INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
WORLD HEALTH ORGANIZATION
SUMMARY OF TOXICOLOGICAL DATA OF CERTAIN FOOD ADDITIVES
AND CONTAMINANTS
WHO FOOD ADDITIVES SERIES NO. 13
The data contained in this document were examined by the
Joint FAO/WHO Expert Committee on Food Additives*
Rome, 3-12 April 1978
Food and Agriculture Organization of the United Nations
World Health Organization
* Twenty-second Report of the Joint FAO/WHO Expert Committee on Food
Additives, Geneva, 1978, WHO Technical Report Series No. 631
XYLITOL
Explanation
Xylitol was evaluated at the twenty-first session of the Joint
FAO/WHO Expert Committee on Food Additives in 1977. Since the previous
evaluation, additional data have become available and are summarized
below.
BIOLOGICAL DATA
Long-term studies
Mouse
Groups each of 100 male and 100 female CFLP mice per group were
fed diets containing levels of 0, 2, 10, or 20% xylitol or 20%
sucrose. The diet of all groups was maintained at 20% carbohydrate
supplementation through the use of rice starch. Protein was maintained
constant in all groups through the addition of casein. A group was
terminated when 20% survival was reached. Initially the highest level
of carbohydrate in any of the diets was 10%. Subsequently, desired
levels of carbohydrate were obtained by increasing the amount in the
diets by 5% each week.
No diarrhoea was observed with up to 10% xylitol or sucrose
during the first three weeks. During the fourth week, mice receiving
15% xylitol (male and female) exhibited diarrhoea. The males also had
associated inflammation of the anogenital region. The 15% sucrose
group also showed some evidence of diarrhoea. These mice were returned
to 10% xylitol and sucrose until week seven when they again received
15% xylitol and sucrose. The same signs as above were again seen. By
week 11 the mice seemed normal and the 20% xylitol and sucrose levels
were achieved by week 14. It therefore took as long as 16 weeks to
achieve dietary accommodation to 20% xylitol and sucrose.
An overall significant increase in mortality was seen for 20%
xylitol males during the first year. Some increases in food intake was
seen for males in the 10 and 20% xylitol groups between weeks one and
106 and for females in these groups between weeks one and 80. The 20%
sucrose group showed increased food intake for the first year of the
study. Males in the 10 and 20% xylitol groups as well as 20% xylitol
females had decreased body weight gains. Water intake was increased
for the 20% xylitol males.
Macroscopic examination indicated a large increase in the
incidence of urinary bladder calculi, urinary bladder nodules and
masses, and urinary bladder distention for the 10 and 20% xylitol
males. No similar effects were seen in the 2, 10, and 20% females, 2%
xylitol males, or the 20% sucrose group. Histological examination of
the 10 and 20% xylitol males revealed hyperplasia, metaplasia, and
neoplasia of the transitional epithelium of the urinary bladder in
male mice, associated with the macroscopically observed calculi. No
metastasis was observed in the bladder tumours. The incidence of
treatment-related tumours, metaplasias or neoplasias was not increased
for the 2% xylitol males nor the 2, 10, and 20% xylitol females.
Analysis of the bladder calculi indicate they are composed of calcium,
phosphate, and oxalate. In the 20% sucrose-fed males there was an
increase in kidney lesions described as cellular infiltration.
Macroscopic examination of mice dying during the study revealed a
statistically significant, dose-related reduction in the number of
male mice bearing liver masses treated with xylitol, as compared to
controls. Among mice killed at termination a lower prevalence of liver
masses was recorded for males treated with 10 or 20% xylitol and
attained a level of statistical significance (P 0.05) when compared to
controls. Histologically, the liver masses were mainly benign
adenomas, a small proportion had a structure suggestive of carcinoma.
The prevalence in the sucrose group was similar to controls. The
differences were statistically significant when 10 and 20% xylitol
males were compared to controls and when 2, 10 or 20% levels of
xylitol compared to 20% sucrose group.
The incidence of hepatocellular tumours (benign) was increased
for the 20% sucrose females. Male 20% sucrose mice also showed an
increase in fatty degeneration of hepatocytes (Hunter et al., 1978b).
