Lecture 4 Flashcards
interpreting anthropometric data
Determined the sensitivity and specificity of BMI, waist circumference, WHR in relation to:
-Insulin resistance
-Insulin sensitivity
-Metabolic syndrome
Sensitivity
How good a measure/test is at correctly identifying people who have the disease
which BMI cutoff for obesity is better at picking up increased risk of insulin resistance, poor insulin sensitivity, and increased risk of metabolic syndrome in Maori?
The cut off at 30 is going to be better and identifying risks
If you have a higher wasit circumference then you have
an increased risk
Growth indices
Derived from a combination of raw measurements (e.g weight-for-height)
Essential for interpretation of measurements
Used to compare individuals/groups
Head circumference: what is it called
Occipital frontal circumference
Head circumference: how to measure
- Flexible, non stretch tape (fiberglass or steel)
-over the most prominent part on back of head (occiput) and just above the eyebrows (supraorbital ridges)-> lagest circumference of head
Head circumference for age: what happens if its low
-Index of chronic protein energy deficiency (<2y)
-Low = decrease brain development
Wasting
Wasting is sometimes referred to as “acute malnutrition” because it is believed that episodes of wasting have a short duration
Stunting
Which is regarded as indicating chronic malnutrition
wasted
stunted
wasted and stunted
Thinner than normal
Shorter than normal
Thinner and shorter than normal
Weight for age: used for
Used to assess over or under nutrition
weight for age limitation
Cant distinguish tall thin children who are underweight from those who are short with adequate weight (stunting)
If rates of stunting are high but rates of wasting are low
Under nutrition under estimated
Length
-For infants and children <85cm
-Calibrated length board
-Measure infant without shoes and wearing light underclothing or nappy
weight for height: Low income countries
-Low (in children)= wasting (failure to gain sufficient weight relative to height)
-Used to identify children likely to benefit from feeding programme
Weight for height: High income countries
-Growth faltering in infants and children more likely to be identified using weight for age
-Weight for height used clinically to identify wasting in hospital patients- especially elderly
Weight for height: Limitation
Stunted -> weight may be appropriate for height ->may be classified as normal-> need to also use height for age
Oedema-. weight may appear normal for height-. need to also use height for age
height for age:Stunting
Due to extended period of inadequate food supply poor dietary quality, increased morbility in childhood (2nd or 3rd year of life
Can result in shorter stature in adulthood-> reduces capacity, poor reproductive outcomes
Height for age: Limitation
Cant identify wasted children so also need to use weight for height
Selection of growth indices: low income countries
weight for height is a good option
Height for age is not as good as an option
Reference data is used to
- Facilitate international comparisons of anthropometric indices across populations
- Evaluate trends over time (surveillance studies)
-Evaluate the effectiveness of intervention programmes
Reference data used in clinical settings
-Monitor growth
-Identify those with under or over nutrition
-Assess the response to treatment
WHO growth standard international reference data:
Growth standard not growth reference
-Growth Reference- Growth pattern of healthy population
-Growth standard - Recommended pattern of growth -> specific health outcomes and decreased long term health risks
Why? old NCHS/WHO growth reference
Growth in infancy not well characterised
-Measurements only every 3 months
-Middle class caucasian
-Formula fed
WHO growth standard -How population was defined
Multiple countries
No known health or environmental contraint or growth
-Mothers do not smoke
-Singleton birth at term
-No significant morbidity
WHO growth standard -How population was defined
0 to 24 mths- Longitudinal
-Predominantly BF birth to 4 mths and continue to BF to 12 mths
-CF introduced by 6 mnths
WHO growth standard -How population was defined
18 to 71 months -Cross sectional
some BF for at least 3 years
WHO Growth standard -why important? I
-BF is ideal method of feeding for an infant
-Exclusively BF grow differently formula fed babies
BUT: BF babies grow similarly or faster in 1st 2-3 months and then grow less rapidly
-Concern misinterpretation -> reduce mother’ confidence ->stop BF
WHO Growth standard - why important? II
-at risk of overweight= 85th to 95th centile
-Overweight = >95th centile
WHO Growth standard - why important? II
Related to 18 year old BMI of
25 (overweight) and 30 (obese)
WHO Growth standard (>5 yrs of age)
Overweight= wt-for-ht z-score >+2
Obesity = wt-for-ht z-score > +3
Evaluation of growth indices
Percentiles ….
Z-scores …..
Percentiles used in high income countries
Z-scores used especially in low income countries, but also high income countries
Percentiles
Position of the measure value in relation to all the measurements for the reference population
Percentiles : Individuals at risk
Individuals at risk- below the 3rd/fth percentiles or above the 97th/95th percentiles
Percentiles; used for
Used for evaluation of well nourished populations from high income countries
Percentiles: should not be used for
Individuals/populations from ow-income countries if using reference data from high income countries
Z-scores definition
A z-score tells us how many standard deviations an individual measurement is away from the population mean
Standard deviation tells us
about the spread of our data around the mean
The higher the spread or variability the higher the standard deviation
Z-score=
(persons measurement- reference mean)/ reference SD
If a z-score is 0 it is
If a z-score is +1 it is
If a z-score is +2 it is
If a z-score is -1 it is
If a z-score is -2 it is
The mean/median
One standard deviation above the mean
2 standard deviations above the mean
one standard deviation below the mean
2 standard deviations below the mean
Interpretation of BMI-for age cut offs
NOTES
