Answer ยท confidence: partial
Did 2000 and 2001 saccharin decisions use the same rat urine evidence?
Research question: Did the NTP 2000 delisting and the FDA 2001 reversal cite the same male-rat urinary protein and microcrystal mechanism, and what dose-response or human comparison data did each agency include in its Federal Register justification?
The verified facts contain nothing on the FDA's 2001 reversal or its Federal Register justification, so that half of the question cannot be answered from them 17. The NTP's 2000 delisting tied rat bladder cancers to urinary pH, osmolality, volume, precipitate, and urothelial damage at dietary concentrations of 3% or higher, with inconsistent findings at lower doses 1011. The male-rat urinary protein point appears in the 1997 NTP background document, which attributes part of the male predilection to high urinary protein 19, but the facts do not show that the 2000 delisting cited protein 1011. For human comparison, NTP (2000) said several epidemiology studies showed no clear association with urinary bladder cancer 1214, and IARC (1999) judged the precipitate mechanism not relevant to humans 9. The newest fact is from the February 2003 NTP final document 1112, roughly 23 years before October 2026.
Checked 2026-10-23. Only documented and supported facts are used.
Dig deeper on this questionSources
[1] supported
The 1979 rat study found no consistent relationship between bladder epithelial hyperplasia and crystalluria, the crystal-based mechanism later invoked for saccharin's bladder effects.
"No consistent relationship between bladder epithelial hyperplasias and crystalluria could be demonstrated, although all 3 bladder tumours were associated with some form of mineralisation."Response of the rat to saccharin with particular reference to the urinary bladder (1979)
[2] documented
The 1980 study reported that saccharin administration did not increase urinary pH, crystalluria, or calculus formation in rats.
"Administration of saccharin did not increase urinary pH, crystalluria or calculus formation, and failed to promote bladder neoplasia after a carcinogenic dose of MNU, though the numbers of proliferative lesions in the bladder were increased."Ortho-toluene sulphonamide and saccharin in the promotion of bladder cancer in the rat (1980)
[3] supported
The 1979 study concluded that male rats showed a particular susceptibility to saccharin treatment.
"Results suggest a particular susceptibility of males to saccharin treatment."Response of the rat to saccharin with particular reference to the urinary bladder (1979)
[4] documented
The study found that the contaminant OTS was not associated with changes in urinary pH, crystalluria, or calculus formation in rats.
"Administration of OTS was not associated with changes in urinary pH, crystalluria or calculus formation"Ortho-toluene sulphonamide and saccharin in the promotion of bladder cancer in the rat (1980)
[5] documented
In the 1979 study, the only bladder tumours occurred exclusively in male rats receiving the higher dietary saccharin dose, starting at 95 weeks, a very low incidence.
"A very low incidence of bladder tumours, exclusively in males receiving the higher saccharin dose in the diet was seen from 95 weeks."Response of the rat to saccharin with particular reference to the urinary bladder (1979)
[6] supported
The authors concluded that the contaminant OTS played no part in the reported promoting activity of saccharin on the rat bladder.
"These results indicate that OTS contamination played no part in the reported promoting activity of saccharin on the rat bladder."Ortho-toluene sulphonamide and saccharin in the promotion of bladder cancer in the rat (1980)
[7] documented
The 1979 study reported the maximum palatable saccharin dose in drinking water as 2 g/kg/day, and double that (4 g/kg/day) was palatable in the diet.
"The maximum palatable dose of saccharin in the drinking water was found to be 2 g/kg/day and, even then, there was some voluntary restriction of fluid intake in the males. By contrast, double this dose--namely 4 g/kg/day, was palatable in the diet."Response of the rat to saccharin with particular reference to the urinary bladder (1979)
[8] supported
The document states that extensive epidemiological studies have shown saccharin does not increase the risk of bladder cancer in humans.
"Extensive epidemiological studies have shown that saccharin does not increase the risk of bladder cancer in humans and laboratory"A review and biological risk assessement of sodium saccharin - ScienceDirect
[9] supported
IARC (1999) attributed sodium saccharin's bladder tumours in rats to a non-DNA-reactive mechanism involving a urinary calcium phosphate-containing precipitate, and judged this mechanism not relevant to humans because of interspecies differences in urine composition.
"This mechanism is not relevant to humans because of critical interspecies differences in urine composition."EVIDENCE ON THE CARCINOGENICITY OF SODIUM SACCHARIN FINAL February 2003
[10] supported
The NTP's 2000 delisting of saccharin attributed the rat bladder cancers to rat urinary physiology, including urinary pH, osmolality, volume, precipitate, and urothelial damage, observed at dietary concentrations of 3% or higher.
"Studies indicate that the observed urinary bladder cancers in rats are related to the physiology of the rat urinary system including urinary pH, osmolality, volume, and the presence of precipitate, and urothelial damage with attendant hyperplasia following consumption of diets containing sodium saccharin at concentrations of 3% or higher with inconsistent findings at lower dietary concentrations."EVIDENCE ON THE CARCINOGENICITY OF SODIUM SACCHARIN DRAFT October 2002
[11] supported
In its Ninth Report on Carcinogens, NTP (2000) linked rat bladder cancers to urinary pH, osmolality, volume, precipitate, and urothelial damage, observed at dietary sodium saccharin concentrations of 3% or higher, with inconsistent findings at lower concentrations.
