Cancer Prevention (Week 2 Lecture 1 ) Flashcards
What are cancer diagnosis related to?
- genetic defects
- environment and lifestyle
How
% cancer diagnosis related to genetic defects
5-10%
% cancer diagnosis related to environment and lifestyle
90-95%
What are some lifestyle factors associated with cancer diagnosis?
- cigarette smoking
- diet
- alcohol
- sun exposure
- pollutants
- infections
- stress
- obesity
- physical inactivity
Cancer-related deaths stats
- 25–30% are due to tobacco
- 15–20% due to infections
- 10-15% other factors
- 30-35% are linked to DIET (american cancer society)
What is CUP (AICR)
The Continuous Update Project (American Institute for Cancer Research) → an ongoing program that analyzes global research on how diet, nutrition and physical activity affect cancer risk and survival.
* 500 page report (2007) synthesizing research in nutrition, metabolism and cancer prevention published since 1996 (earlier report published in 1997 synthesized all previous literature). Updated version available as of 2018
* Synthesized evidence from case-control and cohort studies, as well as the limited number of RCTs that have been done in this area
* Graded evidence as ‘convincing’ , ‘probable’, ‘limited - suggestive’, ‘limited – no conclusion’.
WCRFN
World Cancer Research Fund Network
- To be the most authoritative global report on food, nutrition, weight control , physical activity and cancer prevention
- To enable governments, policy makers, scientists, health professionals, civic society and all people to use the report and it recommendations effectively
- To develop and promote the most reliable methods to collect, assess and judge evidence on the causes and prevention of cancer and other diseases
WCRF/ AICR grades of evidence
- convincing
- probable
- limited - suggestive
- limited - no conclusion
WCRF/ AICR convincing evidence
strong evidence to support a causal relationship which justifies setting a goal/recommendation that may reduce cancer incidence
* Evidence from more than one study type
* AT least 2 independent cohort studies
* No substantial unexplained disparity in findings of different studies
* Good quality studies (accounted for confounding, selection bias, systematic errors)
* Presence of a plausible response or gradient
* Plausible experimental evidence
WCRF/ AICR probable evidence
strong enough evidence to support a probable causal relationship
* Evidence from at least two cohorts, or 5 case-controls
* No substantial unexplained disparity in findings of different studies
* Good quality studies (accounted for confounding, selection bias, systematic errors)
* evidence of biological plausibility
WCRF/ AICR limited-suggestive evidence
Biased, not great quality
* Some evidence suggestive of a direct effect
* Evidence is relatively consistent, despite potential methodological flaws
* Evidence from at least 2 cohorts, or 5 case-controls
* Evidence for biological plausibility
WCRF/ AICR limited-no conclusion evidence
Entry level (i.e. warrants consideration) → not enough evidence
* Low number of studies
* Inconsistent direction of effect (studies show different things)
* Poor quality studies
Current cancer prevention guidelines
KNOW THESE
- body weight
- activity
- energy
- fruit/ veg
- meat
- alcohol
- other
cancer prevention: body weight
Maintain a healthy body weight
* Be as lean as possible without being underweight
* Avoid weight gain in adult life.
Obesity and abdominal fatness – potential mechanisms
- Obesity influences hormone levels: Adipokines are produced by adipocytes and influence tumor growth (disregulation of hormones)
- IGF-1 and insulin tend to be elevated in obesity → IGF-1 and insulin may promote growth of cancer cells (leptin may serve as growth factor)
- Estrogen synthesis occurs in adipose tissue in men and post-menopausal women → May increase risk of certain cancers in chronic inflammatory situations
- Low grade chronic inflammation occurs in obesity → higher concentrations of pro-inflammatory cytokines (can stimulate tumour growth)
cancer prevention: physical activity
Helps to maintain healthy body weight
* Be physically active at least 30 minutes every day
* Be physically active as part of every day life
Physical activity – potential mechanisms
- May help achieve/maintain a healthy body weight
- May help enhance immune function (lower inflammation)
- May be associated with lower levels of estrogen
- May positively enhance gut transit time (may have beneficial impact on colon cancer risk) → positive effect on microbiome and bile acid
challenges with self-reports of activity
- Classifications vary
- Measurement is difficult
- Confounding often happens (health conscious non-smokers, with ‘healthy’ diets tend to be physically active)
- Reporting bias can occur → people recall vigorous acitvity more clearly than low-level but higher duration activities
Cancer prevention: energy
- Avoid sugary drinks → different mechanism in brain from that of food and does not shut off compensation
- Limit consumption of energy dense foods.