Rat
A total of 75 male and 75 female Sprague-Dawley rata of the CD
strain were included in each dosage group. Each group consisted of 50
male and 50 female rats for tumorigenic evaluation (104 weeks), 15
male and 15 female rats for laboratory investigation, and 10 male and
10 female for interim sacrifice of five male and female rats at 26 and
52 weeks. Xylitol was fed at 0, 2, 5, 10, and 20% of the diet. In
addition, one group received 20% sucrose in the diet. All animals were
derived from parents exposed to the respective test diets for 60 days
prior to mating. Following parturition, the diet of all treated dams
was reduced to 5% and gradually increased to the desired levels of 5,
10, 20% xylitol and 20% sucrose. The diet of all groups was maintained
at 20% carbohydrate supplementation through the use of rice starch in
the 0, 2, 5, and 10% groups. Protein was maintained constant in all
groups through the addition of casein. For the 10 and 20% carbohydrate
groups (xylitol and sucrose) the carbohydrate was increased 5% per
week until the desired level was attained.
Lower body weight gain was recorded through the first 78 weeks of
the study for males and females receiving 5, 10, or 20% xylitol. This
decreased weight gain was coupled with a dose-related impairment of
food utilization efficiency for males and females in the 5, 10, and
20% xylitol groups. The 20% xylitol females had statistically higher
water intake during weeks 26, 52, and 78. Urinalysis indicated
increased urine volumes for the female 20% xylitol group. Twenty per
cent. sucrose caused increased urinary protein levels during the first
26 weeks of treatment in some males and females. Haematologic
examination indicated no xylitol-related effects through 78 weeks. At
terminal sacrifice, the 20% xylitol males did, however, show lower PCV
values and RBC counts. For up to 52 weeks, lower alpha-2-globulin was
found in all xylitol-treated males. Lowered SGPT was recorded for 20%
xylitol females at 13 weeks. Lower lactate levels were recorded for
xylitol animals at 26 weeks but not at 52 weeks. Haematological and
clinical chemistry values of serum were within normal limits with the
exception that sucrose treatment increased cholesterol in males at 52
weeks and males and females at 78 weeks. No increased cholesterol was
noted at terminal sacrifice for the sucrose group. Sucrose also
increased insulin levels at 26 and 52 weeks but returned to normal at
78 weeks. Male sucrose animals had elevated insulin at terminal
sacrifice.
At autopsy macroscopic examination indicated that 20% xylitol
treatment caused enlargement of the caecum. No other treatment-related
gross pathological or ophthalmoscopic changes were noted. Organ weight
analysis indicated higher liver weight ratios at 26 weeks for males
receiving 5, 10, and 20% xylitol and females receiving 5 and 10%
xylitol; such effects were not seen at 52 weeks or terminal sacrifice.
At terminal sacrifice, lower absolute thyroid weights were recorded
for males and females in all treated groups but was most marked in the
20% xylitol and sucrose groups. The relative thyroid weights were
decreased only for the 20% xylitol males and 20% sucrose females. No
other treatment-related effects were seen on organ weights.
Histological examination of the animals indicated no treatment-related
effects on the major organ systems. However, the incidence of both
unilateral and bilateral hyperplasia of the adrenal medulla was
significantly increased in males treated with 10 and 20% xylitol and
among females treated with 5, 10 and 20% xylitol. The adrenal
medullary hyperplasia also was strongly dose related and was confined
to only one gland in the control groups. Additionally, a significant
increase in phaeochromocytoma was foundin the 20% xylitol males
(Hunter et al., 1978). For statistical comparison of phaeochromocytoma
the 2% xylitol and control groups were combined.
Dog
Xylitol was administered in the diet of pure-bred beagle dogs
(eight male and eight female animals per group). Dietary concentration
of 0, 2, 5, 10 and 20% xylitol were attained by a gradual increase of
xylitol at the expense of starch. The 20% dietary level was reached by
the fifth week. A further group received 20% sucrose for comparative
purposes. Rice starch was included in the diets of groups receiving 0,
2, 5, and 10% xylitol, so that in each case the diet consisted of
80% normal diet and 20% carbohydrate. After week 42 diets were
supplemented with 5 ml corn oil (during weeks 42-48 once/day, week 48
onward once/week). After 52 weeks there was an interim sacrifice of
two males and two females per group. The study was terminated at 104
weeks.
The 20% xylitol and 20% sucrose groups left significantly more
food than the control group. The 2% xylitol group gained less weight
than controls. All other groups gained more weight than controls.
Haematological parameters and analysis were within normal limits
during the course of the study. Clinical chemistry studies showed that
from week 12 onwards slightly elevated total serum protein levels were
recorded in 20% xylitol group. Particularly in the first year, but
also in the second year, the 20% xylitol group had elevated SAP
values. At almost every interval, SGPT for 20% xylitol group was
elevated. In the second year this was also true for the 10% xylitol
group. Total LDH and alpha-HBDH showed considerable variation. During
weeks 89 and 100 the values for the 20% xylitol group were elevated.
