Final Flashcards
What are the non-experimental/observational study designs?
- ecological
- cross sectional
- prospective cohort/longtitudinal
- retrospective
- case control
What are the experimental/interventional study designs?
- randomized control trials
- pre-post
- repeated measure
- crossover
Randomized controlled trials
The “gold standard” of experimental designs. Randomized - double blinded. Expensive and sometimes not feasible. Careful selection of participants, controls for as many extraneous variables. Designed to answer ONE specific question.
Pre-post study
baseline measurement of dependent variables –> intervention –> after measurement of dependent variables
More open to bias, not randomized. Simple design, less expensive. Long - attrition.
Repeated measure study
intervention & baseline measurements –> day 14 measurements –> day 28 measurements –> end intervention measurements
Would be made stronger with a control. Designed to answer one question.
Crossover study
2 levels of treatment. Everyone receives the intervention. Before and after measurements of each person for each treatment arm. Each person serves as their own control.
Ecological study
Looks at variables observed in geographical regions. Describes and compares different populations. Can establish associations and support further research. Not individual level data - cannot establish causation.
Cross sectional study
“Snapshot” measurements at a single point in time. Variables of interest collected at the same time. Identifies associations between variables and can be used to generate a hypothesis. Can compare two or more groups. Limitations are that only a single point in time - cant establish causation. Sample selection is really important to generalize results.
Prospective cohort (longitudinal) study
Data collected on variables of interest from the same individuals (potentially multiple times). e.g. progression of a disease, impact of aging etc. Participants usually have a common characteristic. Can assess causal associations and assess many variables at the same time. Limitations are they are very long and attrition is likely, expensive.
Retrospective cohort study
Data is collected from existing records. Examines if individuals with differing levels of a factor have different outcomes. e.g. if obesity at the time of surgery will increase complications later. Cohort is a defined group (e.g. all women who had a baby in the last 10 years). Strengths are inexpensive, no burden on the cohort, can establish some causal association. Limitations is that the data may not be present.
Case control study
2 groups - one with the condition and one without. Examines variables in the past (risk factors). Different than retrospective cohort –> the outcome is present and looking back at risk factors. e.g. how to patients characteristics at the time of the surgery differ between those who do and do not develop complications? strengths are you can examine rare conditions, assess causal conditions, cost and time efficient. Limitations are retrospective - data may not be available, relies on recall, the right controls are needed.
Types of evidence
- Convincing: strong, consistent, unlikely to change
- Probable: compelling but not quite strong enough to be convincing
- Limited evidence – suggestive: general consistency in the data
- Limited evidence – no conclusion: too inconsistent
- Substantial effect on risk unlikely: enough evidence to rule out a connection
Types of dietary intervention
- controlled feeding studies
- behavioural counselling studies
Strengths and Limitations of FFQ
Strengths: high respondent rate, can assess a number of people at the same time, relatively low participant burden, lower cost, generally does not affect eating behaviour
Limitations: lacks detail, requires literacy, different populations respond differently, problem with assessing foods in recipes
Strengths and Limitations of 24h recall
Strengths: suitable for illiterate subjects, low participant burden, high compliance, unlikely to interfere with diet, can be detailed
Limitations: relies on memory, relies on portion size estimates, only a “snapshot”, costly for face to face, underreporting is common
Strengths and Limitations of food diaries
Strengths: intake is quantified, does not rely on memory, can include weekends, could be relatively accurate if subjects are trained
Limitations: recording can influence dietary choices (bias), expensive, high participant burden, underreporting
Criteria for establishing causation
Temporality (exposure precedes outcome) strength of association dose response (greater exposure = higher risk) consistency of results biological plausibility
What are the functions of choline?
- Phosphatidylcholine (structural component of biological membranes, transports lipid molecules, structural component of the brain)
- acetylcholine (a neurotransmitter)
- sphingomyelin (nerve fibre myelination)
- methyl donor
- component of plasmalogen
- component of platelet activating factor
What are the effects of choline deficiency?
Steatosis (fatty liver)
- due to the impairment of VLDL secretion from the liver
- likely due to the fact that choline is the precursor for PC, the main phospholipid in VLDL particles
Who is most susceptible to choline deficiency?
men and postmenopausal women
What effects does choline have on CVD?
choline is important for the methylation of Hcy into Met. High Hcy plasma concentrations are related to CVD.
What effects does choline have on intestinal health?
PC is a component of the intestinal mucus barrier
What role does Vit D play in the body?
increases absorption of Ca and P
increases bone mineralization
induces differentiation of immune cells
inhibits proliferation and ingiogensis in tumour formation
What is the best biomarker of Vit D exposure?
Serum 25(OH)D
What are the two forms of vitamin D?
D3 cholecalciferol (fortified foods) D2 ergocalciferol (plant foods i.e. mushrooms)
What influences vitamin D status?
Latitude
Pollution
Skin pigmentation
Sun screen
DRI for vitamin D
600 IU/d
What effect does Vitamin D have on CVD?
low 25(OH)D status associated with CVD risk factors
What effect does vitamin D have on immune effects?
vitamin D down regulates inflammation by macrophages
vitamin D receptor is present on immune cells and important for normal function of T cells
poor vitamin D status associated with increased risk for infectious disease
What effect does vitamin D have on diabetes?
vitamin D important for the normal function of beta cells in the pancreas which play a role in insulin production and release
What effect does vitamin D have on obesity?
when exposed to the same amount of UVB rays, serum vitamin D only goes up half that of a normal weight person in an obese person
- adipose tissue may act as a sink - vitamin D stores may be higher just not released
Acute inflammation
immediate defensive reaction to tissue damage or injury
- usually less than 3 weeks
- neutrophils recruited to site
- variabel systemic effects
- not necessarily associated with tissue destruction
- followed by healing and repair
Chronic inflammation
inordinate activation and/or insufficiently regulated immune system
- long duration
- macrophages, lymphocytes and their mediators predominate
- significant tissue damage
- systemic effects
What are the two processes that chronic inflammation can originate from?
1) follows acute inflammation
2) inflammation begins as an insidious, subclinical low grade process (chronic disease)
Biomarkers of inflammation
C- reactive protein (gold standard)
IL-1
IL-6
How do n-3 PUFAS reduce inflammation?
- change the membrane receptors and signals on inflammatory cells
- modulate expression of inflammatory and anti-inflammatory genes
- regulate eicosanoid production
- promote the function of T cells to regulate inflammation
