MANNITOL EXPLANATION Mannitol was evaluated for acceptable intake at the tenth, eighteenth, twentieth, and twenty-ninth meetings of the Joint FAO/WHO Expert Committee on Food Additives (Annex 1, references 13, 35, 41, and 70). A toxicological monograph was published after the tenth meeting (Annex 1, reference 12). At its twenty-ninth meeting, the Committee extended the temporary ADI of 0-50 mg/kg b.w. to 1986 pending submission of the results of a number of long-term studies completed but not submitted for evaluation. The previously-published monograph has been expanded and is reproduced in its entirety below. BIOLOGICAL DATA Biochemical aspects D-Mannitol occurs widely in nature in a variety of plants, algae, fungi and certain bacteria. L-Mannitol does not occur naturally. Traces of mannitol have been identified occasionally in human urine (Pitkänen & Pitkänen, 1964). When 14C-D-mannitol was given at a dose of 240 mg/rat orally to non-fasted rats, about 50% of the radioactivity was recovered in the expired 14CO2 (Wick et al., 1954). In similar experiments, also using 14C-D-mannitol at 500 mg/kg b.w., fasted rats oxidized 40% of the dose to 14CO2, non-fasted rats oxidized 68%; 9.74% was stored in the carcass, 1.28% in the liver, and 6.32% was excreted in the urine (Gongwer, 1963). Feeding D-mannitol to rats and dogs led to a small but significant increase of liver glycogen (Carr et al., 1933; Todd et al., 1939; Silberman & Lewis, 1933; Carr & Krantz, 1938). When 14C-D-mannitol was administered to rats by i.p. injection, 77-97% of the dose was excreted in the urine within 24 hours, and only 2-3% of the mannitol carbon was oxidized to 14CO2. Additional experiments, in which mannitol was injected directly into the portal vein, showed that mannitol could be oxidized only by the liver (Wick et al., 1954). D-Mannitol administered i.v. was completely cleared by the kidneys of 2 dogs at rates identical to inulin and creatinine (Smith et al., 1940). Mannitol at a dose of 22.5 g/dog did not elevate the blood sugar level of dogs after i.v. injection (Todd et al., 1939). Toxicological studies Special studies on carcinogenicity Mice Diets containing 0, 2.5, or 5% mannitol (0, 3750, or 7500 mg/kg b.w., respectively) were fed to groups of 50 B6C3F1 mice of each sex for 103 weeks. The mice were observed twice daily for clinical signs of toxicity and body weights were recorded weekly. The body weights of treated females were similar to those of controls, while those of the treated males were slightly but not significantly higher than those of controls; feed consumption was similar to controls in both dose groups. There were no significant differences in survival rates nor in tumour incidence between treated animals and controls. Mild nephrosis, characterized by focal vacuolation of the tubular epithelium, was observed in increased incidence in treated mice of both sexes (control males 30%, low-dose males 58%, high-dose males 64%, control females 2%, low-dose females 6%, high-dose females 29%). The authors concluded that this vacuolation was probably caused by osmotic imbalance. Under the conditions of this bioassy, mannitol was noncarcinogenic to B6C3F1 mice (NTP, 1982; Abdo et al., 1983). Rats Groups of 50 male and female F344 rats were fed diets containing 0, 2.5, or 5% mannitol for 103 weeks (corresponding to 0, 1250, or 2500 mg/kg b.w./day). The body weights of treated males were similar to those of controls, while those of treated females were slightly but not significantly lower than those of controls; feed consumption was similar to controls in both dose groups. There were no significant differences in survival rates nor in tumour incidence between treated animals and controls. Retinopathy and cataracts occurred at increased incidences in high-dose male and mid- and high-dose female rats (retinopathy: males-17/50, 6/50, 42/50; females-10/50, 3/50, 33/50; cataracts: males-15/50, 6/50, 40/50, females-9/50, 40/50, 32/50; all for the controls, mid-, and high-dose groups respectively). This increase appears to be associated with the distance of the animals from sources of fluorescent light; however, a contributing effect of mannitol cannot be discounted completely. Dilatation of the gastric fundal gland was observed at increased incidences in dosed females (control, 6/50 (12%); low-dose, 23/50 (46%); high-dose, 23/50 (46%)). Under the conditions of the bioassay, mannitol was not carcinogenic to F344 rats (NTP, 1982; Abdo et al., 1983). Special studies on mutagenicity Mannitol was non-mutagenic in a host-mediated assay in mice using Salmonella typhimurium G46 and TA1530 and Saccharomyces cerevisiae strain D3, in a cytogenic assay in rat bone marrow, and in human W1-38 cells (Green, 1977). Mannitol was not mutagenic in the Ames test using S. typhimurium strains TA98, TA100, TA1535, and TA1537 (NTP, 1981). Results of a dominant lethal assay in rats at doses of mannitol of 0, 20, 200, 