At autopsy there was a significant increase in liver weight in
the 20% xylitol group. Changes in periportal hepatocytes were detected
histologically in at least five of 12 dogs in this group. Electron
micrographic analysis suggested that the changes in hepatocytes
observed were consistent with alterations in glycogen storage. No
evidence of degeneration or necrosis was noted. Similar histological
changes were found in the hapatocytes of three and 12 dogs in the 10%
sucrose group. No other compound-related changes were reported
(Heywood et al., 1977).
Reproduction studies
Rat
A three-generation study was conducted in Sprague-Dawley (CD)
specific-pathogen-free rats with 20 males and 20 females respectively
per group. Each group received the test material by dietary
administration. A control group received 20% rice starch, and a
comparison group 20% sucrose ad libitum. Graded diets of xylitol, 2,
5, 10 or 20% were fed to treatment groups with rice starch q.s. to
bring the level to 20%. For xylitol groups receiving diets greater
than 5%, administration began at the 5% level with 5% weekly
increments until final doses of 5, 10, 15 or 20% were reached. During
parturition, the diets were reduced to 5% xylitol. As soon as possible
after parturition of second litters of each generation, dams receiving
diets greater than 5% were returned to this level. Males and non-
pregnant females continued to receive the full dose. After weaning,
the dose administered to F1b and F2b generations were progressively
increased until full treatment level was attained. The gradual
increase to concentrations greater than 5% and the reduction of
dietary doses during lactation was considered necessary to avoid
diarrhoea and stress associated with exposure to high concentrations
of xylitol. The pups of the F1a, F2a, and F3a generations were
weighed and killed at four days and examined for sex determination or
abnormalities. The F1b, F2b, and F3b pups were weighed, sexed, and
litters culled to eight per dam. Pups were weighed at 8, 12, and 21
days post partum. Observations were made to determine litter size,
litter and pup weights, pup mortality, and gross abnormalities. Gross
and histopathological observations were conducted on rats of the F3b
generation, which were killed at three weeks of age.
Mortalities of parents were randomly distributed. No obvious
clinical signs were noted. At low diet levels (2 and 5%) food intake
was comparable with controls in all generations. At 10% xylitol food
intake was slightly but consistently lower in the second generation.
At the 20% level slight depression of food intake of the F0, and
marked suppresion in F1 and F2 generations was seen, even when
xylitol concentration was reduced to 5%. With this group consistent
but generally marked suppression of food intake was noted in all
generations even at the lowest level fed. With the sucrose group food
intake was comparable with or slightly greater than that of the
control group in all generations. At the lower levels, weight gain of
males of the first generation (2, 5, or 10%) was comparable to the
control group, slight suppression occurred at the 10% level during the
second generation, and at all concentrations in the final generation
(F3b). There was no treatment effect on mating performance and
pregnancy rate. At the highest level (20%) a larger proportion of
litters was born on day 23 or 24 compared to controls, or sucrose.
Caecal enlargement was noted at terminal necropsy of F2b parents of
both sexes for levels greater than 2%.
At the 20% dietary level of xylitol there were lower values for
total and viable litter size at birth and at day four post partum.
This became more accentuated with successive generations. Litter and
mean pup weights were greater than concurrent control values except
for 20% xylitol at which level lower litter weights reflected smaller
litter size. Initially among the F1a pups, when litter size was not
culled, a large mortality was noted between seven to 10 days post
partum. The litter size was culled to eight with the succeeding
generations, at which time no total litter loss was observed. There
was no indication of a treatment effect on occurrence of terata.
Statistical assessment of organ weight data showed in most instances
changes related to differences in body weight. Statistically
significant lower absolute thyroid weights were noted with 20%
xylitol. Other organ weight changes appeared sporadically, unrelated
to treatment. Histopathologically tissues from 10 and 20% xylitol
groups did not show microscopic changes that could be attributed to
xylitol (Palmer et al., 1978).
Special studies
Teratology
Rat
Groups of 31-33 CFT strain-specific pathogen-free female weanling
rats received test diets containing either 20% rice starch, 2, 5, 10,
20% xylitol, or 20% sucrose. The test diets were administered for five
weeks before mating. Groups receiving dietary concentrations greater
than 5% were acclimated to the final dosage by beginning at the 5%
level and weekly increments to the final concentration. Males received
laboratory diets only. After females were acclimated to the final
dietary concentrations they ware mated. Parameters investigated
included food consumption, body weight change, mating performance,
litter data including implantations, pre-implantation loss, litter and
mean foetal weights, major malformations and minor abnormalities, and
skeletal variants.
