Hyperhydrating
with glycerol: implications for athletic performance.
Wagner DR. Exercise and Sports Science Department, Vanguard
University of Southern California, Costa Mesa 92626, USA.
J Am Diet Assoc 1999 Feb; 99(2): 207-12 PMID: 9972189 UI:
99138136
Small decreases in hydration status can result in a dramatic
decrement in athletic performance and greatly increase the
risk of thermal injury. Because of its osmotic properties,
which enable greater fluid retention than the ingestion
of water alone, glycerol has been proposed as a hyperhydrating
agent. In fact, glycerol is now commercially available and
marketed as a sport supplement to be ingested with water
or sport drinks; thus, dietitians need to be cognizant of
this new addition to the sports nutrition table. The results
of glycerol-induced hyperhydration research have been equivocal,
most likely because of methodologic differences between
studies, such as variations in the intensity of exercise,
environmental conditions, and concentration or dose of glycerol
administered. Although the suggested dosage of glycerol
depends on body size and varies between manufacturers, 1
g/kg body weight with an additional 1.5 L fluid taken 60
to
120 minutes before competition is standard. Some test subjects
reported feeling bloated or nauseated after ingesting glycerol.
This review examines glycerol-induced hyperhydration research
and the safety of ingesting glycerol, discusses commercial
availability of glycerol, and makes recommendations for
glycerol-induced hyperhydration research.
Plasticising effect of water and glycerin on human skin
in vivo.
Pedersen LK; Jemec GB. Dept. of Dermatology D, Bispebjerg
Hospital, University of Copenhagen, Denmark. J Dermatol
Sci 1999 Jan; 19(1): 48-52 PMID: 9890375 UI: 99105381
Application of water and glycerin is known to influence
skin mechanics. The kinetics of these processes are of great
interest. A study was performed to show the immediate changes
in skin-mechanics. A Dermaflex machine (R) was used to study
23 healthy volunteers. Water or glycerin was applied to
the flexorside of the forearm, and readings were made after
3, 6, 9, 12 and 15 min. Regional untreated skin served as
baseline. In agreement with earlier studies both substances
influenced hysteresis. Water caused a significant increase
in hysteresis after 12 and 15 min of hydration (P<0.01).
Glycerin caused significantly increased hysteresis after
3 min (P<0.05) and the effect continued to the end of
the observation period. No significant differences were
seen in the distensibility. The onset of action is rapid
for both substances, and the effects are therefore supposed
to take place in the outermost layers of epidermis. The
effect of glycerin on the hysteresis is more rapid in onset
than that of water. Comparing the permeability coefficients,
the effect on the mechanical properties of the skin does
not appear to be determined by the permeability coefficients
as water has a higher permeability coefficient but induces
smaller changes than glycerin. Water alone does not appear
to be the optimal plasticiser of human skin and other substances
soluble in both water and lipids may have an even greater
influence on skin mechanics in vivo.
The effect of glycerol and desmopressin on exercise performance
and hydration in triathletes.
Inder WJ; Swanney MP; Donald RA; Prickett TC; Hellemans
J. Department of Endocrinology, Christchurch Hospital, New
Zealand. Med Sci Sports Exerc 1998 Aug; 30(8): 1263-9 PMID:
9710867 UI: 98376726
BACKGROUND: Hydration is an important determinant of athletic
performance, and glycerol-containing solutions have been
demonstrated to produce a state of hyperhydration. Secretions
of arginine vasopressin (AVP) and/or other renal mechanisms
may account for reduced urine output following glycerol
ingestion. This study examined the effect of glycerol and
the AVP analog desmopressin (DDAVP) on hydration and exercise
performance in triathletes ingesting routine volumes of
prerace fluids.
METHODS: Eight male triathletes ages 19 to 43 participated.
After determination of their VO (2peak), each athlete completed
a strenuous exercise protocol three times involving 60 min
of exercise at 70% VO (2peak) followed immediately by an
incremental increase in workload every 2 min until exhaustion.
RESULTS: Pretreatment with 1 gxkg(-1) glycerol or 20 microgram
of DDAVP intranasally failed to produce hyperhydration or
any enhancement of athletic performance. There was a significant
difference in reduction in body mass between DDAVP and control
(P < 0.05) but no change in sweat volume. No physiologically
relevant differences in plasma sodium, renin, or hemoglobin
were seen with either active agent. Plasma osmolality did
have a different time course in response to exercise following
glycerol (P < 0.03) owing to a smaller incremental increase.
Urine osmolality was also raised at baseline following glycerol
(P < 0.05). Responses to exercise of plasma AVP, cortisol,
and indices of carbohydrate metabolism were similar, although
AVP was elevated following DDAVP administration (P <
0.01) owing to assay cross- reactivity.
CONCLUSION: Although maintaining adequate hydration remains
important for the endurance athlete, the routine use of
either glycerol of DDAVP before athletic training or competition
in a thermoneutral environment does not seem to confer any
advantage over conventional fluid replacement.
