Color blindness increases the death rate from bladder cancer… What is the connection?

Researchers from Stanford University School of Medicine, Columbia University, and Beaumont Hospitals in the United States have revealed striking findings regarding a link between color blindness and bladder cancer.

The study, recently published in the journal Nature Health, showed that death rates from bladder cancer are about 52% higher in people with color blindness compared to patients without the condition.

Bladder and colon cancer

The study relied on analyzing patient data from their medical records stored on the TriNetX platform over a period of 20 years (2004–2025). After data refinement, the sample included 135 patients with bladder cancer and color blindness, and 187 patients with colorectal cancer and color blindness.

The study, a retrospective cohort study, aimed to assess the impact of color blindness on the health status of these patients when diagnosed with these cancers, by comparing them to another group of patients with bladder or colorectal cancer, but without color blindness.

The results showed a 52% higher mortality rate from bladder cancer among colorblind patients compared to those without color blindness. This is attributed to the difficulty in recognizing one of the most important early warning signs: the presence of blood in the urine, which appears red but is painless, leading to a delay in recognizing the condition.

As a result of this delay, the disease is often only discovered in advanced stages after the cancer has developed and spread, especially since this symptom is not accompanied by pain that would prompt the patient to seek medical care early.

The color red and color blindness

Color blindness, also known as color vision deficiency, is a genetic visual problem that impairs a person’s ability to distinguish certain colors of the visible spectrum within certain wavelengths, specifically one of the primary colors (red, blue, green). The most common is impaired red and green vision, so their ability to perceive and distinguish these colors with somewhat weak accuracy is limited.

Although color blindness is a genetic problem related to genes on the mother’s side specifically (carried on the X chromosome), it can be acquired as a result of other diseases, taking certain medications, or possibly due to damage to the cornea or optic nerve and other possible causes. It is more common among males (8%) than females (0.5%), at a rate of one in 12 men and one in 200 women.

Color blindness and colorectal cancer

The study also revealed an almost negligible effect after tracking the impact of color blindness on colorectal cancer patients when compared to those without color blindness. Blood in the stool appears as one of the early warning signs in the case of colorectal cancer, and although colorblind patients have a reduced ability to distinguish the red color of blood coming out with the stool, the results did not show significant differences between the two groups.

Colorectal cancer is the second leading cause of cancer death worldwide and the third most common cancer. In recent years, it has been observed to be increasingly common among younger age groups, including people in their twenties, thirties, and forties, whereas it was previously more prevalent among those over fifty.

This shift is partly attributed to changing lifestyles, such as the increasing popularity of fast food rich in processed meats, and the low intake of fiber found in vegetables and fruits, along with rising obesity rates and low levels of physical activity.

Similar symptoms, different effects

The high mortality rates among colorblind bladder cancer patients were not surprising, given their difficulty in distinguishing the red color of blood in the urine, which is one of the most prominent early signs of the disease, leading to delayed diagnosis and its discovery in advanced stages that are difficult to treat.

But what is striking about the results is the absence of a similar effect of color blindness on colorectal cancer patients, although the appearance of blood in the stool is also a common early symptom, as is the case in bladder cancer.

After analyzing and evaluating the results, the researchers suggested a range of reasons behind this difference in impact between bladder cancer and colorectal cancer in colorblind patients with similar early symptoms, summarized in the points below:

Painless blood in the urine is classified as the only warning sign associated with bladder cancer, as it appears in between 80% and 90% of patients. The inability to detect it means a delay in diagnosis due to the patient’s inability to distinguish blood in the urine, especially since there is no pain to indicate it. Cancer cells gain additional time that allows them the opportunity to multiply and spread before they are discovered.

Colorectal cancer differs from bladder cancer in its more varied early symptoms, which are not limited to blood in the stool. According to a study published in the journal Surgery, 63% of patients experienced abdominal pain, 54% complained of changes in bowel habits, 53% experienced rectal bleeding, and approximately 32% experienced weight loss.

This variety of symptoms gives those with color blindness a greater chance of early detection, relying on indicators that do not require visual discrimination. Conversely, bladder cancer relies primarily on a single symptom, often painless, making it more difficult to detect in this group.

Therefore, it is essential to participate in early and regular screening programs for colorectal cancer. Such programs, along with their extensive awareness campaigns, are becoming increasingly common, which can contribute to the early detection of colorblind individuals who may be unaware of their condition. This, in turn, supports the hypothesis linking colorblindness to color cancer; without regular screening, these individuals would be unable to recognize and detect the symptoms.

Recommendation for colorblind patients and doctors alike

The study concluded with a clear recommendation urging people with color blindness to undergo regular checkups to identify early signs that may be related to bladder cancer, thus reducing the risk of the disease worsening and potentially saving the patient from a health problem that is poised to attack and destroy their cells, making it difficult to treat once discovered.

Doctors and specialists also recommended that color blind patients be directed to undergo tests and examinations that would reveal their condition and verify that their urinary system is free of any problems that may arise secretly without their knowledge and worsen later on.