Changes
in total
body
water
with
age3
Dale A Schoeller
Extensive cross-sectional
studies demonstrate
a diminution
oftotal body water in elderly and very old subjects. These findings are supported
by less extensive longitudinal
studies. Cross-sectional
studies indicate that the decrease in total body water is mainly due to
ABSTRACT
decreased
Despite
little
or
aging.
intracellular
water,
the observed
no
change
in
the
AmfClinNutr
KEY WORDS
but
changes
this
is not
in total body
relationship
Intracellular
waste
water,
extracellular
removal,
and
thermal
regulation.
Water
is distributed
intraand extracellularly, and its total volume
is well regulated
in healthy
individuals
(1). The distribution
of body water is not universal, however,
but is limited
to the fat-free
compartment
of body
because
fat is anhydrous.
Pace and
Rathbun
(2) investigated
the relationship
between
the total body water and fat-free
mass and found a relatively
constant
relationship.
Pace and Rathbun
(2) therefore
suggested
that fat-free
mass and hence fat mass could be
estimated
by in vivo measurement
of total body water.
Subsequent
investigations
of
body
composition
have
generally
supported
the suggestion
ofPace
and Rathbun.
As a result it is now generally,
but not universally
(3),
accepted
that total body water comprises
72% of fatfree mass in young adults (4).
The 72% hydration
factor,
however,
is not constant
throughout
the life span. At birth, total body water accounts
for > 80% offat-free
mass (5). During growth and
development,
the absolute
amount
of total body water
increases
with body size, but its percentage
of fat-free
mass decreases
until it reaches
72% at maturity
(3-5).
During subsequent
aging, body weight and body composition continue
to change,
but generally
at a much slower
rate. Herein,
the changes
oftotal
body water, water com-
partmentalization,
aging
and
hydration
offat-free
mass
during
are reviewed.
Total body
water
Watson
water
and
et al (6) reviewed
the
selected
cross-sectional
total
body
water,
oflongitudinal
studies.
and human studies indicate
water and fat-free mass with
literature
data
Am
on total body
from
numerous
J Clin
Nuir
l989;50:
hydration
offat-free
mass
in vivo dilution
studies to calculate
mean values of total
body water for adults between
ages 17 and 86 y. Most of
the studies
included
in the review by Watson
et al (6)
used deuterium
or tritium
oxide dilution
to measure
total body water, although
a few used antipyrine
dilution.
Figure
1 summarizes
the values
from
this review.
Throughout
life, average
total body water was always
lower in females than males. In the 458 males, total body
water
was observed
to be relatively
constant
in early
adulthood
and then to begin a gradual
decline
of 0.3
kg/y until reaching
a nadir in the 70- to 80-y-old
subjects.
In the 265 females,
total body water was observed
to be
quite constant
in young adulthood
and middle
age, but
there was a dramatic
decrease
of 0.7 kg/y after age 70
y. When
the total
body
water
was normalized
by body
weight, a somewhat
different
picture
emerged
(Fig 2). In
both males and females,
the percentage
of body weight
contributed
by total
body water
gradually
decreased
throughout
early
slight increase
cate increased
adulthood
and
middle
age
indicating
a
which is presumed
to mdiAfter age 70 y, the pattern
changed.
The percentage
of total body water
increased
with advancing
age, indicating
a decrease
in body solids
which is presumed
to indicate
decreased
body fatness.
Cross-sectional
studies
like those of Watson
ct al (6)
cannot
in body solids
body fatness.
distinguish
between
true
effects
ofaging
and
arti-
facts due to sampling.
These distinctions
require
longitudinal studies,
which
unfortunately,
are very limited
in
humans.
In one longitudinal
study ofmalcs
and females
between
ages 70 and 8 1 y, however,
the above described
pattern
ofa decrease
in absolute
total body water and an
I
From
cago,
IL.
the Department
of Medicine,
University
of Chicago,
Chi-
Supported
by NIH
grants DK26678
and DK3003
1.
Address
reprint
requests
to DA Schoeller,
Department
of Mcdicine, Box 223, 5841 South Maryland
Avenue,
Chicago,
IL 60637.
2
1 176
findings
3
1 176-81.
Printed
in USA.
© 1989 American
Society
for Clinical
Nutrition
Downloaded from www.ajcn.org by guest on March 11, 2011
transport,
both animal
between
Water
is the most abundant
chemical
in the human
body and it plays a central
role in the regulation
of cell
nutrient
by the
water,
1989;50:l176-8l.
Introduction
volume,
supported
TOTAL
BODY
WATER
AND
AGING
1177
50
4846
-
44.
