Epidemiological studies and biomarkers Flashcards
What is epidemiology used for?
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in defined populations.
What can observational studies be divided into?
- Prospective/retrospective
- Survey, case-kontroll. cohort
- longitudinall/cross-section
What defines a cohort study?
A cohort study is a particular form of longitudinal study that samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation), performing a cross-section at intervals through time.
Which type of study can you see a general effect?
Observational
Which study can be used to get more causal connections?
Intervention/Experimental
What can experimental/intervention studies be divided into?
Parallell/ cross-over
longitudinal
Which sort of study is good for looking at risk factors?
Experimental
During a intervention/Randomized control trial, what are important factors to avoid bias (= systematic errors)
Controlled
Balanced (as many in different groups)
Randomized (critical part)
Blinding (single and double blinding)
What is internal validity and external validity?
Internal validity = if high – subjects will follow what they have been told to do – retention – datakvalitet – study will be able to answer the question
- External validity – be able to translate the study into a broader population – You then need a very diverse group - but because of that can also end up failing what you want to measure …
How does a cross-over study work?
It is intrapersonal - every individual is measured in comparason to herself.
First one treatment then wash-out period to cleanse (expected to go back to regular diet) then the other treatment.
What are some negative aspects with cross-over?
RCT
Risk of carry-over effect. Can “spill” between the treatments
Only reversible effects can be studied
Takes a long time
Positive aspects of cross-over?
Because intrapersonal effects - don’t need to take as many parameters into consideration - need way less people !
Also because there are more check ups –> more compliance !
How is a paralell RCT performed?
Positive vs negative aspects
By dividing the participants in different groups with different people and then measure the effects.
+ no risk of carry-over between treatments
+ shorter time than cross-over
- Alot more people needed (because of interpersonal variations) –> more money
What is CONSORT?
- Made to reduce problem following false rapporting of data from randomised trials
- Standardised way to rapport data
Need to write the protocol in beginning and register – - Have to adhere to the hypothesis
What groups can observational studies be divided into?
Descriptive and analytical
What are the different Descriptive observational studies?
Prevalens: nr of cases right now
Incidens: nr of cases per time period
How is analytical observational studies made?
Mapping reasons through associatonal studies
Use statistical analysed data
- what is causing the diseases – typical routes – causative agents etc.
What are prospective observational studies?
When the participants are choosen, or a randomized selection of the entire population, before the “endpoint” occur.
- Risk that the choice of participants can lead to bias!
What are retrospective observational studies?
A group is choosen after the endpoint.
(ex. focus on a rare disease)
Risk: memory can be sensitive for measuring errors as “recall bias”
Epidemiological studies are often….?
Analytical
Describe a Kohort study?
Observational
- Use a group of individuals with “something in common” that has been followed over a period of time.
frequency of endpoint between exposure and no-exposed is measured and compared as a relative risk.
What are the calculation used in a Kohort study?
Relative risk = RR = Re/Ru
Re= Nr cases under that period of time/total nr people in the exposed group
Ru= Nr cases under that period of time/total amount of people in the un-exposed group
RR = 1 –> no differense in risk
RR > 1 –> higher risk of exposure
(1.9 = 90% higher risk)
What does longitudinal studies mean?
A longitudinal study (or longitudinal survey, or panel study) is a research design that involves repeated observations of the same variables (e.g., people) over short or long periods of time (i.e., uses longitudinal data).
Cohort studies are longitudinal and prospective. What are some negative aspects?
Long follow up–> expensive and results take time
Problem with
- choice of participants -ex. in a certain area
- people quite
- Assume people have same habits during the long time - but people may change work and therefore are exposed to other risk factors
What kind of study is a case control study and what does it do?
Retrospective study
- Risk factors are estimated backwards in time
- Cases are identified (ex. cases of heart attack)
- Controls are taken out (people that hasn’t had heart attack but are similar in other ways)
- Comparason by exposure of riskfactors
How are case control studies measured?
By association between exposure and disease
being measured as “odds ratio” (OR)
What does OR = 1 OR = 1.9 OR = 0.9 mean?
1 = no connection
- 9 = 90% increased risk
- 9 = 10% decreased risk
Positive and negative aspects with case control studies?
\+ Cheap and easy \+ good study for rare diseases - Big risk bias in comparason between case and controls - cases can affect riskfactor --> bias - hard to select representative controls
What is a cross-sectional study and when can it be used?
is a type of observational study that analyzes data from a population, or a representative subset, at a specific point in time
- Can only get correlation between those measurments
- But can’s say anything about what comes first – exposure or outcome
- Very cheap – can be used in first investigation –
can then move on with more complicated design
- Hypothesis generated design
What are some general problems with observational studies?
Bias
- Bias leads to wrong interpretation of the results
Confounding
- Collection of factors that affect the disease
- When another riskfactor is correlated to the one you observe affect the disease seperately
Give example of confounding
Coffee’s association with lung cancer
- coffee connected to smoking –> lung cancer
What are the 6 criteria that can be used as epidemiologic evidence of a causal relationship between a presumed cause and an observed effect
- Statistical power
- Biological plausability
- Relevant control group
4) Time of exposure
5) Dose response
6) Reproducability
What is a meta-analysis?
Meta-analysis is a quantitative, formal, epidemiological study design used to systematically assess the results of previous research to derive conclusions about that body of research. Typically, but not necessarily, the study is based on randomized, controlled clinical trials.
Positive aspects of meta-analysis?
- Many studies are too small to descover a effect (too low statistical power) - but can be used when combined with several
Get an overview so don’t have too read every paper
Can indicate publicationbias
more general reflection of the results
What are the consequenses of the problems in estimation of food in nutritional epidemiological studies?
- Lack of precision and accuracy
- Bias as a cause of randomized errors (as memory etc)
- Hard to esimate long time consumption
What are biomarkers and what can they be used for?
A molecule that reflects the intake and can be analysed in biological samples
Where can biomarker be sampled from?
urine, whole blood, plasma, serum, adipose tissue, saliva, hair
Serum vs plasma?
Serum (coagulated) = plasma minus proteins which were captured in the coagulation.
Plasma have not been coagulated only centrifuged.
(Serum can be seen as a bit cleaner)
What are the three types of biomarkers?
“Recovery biomarker” -
“Concentration biomarker” - huge diversity
“Prediction biomarker”
- strongly correlated – very clear relation o intake – not effected by bioavailability in same extent
Biomarker of whole grain?
Alkylresorcinoler DHPPA, DHBA
Plasma, urin, adipose tissue, short-long
Biomarker for protein?
Nitrogen
24-Urin
Short time
What can biomarkers be used for?
- Can be used as ranking tool - can rank into different groups depending on intake
- Include difference in bioavailability and denaturing in cooking - reflects internal dose
- Can be used to validate other methods - also in combination to other methods
What are the criteria fpr the perfect biomarker?
- Needs to be specific molecule
- Stable thorughout cooking
- Known ADME (absorption, distribution, metabolism, and excretion)
- SMall inter-individual variation of ADME
- Easy to analyse in biological tests
- Plausibelt dose respond relationship
- Nothing else should effect results
- Stay stable in biological tests
- Reflect intake at specific time period (can calculate the half life – to know if it is reflecting what you have yesterday or last months)
What affect the biomarker concentration?
- Absorption
- Distribution (to tissues)
- Elimination (metabolism, excretion)
Top down vs bottom up?
Top down:
- whan to analyse certain food with already known biomarkers - can use that
Bottom up -
Approach to find new biomarkers of food and diets. Feed people a food and then look for new biomarkers
What method is used to find biomarkers?
Metabolomics
