SOURCES: Julian Benito-Leon, M.D., Ph.D., staff physician, Department of Neurology, Hospital Universitario 12 de Octubre, Madrid, Spain; Catherine Roe, Ph.D., assistant professor, neurology, Washington University in St. Louis, St. Louis, Mo.; April 9, 2014 online issue, Neurology.
WEDNESDAY, April 9, 2014 (HealthDay News) -- The scourge of dementia may come with a silver lining: Those with declining memory and thinking skills may be significantly less likely to die from cancer, new research indicates.
Analyzing more than 2,600 Spaniards over the age of 65, scientists found that people experiencing the fastest decline in mental skills were about one-third less likely to die of cancer over an average of 13 years.
The results echo those of numerous prior studies done worldwide suggesting an inverse relationship between Alzheimer's disease and cancer. Having one appears to markedly lower the odds of developing the other, though scientists don't yet know why that may be.
"I wasn't surprised by the results since there were other papers that suggested dementia decreased the risk of cancer," said study author Dr. Julian Benito-Leon, a staff physician in neurology at Hospital Universitario 12 de Octubre, in Madrid, Spain. "If, in the future, we could disentangle the mechanisms that trigger Alzheimer's disease, we could design and develop new and improved drugs that specifically damage cancer cells."
The study is published online April 9 in the journal Neurology.
More than 5 million Americans are affected by Alzheimer's, and one in three seniors dies with Alzheimer's or another dementia, according to the Alzheimer's Association. Meanwhile, cancer is the second-leading cause of death in the United States and accounts for one in every four deaths, according to the American Cancer Society.
For the new study, Benito-Leon and his team, who had published previous research on this topic, analyzed 2,627 people who took memory and thinking skills tests at the start of the study and again three years later.
Participants were split into three groups: those whose scores were declining the fastest, those whose scores improved and those in the middle.
About 21 percent of participants in the fastest-declining group died of cancer by the end of the study, compared to 29 percent of those in the other two groups. When results were adjusted to control for health factors such as smoking, diabetes and heart disease, those with the fastest decline in memory and thinking skills were still 30 percent less likely to die of cancer than those in the other groups.
The results were observational and do not prove a cause-and-effect relationship between dementia and cancer death risk.
Benito-Leon said that scientists need to better understand the link between Alzheimer's disease, which causes abnormal cell death, and cancer, which causes abnormal cell growth.
Catherine Roe, an assistant professor of neurology at Washington University in St. Louis, agreed.
"It's possible that these two share certain biological pathways that, tipped in one direction, mean cancer, or tipped in the other direction mean Alzheimer's," said Roe, who wasn't involved in the new study. "I think it's neat to see that researchers are finding the same things in different samples [of participants] and different geographic groups. It makes the results more believable."
The American Academy of Neurology offers guidelines on recognizing, diagnosing and treating Alzheimer's patients.