Science News from research organizations Stanford scientists say colorblindness may hide a deadly bladder cancer warning Colorblindness may hide the red flag of bladder cancer — and researchers found it’s linked to a 52% higher long-term mortality risk. Date: March 10, 2026 Source: Stanford Medicine Summary: Colorblindness may be doing more than making traffic lights confusing — it could also be hiding a life-threatening warning sign. Researchers analyzing millions of medical records found that people with bladder cancer who are also colorblind have a 52% higher mortality rate over 20 years compared to those with normal vision. The likely reason: many people with color vision deficiency struggle to see red, making it harder to notice blood in urine, the most common early sign of bladder cancer. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY Colorblind people may be missing one of bladder cancer’s most important early warning signs: blood in the urine. Credit: Shutterstock Seeing blood in urine is often the first clue that something is wrong. For many people, noticing this symptom prompts a medical visit that can lead to an early diagnosis of bladder cancer. However, for people with colorblindness, detecting that warning sign may be far more difficult. Because many forms of color vision deficiency make it hard to perceive red tones, blood in urine can go unnoticed. Researchers from Stanford Medicine and collaborating institutions report that missing this early symptom may have serious consequences. After analyzing health records, the team found that people who had both bladder cancer and colorblindness faced a 52% higher mortality rate over 20 years compared with bladder cancer patients who have normal vision. The researchers believe that people with colorblindness may delay seeking care because they fail to recognize blood in their urine. As a result, the disease may be diagnosed at a later stage, when treatment is more difficult and survival rates are lower. "I'm hopeful that this study raises some awareness, not only for patients with colorblindness, but for our colleagues who see these patients," said Ehsan Rahimy, MD, adjunct clinical associate professor of ophthalmology and senior author of the study published in Nature Health . The study's lead author is Mustafa Fattah, a medical student at Columbia University Vagelos College of Physicians and Surgeons. Colorblindness and Cancer Risk Colorblindness, also known as color vision deficiency, is more common than many people realize. About 1 in 12 men and 1 in 200 women are affected. The most widespread types interfere with distinguishing between red and green shades. This can create everyday challenges such as interpreting traffic lights, coordinating clothing, or judging whether meat is fully cooked. Bladder cancer also occurs much more frequently in men, who develop the disease about four times as often as women. In 2025, roughly 85,000 Americans were expected to receive a bladder cancer diagnosis. Earlier reports and smaller studies had already suggested that colorblindness might delay the diagnosis of certain diseases. If someone cannot easily recognize blood in stool or urine, conditions such as colorectal cancer or bladder cancer could be detected later. A 2009 study involving 200 men with bladder cancer found that those with color vision deficiency were often diagnosed at more advanced and invasive stages than those with typical vision. Another experiment conducted in 2001 asked participants to identify which images of saliva, urine, and stool contained blood. People with normal vision correctly identified the samples 99% of the time, while participants with colorblindness were correct only 70% of the time. These earlier findings prompted Rahimy and his colleagues to investigate whether colorblindness might ultimately affect survival in people diagnosed with bladder cancer or colorectal cancer. Searching Millions of Health Records To explore the question, researchers used a large research platform called TriNetX. The system compiles real time electronic health records from around the world and contains about 275 million de identified patient records. Because the database is so large, scientists can identify groups of patients who share unusual combinations of conditions using diagnostic codes. "The power in this type of study is the ability to curate a particular population of interest -- in this case, patients who are colorblind who develop bladder cancer or colorectal cancer," Rahimy said. "It's unusual to have that combination, but when you're casting a net in an ocean's worth of data, you have a better shot at capturing a rare fish." From roughly 100 million U.S. patient records, the researchers identified 135 people diagnosed with both colorblindness and bladder cancer, along with 187 patients who had both colorblindness and colorectal cancer. For each group, the team created a comparable control group