"Studies indicate that the observed urinary bladder cancers in rats are related to the physiology of the rat urinary system including urinary pH, osmolality, volume, and the presence of precipitate, and urothelial damage with attendant hyperplasia following consumption of diets containing sodium saccharin at concentrations of 3% or higher with inconsistent findings at lower dietary concentrations."EVIDENCE ON THE CARCINOGENICITY OF SODIUM SACCHARIN FINAL February 2003
[12] supported
NTP (2000) stated that several epidemiology studies showed no clear association between saccharin consumption and urinary bladder cancer in humans.
"Results of several epidemiology studies indicate no clear association between saccharin consumption and urinary bladder cancer."EVIDENCE ON THE CARCINOGENICITY OF SODIUM SACCHARIN FINAL February 2003
[13] supported
The NTP delisting vote was split: the RG1 and RG2 review groups voted to delist saccharin (7/3 and 6/2), while the NTP Board of Scientific Counselors subcommittee voted 4/3 against delisting.
"vo ... ted to delist saccharin (7/3 and 6/2, respectively), while the NTP Board of Scientific Counselors Report on Carcinogens Subcommittee (the External Peer Review Group) voted against delisting and in favor of keeping saccharin listed as reasonably anticipated to be a human carcinogen (4/3)."EVIDENCE ON THE CARCINOGENICITY OF SODIUM SACCHARIN FINAL February 2003
[14] supported
The NTP's 2000 delisting cited epidemiology studies showing no clear association between saccharin consumption and urinary bladder cancer in humans.
"Results of several epidemiology studies indicate no clear association between saccharin consumption and urinary bladder cancer."EVIDENCE ON THE CARCINOGENICITY OF SODIUM SACCHARIN DRAFT October 2002
[15] supported
The NTP removed saccharin from its list of reasonably anticipated human carcinogens only after a reevaluation requested by the Calorie Control Council.
"NTP removed saccharin from the list of substances reasonably anticipated to be a human carcinogen in the Ninth Report on Carcinogens (NTP, 2000) after a request for reevaluation from the Calorie Control Council."EVIDENCE ON THE CARCINOGENICITY OF SODIUM SACCHARIN DRAFT October 2002
[16] supported
Within the NTP review, Review Group 1 and Review Group 2 voted to delist saccharin, while the Board of Scientific Counselors subcommittee voted 4-3 against delisting.
"voted to delist saccharin (7/3 and 6/2, respectively), while the NTP Board of Scientific Counselors Report on Carcinogens Subcommittee"EVIDENCE ON THE CARCINOGENICITY OF SODIUM SACCHARIN DRAFT October 2002
[17] supported
In 2000, the National Toxicology Program (NTP) and the U.S. Department of Health and Human Services removed saccharin from the list of substances reasonably anticipated to be carcinogens.
"On the basis of this information, in 2000, NTP and the United States Department of Health and Human Services removed saccharin from the list of substa..."Lack of Genotoxic and Carcinogenic Potential for Nonsugar Sweeteners: A Review of Animal and Mechanistic Evidence - ScienceDirect
[18] supported
Following a formal NTP review, saccharin was delisted from the 10th Report on Carcinogens because the rodent cancer data were judged insufficient.
"Following a formal review by NTP, saccharin was delisted from the 10th Report on Carcinogens, because the rodent cancer data are not sufficient to mee..."Saccharin Sodium - an overview
[19] documented
The NTP attributes part of the male rat's sex predilection for saccharin-induced bladder tumors to the high levels of urinary protein that male rats characteristically produce.
"The high levels of urinary protein characteristically produced by male rats may partially explain"15th RoC: Appendix B - National Toxicology Program (NTP)
[20] supported
The NTP lists urinary conditions that must be simultaneously or sequentially present for saccharin to induce bladder tumors in rats, including urinary crystals or precipitate.
"These conditions include a urinary pH greater than 6.5, increased urinary sodium concentration, increased urine volume, decreased urine osmolality, and presence of urinary crystals or precipitate"15th RoC: Appendix B - National Toxicology Program (NTP)
[21] documented
In rat studies, sodium saccharin produced a dose-related increase in urinary-bladder neoplasms at dietary concentrations above 1%.
"as evidenced by a dose-related increased incidence of benign or malignant urinary-bladder neoplasms at dietary concentrations greater than 1%"15th RoC: Appendix B - National Toxicology Program (NTP)
[22] supported
The NTP's delisting decision for saccharin rested on the perception that the rat bladder tumors arise by mechanisms not relevant to humans, together with the lack of human data suggesting a carcinogenic hazard.
"This decision is based on the perception that the observed urinary-bladder tumors in rats arise by mechanisms not relevant to humans"15th RoC: Appendix B - National Toxicology Program (NTP)