Also, more than half of these patients also suffer from persistent fatigue, and about 20% indicate that these persistent symptoms continue to limit their work and other life activities, the data showed.
In addition, 41% of those who have memory problems months after infection say their overall health has worsened over the past year.
"Our findings suggest that [COVID-19] may negatively impact memory even eight months after having a mild case of the disease, and this can be associated with a worsening of health," researchers from Oslo University Hospital in Norway wrote.
"The findings are a strong impetus to reconsider the notion that COVID-19 can be a mild disease," they said.
Since the start of the pandemic, several studies have shown that many people infected with the coronavirus experienced lingering symptoms, including cognitive problems, for months, a complication that has been dubbed "long-haul" COVID-19.
For this study, the researchers compared more than 2,100 adults who tested positive for the virus in Norway between Feb. 1 and April 15 last year with 31,000 adults who tested negative and 20,000 untested adults, based on various health measures.
All participants were asked to report on their health status, as well as any memory loss and problems concentrating, the researchers said.
Of the 651 participants who tested positive for COVID-19 and responded to the study questionnaire eight months after getting infected, 72, or 11%, reported memory loss and 81, or 12%, indicated that they had problems concentrating.
Over the study period, those who tested positive for the virus were more than twice as likely to report cognitive problems compared with those who tested negative or never underwent testing.
"Subjective memory concerns have been shown to reflect objective problems and observable changes in everyday function, even when controlling for associated factors, such as depression," the researchers wrote.
"Self-reported memory problems are also a risk factor for later mild cognitive impairment or dementia," they said.