A new meta-analysis published in the journal Sleep Medicine found that middle-aged adults who suffered from insomnia, nightmares and regular bouts of broken sleep were more likely to face cognitive impairment in their later years, reports the American Council on Science and Health.

The counterpoint to these findings, however, is that they were derived from self-reported data from four Scandinavian studies, so the data was not subjected to objective measurement by researchers. But given the large number of participants – two of the studies followed more than 3,300 subjects for over 20 years – the results carry some insight.

The authors of the study, “Sleep disturbances and later cognitive status: A multi-centre study,” from the Karolinska Institute in Stockholm, Sweden, and Imperial College London, used a test called the Mini Mental State Exam.