Malnutrition
in an Ageing Population
Authors:
Dr Dylan Harris MBBCh(Hons) MRCP
Specialist Registrar in Geriatric and General Medicine,
Department of Geriatric Medicine, Nevill Hall Hospital, Abergavenny,
South Wales
Dr Nadim Haboubi
MD(Birm) FRCP(Lond) FRCP(Edin)
Consultant Physician, Nevill Hall Hospital, Abergavenny, South
Wales
Clinical Teacher, Academic Department of Medicine, University
of Wales College of Medicine
Member of Nutritional Steering Group and Nutrition Support Team,
Gwent Healthcare NHS Trust
Secretary, Special Interest Group for Gastroenterology and Clinical
Nutrition, British Geriatric Society
Correspondence
Dr Nadim Haboubi
Day Hospital
Nevill Hall Hospital
Abergavenny
Wales, UK NP7 7EG
Telephone 01873 732158
Fax 01873 732157
|
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Dylan Harris, 29/03/2006
Nadim Haboubi 29/03/2006
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Dylan Harris, 29/03/2006
Nadim Haboubi 29/03/2006
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Nadim Haboubi 29/03/2006
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Dylan Harris, 29/03/2006
Nadim Haboubi 29/03/2006
|
Malnutrition
may be defined as a state of nutrition in which a deficiency,
excess or imbalance of energy, protein and other nutrients causes
adverse effects on body form, function and clinical outcome
(1).
The term undernutrition is often used
interchangeably with malnutrition. Undernutrition rather than
overnutrition has been agreed to be the main cause for concern
in the older population (principally due to increased morbidity
and mortality with undernutrition compared to obesity) (2).
There is no gold standard for determining
nutritional status and there are no universally accepted criteria
to define malnutrition (3) (4) (5) (6).
The elderly are a particularly nutritionally
vulnerable group. In the UK 12.4% of those aged 65 or over living
in the community at high or medium risk of malnutrition, rising
to 20.4% in people in residential accommodation and up to 40%
of patients admitted to hospital of this age (7).
| Malnutrition and the elderly population |
The prevalence of malnutrition increases
with escalating frailty and physical dependence (1) and malnutrition
has been repeatedly highlighted as an unrecognised problem with
negative consequences for physical and psychosocial outcomes
(7) (8) (9).
Malnourished older people have been
shown to be at increased risk of falls, prolonged hospitalisation,
institutionalisation, postoperative complications, infections,
pressure ulcers, poor wound healing and mortality (1) (26) and
some malnutrition screening tools include age as a specific
risk factor (such as the Nutritional Risk Screening 2002 system)
(10).
Ageing is a complex biological process, which is accompanied
by many socio-economic factors that also impact on the nutritional
status of the older individual (11).
There are a number of age-related physiological and pathological
changes relevant to nutrition.
Anorexia and weight loss are common
in the elderly and the anorexia of ageing describes the physiological
decrease in appetite and food intake that accompanies normal
ageing. (12) These processes can be augmented by acute and chronic
disease.
There are also a number of gastrointestinal
changes which may contribute (such as altered smell/taste, poor
dental health and age-related achlorhydria) and ageing is associated
with a decrease in physical activity and lean body mass and
an increase in body fat (5)(12)(13).
Key non-physiological factors are also
important: social factors (such as poverty, social isolation),
psychological factors (such as depression and dementia) and
medical factors (such as decreased visual acuity and prescribed
medication) (1)(5)(12)(14) .
Micronutrient deficiencies are more
likely in the older population (10) (15), particularly calcium
and vitamin D (related to age-related renal impairment decreasing
the hydroxylation of vitamin D, inadequate vitamin D intake,
and sunlight deprivation) with the associated morbidity and
mortality related to low trauma fractures secondary to osteoporosis
(13).