0
0
42
-
0
40-
0
380
01
36-
34.
0
+
32-
+
+
0
+
4.
3028
-
26-
4.
4.
22
-
20-
.
I
#{149}
20
40
60
80
AGE, y
FIG
1.
Total
70
-
68
-
body water
values in men (0) and women
(+) from cross-sectional
studies.
Adapted
from reference
6.
66
6462
60
58-
0
0
56-
0
0
:
a
50
4.
484.
46
4.
4.
-
44.
42
4.
-
40
.
20
I
1
40
60
#{149}
80
AGE, y
FIG 2. Total
Adapted
from
body
reference
water
6.
as percent
of body
weight
in men
(0)
and
women
(+)
from
cross-sectional
studies.
Downloaded from www.ajcn.org by guest on March 11, 2011
24-
1 178
SCHOELLER
increase
in the percentage
body weight was confirmed
Water
oftotal
(7).
body
water
per unit
of
compartmentalization
Hydration
of fat-free
mass
Total body water is the largest component
of fat-free
mass and can be used to estimate
fat-free
mass and fat
mass ifit can be shown that the hydration
offat-free
mass
is constant.
Two lines ofevidcnce
can be pursued
to test
whether
the hydration
of fat-free
mass remains
constant
during
aging. These are direct chemical
analysis
of cadavers or in vivo studies
in which total body water and
fat-free mass are measured
by independent
techniques.
Results
from direct chemical
analysis
are available
for
six nonedemitous
adults (4, 1 3) between
ages 25 and 63
y (Fig 4). Mean hydration
of fat-free mass was 73 ± 3%
and there was no trend with age. The number
of cadaver
analyses,
however,
is small and does not include
subjects
aged > 63 y. Using an animal
model,
Yiengst
et al (14)
determined
the fat-free hydration
ofliver
and muscle tissue obtained
from McCollum
rats at 12-14 and 24-27
m. A tendency
towards
increased
hydration
of
1% was
noted
in liver and muscle
tissue in both sexes, but the
increase
was only statistically
significant
in muscle tissue.
There are two humans
studies in which total body water and fat-free mass were determined
in vivo using mdcpendent
techniques.
The first of these was a cross-seetional study by Lesser et al (1 1) in which total body water
was determined
by isotope
dilution
and fat mass was determined
by the uptake
of a fat soluble
gas. The hydration offat-free
mass calculated
from the data ofLesser
et
al (1 1) indicated
an increase
in hydration
of 1% in 59- to
89-y-old
males relative to a 17- to 39-y-old
control
group
(Fig 5). There was no change
in the hydration
of fat-free
mass in 59- to 89-y-old
women
compared
to 16- to 38y-old women
(Fig 6). In the second
study,
Cohn et al
(15), determined
fat-free-mass
solids by neutron
activa‘‘
Downloaded from www.ajcn.org by guest on March 11, 2011
Total body water is divided
between
an intracellular
compartment
and an extracellular
compartment.
The
intracellular
water
is closely
related
to the concept
of
body cell mass, which is defined
as the potassium-rich,
oxygen-consuming,
metabolically
active
compartment
ofthe
body (8). Because
the intracellular
water is associated with the more metabolically
active compartment
of
the body than is extracellular
water, it is ofgreat
interest
to identify
whether
the changes
in total body water with
age are due to changes
in the volume
of intracellular
or
extracellular
water.
The total body volumes
ofintracellular
and extracellutar water are determined
by in vivo dilution
using principles similar
to those for measuring
total body water. Intracellular
and extracellular
water compartments,
however, are not fully defined
in an anatomical
sense, nor
are the various
tracers
for intracellular
and extracellular
water thought
to distribute
perfectly
within our concepts
of these compartments.
The accuracy
with which intracellular
and extracellular
water volumes
can be measured is therefore
not well defined.
In general,
the in vivo
techniques
depend
on measuring
total body water with
an isotopic
tracer ofwater
and extracellular
water with a
tracer that does not enter the intracellular
space. Intracellular water is measured
by difference.
Cross-sectional
studies of intracellular
and extracellular water have been performed
by a number
of investigators (9- 1 1). For the purposes
ofcomparing
these studies,
values for young subjects
between
ages 1 7 and 39 y and
elderly
subjects
between
ages 59 and 89 y are grouped
together.
Figure
3 summarizes
the results.
In males
(panel A), a modest
to large decrease
in intracellular
water was noted in elderly
subjects,
whereas
extraccllular
water was either slightly
smaller
(one study),
or slightly
larger (two studies).