Modification of stratum corneum quality by glycerin-containing
external ointments
Gloor M; Bettinger J; Gehring W. Hautklinik am Klinikum,
Stadt Karlsruhe gGmbH. Hautarzt 1998 Jan; 49(1): 6-9 PMID:
9522186 UI: 98182654
The effects of glycerol are discussed in detail. Glycerol
can lead to a transition of crystalline lipid structures
within the horny layer lipids into liquid crystalline states.
Especially if applied in oil/water-emulsions it improves
the hydration of the horny layers better than urea. In addition,
if facilitates the dissolution of desmosomes within the
superior layers of the horny layer enhancing desquamation.
Furthermore, by using glycerol, the mechanical properties
of the skin can be influenced; long term used leads to increased
elasticity. The roughness of the horny layer is reduced,
which can be explained by the abrasive and/or the hydrating
effect. Glycerol used in o/w-emulsions also protects against
the influence of tensides or noxious lipophilic agents.
Presumably a flux from the base of the epidermis towards
its surface triggers the regeneration of the barrier. Finally,
glycerol can lead--similarly to ureaóto an improvement
in active agent penetration, as has been proven for hexylnicotinate.
Pre-exercise glycerol hydration improves cycling endurance
time.
Montner P; Stark DM; Riedesel ML; Murata G; Robergs R;
Timms M; Chick TW. Department of Medicine, Veterans Affairs
Medical Center, Albuquerque, NM 87108, USA.
Int J Sports Med 1996 Jan; 17(1): 27-33 PMID: 8775573 UI:
96371750
The effects of glycerol ingestion (GEH) on hydration and
subsequent cycle ergometer submaximal load exercise were
examined in well conditioned subjects. We hypothesized that
GEH would reduce physiologic strain and increase endurance.
The purpose of Study I (n = 11) was to determine if pre-exercise
GEH (1.2 gm/kg glycerol in 26 ml/kg solution) compared to
pre-exercise placebo hydration (PH) (26 ml/kg of aspartame
flavored water) lowered heart rate (HR), lowered rectal
temperature (Tc), and prolonged endurance time (ET) during
submaximal load cycle ergometry. The purpose of Study II
(n = 7) was to determine if the same pre-exercise regimen
followed by carbohydrate oral replacement solution (ORS)
during exercise also lowered HR, Tc, and prolonged ET. Both
studies were double-blind, randomized, crossover trials,
performed at an ambient temperature of 23.5-24.5 degrees
C, and humidity of 25-27%. Mean HR was lower by 2.8 +/-
0.4 beats/min (p = 0.05) after GEH in Study I and by 4.4
+/- 1.1 beats/min (p = 0.01) in Study II. Endurance time
was prolonged after GEH in Study I (93.8 +/- 14 min vs.
77.4 +/- 9 min, p = 0.049) and in Study II (123.4 +/- 17
min vs. 99.0 +/- 11 min, p = 0.03). Rectal temperature did
not differ between hydration regimens in both Study I and
Study II. Thus, pre-exercise glycerol-enhanced hyperhydration
lowers HR and prolongs ET even when combined with ORS during
exercise. The regimens tested in this study could potentially
be adapted for endurance activities.
Failure to reduce body water loss in cold-water immersion
by glycerol ingestion.
Arnall DA; Goforth HW Jr. Northern Arizona University,
Flagstaff 86011. Undersea Hyperb Med 1993 Dec; 20(4): 309-20
PMID: 8286985 UI: 94115252
The efficacy of ingesting an aqueous glycerol solution
to enhance body water retention during prolonged cold-water
dives was evaluated. Nine Naval Special Warfare divers performed
a 3-h dive in 13 degrees C water. Divers were assigned to
either a water-treatment group (WT) or a glycerol-treatment
(GT) group. WT ingested 30 ml water/kg lean body mass (LBM).
GT ingested a solution consisting of 1.2 ml glycerol/kg
LBM and 30 ml water/kg LBM. Blood was drawn at prehydration,
90 min after hydration, and 20 min after the 3-h dive for
serum glycerol, glucose, free fatty acids, lactate, and
electrolyte determinations. Fluid intake and output was
recorded and urine analyzed for osmolality, electrolytes,
and specific gravity. Serum glycerol values in GT were 200
times greater at posthydration than prehydration and 100
times greater at postdive than at prehydration. Urine output,
total body weight loss, and non-urine weight loss during
posthydration and dive sampling periods were not significantly
different between treatment groups. Hyperhydration with
an aqueous glycerol solution of 1.2 ml glycerol/kg LBM seems
ineffective in significantly reducing body water loss in
divers during prolonged cold-water immersion.
The influence of a single application of different moisturizers
on the skin capacitance.
