Study finds link between color blindness and bladder cancer mortality

The study authors concluded that people with color blindness are more likely to seek medical help later because they do not recognize blood in their urine. As a result, the disease is detected at later stages, when the effectiveness of treatment is much lower. Anecdotal evidence and small studies have previously suggested that color blindness may contribute to late detection of diseases such as colon and bladder cancer. The reason is that patients with color vision impairment often do not notice blood in their stool or urine. For example, a 2009 study of 200 men with bladder cancer found that patients with color blindness were more likely to have the disease at a later and more aggressive stage compared to men with normal vision. Even earlier, in a 2001 study, researchers showed participants with and without color blindness images of saliva, urine, and feces and asked them to determine whether they contained blood. People with normal color vision coped with the task 99% of the time, while participants with color blindness did it only about 70%.

Intrigued by these findings, Rahimi’s team decided to study whether color blindness ultimately leads to worse outcomes in patients with bladder and colorectal cancer. To analyze the data, the scientists used the TriNetX research platform, which integrates electronic medical records from different countries in real time and contains about 275 million anonymized patient records. Such a large-scale database makes it possible to find groups of people with rare combinations of characteristics, based on diagnostic codes. After analyzing approximately 100 million medical records of patients in the United States, the researchers identified 135 people with concurrent diagnoses of color blindness and bladder cancer, and 187 patients with color blindness and colorectal cancer.

For each of these groups, the platform created a matched control group: patients with the same type of cancer, similar demographics and health status, but with normal color vision. The results showed that among bladder cancer patients, people with color blindness had lower survival rates compared to patients without visual impairment. Over 20 years, their overall risk of death was 52% higher, when mortality from all causes was taken into account. Scientists expected to see a similar picture in patients with colorectal cancer, but there were no statistically significant differences in survival between people with color blindness and normal vision.

Additional analysis found that nearly two-thirds of colon cancer patients initially see their doctor because of abdominal pain, and more than half notice changes in their bowel movements. In the case of bladder cancer, the situation is different: in 80-90% of patients, the first symptom is the painless appearance of blood in the urine. Additionally, the widespread use of colorectal cancer screening—recommended for most people ages 45 to 75—reduces the role of self-detection of blood in stool for early diagnosis of the disease.