Food and Cancer- L6 Flashcards
In 2008, how many people was it thought to develop new case of cancer per year?
12 million people every year will be diagnosed as a new case of cancer
- it is a global estimate
- huge number of people and there are still millions who already have it
How many people will have cancer as their primary cause of death ?
7.6 million people
What does it mean if there is likely to be 12 million new cases of cancer per year and 7.6 million people per year will have it as their primary cause of death ?
there is a huge difference between these values and therefore it demonstrates that people are surviving from cancer
Throughout the world how do cancers vary ?
enormous variation in the frequency of different types of cancer world wide
Why is the incidence of cancer age-standardized and what is the difference between well developed and less developed countries ?
it creates a fairer playing field to allow different countries to be compared
- more developed countries demonstrate higher rates than less developed due to the age standardisation
- less developed countries have a greater burden even though rates a lower because they have larger populations
What are the top 3 most common cancers in males worldwide?
lung
prostate
colorectal
What are the top 3 most common cancers in females worldwide ?
breast- in the uk we have a higher prevalence in comparison to the rest of the world however the survival rates have dramatically improved
colorectal
cervix
Why did prostate cancer increase in the 90s?
massive rise due to increased screening, however it can predict false results
In men what 2 cancers declined between 1971-2005?
lung and stomach cancer
Why did breast cancer increase markedly in the 90s?
because a screening programme was brought in so incidence subsequently increased
Why did lung cancer in women increase between 1971-2005?
because more women started taking up smoking, originally it was a very male habit
What did migrant studies of female iranian migrants show about cancer incidence?
they had a much much greater incidence of breast cancer after migration but it was less than the natives
they also had an increased risk of developing colorectal cancer
What early evidence suggests that there is a link between diet and cancer ?
- variation in incidence between countries
- changes in cancer rates over time
- studies of migrant populations
these are indicative that environmental factors are contributing to cancer risk
What did Doll and Peto do ?
They determined the proportional of cancer deaths attributed to various factors
they provided a value and a range- for example there was a large range for diet because they didn’t have sufficient evidence to link diet to cancer
they demonstrated a very definite link between smoking and lung cancer
What is key about cancer and smoking?
there are very few cancers that dont have a link to smoking
the relative risk to lung cancer due to smoking is 20-30 which is about 4-5 times greater than for renal cancer
In non-smokers what is the predicted % of diet responsible for cancer deaths ?
10-30%
What are the types of epidemiological studies used to investigate the link between diet and cancer?
Ecological studies Observational analytical studies - cross sectional studies - case control studies - cohort studies Experimental studies - randomized controlled trials
What are the principles of Ecological studies ?
UNIT of ANALYSIS is a POPULATION rather than an INDIVIDUAL
- used to identify CHANGES in the FREQUENCY of a HEALTH EVENT in SPACE/or TIME
- RELATE CHANGES with ENVIRONMENTAL FACTORS
What are the limitations of Ecological studies?
unlikely to give reliable estimates of risk - especially on an individual basis
What are Ecological studies used for ?
- generate or test etiologic hypotheses - approach was carried out a lot to allude the link between diet and cancer
- evaluate the impact of intervention programs or policies
What is Ecological fallacy ?
the conclusion observed at the population level may not be true at an individual level - this may be due to differences between populations
e.g. at population level it may be concluded that increased chlorination of water increased incidence rates of cancer, however this relationship was not seen at the individual level
What are case control studies ?
You have 2 groups, one group of cancer cases and another group of cancer-free controls
What are case-control studies useful for ?
looking at rare cancers
What are the limitations of case-control studies ?
the cancer cases may change their diet after diagnosis therefore you will need these patients to recall info from a long time ago so its not that reliable
the control group has to be appropriate as if you have a group of people who are very into their diet, the results won’t be representative
also the control group dont actually have any reason to carry out the study, therefore this can cause bias, leading to false results
What is the cohort study design ?
you have a group of healthy people and their diets are monitor, looking at a specific dietary factor and then in the future the group is split into cancer free and cancer cases to observe results
What are the limitations of cohort studies ?
diets change over time so its difficult to quantify relationshiips between diet and risk
cost of this type of study is very expensive as it takes such a long time
if you have many people in the study you may have to use questionnaires which are not that reliable
What are randomised controlled trials?
in this type of study you start with a group of healthy people or people that have a condition which increases their risk of getting cancer and you observe a dietary factor and look at the effects it has had in the future
What is a major limitation of RCTs?
compliance is very challenging
What are the better studies to carry out ?
the analytical studies such as case-control, cohort and RCTs , not the descriptive studies
RCTs are the best evidence but cohort form the bulk of evidence we already have
What do we mean by risk ?
risk= a term encompassing a variety of measures of the probability of an outcome. It is usually used in reference to unfavourable outcomes such as illness or death
What is absolute risk ?
- chance of a person developing a specific outcome over a specified time period
- can also be expressed as a percentage or decimal
What is relative risk ?
- used to compare risk in 2 different groups of people that differ in their exposure to a factor
e. g alcohol intake
What is the risk between breast cancer and alcohol consumption ?
women drinking alcohol have a higher risk of breast cancer
if non-drinkers have risk of 1 then women who drink may have a relative risk of 1.13 so a 13% increased risk
On a individual level what are the methods to asses dietary intake ?
- food frequency questionnaires
- recalls
- food diaries
- diet history
- biomarkers
- novel- till receipts
On a population level what are the methods to assess dietary intake ?
- food balance sheets
- household budgets/expenditure
What is associated with food frequency questionnaires?
high degrees of error
What was shown about the incidence of breast cancer and saturated fat consumption?
in the food diary method it showed that consumption of saturated fats was linked to increased risk of breast cancer
whereas
in the food frequency questionnaire it didn’t demonstrate a significant link
2 different methods gave 2 different results
What shows that food diaries are more precise than questionnaires ?
biomarkers
at least over short periods
What are the limitations of food diaries ?
slow and very expensive to code
nested case-control design in contrast to full cohort analysis in questionnaires
it is subject to errors though coding
What is the future for large scale epidemiology studies ?
electronic method
