What is E132?

Complete guide to understanding E132 (Indigotine) — a widely-used synthetic blue dye with controversial safety signals

The Quick Answer

E132 (Indigotine) is a bright blue synthetic dye used to color a wide variety of foods and beverages worldwide.

It’s also used medically — surgeons inject it during urological surgeries to visualize the urinary tract.

The safety question is complicated: animal studies showed brain tumors at very high doses, but regulators concluded this finding is “not biologically significant.” Consumer advocacy groups disagree, expressing ongoing concern.

What Exactly Is It?

E132 is a 100% synthetic blue dye created entirely in a laboratory from coal tar and petroleum-derived chemical precursors.

It’s different from the red synthetic dyes (E127, E128, E129) in its chemical family. While those are azo dyes, E132 belongs to the indigoid dye family, which includes compounds derived from the natural indigo that has been used to dye textiles for centuries.

The chemical formula is C₁₆H₈N₂Na₂O₈S₂ — a water-soluble powder that produces a vivid sky-blue color in solution.

One interesting property: E132 is a pH indicator, meaning it changes color depending on acidity. It’s blue at neutral pH but turns yellow in strongly alkaline solutions. This property makes it useful in both food coloring and laboratory applications.

Where You’ll Find It

E132 is one of the most commonly used blue synthetic food colorants globally. It appears in a huge range of foods:

If you’ve consumed any blue-colored processed foods in the past month, you’ve almost certainly had E132.

Medical & Surgical Use

E132’s medical use is significant and FDA-approved:

– Urological surgery: Surgeons inject indigo carmine IV to visualize the urinary tract during procedures
– Cystoscopy: FDA-approved surgical dye (brand name Bludigo, approved July 2022)
– Obstetric surgery: Detecting amniotic fluid leaks during pregnancy-related procedures
– Diagnostic imaging: Highlights anatomical structures during surgery
– Laboratory use: pH indicator, histological staining, research applications

Why Do Food Companies Use It?

E132 produces a bright, stable blue color that appeals to consumers and lasts throughout shelf life.

Food companies use it because:

– Vibrant blue color: Consumers associate bright blue with freshness, quality, and fun (especially in candies and drinks)
– Extremely stable: Resistant to heat, light, and acidic pH — color doesn’t fade like natural dyes
– Inexpensive: Far cheaper than natural blue alternatives
– Reliable: Consistent color batch-to-batch; blends predictably with other dyes
– Low GI absorption: Most passes through unchanged, reducing internal exposure concerns

Natural blue alternatives (spirulina, butterfly pea) cost much more and are less stable, making them impractical for most manufacturers.

Is It Safe? The Controversy

The Official Position

Major regulatory agencies say E132 is safe at permitted use levels.

The ADI (Acceptable Daily Intake) is 0-5 mg/kg of body weight per day, set by EFSA and endorsed by JECFA and FDA.

For a 70 kg adult, this means approximately 350 mg per day is considered safe — far more than typical consumption.

In other words: most people consume E132 in tiny fractions of the amount regulators consider safe.

The Brain Tumor Controversy

What the 1985 Rat Study Found

Scientists fed E132 to rats at very high doses (0.5%, 1.0%, 2.0% of diet) for 30 months — the longest exposure period used in animal testing.

Key findings:

• High-dose male rats showed statistically significant increase in brain gliomas (tumors)
• This finding was NOT replicated in female rats or in mice (separate study)
• Tumor incidence was within the range typical for aging rats in this strain
• No clear dose-response relationship (tumors didn’t increase proportionally with dose)
• Researchers concluded: “Not biologically significant”
• Overall conclusion: “FD&C Blue No. 2 did not produce evidence of toxicity, including carcinogenicity”

Why Regulators Said “Not Biologically Significant”

Regulatory agencies rely on specific criteria for determining carcinogenicity:

– Dose extremity: 2% in diet = ~500 times normal human food exposure
– Incidence within normal range: Brain tumor rate similar to control group aging naturally
– Lack of dose-response: If E132 caused tumors, more tumors should appear at higher doses
– Sex and species differences: Only males affected; mice unaffected (suggests not universal carcinogen)
– No human evidence: Zero documented cancer cases linked to food E132 consumption
– Poor bioavailability: E132 poorly absorbed, so internal exposure is minimal

Why Advocacy Groups Remain Concerned

Consumer advocates and some researchers interpret the same data differently:

– Precautionary principle: If ANY tumor signal appears in animals, it’s concerning
– Statistical significance: The increase was statistically significant, even if small
– Long-term exposure: 30-month rat study is longest-duration test; real finding?
– Species extrapolation: Humans could be more sensitive than rats
– Unknown mechanisms: Why tumors only in males? Suggests mechanism we don’t understand
– Cost of error: If E132 truly causes cancer, false reassurance could cause harm

The Bottom Line on Brain Tumor Controversy

Both interpretations are scientifically defensible.

The regulatory approach prioritizes: dose relevance, mechanism understanding, and human epidemiological absence of cases → Conclusion: safe at permitted levels

The advocacy approach prioritizes: precaution, any tumor signal, potential unknown mechanisms → Conclusion: concerning; avoid when possible

Most scientists and regulators conclude the regulatory assessment is correct, but honest disagreement exists about how much precaution is warranted.

Other Documented Health Concerns

Behavioral Effects in Children

E132 is included in studies on synthetic dyes and hyperactivity. Some evidence suggests it may increase inattention and hyperactivity in children, though:

– Effect size is small
– Not clear if E132 alone or combination of dyes
– Not as well-studied as E129 (Allura Red)
– Mechanism unclear

Allergic Reactions

Documented but uncommon. Some people may experience:

– Itching, hives, urticaria
– Nausea, GI distress
– Bronchospasm/asthma-like symptoms
– Anaphylaxis (rare)

Risk higher in people with history of dye sensitivities.

Medical Adverse Effects

When injected surgically (not food exposure):

– Low blood pressure (hypotension)
– Respiratory distress
– Anaphylactic shock (rare)
– May compromise renal function in some patients

Natural vs. Synthetic

E132 is 100% synthetic. While indigo itself is a natural dye (used historically for textiles), commercial E132 is entirely laboratory-manufactured.

Natural Alternatives to E132

Limited natural blue colorants exist, but they’re expensive and less stable:

The lack of affordable, stable blue natural dyes explains why manufacturers continue using E132 despite the concerns.

The Bottom Line

E132 (Indigotine) is a widely-used synthetic blue dye approved globally by major regulatory agencies.

What you should know:

• It’s common: In blue candies, drinks, ice cream, and many other foods worldwide
• It’s deemed safe by regulators: At permitted levels, below ADI by hundreds of times for most consumers
• It has a controversial safety signal: Brain tumors in high-dose rats; regulators say “not significant”; advocates disagree
• You consume tiny amounts: Most people eat far below the established safety limit
• It’s poorly absorbed: Most passes through your digestive system unchanged, minimizing internal exposure
• Behavioral effects possible: May increase hyperactivity in sensitive children; small effect size
• Allergic reactions rare: But possible in sensitive individuals
• Medical controversy exists: Safe at food levels, but can cause serious effects when injected surgically