2000, and 5000 mg/kg b.w. by gavage were negative (U.S. FDA, 1974). Special study on renal reabsorption Intravenous administration of mannitol at an initial dose of 0.3 g followed by hourly injections of 1 g to Sprague-Dawley rats resulted in complete inhibition of salt and water reabsorption from the medullary collecting system of the kidney (Sonnenberg, 1978). Special studies on teratogenicity Mannitol was tested for teratogenic effects in mice, rats, and hamsters. Pregnant mice and rats given oral doses of mannitol up to 1.6 g per kg for 10 consecutive days and hamsters up to 1.2 g per kg for 5 consecutive days showed no effects on maternal or fetal survival. Mannitol was not teratogenic under the test conditions (FDRL, 1972). Acute toxicity LD50 Animal Route (mg/kg b.w.) Reference Mouse oral 22,000 Gongwer, 1960 i.v. 16,800 Robb, 1964 i.p. 14,000-16,000 Beck et al., 1936 Rat oral 17,300 Gongwer, 1960 Mice died with signs of central nervous system depression and gastrointestinal tract mucosal damage; rats died with predominantly gastrointestinal tract signs (Gongwer, 1960; Gongwer, 1961). Short-term studies Mice Groups of five male and five female B6C3F1 mice were fed diets containing 0.6, 1.25, 2.5, 5.0, or 10.0% mannitol for 14 days. No control groups were used. Animals were killed on days 16-20 and necropsies performed on all animals. All animals survived to the end of the dosing periods and all groups had similar increases in body weight. No compound-related effects were observed (NTP, 1952). Groups of 10 male and 10 female B6C3F1 mice were fed diets containing 0, 0.3, 0.6, 1.2, 2.5, or 5.0% mannitol for 13 weeks. On one day animals from the 0.3 and 0.6% dose groups were accidently given diets containing 0.3 or 0.6% Ziram. Animals were checked for mortality/ morbidity twice daily. Each animal was subjected to clinical examination and palpation weekly, and body weights and food intake were recorded weekly. Necropsies were performed on animals in the control and top two dose groups. Mean body-weight gain was higher than controls in all dose groups except males of the top-dose group, where weight gain was similar to controls. All animals survived to termination and no compound-related effects were observed at necropsy or on histopathological examination (NTP, 1982). Rats Groups of 20 rats were fed 35% sucrose plus 5% mannitol or 40% sucrose (control group) over a period of 3 months. The growth curves showed that mannitol was nutritionally inferior to sucrose (Ellis & Krantz, 1941). These results are in accord with earlier findings that mannitol is inferior to sucrose, as judged by weight gain of rats (Ariyama & Takahasi, 1929). Groups of 5 male and 5 female F344/N rats (6 weeks of age) were fed diets containing 0.6, 1.2, 2.5, 5.0, or 10% mannitol for 14 days. No control groups were used. Animals were killed on days 16-20 and necropsies performed on all animals. All animals survived to the end of the dosing period. Females fed diets containing 10% mannitol gained less weight than did other groups. Two of 5 males in the top-dose group developed diarrhoea from days 4 to 6. No gross lesions were reported at autopsy (NTP, 1982). Groups of 10 male and 10 female F344 rats were fed diets containing 0, 0.3, 0.6, 1.25, or 5.0% mannitol for 13 weeks. On one day, animals from the 0.3 and 0.6% dose groups were accidentally given diets containing 0.3 or 0.6% Ziram. Animals were checked for mortality/morbidity twice daily. Each animal was subjected to clinical examination and palpation weekly, and body weights and food intake were recorded weekly. Necropsies were performed at termination and haematological and histopathological examinations were performed on animals in the control and two highest-dose groups. Mean body-weight gains of the top-dose group males were depressed by 9.6% relative to controls; mean body-weight gains of other groups were similar to controls. All animals survived and no compound-related clinical signs or histopathologic effects were observed (NTP, 1982). Monkeys Three rhesus monkeys were fed 3 g mannitol daily for 3 months. Two animals were employed as controls. No toxic signs nor pathological changes were observed (Ellis & Krantz, 1941). Long-term studies Rats Wistar-derived SPF albino rats were fed 0, 1, 5, or 10% mannitol in their diets for 94 weeks (40 males and 40 females/group). Decreasing amounts of corn starch (10, 9, 5, or 0% respectively) were added to each diet. Body weights were generally decreased by approximately 5-7% in the medium- and high-dose male rats. Food consumption, haematology, haemochemistry, histopathology, and most urinalyses were unaffected by mannitol administration. Total urinary calcium and magnesium were elevated in a dose-related manner, but these were not considered to be pathological changes. Histopathological evaluation revealed that most neoplasms were unrelated to treatment, but a low incidence of benign thymomas in