sia Pacific J Clin Nutr (1995)4: 57-58
Body composition and aging: a practising
clinician's point of view
Derek M Prinsley
19/37 Foley St, Kew, Victoria 3101, Australia
Human size and shape vary widely. Relative obesity
or apparent under nutrition may not limit survival into old age.
Normal body appearance can mask gross malnutrition, particularly
mineral and vitamin deficiency, problems of measurement in the elderly.
Obesity is associated with joint degeneration and systemic disease
but with reduced incidence of fractures. Undenutrition is associated
with skin breakdown, poor wound healing and fractures. Body composition
changes due to disease include dysphagia, myxoedema, anaemia, chronic
cardiac and renal disease. Skeletal changes include osteoporosis
and Paget's disease. Body composition can change due to treatment,
control of dietary energy intake and tube-feeding.
It is not practical to generalize about changes in
body composition of elderly people. Fortunately aging does not affect
all body tissues and functions uniformly and simultaneously. The clinical
impression that most old people are thin and frail is then contradicted
by the picture of robust, active and bright 80 year-olds off to bowls
or the University of the Third Age.
Certain inevitable changes have to be faced due to
physiological aging of body tissues, particularly collagen. There
are widespread consequences from reduced elasticity and stiffening
with aging of this structural item of body composition. A very early
effect is the stiffening of the ocular lens which results in a need
for reading glasses by the age of 50 for many people. Skin wrinkles
and thinning hair are external signs of aging changes of body composition.
Internal organs are also aging.
The liver becomes smaller and has diminished blood
flow with consequent reduced protein synthesis and ability to metabolize
drugs. Kidney size diminishes with parallel loss of glomerular and
tubular substance. Fewer functioning nephrons and reduced blood flow
results in vulnerability to renal insufficiency in any acute illness.
Ideal body weight in old age covers a wide range but
it seems that significant levels above or below this range carry increased
mortality risk. At what point is intervention justified? Overindulgence
in food may be the only pleasure in old age but often stems from bad
habits in earlier years with both cultural and genetic factors involved.
Reduced physical activity and accompanying reduced appetite often
leads to weight loss. Unchecked weight gain soon becomes obesity which
leads to degenerative arthritis, diabetes and hypertension. Overeating
is usually denied. Probing enquiries into food intake will often reveal
a pattern of almost continuous snacking. 'Only a sandwich' needs to
be described, particularly in the USA. The enormous quantity of filling
plus sauce plus 'French fries' is not just a snack. Frequent fare
of this type is far in excess of energy needs. Food availability,
financial resources, ethnicity and geography all have an influence
on body composition of people reaching old age. Body weight finally
tends to stabilize by coordination of level of physical activity,
economic access to food and activity of hypothalamic centres for appetite
and satiety.
Physicians are aware of a multitude of social and
medical risk factors which may upset this physiological stability.
Adverse social conditions include poverty, bereavement and isolation.
Poor housing and cooking facilities, lack of food storage and decent
local food shops exacerbates life-long bad food habits. Immobility,
alcohol and bad weather are further reasons for prolonged mismanagement
of nutrition.
Chronic neurological conditions with feeding difficulty,
depression, arthritis, failing eyesight and poor dental health are
to be added to more florid conditions which are medical risk factors.
A clinician needs to be fully aware of less obvious background factors
in health care of elderly patients which may only come to light when
a home visit is made.
Disease caused by malnutrition may be discovered in
apparently well-nourished patients. Zinc deficiency presents with
a complex nonurgent clinical picture without evidence of change in
body composition. Scurvy always produces anaemia but calorie intake
is otherwise adequate to maintain body weight in this malnutrition
disease.
Measurement of body composition in the elderly is
no easier than in other age groups. Haematological indices can be
accurately measured and should be within normal range for all age
groups. Biochemical indices in healthy old people have wider ranges
for both low and high 'normal' levels. Anthropometry, apart from weight
measurement, is full of practical difficulties. Measurement of height
is disturbed by the stooped posture of many old people. A calculation
of height can be made from iliac crest to knee joint in bedfast or
chair fast patients. This measure is not affected by osteoporosis.
Arm circumference seems to be unreliable due to muscle wasting and
centripetal redistribution of body fat. Waist and hip circumference
ratios are also unreliable due to general loss of abdominal muscle
tone. Bioelectrical impedance studies in the elderly suggest that
the proportion of body fat remains the same but total fat increases
due to increased body weight. Large amounts of body fat and reduced
muscle mass have important implications for drug management.
Avoidance of obesity in old age is clearly indicated.
The major geriatric diseases of stroke, diabetes, hypertension and
arthritis are all associated with obesity. Elderly diabetics suffer
accelerated arterial degeneration. While diet control is the obvious
approach to management this is less than satisfactory where food is
there and resolve is lacking. The USA practice of treating all elderly
diabetics with insulin rather than attempting diet control is understandable.