It is important to note that most factors
which may predispose to malnutrition in the elderly person (i.e.
social, psychological, physical and medical factors) are reversible
or responsive to treatment (12).
| Individual methods of malnutrition
screening |
Nutritional screening (as opposed to
nutritional assessment) is defined as the process of identifying
characteristics known to be associated with nutritional problems
with the purpose of identifying malnourished individuals or
those at risk of becoming malnourished so that a nutrition assessment
and intervention can be implemented <(16).
The screening process should be simple,
rapid and easy to use, acceptable to patients and healthcare
workers, reliable valid and have a high positive predictive
value i.e. that there is a likely health benefit for the individual
from the intervention resulting from the screening process (10)(17).
Ideally, a single nutritional marker
would fulfil the following criteria:
- consistently abnormal in patients with protein-energy malnutrition
(high sensitivity)
- consistently normal in patients without protein-energy malnutrition
(high specificity)
- nutrition-specific (unaffected by non-nutritional factors)
- normalised by nutritional support (high sensitivity to nutritional
depletion) (18)
The initial nutritional screening processes
may involve assessment of body mass index, anthropometric measures
and measurement of biochemical markers, the role of each of
these is discussed below.
(a) Anthropometry
Anthropometric indices include body mass index, skin fold thickness
at defined sites, limb muscle circumferences and waist:hip ratio.
Body mass index [BMI=weight (kg)/ height
(m2)] has been used as a method of defining undernutrition and
has been extrapolated as a single assessment of nutritional
status (19). However, body mass index may be unreliable in the
presence of confounding factors such as oedema or ascites (20)
and may fail to identify unintentional weight loss (19)(20)
.
Furthermore, measuring height reliably
in the elderly is often problematic due to an age-related decline
in sitting and standing height due to vertebral compression,
change in height and shape of vertebral discs, loss of muscle
tone and postural changes (15).
There is some difficulty in the extrapolation
of BMI cut-off values from public health initiatives (primarily
intended for people without overt disease) to clinical practice
(and often people with overt disease) and a wide range of BMI
cut-off points (<17 to <24 kg/m2) have been used to indicate
malnutrition in elderly subjects (2)(19). A reasonable cut-off
value is 20, given that a normal body function has been demonstrated
in elderly subjects with a BMI over 20 and the benefits of nutritional
support has been shown particularly in elderly people with BMI
<20 in randomised controlled trials (2).
Skin fold thickness can be measured
with standardized callipers and to be done accurately requires
a skilled technique. Up to 60% of total body fat is located
subcutaneously and skinfold thickness can be measured at various
sites: subscapular, suprailiac, biceps, triceps, thigh and calf.
Some variation in the distribution of skinfold thickness has
been observed with ageing and between sexes and different ethnic
groups (18).
Measuring arm circumference can be used
on the assumption that the mass of the muscle group measured
is proportional to its protein content and also a reflection
of total body muscle mass (18). Mid-upper arm circumference
(MUAC) is a useful indicator of malnutrition and can be used
in ill patients (normal MUAC >2cm males, >22cm females)
(21).
Anthropometric parameters are simple,
non-invasive and inexpensive measures of assessing nutritional
status (22). However, the usefulness of anthropometry as an
indicator of nutritional status is limited by its dependence
on the availability of comparative age, gender and ethnic related
data (15). Furthermore anthropometric indices are not clearly
reliable as indicators of nutritional status in any condition
causing limb oedema and there are problems of measurement error
between individual assessors.
(b) Biochemical markers
Certain serum proteins, synthesized by the liver, have been
used as markers of nutrition, namely: albumin, transferrin,
retinol binding protein and thyroxine binding prealbumin. Although
these proteins are decreased by protein-energy malnutrition
related effects (decrease in liver mass and diminished hepatic
protein synthesis) there are also a number of other factors,
which contribute, for example, infection (6)(9).
Serum albumin has often been used as
a marker of nutritional status and is predictive of mortality
and other outcomes (for example, peri-operative complications)
in older people. However, acute illness or inflammation causes
a rapid decrease in albumin levels by the production of cytokines,
which inhibit albumin synthesis and facilitate migration from
intravascular or extravascular space (23) and other catabolic
conditions and liver and renal disease may also reduce albumin
levels (13).