female rats was apparently treatment-related (2 benign thymic tumours in female controls, 6 in each of the 1 and 5% mannitol groups, and 10 in the 10% mannitol group). No significant group differences occurred for thymomas in male rats (0 in controls, 3 at 1%, 1 at 5%, and 0 at 10% of mannitol in the diet). No additional treatment-related neoplasms occurred in other lymphopoietic tissues (Saatman et al., 1978). Female rats of the Sprague-Dawley strain were administered mannitol at dose levels of 0, 1, 5, or 10% of the diet. All surviving rats were killed after 27 months of treatment, when mortality of the rats receiving 10% mannitol was 68%. Evaluation of mortality, general health and behaviour, body weight, food consumption, urinary chemistry, organ weights, and subcutaneous tissue masses observed in-life did not indicate any effects due to the administration of mannitol. In addition, evaluation of all gross necropsy findings, as well as histopathological evaluations of the thymus of all rats, and histomorphology of all other tissues of those rats with thymic abnormalities, resulted in the conclusion that there was no effect of mannitol on Sprague-Dawley rats in this study (Gongwer et al., 1978). Female rats of the Wistar strain (100 animals/group) were administered mannitol at dose levels of 0, 1, 5, or 10% of the diet for 30 months. Histopathological evaluations of the thymus of these rats revealed no effect of mannitol on the development of primary thymic neoplasms. Other findings in the thymus, and in other tissues examined histopathologically in those rats with thymic abnormalities, were not attributable to the administration of mannitol. There was no indication that the incidences of gross necropsy findings were related to the administration of mannitol. Slightly increased incidences of tissue masses in the cervix and/or uterus noted in the compound- treated groups as compared to the control were considered of no biological importance because of their low overall incidence. Mean adjusted body-weight values of the group which received 10% mannitol in the diet were lower (and occasionally statistically significant) than in the concurrent control group when all animals were weighed at weeks 26 and 52, and when rats of selected replicates were weighed at weeks 88-120. Most mean values of the rats receiving 1% of the compound in the diet were slightly lower than those of controls throughout the study; mean body weights of rats receiving 5% mannitol were slightly lower than control weights from approximately weeks 88-120. Differences in these two groups, however, were slight and not statistically significant. Evaluation of mortality, general health and behaviour, food consumption, urinary chemistry and volume, terminal organ and body weights, and subcutaneous tissue masses observed in-life did not indicate any effects which could be attributed to the administration of mannitol at levels of 1, 5, and 10% of the diet (Gongwer et al., 1978). Female Fischer rats (100 animals/group) were administered mannitol at dose levels of 0, 1, 5, or 10% of the diet for 30 months. Histopathological evaluation of the thymus of these rats revealed no effect of mannitol on the development of primary thymic neoplasms. Other findings in the thymus, and in other tissues examined histopathologically in those rats with thymic abnormalities, were not attributable to the administration of mannitol. The incidences of gross necropsy findings were not related to the administration of mannitol. Slightly increased incidences of tissue masses in the anogenital area, cervix, and uterus were noted in the 10% Fischer rat group as compared to the control group. These findings were not considered to be of biological importance; the incidence of uterine masses in this study were well within the expected spontaneous incidence rate for this strain of rats. The combined incidence of focal medullary hyperplasia and medullary pheochromocytoma was higher in the high-dose group than in the control or other test groups. However, there was no clear dose response of focal medullary hyperplasia and pheochromocytoma, and the investigating pathologists concluded that this increased incidence was probably a chance occurrence unrelated to the administration of mannitol. Mean body weights of Fischer rats receiving mannitol at dietary levels of 5 and 10% were slightly lower than concurrent control weights from weeks 13 and 60, respectively, through termination of the study (with the exception of week 108 in the 5% group). These differences were generally small (less than 9%), and the majority were not statistically significant. No consistent dose relationship was evident. Evaluation of mortality, general health and behaviour, food consumption, urinary chemistry and volume, terminal organ and body-weights, and subcutaneous tissue masses observed in-life did not indicate any effects which could be attributed to the administration