March 24 (UPI) -- Adults who experience loneliness during middle age are more likely to develop dementia and Alzheimer's disease later in life, a study published Wednesday by the journal Alzheimer's and Dementia found.
People who were "persistently lonely" between ages 45 and 64 had a 91% higher risk for dementia and a 76% higher risk for Alzheimer's disease compared to people who don't feel lonely, the data showed.
Preventing persistent feelings of loneliness, or consistent and continuous social isolation, may help limit the risk for cognitive decline in older adults, the researchers said.
"We think because human beings are social and need social interaction, without ... interaction, the brain can lose external stimulation, which can increase Alzheimer's risk," study co-author Dr. Wendy Qiu told UPI in an email.
"We think that persistent loneliness reflects a person's coping skills and life stressors, such as financial situations, medical conditions [and] family change, which middle-aged people often face," said Qiu, a professor of psychiatry and pharmacology at Boston University School of Medicine.
About 6 million adults in the United States have dementia, the Alzheimer's Association estimates. Alzheimer's disease is a severe form of dementia that tends to strike adults at a younger age, according to the association.
Social isolation, lack of physical exercise and intellectual stimulation and poor physical health are among the risk factors for all forms of dementia, including Alzheimer's disease, Qiu and her colleagues said.
Increased feelings of loneliness have been linked with steeper declines in cognitive function in earlier studies, but the reasons for the relationship are unclear.
Loneliness is a subjective feeling resulting from a perceived difference between desired and actual social relationships.
Although loneliness does not itself have the status of a clinical disease, it is associated with a range of negative health outcomes, including sleep disturbances, depressive symptoms, cognitive impairment and stroke.
For this study, the researchers assessed 2,880 participants age 45 to 64 in the Framingham Heart Study, an ongoing analysis of heart disease risk launched in 1948, for levels of loneliness and dementia onset.
Among the participants, 74% reported no loneliness and 8% reported "transient loneliness," meaning they expressed feelings of social isolation one or two days per week at one exam, but not the next, the researchers said.
In addition, just over 8% reported "incident loneliness," meaning they expressed feelings of social isolation at a follow-up exam after not indicating them initially.
About 9% of the participants indicated they experienced persistent loneliness, meaning they reported feelings of social isolation one or two days per week or more at more than one exam, the researchers said.
Of the 2,880 study participants, 218, or about 8%, developed dementia during roughly 20 years of follow-up, and more than 80% of them were diagnosed with Alzheimer's disease.
Among those who reported no feelings of loneliness, 7% developed dementia and 6% were diagnosed with Alzheimer's disease.
However, of those who reported persistent loneliness, 13% developed dementia and 11% were diagnosed with Alzheimer's disease.
No differences existed in dementia and Alzheimer's disease risk among middle-aged adults who reported incident or transient loneliness and those who reported no loneliness at all, according to the researchers.
"People in this age group should realize the existence of the risk and prepare to face mid-life challenges," Qiu said.
"As a society, we can do things to intervene in loneliness, like providing counseling and reaching out to those who are facing life stressors or grieving," she said.