Lifestyle Measurements Flashcards
What are the lifestyle markers?
- Physical Activity
- Nutrition
Physical activity measures
*Needed for the descriptive epidemiology of physical activity (i.e. variation in physical activity by age, sex, race, ethnicity, health status, and geographic location)
*To track population trends in physical activity over time
*For assessing mediators of physical activity
*To evaluate effectiveness of interventions designed to increase the level of physical activity
Methods of assessment for physical activity (in general)
- Occupational classification
- Behavioural observation (energy expenditure, indirect calorimetry, pedometer, accelerometer)
- Physiological markers (heart rate monitors, doubly labelled water)
- Dietary intake
- Motion sensors
- Self-reported questionnaires
- Occupational and leisure-time physical activity habits
Validity of PA questionnaires
- Questionnaires can be cost and time-efficient
- How do we know that it produces valid results?
- 24hrs surveillance is impractical – so validation through dietary intake, physiological variables, heart rate monitoring, motion sensors, direct or indirect calorimetry, body fat, blood pressure, blood lipids, etc.
- Most physical activity questionnaires aim to estimate energy expenditure due to specific types of physical activity (household, occupation, leisure activity).
Types of PA questionnaires
To obtain physical activity information from a large number of individuals in a time- and cost-efficient manner:
Many different questionnaires:
- Time period over which activity is assessed
- Type of activity
- Outcome measurement
Example: Minnesota leisure time physical activity questionnaire: interview-administered instrument, recall list of leisure-time physical activities over the past year, outcome scored as an activity metabolic index per week based on MET values.
OR Harvard alumni physical activity survey
Examples of PA questionnaires
Minnesota leisure time physical activity questionnaire: interview-administered instrument, recall list of leisure-time physical activities over the past year, outcome scored as an activity metabolic index per week based on MET values.
OR
Harvard alumni physical activity survey.
OR
International physical activity questionnaire (IPAQ)
OR
Global physical activity questionnaire
Health related components of PA
Attribute that has a genetic basis but also sensitive to changes in type and amount of physical activity, especially as people age.
Health related components:
- BMI
- Subcutaneous fat distribution
- Abdominal visceral fat
- Bone density
- Strength and endurance of the muscles in the abdomen and low back
- Heart and lung functions
- Blood pressure
- Glucose and insulin metabolism
- Blood lipoproteins
- Ratio of lipid carbohydrate oxidation
Summary of Physical Activity
Introduction of commonly accepted definitions and measures of physical activity and physical fitness.
Physical activity occurs in many forms, intensities and amounts.
Relation with development of disease and premature death can differ between studies.
Important for forming public policy.
Nutrition markers
Nutritional Epidemiology
Dietary measurement
Nutrient Database
Body composition/anthropometry & obesity and mortality
Total energy intake
Biochemical assessment of nutritional status
Types of diet studies
Descriptive – person, place and time
Migrant studies
Analytic epidemiology
- Case-control
- Cohort
Experimental
- Animal
- Human
Mechanistic – e.g. lipids, muta-genicity, hormones
How do we measure diet?
Food intake
- Short-term: 24 hour recall, diet records
- Long-term: diet history, food frequency
Biochemical
Anthropometric – body composition
Objective of dietary measurement?
Assessment of long-term intake
Individual versus group
Absolute intake versus ranking
Sources of error in long-term measure
Recall (use, frequency, size)
Coding (interpretation, size)
Nutrient database
- Natural variation due to variety, soil, ripeness, storage, etc
- Processing
- Lab error
Variation over time (e.g. seasonality)
Advantages: foods vs nutrients
Advantages of studying nutrients:
- Effect may be missed if nutrient is distributed over many foods.
- Veritas: Effects are ultimately related to specific substance.
- For supplementation specific identity is necessary.
Advantages of studying foods:
- May miss an important effect if correct nutrient or other substance is not measured
- Dietary recommendations can be made without identifying specific chemicals
- Foods are extremely complex – a food could contain an antagonistic factor to a nutrient
Optimal – Look at both
- Evidence is enhanced if nutrient effect is seen, and similar effect is seen for several foods rich in this nutrient
- Recommendations for eating foods should have empirical basis
Advantages of administering a Food Frequency Questionnaire
Advantages:
- Cost: Self-administered – computer-processed
- Easy for participant
- Provides time-integrated data
- Provides data on foods directly
- Relatively advantageous for nutrients with large within-person variation
Disadvantages:
- Many misclassify individuals with unusual diets – culture-specific
- Errors not random
Eg. small change in income may change diet in developing countries (e.g. use of cow milk)
- Bias of current intake
Approaches for evaluating dietary questionnaires
Various approaches have been used to assess performance of FFQ including:
- Comparison of means
- Proportion of total intake accounted for by foods included on the questionnaire
- Reproducibility
- Validity (comparison with independent standard)
- Comparison with biochemical markers
- Correlation with a physiologic response
- The ability to predict disease
Summary of dietary measurement
Optimal dietary intake method depends on study setting.
