Epidemiological studies and biomarkers

Question 1

What is epidemiology used for?

Answer 1

Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in defined populations.

Question 2

What can observational studies be divided into?

Answer 2

• Prospective/retrospective
• Survey, case-kontroll. cohort
• longitudinall/cross-section

Question 3

What defines a cohort study?

Answer 3

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.

Question 4

Which type of study can you see a general effect?

Answer 4

Observational

Question 5

Which study can be used to get more causal connections?

Answer 5

Intervention/Experimental

Question 6

What can experimental/intervention studies be divided into?

Answer 6

Parallell/ cross-over

longitudinal

Question 7

Which sort of study is good for looking at risk factors?

Answer 7

Experimental

Question 8

During a intervention/Randomized control trial, what are important factors to avoid bias (= systematic errors)

Answer 8

Controlled
Balanced (as many in different groups)
Randomized (critical part)
Blinding (single and double blinding)

Question 9

What is internal validity and external validity?

Answer 9

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 …

Question 10

How does a cross-over study work?

Answer 10

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.

Question 11

What are some negative aspects with cross-over?

RCT

Answer 11

Risk of carry-over effect. Can “spill” between the treatments
Only reversible effects can be studied
Takes a long time

Question 12

Positive aspects of cross-over?

Answer 12

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 !

Question 13

How is a paralell RCT performed?

Positive vs negative aspects

Answer 13

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

Question 14

What is CONSORT?

Answer 14

• 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

Question 15

What groups can observational studies be divided into?

Answer 15

Descriptive and analytical

Question 16

What are the different Descriptive observational studies?

Answer 16

Prevalens: nr of cases right now
Incidens: nr of cases per time period

Question 17

How is analytical observational studies made?

Answer 17

Mapping reasons through associatonal studies
Use statistical analysed data
- what is causing the diseases – typical routes – causative agents etc.

Question 18

What are prospective observational studies?

Answer 18

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!

Question 19

What are retrospective observational studies?

Answer 19

A group is choosen after the endpoint.
(ex. focus on a rare disease)
Risk: memory can be sensitive for measuring errors as “recall bias”

Question 20

Epidemiological studies are often….?

Answer 20

Analytical

Question 21

Describe a Kohort study?

Observational

Answer 21

• 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.

Question 22

What are the calculation used in a Kohort study?

Answer 22

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)

Question 23

What does longitudinal studies mean?

Answer 23

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).

Question 24

Cohort studies are longitudinal and prospective. What are some negative aspects?

Answer 24

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

Question 25

What kind of study is a case control study and what does it do?

Answer 25

Retrospective study - Risk factors are estimated backwards in time 1. Cases are identified (ex. cases of heart attack) 2. Controls are taken out (people that hasn't had heart attack but are similar in other ways) 3. Comparason by exposure of riskfactors

Question 26

How are case control studies measured?

Answer 26

By association between exposure and disease | being measured as "odds ratio" (OR)

Question 27

``` What does OR = 1 OR = 1.9 OR = 0.9 mean? ```

Answer 27

1 = no connection 1. 9 = 90% increased risk 0. 9 = 10% decreased risk

Question 28

Positive and negative aspects with case control studies?

Answer 28

``` + 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 ```

Question 29

What is a cross-sectional study and when can it be used?

Answer 29

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

Question 30

What are some general problems with observational studies?

Answer 30

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

Question 31

Give example of confounding

Answer 31

Coffee's association with lung cancer | - coffee connected to smoking --> lung cancer

Question 32

What are the 6 criteria that can be used as epidemiologic evidence of a causal relationship between a presumed cause and an observed effect

Answer 32

1. Statistical power 2. Biological plausability 3. Relevant control group 4) Time of exposure 5) Dose response 6) Reproducability

Question 33

What is a meta-analysis?

Answer 33

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.

Question 34

Positive aspects of meta-analysis?

Answer 34

- 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

Question 35

What are the consequenses of the problems in estimation of food in nutritional epidemiological studies?

Answer 35

- Lack of precision and accuracy - Bias as a cause of randomized errors (as memory etc) - Hard to esimate long time consumption

Question 36

What are biomarkers and what can they be used for?

Answer 36

A molecule that reflects the intake and can be analysed in biological samples

Question 37

Where can biomarker be sampled from?

Answer 37

urine, whole blood, plasma, serum, adipose tissue, saliva, hair

Question 38

Serum vs plasma?

Answer 38

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)

Question 39

What are the three types of biomarkers?

Answer 39

"Recovery biomarker" - "Concentration biomarker" - huge diversity "Prediction biomarker" - strongly correlated – very clear relation o intake – not effected by bioavailability in same extent

Question 40

Biomarker of whole grain?

Answer 40

Alkylresorcinoler DHPPA, DHBA | Plasma, urin, adipose tissue, short-long

Question 41

Biomarker for protein?

Answer 41

Nitrogen 24-Urin Short time

Question 42

What can biomarkers be used for?

Answer 42

- 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

Question 43

What are the criteria fpr the perfect biomarker?

Answer 43

- 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)

Question 44

What affect the biomarker concentration?

Answer 44

- Absorption - Distribution (to tissues) - Elimination (metabolism, excretion)

Question 45

Top down vs bottom up?

Answer 45

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

Question 46

What method is used to find biomarkers?

Answer 46

Metabolomics