Saccharin vs Blue Dye 2: which is worse?

What is Saccharin?

Saccharin is the oldest artificial sweetener, discovered accidentally at Johns Hopkins in 1879. It is a sulfonamide compound approximately 300-400 times sweeter than sucrose with no caloric value. It has a slightly bitter metallic aftertaste at higher concentrations. Saccharin's sodium salt (sodium saccharin) is the form used in most food applications.

What is Blue Dye 2?

Blue Dye 2 (Indigotine/Indigo Carmine) is a synthetic disulfonated derivative of indigo. Unlike natural indigo from the indigo plant, the FD&C version is synthetically manufactured from petroleum. It produces a dark royal blue to indigo color and is used in food, pharmaceuticals, and medical diagnostics.

Documented risks

Saccharin: Saccharin's carcinogenicity history is one of the most tumultuous in food regulatory history. In 1977, the FDA proposed banning saccharin after studies found it caused bladder cancer in rats at very high doses. Congress passed the Saccharin Study and Labeling Act, which put a moratorium on the ban and required a cancer warning label on saccharin products ('Use of this product may be hazardous to your health. This product contains saccharin which has been determined to cause cancer in laboratory animals.'). By 2000, saccharin was removed from the US National Toxicology Program's Report on Carcinogens after subsequent research determined that the bladder cancer in male rats was caused by a rat-specific mechanism — high pH, high protein, and calcium phosphate in rat urine — that does not apply to human urine. The cancer warning label requirement was repealed. IARC also removed saccharin from its Group 2B list in 1999. However, Canada maintained its ban on food use saccharin, citing continued precautionary concern. A 2022 study in Cell found saccharin was among the artificial sweeteners most significantly altering gut microbiome composition and glucose tolerance in previously non-sweetener-using participants. Saccharin showed the largest effect on glucose tolerance among the sweeteners studied (saccharin, sucralose, aspartame, stevia). Saccharin passes through the placenta and appears in breast milk, raising questions about infant exposure that have not been fully resolved.

Blue Dye 2: Animal studies conducted in the 1980s found that high-dose Blue Dye 2 caused brain tumors in male rats. An NTP bioassay (1987) found statistically significant increases in brain gliomas (astrocytomas) in male rats given high doses. The FDA reviewed these findings and determined that the doses far exceeded typical human dietary exposure. Nonetheless, the tumor finding remains in the scientific record as a concerning data point. EFSA's 2010 safety evaluation of Indigo Carmine (E132) reached an unusual conclusion: it could not establish an ADI due to data limitations, including the brain tumor findings. This means EFSA adopted an implicit conservative position — it neither declared Blue 2 safe nor formally banned it, but the absence of an established ADI signals scientific uncertainty. In medical diagnostic use, high intravenous doses of Indigo Carmine can cause hypertension, bradycardia, and in rare cases anaphylaxis. These are dose-specific clinical pharmacological effects, not relevant to dietary consumption at food use levels. Blue 2 was not included in the 2007 Lancet hyperactivity study. Limited direct research links Blue 2 to behavioral effects. The FDA's April 2025 announcement includes Blue 2 in the class of petroleum-based synthetic dyes to be phased out of the US food supply, reflecting updated policy on the category rather than specific new Blue 2 toxicity data.