Bladder cancer is often discovered because a person notices blood in their urine. For many patients, this is the first warning sign that something is wrong.
Seeing this change usually encourages people to visit a doctor, and early medical attention can greatly improve the chances of successful treatment.
However, a new study suggests that some people may have difficulty noticing this important symptom. Individuals with color vision deficiency, commonly known as colorblindness, may struggle to detect red tones, which could make it harder for them to recognize blood in their urine.
Researchers from Stanford Medicine and several collaborating institutions recently examined whether this difficulty could affect health outcomes.
Their findings suggest that people who have both colorblindness and bladder cancer may face a higher risk of death than patients with normal color vision. The study was published in the journal Nature Health.
Colorblindness is a condition that affects how people perceive certain colors. The most common form makes it difficult to distinguish between red and green shades. While this may sound like a minor issue, it can influence many everyday activities.
For example, people with color vision deficiency may find it harder to read traffic lights, match clothing colors, or judge whether certain foods are cooked properly.
The condition is more common than many people realize. About one in twelve men has some form of colorblindness, while it affects about one in two hundred women.
This difference exists because the genes responsible for color vision are located on the X chromosome. Since men have only one X chromosome, they are more likely to show the condition if the gene is affected.
Bladder cancer also occurs much more frequently in men than in women. In the United States alone, about 85,000 people were expected to be diagnosed with bladder cancer in 2025.
One of the most common early signs of this disease is blood in the urine, a symptom known as hematuria. In fact, medical studies show that between 80 percent and 90 percent of bladder cancer patients first notice painless blood in their urine before receiving a diagnosis.
If a person cannot easily see that blood, the warning sign may be missed. Researchers believe that this delay could allow the cancer to progress before medical care is sought. When bladder cancer is discovered later, it is often more advanced and harder to treat.
To explore this possibility, the research team analyzed large amounts of medical data using a platform called TriNetX. This system collects electronic health records from around the world and contains information from roughly 275 million patients. Large databases like this allow scientists to identify patterns that would be difficult to detect in smaller studies.
From approximately 100 million U.S. patient records, the researchers identified 135 people who had both bladder cancer and colorblindness. They also found 187 patients who had both colorblindness and colorectal cancer. For each of these groups, the researchers created comparison groups of patients with the same cancers but normal color vision.
The results showed a clear difference for bladder cancer patients. Over a 20-year period, individuals with colorblindness had a 52 percent higher overall risk of death compared with patients who had normal vision. This measure included deaths from all causes, not just cancer.
The researchers believe this difference likely reflects delayed diagnosis. If someone cannot easily detect blood in their urine, they may wait longer before seeking medical care. By the time the cancer is discovered, it may already be more advanced.
Interestingly, the same pattern did not appear in people with colorectal cancer. The researchers expected that colorblindness might also delay detection of blood in stool, which can be a sign of colorectal cancer. However, the data did not show a significant difference in survival between colorblind and non-colorblind patients with this disease.
One explanation is that colorectal cancer often produces several early symptoms. Many patients experience abdominal pain, changes in bowel habits, or unexplained weight loss before blood in stool becomes noticeable.
In addition, routine screening tests such as colonoscopies are widely recommended for adults between the ages of 45 and 75. These screening programs help detect colorectal cancer early, even if people do not notice symptoms themselves.
Another factor may be that colorblindness is not always diagnosed. Many people with color vision deficiency do not realize they have it, especially if their condition is mild.
Because this study relied on medical records, some individuals with undiagnosed colorblindness may have been counted as having normal vision. This means the real difference in survival could potentially be even larger than reported.
The findings highlight the importance of awareness for both patients and doctors. People with color vision deficiency may benefit from regular medical checkups that include urine testing. In some cases, they may also consider asking a partner or family member to help monitor changes in urine color.
From a medical perspective, doctors may want to ask patients about color vision when discussing symptoms or screening practices. Even a simple question about colorblindness could help identify patients who might need additional monitoring.
In reviewing these findings, it is important to remember that the study shows an association rather than direct proof of cause.
Other factors could also influence survival differences between groups. However, the results strongly suggest that difficulty recognizing blood in urine may contribute to delayed diagnosis for some patients.
Overall, the research provides a new perspective on how a common visual condition could influence the detection of disease. It also highlights how small barriers in recognizing symptoms can have significant consequences for long-term health outcomes.
Further research will help clarify these relationships and may lead to improved screening strategies that ensure all patients have an equal chance of early diagnosis and treatment.
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