A study from April 2016 in the Journals of Gerontology calls into question the notion that cancer may protect against Alzheimer’s disease.
Investigators analyzed data from almost 93,500 individuals from age 65 to 79 with or without a history of cancer and followed them for up to 18 years, checking for the development of Alzheimer’s disease.
While they confirmed that having cancer is indeed associated with reduced risk of subsequently developing Alzheimer’s, this is not because cancer protects against it.
A much simpler explanation accounts for the reduced risk: Many people with cancer simply don’t live long enough to get Alzheimer’s.
Analyzing the data from the Utah Population Database, which includes demographic, medical, and other records, the researchers used three different statistical methods, each of which took into account the higher rates of death among individuals with cancer. Doing so showed that participants with cancer were not less likely to develop Alzheimer’s than their cancer-free peers.
This suggests that increased death rates in survivors of cancer, not the disease itself, account for the observed association between cancer and reduced dementia risk.