Having colorblindness could be even more of a disadvantage than commonly thought. Research published this month might indicate that colorblind people are less able to literally spot certain cancers before it’s too late.
Researchers at Stanford University and others examined the medical records of people with color blindness and cancer. Compared to others, colorblind people had a higher chance of not surviving their bladder cancer, they found. The results suggest that individuals with colorblindness often don’t perceive blood in their urine, the researchers say—a key early warning sign of the disease.
“I’m hopeful that this study raises some awareness, not only for patients with colorblindness, but for our colleagues who see these patients,” senior study author Ehsan Rahimy, adjunct clinical associate professor of ophthalmology, told the Stanford Report over the weekend.
A color disadvantage
Colorblindness, or color vision deficiency, is relatively common, though much more so in men. About 8% of men are estimated to have some degree of colorblindness, compared to 0.5% of women.
Most cases are caused by genetic mutations, and the condition comes in several forms depending on how a person’s cone cells function abnormally. Our cones normally recognize blue, red, and green light and send corresponding signals to the brain; the perception of other colors then comes from the mixing and interpretation of these signals by the brain. That said, many colorblind people tend to have trouble seeing both red and green.
It’s sometimes so mild that people will go years or even their entire lives without knowing they have it. But some case reports and small studies have hinted that colorblind people have a worse time on average when they develop bladder or colorectal cancer. Since these cancers regularly cause blood to show up in urine or stool (often without pain) before more apparent symptoms, some researchers have hypothesized that colorblind people simply don’t see these early indicators.
To better unravel this potential phenomenon, the researchers examined a large database of electronic health records. They analyzed the records of 136 colorblind people diagnosed with bladder cancer, as well as 187 colorblind people with colorectal cancer. Both groups were compared to similar non-colorblind people with these cancers.
Colorblind people with bladder cancer lived shorter lives compared to their non-colorblind counterparts, the researchers found. Over a 20-year span, colorblind people with bladder cancer had a 52% higher risk of dying in general. Interestingly, though, there was no apparent difference in survival between colorblind and non-colorblind people who had colorectal cancer.
The researchers aren’t exactly sure why this pattern was only seen with bladder cancer. But they note that colorectal cancer can cause other early, noticeable symptoms besides a bloody stool, including chronic diarrhea or constipation. The average person is routinely advised to start getting screened for colorectal cancer as early as age 45, which could reduce the time it takes for people with colorblindness to notice something wrong compared to everyone else.
What should this mean for colorblind people?
The researchers caution their findings shouldn’t be seen as definitive proof of a causative link between colorblindness and worse outcomes for bladder cancer. Nor are they calling for radical changes in the advice that doctors give to such individuals, at least right now. But the study does warrant further research and awareness of the potential perception gap that colorblind people might face with these cancers, they argue.
“This is a hypothesis-generating paper that should raise clinicians’ diagnostic suspicion for bladder cancer in patients with color vision deficiency and prompt further investigation into whether screening for bladder cancer should be introduced for high-risk individuals with color vision deficiency,” they wrote in their paper, published this month in Nature Health.