In addition, the relatively long half-life
of albumin means that serum albumin does not respond to short-term
changes in protein and energy intake (9).
Transferrin is a more sensitive indicator
of early protein-energy malnutrition than albumin but is unreliable
in a number of conditions including pregnancy, iron deficiency
, hypoxaemia, chronic infection and hepatic disease (9).
Whilst Retinol binding protein (RBP)
and thyroxine binding prealbumin (TBPA) possess the greatest
sensitivity to protein-energy malnutrition and have been found
to change more rapidly in response to dietary restriction and
refeeding, they also are unreliable markers in the presence
of a number of conditions such as hyperthyroidism, acute inflammation,
and trauma. (9)
A low total lymphocyte count is independently
a poor prognostic indicator and is often associated with a low
serum albumin (13). It is known that malnutrition contributes
to age-related immune dysregulation including decreased lymphocyte
proliferation (12).
A low total cholesterol has also been
correlated with risk of malnutrition (4) and assessment of vitamin
and trace element status is also important as mentioned previously
(including b1 thiamine, b2 riboflavin, b6 pyridoxine, calcium,
vitamin D, B12, folate and ferritin).
None of these biochemical markers are
entirely satisfactory as indices of nutritional status but some
may be useful in monitoring certain non-catabolic patients.
In addition, although the individual
assessment methods described (i.e. biochemical markers, anthropometry
and body mass index) correlate with significant morbidity outcomes
(such as risk of infection and postoperative complications)
and mortality (6)(9), no single assessment method meets all
the criteria set out above and a move toward the use of screening
tools has developed. Two such tools are described below.
(c) Malnutrition Screening Tools
There are over 50 published nutrition
screening tools with differing criteria and scoring systems
(2). A number of these tools are not supported by sufficient
reliability and predictive validity data or a defined area or
use (hospital or community).
The Malnutrition Universal Screening
Tool (MUST) derives a score classifying malnutrition risk (as
low, medium or high) on the basis of three components:
(a) BMI,
(b) history of unexplained weight loss
(c) acute illness effect (2)
MUST was primarily developed for use
in the community but has also been demonstrated to have a high
degree of reliability, practicability and predictive validity
(of length of hospital stay, mortality in elderly wards and
discharge destination in orthopaedic patients) in the hospital
environment (2)(10) and rates of hospital admissions and GP
visits in the community (2).
The Mini Nutritional Assessment (MNA)
was developed to evaluate the risk of malnutrition in the elderly
in home-care programmes, nursing homes and hospitals (10). It
has been suggested that the MNA is more likely to identify frail
elderly patients at risk of undernutrition as it encompasses
physical and mental aspects of health (10)(16)(23). The screening
component comprises a score derived from six components:
(a) reduced food intake in the preceding three months
(b) weight loss during the preceding 3 months
(c) mobility
(d) psychological stress or acute disease in the preceding 3
months
(e) neuropsychological problems
(f) body mass index (16)
The MNA has predictive validity for
adverse health outcome, social functioning, mortality and rate
of visits to the general practitioner as well as length of hospital
stay, likelihood of discharge to a nursing home and mortality
(10) (16). A score of 11 or more on the screening component
of the MNA predicts absence of malnutrition with 100% sensitivity
and 100% negative predictive value (24). The MNA as also been
demonstrated to be practical and reliable (10)(25)(26).
A number of physical, mental, social
and environmental changes which take place with ageing, may
affect the nutritional status of elderly people. Given the expanding
elderly population, the prevalence of malnutrition risk in this
population and the potential of appropriate screening processes
to remove this risk, nutritional screening should be given a
high priority.
A number of screening methods exist,
use of individual markers for malnutrition screening has significant
limitations and screening tools are better suited to facilitate
this process.
Nutritional "screening tools",
using combinations of markers of malnutrition have been demonstrated
to be simple, rapid, acceptable, reliable and valid methods
of nutritional screening.
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