In females
(panel
B), where results
for these ages groups
are only available
for two of the
three studies,
intracellular
water was found to be considerably smaller
in elderly
subjects
whereas
extracellular
water did not differ. The results ofthcse
studies
indicate
that the changes
in total body water with age are mostly
due to changes
in the volume
of intracellular
water and
hence body cell mass.
Longitudinal
studies
or colony
controlled
animal
studies do not support
the findings
ofcross-sectional
human studies
of intracellular
and extraccllular
water.
Lesser et al (12) measured
intracellular
and extracellular
water in rats from the same colony
that were sacrificed
at roughly
lOO-d intervals
between
362 and 849 d. These
investigators
suggest that each 100 d is roughly
equivalent to 10 y in humans.
Total body water increased
between 362 and 7 15 d (370 ± 9 vs 398 ± 8 g) and decreased
only slightly in the 849-d-old
rats (389 ± 8 g). Extracellular water accounted
for most of these changes
in total
body water and thus there was almost
no change in intracellular
water between
579 and 849 d. Not dissimilarily,
the longitudinal
human
study by Steen et al (7) demonstrated
that the decrease
in total body water between
70
and 8 1 y was mostly due to the changes
in extracellular
water in males and almost
totally accounted
for by the
decrease
in extracellular
water in females.
In summary,
most studies indicate
that total body water is decreased
in elderly subjects
and that it is decreased
even more in very old subjects.
It is not clear, however,
if this change
is due to a decrease
in intracellular
water,
extracellular
water or both. Cross-sectional
studies
suggest that the major
decrease
in total body water is due
to a decrease
in intracellular
water, whereas
longitudinal
studies suggest that it is due to a decrease
in extracellular
water. This difference
may be due to differences
in survival characteristics,
differences
in early or late nutrition,
differences
in early or late life styles, or difficulties
in
measuring
extracellular
water. Although
there is consistent evidence
that total body water does decrease
during
the normal
aging process,
it cannot
be concluded
that
there is an obligatory
change
in intracellular
compartment with aging.
TOTAL
BODY
WATER
AND
1179
AGING
A
80’
70
‘I
/
/
/
/
60
/
/
/
/
/
/
50#{149}
40
3O
20’
10’
J
0
young
I
#{188}
I
old
I
young
II
old
I
J
I J
I
young
II
(H
old
Ill
7
/
60
50
4/
30
:7
7
/
/
/
/
/
/
/
/
/
/\/\
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/\/\
/\
/\
/\
;;
/\
/\
/\
/\
/\
/#{188}\
20/\
t0
/\
/\
/\
k
/\7
//\
0
-
/\
v
,
/\k
/\#{216}(/Ax’\N
young
vzl
II
.
old
WI
II
mw
/\
k1
/ N
/\77:k;:i
/\:
I
-
k
kk1
..
young
ECW
/\/
N
\
/\/
YA\’
Ill
old
Ul
(0W
FIG 3. Distribution
oftotal
body water between
intracellular
and extracellular
compartments
in young (17-39 y)
and elderly (59-89
y) subjects.
Males are shown in panel A and females in panel B. I, H, and III are adapted
from
references
9, 10, and 1 1, respectively.
tion and total body water by isotope dilution
in subjects
between
ages 20 and 80 y. The hydration
constants
calculated
from this data do not show a statistically
significant trend with age. In men, the hydration
constant
was
(%H2O = 69.7
0.0035
X Age) and in women
it was
(%H2O
68.4 + 0.035 X Age), where Age is in years.
The standard
errors
of these slopes were 0.019%
and
0.0l7%/y,
respectively.
The human
data described
above
do not indicate
a
change in the average hydration
offat-frec
mass in normal
aging. Neither
direct chemical
analysis nor indirect
in vivo
_
-
methods
demonstrate
consistent
age-related
changes.
The
direct chemical
analyses,
however,
are based on a small
sample,
whereas
the indirect
methods
show considerable
individual
variation
and thus, the sensitivity
ofthe analysis
are no better than 1% or 2%. In contrast,
direct chemical
analysis of animal
tissues does demonstrate
a statistically
significant
1% change in the hydration
of fat-free muscle.
Thus, it is likely that the hydration
of fat-free mass does
increase
in normal
aging,
but the increase
is small and
would have very little effect on the estimation
ofbody
composition in healthy subjects.
Downloaded from www.ajcn.org by guest on March 11, 2011
B
70
1 180
SCHOELLER
80
-
______________________________________
79
-
78
-
77
-
76
-
75
-
0
74Li.
73-
Li.