There was a low overall pregnancy rate of approximately 50% for
all groups. No clinical signs of toxicity were noted. Five major
malformations were noted in test groups receiving xylitol, and two in
the group receiving sucrose. These had been previously seen among
control pups and not attributed to treatment since there was no
relationship to dose level. No skeletal variations were attributed to
treatments. Other parameters were within normal limits (Palmer and
Bottomley, 1977).
Rabbit
Groups of 20 yellow-silver does of a closed, randomized outbred
rabbit strain, aged three to four months and weighing 2.7-3.0 kg
received test diets ad libitum containing 2, 5, 10 and 20% xylitol
or 20% sucrose, for comparison, baked into the food pellets. Males
were untreated. The test diets were administered from days 7-19 of
gestation. Parameters investigated were: body weights of does, litter
data including implantations and pre-implantation loss, litter size
and post-implantation loss, litter and mean foetal weights, major and
minor anomalies and skeletal variants. Young were incubated for 24
hours to determine neonatal viability. Gross and X-ray examinations
were conducted to discover external and skeletal malformations.
Alizarin red technique was utilized where necessary. The Wilson
technique was used to examine for mal-formations of brain and skull.
No compound-related effects were noted. The incidence of skeletal
malformations was similar in offspring of the treatment and sucrose
control groups. No major visceral abnormalities were noted (Hummler,
1978).
Mutagenicity
The following mutagenic test procedures were carried out with
xylitol:
(1) AMES test with Salmonella typhimurium TA 1535, TA 1537, and TA
1538 with and without S-9 metabolic activation;
(2) host-mediated assay in the mouse with Salmonella typhimurium TA
1530, TA 1532, and TA 1964;
(3) micronucleus test with Fullinsdorf albino mice;
(4) chromosome analysis of cultured, PHA-stimulated human lymphocytes.
Xylitol caused no observable mutagenic effects in any of the
systems studied (Gallandre, 1978).
REFERENCES
Gallandre, F. (1978) Mutagenicity studies with xylitol using various
methods for Hoffman-La Roche Laboratories. Submitted to the World
Health Organization by F. Hoffman La Roche Co., Ltd., Basle,
Switzerland
Heywood, R., Chesterman, H., Allen, T. R., Sheet, A. E., Kennedy, S.
J., Majerd, S. K. and Prentice, D. E. (1977) Xylitol toxicity studies
in the beagle dog. Unpublished report from Huntingdon Research Centre,
submitted to the World Health Organization by F. Hoffman La Roche,
Co., Ltd., Basle, Switzerland
Hummler, H. (1978) Reproduction study in rabbits in oral
administration of Ro 06-7045=Xylitol, Phase II - teratology study.
Unpublished company report submitted to the World Health Organization
by F. Hoffman La Roche, Co., Ltd., Basle, Switzerland
Hunter, B., Colley, J., Street, A., Heywood, R., Prentice, D. and
Magnusson, G. (1978a) Xylitol tumorigenicity and toxicity study in
long-term dietary administration to rats. Unpublished report from
Huntingdon Research Centre, submitted to the World Health Organization
by F. Hoffman La Roche, Co., Ltd., Basle, Switzerland
Hunter, B., Grahan, C., Heywood, R., Prentice, D., Roe, R. and Voakes,
D. (1978b) Tumorigenicity and carcinogenicity study with xylitol in
long-term dietary administration to mice. Unpublished report from
Huntingdon Research Centre submitted to World Health Organization by
F. Hoffman La Roche, Co., Ltd., Basle, Switzerland
Palmer, A. K. and Bottomley, A.M. (1977) Effect of xylitol during a
modified teratology study in rats. Final report. Unpublished report
from Huntingdon Research Centre, Huntingdon, Cambridgeshire, England;
submitted to the World Health Organization by F. Hoffman La Roche,
Co., Ltd., Basle, Switzerland
Palmer, A. K., Bottomley, A.M., Wight, D.G. D. and Cherry, C. P.
(1978) Effect of xylitol on reproductive functions of multiple
generations in the rat. Final report. Unpublished report from
Huntingdon Research Centre, Huntingdon, Cambridgeshire, England;
submitted to the World Health Organization by F. Hoffman La Roche,
Co., Ltd., Basle, Switzerland
See Also:
Toxicological Abbreviations
Xylitol (WHO Food Additives Series 12)
Xylitol (WHO Food Additives Series 18)
XYLITOL (JECFA Evaluation)