There’s no positive side to developing skin cancer, but the latest research ties certain forms of the disease to a reduced risk of dementia.
In the study, published in the journal Neurology, 1,100 people around age 79 without dementia were studied for an average of 3.7 years. At the beginning of the study, 109 of the participants already had skin cancer, and during the study, 32 more people developed the disease, while 126 eventually developed dementia. Among those participants, 100 developed Alzheimer’s dementia.
The participants who had skin cancer were about 80% less likely to have Alzheimer’s disease compared to the participants without a history of skin cancer. Among those with skin cancer, only two developed Alzheimer’s. The association, however, was not seen with people who developed melanoma, nor did the correlation hold for other types of dementia such as those related to circulatory issues.
“The apparent protective effect is enormous, and we were surprised by the magnitude,” says study author Dr. Richard Lipton, a professor at Albert Einstein College of Medicine.
The findings don’t establish that skin cancer patients are always protected from developing Alzheimer’s however. And it’s not clear which factors might be behind the association. But Lipton and his colleagues believe environmental factors could be contributing to the result. Studies have found, for example, that exercise is linked to a lower risk of Alzheimer’s. It’s possible that people who are more active may spend more time outdoors and in the sun, which could put them at a greater risk for skin cancer, while at the same time reducing their chances of developing Alzheimer’s.
In addition, people who are more exposed to the sun’s ultraviolet rays may also absorb more vitamin D, which other research suggests could protect against Alzheimer’s.
On a more speculative level, Lipton says Alzheimer’s disease and cancer represent different aspects of cell regulation. In cancer, the cells divide out of control and form tumors. In Alzheimer’s, specific cell populations degenerate and die. He says that among skin cancer patients, there may be a balance between the cells that divide and the cells that die. “The propensity for cells to divide may increase the risk of cancer, but decrease the risk of cell degeneration and Alzheimer’s,” he says. If that’s true, it might also explain why people with melanoma don’t show the apparent protection against Alzheimer’s, since melanoma is a particularly aggressive form of skin cancer.
Regardless of why the association exists, Lipton says the results should not be a license to abandon sunscreen or to protect the skin from ultraviolet rays. “Whatever we learn from this might lead to interventions. If it turns out the vitamin D hypothesis is correct, no doctor will say, ‘get skin cancer,’ but they might recommend taking vitamin D supplements.”
Lipton is particularly eager to follow that research, and hopes more scientists will explore the connection to see whether there are better ways of addressing Alzheimer’s. He recently visited his dermatologist, and was diagnosed with squamous cell skin cancer, one of the most common forms of the disease. ”I said, ‘Oh good,’ because my mom died of Alzheimer’s disease and I live in fear of it. It’s not that having skin cancer makes it a guarantee, but you’re at a reduced risk and that provides a little upside to something that otherwise has only downsides,” he says.