventional design > prospective cohort > case-control > descriptive in decreasing order of the strength of associations between diet and cancer

Question 18

What are the limitations of studies addressing diet and cancer?

Answer 18

Descriptive: diet is only one of many variable, nutrient intake data are difficult to collect and it is best used to generate hypotheses.
Case-control: possible recall bias and selection bias, as well as proxy respondents with rapidly fatal CA
Prospective cohort: thousands of people need to be enrolled and health monitored for many years for statistical power, difficult for rare types of CA
Interventional: adherence to dietary changes is difficult, blinding is often not possible, optimal dosages needed to be ascertained, and duration is unknown and may be long

Question 19

True or False: Rapid growth rates before puberty play an important role in future risk of breast and perhaps other CA.

Answer 19

True. Early age at menarche is also a risk factor for breast CA.

Question 20

What kind of cancers is adult obesity associated with?

Answer 20

Colon, kidney, pancreas, esophagus, endometrium, gall bladder, liver. A greater risk of developing breast cancer after menopause in obese women.

Question 21

What is the relationship between dietary fat and breast cancer?

Answer 21

A large prospective study showed a positive association between animal fat and premenopausal breast cancer, but intervention trials of low-fat diets did not show a benefit. There were also low rates of breast cancer in southern European countries associated with the use of olive oil.

Question 22

What is the relationship between colon cancer and dietary fat intake?

Answer 22

Colon cancer is more associated to excess weight and low PA than dietary fat.

Question 23

What meats are associated with stomach, colon and rectum cancers?

Answer 23

Red and processed meats, due to the presence of preservatives (nitrites and salt) as well as the methods of cooking (fat of meats that flame up in the BBQ). The increase is very low though when applied to the original risk.

Question 24

What association was found between dairy products and colon cancer?

Answer 24

High milk and dairy consumption is associated with a decreased risk of colon cancer due to calcium and possibly vitamin D.

Question 25

What association was found between F&V and cancers?

Answer 25

The phytochemicals and their potential anticarcinogenic properties were associated with lowering the risk of many cancers, but is hard to tell because consuming many different F&V at the same time may obscure effects. Nevertheless, more specific associations were found between lycopene and prostate CA, cruciferous vegetables and several CA sites, allium vegetables and stomach CA, folate-rich F&V and colon CA, as well as citrus fruits and lung CA.

Question 26

What is the mechanism behind high fiber intake and low rates of colon CA?

Answer 26

Fiber dilutes or bind potential carcinogens, limits contact with mucosa by speeding transit, alters colonic flora, reduces the pH, serves as substrate to flora producing short-chain FAs (i.e. butyrate has anti-proliferative effect). A conclusion was also drawn from dose-response meta-analysis studies saying that dietary fibers probably protect against colon CA, so it is suggested to increase their intake.

Question 27

What is the effect of alcohol on cancer?

Answer 27

It has been shown to cause cancer in the oral cavity, larynx, esophagus and liver especially when combined with smoking (due to direct contact and toxicity in the liver). It might also increase the risk of breast and colon cancer with 2 drinks/day due to the anti-folate effect of alcohol in a methyl-poor diet (high EtOH, low folate, low methionine). High intakes of folate would reduce the risk of breast cancers associated with EtOH.

Question 28

What is the effect of calcium on cancer?

Answer 28

Calcium would reduce the risk of colon CA by binding toxic secondary bile acids and ionizing fatty acids to form soaps in the lumen, or by reducing proliferation and inducing apoptosis in the mucosal cells. 700-800 mg/day of calcium would reduced risk of colorectal cancers by 22% in prospective studies.

Question 29

What effect does vitamin D have on cancer?

Answer 29

Observed low risks of breast, colon and prostate cancers in populations with greater sun exposure. Recent evidence also suggest that vitamin D might be important to limit cancer progression.

Question 30

What do the studies about vitamin C, E and selenium and cancer conclude?

Answer 30

Vitamin C and E have antioxidant properties by neutralizing ROS that cause DNA damage. There is no consistent evidence of their role in cancer risk. Selenium in the form of selenoproteins (glutathione peroxidases) also defend against oxidative stress, but trials using Se and vit E supplements showed no decrease in prostate CA, so no supplementation is recommended.

Question 31

What is the recommendation for folate in regards to cancer?

Answer 31

Folate being involved in DNA methylation, repair and synthesis, is linked with higher risks of colorectal, breast and possibly cervical CA when taken in low amounts. No benefits were shown with folic acid supplementation and decreased cancer risk, so no supplements are recommended, just reach the recommended intake.

Question 32

What is the association between B-carotene intake and cancer?

Answer 32

There were observations of increased lung cancer risk with low vitamin A intake. There is an increased risk in smokers especially when combined with alcohol. There is still a lack of knowledge about how long B-carotene stays in the body and its interactions with other factors.

Question 33

What are the different levels of evidence of cancer risks and what do they state?

Answer 33

Level of evidence - Convincing: Decreased risk of cancer (especially colon) with physical activity Increased risk of cancer with overweight and obesity (many cancers), alcohol intake (oral cavity, pharynx, larynx, esophagus, liver, breast) and processed meat intake (colorectal) Level of evidence - Probable: Decreased risk of cancer with physical activity (breast cancer), dairy product and calcium intake (colon), whole grains and fiber intake (colon), and coffee (liver and uterus) Increased risk of cancer when consuming red meat (colorectum) and salt preserved foods (stomach) Level of evidence - Limited/suggestive: Decreased risk of cancer when consuming foods containing carotenoids, vitamin C - F&V (oral cavity, oesophagus, stomach, colorectum), and fish and vitamin D consumption Increased risk of cancer with grilled or barbecued meat and fish (heterocyclic amines, polycyclic aromatic hydrocarbons, nitrosamines from heme) Level of evidence - Limited/no conclusion: Decreased risk of cancer when consuming omega-3 FA, carotenoids, vitamins B6, B12, folate, C, D, E, Se, non-nutrient plant constituents, garlic, soy, sugar, tea, etc.

Question 34

What are the general recommendation of the American Cancer Society for cancer?

Answer 34

Achieve and maintain a healthy weight throughout life Be physically active Eat a healthy diet, with an emphasis on plant foods such as limiting processed/red meats, eating at least 2 ½ cups of F&V each day, choosing whole grains instead of refined grains If you drink alcohol, limit your intake by drinking no more than 1 a day for women and 2 a day for men