We tend to visualize little old ladies as ideal, implying
that thin and small is good. However, recent life tables of insurance
companies seem to indicate that being moderately above accepted normal
weight for age and height carries a better prognosis for long survival.
Body composition can be drastically affected by diseases
which are common in geriatric practice. Fluid overload in congestive
heart failure is readily recognized. Increase in body weight and apparent
fluid retention in thyroid deficiency is less obvious. Loss of bone
mass and skeletal changes due to osteoporosis are more of a challenge.
Vertebral body compression with height loss is more apparent than
changes in bone shape of the mandible which results in the foramen
for exit of the mandibular nerve becoming directly and painfully compressed
when chewing harder fibre containing foods. The cycle is thus established
for soft foods only, increasing constipation, loss of appetite and
loss of weight.
The most significant aspect of changes in body composition
in old age for the clinician is in the use of drugs. Many older patients
are justifiably on treatment for more than one disease with multiple
potent drugs. Unwanted and unexpected effects associated with old
patients are becoming better understood with development of clinical
geriatric pharmacology. Absorption, distribution, metabolism and excretion
of drugs are all altered by changes in body composition.
General unreliability about which drug, which dose
and when to take it is only the beginning of medication problems.
After the drug has been swallowed absorption takes place into a generally
less hydrated body. Older people have diminished thirst sensation
and do not drink enough. Consequently distribution of water soluble
drugs occurs in increased concentration. This includes alcohol which
is rapidly absorbed through the stomach. Older people have increasing
difficulty in handling alcohol and the wiser ones learn to limit their
intake.
Increased body fat stores create hazards with fat
soluble drugs. Typical problems caused by hypnotics are related to
storage of early doses in fat depots with consequent apparent I ineffectiveness.
Increased doses are prescribed and the full potential of the drug
then is revealed. Toxic drowsiness will persist for days even if the
hypnotic is discontinued immediately. The fat stored drug continues
to be released into the circulation for several days.
Drugs which are stored in muscle may reach toxic levels
because more free drug remains in the circulation when muscle mass
is reduced. Digitalis is stored in muscle. Older patients do not require
a loading dose and maintenance doses < are smaller.
Serum albumen levels in old age may be low which indicates
that drugs which are usually protein bound may be in the free form
in large amounts. Competitive binding in the: reduced albumin pool
may result in one of two normally protein-bound drugs being released
in toxic quantity. For example, bound warfarin may be displaced by
another acidic binder such as aspirin, causing bleeding.
Drugs which are metabolized and broken down in the
liver depend on integrity of the liver. Liver mass and liver function
diminish with increasing age and allowances must be made by prescribing
smaller doses and restricting use of some drugs.
Metabolized drugs are excreted through the kidneys.
Drugs which are not broken down, such as digitalis, are excreted intact
through the kidneys. Kidney size and function diminishes but does
not impede drug excretion unless renal disease is also a factor. Impaired
renal function tests make for caution in drug management.
Clinical trials of new drugs have used younger adults
but recently trials have included older subjects and drug manuals
are increasingly showing adult and geriatric doses. Pharmacology of
old age is now receiving recognition.
Clinicians treating acutely-ill old patients have
major concerns with fluid. Dehydration and failing cardiac and renal
function are priority issues. Fluid overload in congestive heart failure
requires equally urgent treatment. Other body components are barely
considered in emergency situations. In less acute conditions, and
in general long-term supervision of elderly patients, more attention
can be directed towards body composition as a whole and the possibility
of modification if indicated.
There is scope for education of older people about
lifestyle, nutrition and use of drugs. The importance of weight control
needs to be emphasized. A daily half-hour walk and cutting out saturated
fat in the diet were the conclusions reached by a recent Conference
on Nutrition and Fitness in Athens which should help us all, including
the elderly, to reach an Olympic ideal. Drinking more fluid would
also seem to be useful advice for the majority of older people. Many
of the changes in body composition cannot be influenced and need to
be kept in mind particularly in medication. Any possible improvement
would be achieved mostly by weight control and better nutrition. The
best contribution the clinician can make is to be fully aware of important
changes in body composition of the elderly and act accordingly.
Bibliography
- The adult. Chapter 5 in Human body composition.
Gilbert B. Forbes - 96394 - 4. Springer-Verlag, 1987.
- Estimating Body Composition in Children and the
Elderly. Chapter 6 in Advances in Human body composition assessment,
Timothy C;. Lohman.
- Nutrition and Aging, Clinics in Applied Nutrition,
vol 1, No 4, 1991.
- Steen B. Body composition. In Horwitz A, MacFayden
DM, Munro H, Scrimshaw NS, Steen B, Williams TF eds. Nutrition in
the Elderly. Oxford: Oxford University Press, 1989.
- Warne RW, Prinsley DM, eds. A manual of geriatric
care. Williams & Wilkins, 1988.
Copyright © 1995 [Asia Pacific Journal of Clinical
Nutrition]. All rights reserved.
Revised:
January 19, 1999
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