Cancer prevention: plant foods
- Eat more of a variety of veg, fruits, whole grains and pulses
- Colour matters! Protective vitamins, minerals and phytochemicals
fruits and vegetables to eat for cancer prevention
- Crucifers → 1 serving per day → help eliminate carcinogens once broken down in the body → arugula, bok choi, broccoli, kale, cabbage, brussel sprouts, radish, cauliflower etc.
- Allium → onion, garlic, scallion, shallot, leek, chives
- Phytoestrogens → Isoflavones (Legumes/ soybeans), Lignans (Flaxseed, seaweed, whole grains), Stilbenes (Resveratrol), Coumestans
cancer prevention: animal foods
Limit intake of red meat and avoid processed meat
Evidence for processed and red meat association with cancer
WCRF/AICR 2007
* Convincing increased risk of colorectal cancers
* Limited suggestive increased risk of cancers of the esophagus, lung, pancreas, endometrium (red meat)
Processed and red meat intake – potential mechanisms
- High temperature cooking – promotes formation of heterocyclic amines and polycyclic aromatic hydrocarbons (mutagens and carcinogens)
- Nitrates/nitrites/salt used to cure meats can form nitrosamines (mutagens and carcinogens in animal studies)
- Iron (heme) in myoglobin may catalyse nitrosamine formation
- Relatively high fat content in some meats/processed meats may increase concentration of secondary bile acids in stool (faeces) that may be carcinogenic in colon/rectum
What is relative risk
the ratio of those exposed versus those who are not – For foods, the group with highest intake determines estimated risk
- RR for colon cancer & processed meat
- RR for lung cancer & cigarette smoking
- RR for liver cancer & aflatoxin contaminated
- RR for colon cancer & processed meat: - 1.18 per 50 g/day or 18% ↑
- RR for lung cancer & cigarette smoking = 10-30 or 1000-3000% ↑
- RR for liver cancer & aflatoxin contaminated grain = 6 or 600% ↑
What is absolute risk
the probability or chance of an event.
* It is usually used for the number of events (such as a disease) that occurred in a group, divided by the number of people in that group. Absolute risk is one of the most understandable ways of communicating health risks to the general public.
Lifetime risk of colon cancer among vegetarians (absolute risk)
4.5%
Lifetime risk of colon cancer among people who eat two ounces of processed meat every day (absolute risk)
5.3%
cancer prevention: alcoholic drinks
Limit intake of alcoholic drinks
* Those who drink, consume no more than 1 (women) to 2 (men) drinks per day
Cancer prevention: special recommendation 1
Dietary Supplements
* Aim to meet nutritional needs through diet alone
* Dietary supplements are not recommended for cancer prevention
Cancer prevention: special recommendation 2
Breastfeeding
* Mothers to breastfeed; children to be breastfed → also linked to reduction in obesity for both mom and child and lower risk for child
* infants exclusively up to 6 months and continue with complementary feeding thereafter
Cancer prevention: special recommendation 3
Cancer Survivors → Follow the recommendations for cancer prevention
* stay away from tobacco
* Maintain healthy weight
* Eat healthy
* Keep moving
* Dont drink alcohol
* Protect skin from sun
* Know family history
* To regular check-ups