In many situations, FFQ is only option.
Validity is sufficiently established such that important effects will not be missed and null results will be informative for most nutrients.
Low cost means that diet can be measured in almost any study remotely involving nutrition and in large, prospective studies.
Nutrient database
Food composition
- nutrients
- energy sources
- natural toxins
- other natural compounds
The uses of nutrient database
- Government
- Research institutions
- Manufacturers
- Health care facilities
- Import/export organisations
- Supermarkets
- Consumers
- Educators
Issues in establishing/maintaining a database
- Requires appropriate analytical methodologies
- Requires standards
- Requires compilation of data
- Requires software interface
Nutrient database features
- Requires food composition
- Requires software
- Usually 2 general needs:
Analyse open-ended dietary data requires extensive comprehensive tables
- Food frequency questionnaires customised nutrient database
General database requirements
- Accurate
- Timely
- Uniform analytical methodology
- Comprehensive list of foods
- Specificity
- Quality control
- Completeness of data
Measures of body size and composition
Height and weight (BMI)
Measures of absolute body compartments (lean body mass proportional to height, dilution, impedance and conductance and DXA) ???
Measures of relative body components
Skinfolds (Subcutaneous fat, can be substantial inter-observer variation in measurement)
Circumference measures (information about fat distribution, waist, hip, waist-to-hip ratio and sagittal diameter)
–>
Direct measurements
self-reported
Validity:
- past recall (military or school records)
Advantages and disadvantages of BMI
Advantages:
Only information on height and wegith needed
Same definition for men and women
Frequently used: facilitates comparison with other studies
Disadvantages:
Both fat mass and fat-free mass are assessed
Ethnicity/elderly
Fat distribution is also important
Problems with BMI in the elderly
BMI less good as a marker of body fat
- Height can decrease
- Variation in loss lean body mass
Health status affecting BMI
- Reverse causation: weight loss due to poor health
Problems in obesity- mortality studies
- Lack of control for smoking
- Early disease causes weight loss (reverse causation)
- Statistical over-control for intermediates in the cause pathway linking obesity and mortality (e.g. blood pressure)
- Distinction fat mass and lean body mass
Total energy intake
Physical activity
Metabolic efficiency
Body size
Weigh change (balance)
Total energy intake implications (general)
- Energy intake may be a primary determinant of disease.
- Individual differences in energy intake may lead to extraneous variation in intake of other nutrients.
- Associations with specific nutrients may be confounded by total energy intake when energy intake is related to disease.
- Total energy intake is largely out of direct control of individual
- Long-term balance cannot be measured in epidemiologic studies – calories are actually negatively correlated with obesity
- All else equal, even a small excess in calories may result in obesity (i.e. depends on metabolism)
TEI implications for specific nutrients
Biological
- Crude: Specific requirement for (or effect on) an organ (eg. calcium -> bone)
- Adjusted: If metabolised or consumed in proportion to total intake
Public health
- Question is how does the composition of the diet affect disease?
–> adjusted
TEI practical implications
- Adjustments can correct for over/under reporting
- All variables (including energy) are measured imperfectly
Residual confounding
Can check in validation study
Summary of total energy intake
Isocaloric analyses (adjusted for total energy intake) should be conducted in almost all epidemiologic studies.
Total caloric intake has major implications for interpretation of other nutrients: best to measure it!
Validation studies should examine calorie-adjusted as well as crude nutrients.
Biochemical assessment of nutritional statues
Objectives:
To measure long-term dietary intake
To measure nutritional status
Uses:
Indicators of specific nutrient intakes
To validate alternative measures of nutrient intake (e.g. FFQ)
Advantages and disadvantages of biomarkers of diet
Advantages:
- Objective
- May represent information not available from food intake data
- Especially for nutrients which are highly variable in individual foods
- May be available in retrospect (analysis of stored samples
Disadvantages:
- May not be sensitive to intake
- May not be time-integrated
- Markers not available for many nutrients
- Specimens may be difficult to obtain
- Can be expensive