of mannitol at levels of 1, 5, and 10% of the diet (Gongwer et al., 1978). Observations in man mannitol has a slow rate of absorption from the intestinal tract and exerts laxative properties. The laxative threshold for man was found to lie between 10 and 20 g of mannitol per single dose (Ellis & Krantz, 1941). In man, i.v. administration of mannitol is practiced for induction of diuresis in oliguria, for forced diuresis in poisoning cases, or to measure the extracellular fluid compartment. There is an extensive literature available on these aspects (Milde, 1965; Widdowson & Dickerson, 1964). Following the i.v. injection of 10 g mannitol into man, 81% of the dose was excreted unchanged in the urine and up to 80 g produced no toxic effect (Smith et al., 1940). Administration of 25 g mannitol on 3 subsequent days did not significantly influence either the blood-sugar level or the respiratory quotient (Ellis & Krantz, 1941). When 100 g mannitol was fed, the maximum increase in blood sugar level was 10 mg/dl (Field, 1919). The i.v. injection of 10 g of mannitol daily over a period of 1 month produced no significant changes in non-protein nitrogen, CO2-combining power of blood, red cell count, or renal function (Ellis & Krantz, 1941). Ten patients fasted overnight were administered 28 to 100 g of (U-14C)-mannitol orally as a 5% aqueous solution. Within this dose range, about 20% of the mannitol ingested was excreted unchanged in the urine, indicating appreciable absorption. The level of radioactivity in the blood rose for the first 2 hours and remained at a plateau for 2 to 4 hours; the radioactive compounds present in blood were not identified and data on blood glucose levels were not reported. Expired 14CO2 increased for 8 hours after mannitol ingestion; however, (U-14C)-mannitol administered i.v. produced very little radioactive CO2. Oral doses of 40 g or more generally caused frequent bowel movements, diarrhoea, and excretion in the stool of a higher percentage of the dose. Only traces of radioactivity occurred in the urine and stools after 48 hours. It was concluded that within an oral dose range of 40 to 100 g, approximately 65% of ingested mannitol was absorbed; about one-third of the absorbed mannitol was excreted in the urine, the remainder being metabolized presumably in the liver (Nasrallah & Iber, 1969). Based on the above study, the caloric value of dietary mannitol was considered to be about 2 kcal per g (Dwivedi, 1977). Comments Mannitol is dehydrogenated to fructose and then metabolized through the mammalian glycolytic pathway; it occurs endogenously in humans. No mutagenic or cytotoxic effect was found when mannitol was tested in vitro and in vivo. Teratogenic studies in several species did not reveal any compound-related adverse effects. Mannitol, when fed to rats and mice at up to 5% of the diet, was not carcinogenic. Retinopathy and cataract formation occurred at increased incidences in male rats in the earliest carcinogenicity study, but these effects were not seen in four subsequent studies. An increase in the number of benign thymomas was noted in female Wistar rats, observed in a lifetime feeding study, and this was not reproduced in three other studies designed to evaluate the species specificity of this finding. One of the species tested (female Fischer rats) had an increased incidence of adrenal medullary hyperplasia plus pheochromocytoma (for a discussion of adrenal medullary lesions produced by polyols, see Annex 1, reference 62, section 2.5). Clinical experience with this substance as a therapeutic agent in man has indicated no adverse effects. Mannitol is poorly absorbed and exerts a laxative effect on man and animals, a common feature of all polyols. EVALUATION Estimate of acceptable daily intake for man ADI "not specified". The fact that high doses of mannitol exert a laxative effect in man, which is common feature of all polyols, should be taken into account when considering appropriate levels of use of polyols, alone and in combination. REFERENCES Abdo, K.M., Haseman, J.K., Boorman, G., Farnell, D.R., & Kovatch R. (1983). Absence of carcinogenic response in F344 rats and B6C3F1 mice given D-mannitol in the diet two years. Fd. Chem. Toxicol., 21, 259-262. Ariyama, T. & Takahasi, K. (1929). J. Agric. Chem. Soc. Japan, 5, 674. Beck, F.F., Carr, C.J., & Krantz, J.C. Jr. (1936). Acute toxicity of certain sugar alcohols and their anhydrides. Proc. Soc. Exp. Biol. Med. 35, 98-99. Carr, C.J., Musser, R., Schmidt, J.E., & Krantz, J.C. Jr. (1933). Fate of mannitol and mannitan in animal body. J. Biol. Chem, 102, 721-732. Carr, C.J. & Krantz, J.C. Jr. (1938). Sugar alcohols; fate of polygalitol and mannitol in animal body. J. Biol. Chem., 124, 221-227. Dwivedi, B.K. (1977). 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See Also: Toxicological Abbreviations Mannitol (FAO Nutrition Meetings Report Series 40abc) MANNITOL (JECFA Evaluation)