Washington: A common vision condition that affects millions of people worldwide may be quietly hiding an early warning sign of bladder cancer, potentially delaying diagnosis and increasing long-term health risks, according to a new research.
Scientists from Stanford Medicine have found that people with color vision deficiency — commonly known as colorblindness — may be less likely to notice blood in their urine, one of the earliest and most important signs of bladder cancer. The study suggests that this overlooked factor could significantly affect survival outcomes.
The research, published in Nature Health, found that bladder cancer patients who were also colorblind had a 52 percent higher risk of death over a 20-year period compared to patients with normal color vision.
Blood in urine is often the first visible symptom of Bladder Cancer. For many patients, spotting this change prompts a medical consultation that leads to early detection and treatment. But for individuals with color vision deficiency, distinguishing red shades can be difficult, meaning the warning sign may go unnoticed.
“I’m hopeful that this study raises awareness, not only for patients with colorblindness but also for clinicians who treat them,” said Ehsan Rahimy, senior author of the study and adjunct clinical associate professor of ophthalmology at Stanford. The study’s lead author was Mustafa Fattah.
Colorblindness is far more common than many people realize. Experts estimate that roughly one in twelve men and about one in two hundred women have some form of color vision deficiency. The most common types make it difficult to distinguish between red and green tones — a limitation that can affect everyday activities ranging from interpreting traffic lights to identifying whether food is fully cooked.
The research team suspected that the same limitation could interfere with the ability to detect blood in bodily fluids, an important early sign not only of bladder cancer but also other illnesses.
To explore the connection, the researchers examined millions of electronic health records using the TriNetX research platform, a global medical database containing information from hundreds of millions of patients.
From roughly 100 million US medical records, the team identified a small group of patients who had both bladder cancer and colorblindness. They then compared these patients with a similar group of bladder cancer patients who had normal vision.
The findings were striking: over two decades, mortality rates were significantly higher among the colorblind group.
“This was something we suspected based on earlier studies,” Rahimy said, explaining that patients who cannot easily recognise blood in urine may delay seeking medical attention. When bladder cancer is diagnosed later, it is often more advanced and harder to treat.
Interestingly, the researchers did not observe the same survival difference among patients with Colorectal Cancer. Scientists believe that may be because colorectal cancer usually presents with several symptoms, such as abdominal pain or changes in bowel habits, rather than relying primarily on visible blood as an early signal.
Bladder cancer, however, presents differently. In up to 90 percent of cases, the first noticeable sign is painless blood in urine, making visual detection particularly important.
The researchers also warn that the real impact could be even greater than the study suggests. Many people with color vision deficiency never receive a formal diagnosis, meaning they may not appear as colorblind in medical records.
The findings have sparked conversations among doctors about whether patients should be routinely asked about color vision deficiency during medical screening.
For individuals who are colorblind, the researchers say simple precautions may help. Routine urine tests during health checkups, or asking a partner or family member to help monitor changes, could assist in identifying potential problems earlier.
“If this study raises awareness and encourages people to think about this possibility, then it has done its job,” Rahimy said.
