However, senior author, Dr. Gary Small, director of the University of California, Los Angeles, Longevity Center, said depression was the strongest single risk factor for memory complaints in all of the adults.
"In this study, for the first time, we determined these risk factors may also be indicative of early memory complaints, which are often precursors to more significant memory decline later in life," Small, who is also a professor of psychiatry and biobehavioral sciences at the Semel Institute for Neuroscience and Human Behavior at UCLA, said in a statement.
The UCLA researchers and Gallup surveyed 18,552 individuals ages 18 to 99 about their memory and lifestyle factors previously shown to increase the risk of Alzheimer's disease and dementia -- depression, lower education levels, physical inactivity, high blood pressure, diabetes, obesity and smoking.
The study, published in the journal PLOS ONE, found 20 percent said they had memory complaints, including 14 percent in adults ages 18 to 39, 22 percent of adults ages 40 to 59 and 26 percent of adults ages 60 to 99. One risk factor significantly increased the frequency of memory complaints and the more the risk factors, the level of memory complaints increased.
The study authors said they were surprised by the prevalence of memory issues among younger adults.
The Gallup poll was conducted from December 2011 to January 2012 and was part of the Gallup-Healthways Well-Being Index, which includes health and lifestyle questions.
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