Loden M; Lindberg M. Medical Department, ACO AB, University
Hospital, Uppsala, Sweden. Acta Derm Venereol 1991; 71(1):
79-82 PMID: 1676227 UI: 91281370
Moisturizers are believed to improve the skin condition
by increasing the water content of the stratum corneum.
A variety of techniques for assessing skin hydration has
been developed. In the present study the capacitance following
a single application of different moisturizers to normal
skin on 12 volunteers was measured with the commercial available
Corneometer 420. The moisturizers were pure petrolatum and
three oil-in- water creams. The latter contained glycerine,
glycerine and pyrollidone carboxylic acid, or urea as humectant
agents. The first measurement of the change in the capacitance
was done 2 h after application of the products. All tested
products increased the capacitance in the same order of
magnitude. For the creams the values were significantly
enhanced during the experimental period (6 h). Excess products
were removed from some skin areas after the 2 h measurement.
This caused immediately a significant decrease in the capacitance
of the cream treated sites, whereas tendencies towards higher
values were noted on the petrolatum-treated sites. These
findings indicate that the non-absorbed components influence
the capacitance values. Hence, the interpretation of electrical
measurements with respect to skin moisture should be made
with caution.
Effect of a new amino acid solution in the oral hydration
of nursing infants with acute diarrhea. A prospective study
Velasquez-Jones L; Mota-Hernandez F. Servicio de Hidratacion
Oral, Hospital Infantil de Mexico Federico Gomez. Gac Med
Mex 1990 Jul-Aug; 126(4): 315-22; discussion 322-3 PMID:
2093568 UI: 91235895
Thirty-two one- to 12-month-old male infants with diarrheal
dehydration treated with either the oral rehydration solution
recommended by the World Health Organization (WHO), or the
same solution modified by the addition of glycerine (60
mmol/L) and glycil-glycine (30 mmol/L), with a total osmolality
of 379 mOsm/kg. The patients belonging to the latter group
exhibited greater stool losses (10.3 +/- 8.3 vs 8.0 +/-
6.4 mL/kg/hour) and a greater urine volume (10.4 +/- 14.2
vs 4.6 +/- 4.0 mL/kg/6 hours), during the first four to
six hours of the rehydration period. The results of this
study show, that in contrast with those of other series,
the addition of glycine and glycil-glycine to the WHO solution,
at the concentrations used in the study, produces greater
fecal water losses in children with dehydration due to acute
diarrhea.
The kinetics of swelling in muscle exposed to hypertonic
glycerol solution.
Hummel Z. Department of Biophysics, University Medical
School, Pecs, Hungary. Physiol Chem Phys Med NMR 1988; 20(3):
241-7 PMID: 3266674 UI: 89221307
In frog skeleton muscle treated with glycerol, the efflux
of the slow potassium fraction is four times faster than
the hydration of macromolecules being a little faster than
the total swelling process. The slow K fraction is assumed
to exist in special salt linkages called intra- and intermolecular
K bridges for describing the correlation between the solubilization
of proteins and K release. Conformational change involving
helix-coil transition and cooperative effects in the K release
could produce together the time-lag between the efflux of
slow K fraction and swelling of the muscle.
Glycerol dynamics in weight-losing cancer patients.
Eden E; Edstrom S; Bennegard K; Lindmark L; Lundholm K.
Surgery 1985 Feb; 97(2): 176-84 PMID: 4038560 UI: 85115955
This study was designed to show whether weight-losing cancer
patients have an elevated glycerol turnover. Four groups
of patients were examined: weight-losing cancer patients,
weight-losing patients without cancer, cancer patients without
weight loss, and weight-stable and well- nourished hospitalized
control patients. Glycerol was infused intravenously at
three different rates (200, 400, and 800 mumol/hr/kg body
weight) after an overnight fast. This allowed measurement
of clearance and plasma glycerol turnover. Weight-losing
cancer patients (group 1) had an almost threefold higher
glycerol turnover per kilogram of body weight compared with
malnourished and well-nourished noncancer patients. However,
both malnourished cancer and noncancer patients had an elevated
glycerol turnover compared with well-nourished patients
when glycerol turnover was related to whole body lipids.
The results how that progressive clinical cancer is associated
with an elevated plasma glycerol turnover, probably indicating
an increased whole body lipolysis. This may explain the
loss of body fat during the development of cancer cachexia.
Body weight: reduction by long-term glycerol treatment.
Wirtshafter D; Davis JD. Science 1977 Dec 23; 198(4323):
1271-4 PMID: 929200 UI: 78054759
Elevation of body glycerol concentration by multiple daily
injections of glycerol was shown to lead to hypophagia and
body weight loss followed by normal food intake and normal
rate of body weight increase in rats. Termination of injections
was followed by hyperphagia and an accelerated rate of growth.
These findings suggest that the blood glycerol concentration
plays an important role in the control of body weight and
may be one signal by which the central nervous system monitors
body lipid content.