0
0
0
72-
il::
71-
70
-
69
-
68
-
67
-
66
-
0
1
1
20
I
40
60
AGE.
FIG 4. Hydration
references
4 and
80
of fat-free
mass
in human
cadavers
yr
determined
by direct
chemical
analysis.
Adapted
from
13.
-
_
70-
_
:
I_bL1L1I_I
m:
1 7-39
m:
zzJ
FiG
5. Hydration
and fat mass
59-89
ECW
f:
1 6-38
f: 62-77
IJ
of fat-free mass calculated
from in vivo determination
of total body water
by fat soluble gas absorption.
Labels indicate
subject gender and age range. Adapted
by isotope dilution
from reference
I 1.
Downloaded from www.ajcn.org by guest on March 11, 2011
65-
TOTAL
BODY
WATER
AND
1181
AGING
80
79
78
77
76
75
74
73
72
Li.
Ii.
71
K
70
Lii
69
68
67
66
65
64
62
61
60
20
40
80
60
AGE. y
FIG 6. Hydration
and bone
mineral
of fat-free mass calculated
from in vivo determination
of total body water
mass and protein mass by neutron
activation.
Adapted
from reference
15.
In summary,
total body water
decreases
with age.
Among
women,
the decrease
is small through
middle age
and rapid after age 60 y. In men, the decrease
begins in
middle
age and continues
throughout
most of the life
span. It is not clear if the decrease
in total body is due
to a change in extraeellular
water, intracellular
water, or
both. Throughout
the adult life span, however,
the average hydration
of fat-free
mass remains
relatively
constant in healthy
individuals.
The decreases
in total body
water with age are therefore
indicators
of decreases
fatfree mass.
a
References
adult males
measurements.
by isotope
dilution
females estimated
from simple anthropometric
Am J Clin Nutr 1980; 33:27-39.
7. Steen B, Lundgren
BK, Isaksson B. In: Chandra
RK, ed. Nutrition,
immunity,
and illness in the elderly. New York: Pergamon
Press,
1985:49-52.
8. Moore
H), Olesen
KO, McMurrey
JD, Parker
HV, Ball MR.
Boyden CM. The body cell mass and its supporting
environment.
Philadelphia:
and
WB
Saunders,
1963.
9. Shock NW, Watkin DM, Yiengst MJ. Age differences
in the water
content
of the body as related
to basal oxygen consumption
in
males. J Gerontol
1963; 18:1-8.
10. Fulop T Jr, Worum
I, Csongor
J, Foris 0, Leovey
A. Body
composition
in elderly
people.
I. Determination
of body
composition
by multiisotope
methods
and the elimination
kinetics
of these isotopes
in healthy elderly subjects.
J Gerontol
1985;31:
6-14.
1.
2.
3.
Regulation
of extracellular
fluid composition
and volume.
In:
Ganong
WF, ed. Review of medical
physiology.
Los Altos, CA:
Lange Medical Publications,
1985:600-7.
Pace N, Rathbun
EN. Studies on body composition-Ill,
the body
water and chemically
combined
nitrogen
content
in relation
to fat
content.
J Biol Chem 1945; 158:685-91.
Sheng H-P. Huggins
RA. A review of body composition
studies
with emphasis
on total body water and fat. Am J Clin Nuts
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Keys A, Brozek J. Body fat in adult man.
245-325.
5. Fomon
SJ, Haschke
F, Ziegler EE, Nelson
4.
of reference
children
l982;35:l 169-75.
6. Watson
PE, Watson
from
birth
ID, Batt
to age
Physiol
Rev
SE. Body
10 years.
Am
RD. Total body water
l953;33:
composition
J Clin
volumes
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Lesser GT, Markofsky
J. Body water compartments
aging using fat-free mass as the reference
standard.
l979;236:R2
12. Lesser
water,
15-20.
GT, Deutsch
and
with human
Am J Physiol
intracellular
5, Markofsky
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in
J. Fat-free
the
aged
mass,
rat.
Am
total
body
J Physiol
l980;238:R82-90.
13. Knight GS, Beddoe AH, Streat SJ, Hill GL. Body composition
of
two
human cadavers
by neutron
activation
and chemical
analysis.
AmJ Physiol l986;250:E179-85.
14. Yiengst
MJ, Barrows
CH Jr. Shock
NW. Age changes
in the
chemical
composition
of muscle and liver in the rat. J Gerontol
1959; 14:400-4.
15. Cohn
SH, Vartsky
D, Yasumura
S. Compartmental
body
composition
based
on total-body
nitrogen,
potassium,
and
calcium.
Am J Physiol l980;239:E524-30.
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63