Little is known about the risks that adults with ADHD have for developing dementia or mild cognitive impairment (MCI). This study aimed to understand this relationship using the medical data available in the national registers of Sweden. It also aimed to understand whether there is an association between ADHD and the onset of dementia depending on sex, as the two conditions have different prevalence rates in men and women (Fayyad et al, 2017; Ruitenberg et al, 2001).

The total study cohort included over 3 million adults born in Sweden between 1932 and 1963, who were still residents in Sweden and alive in 2001. Individuals were followed-up from their 50th birthday until dementia or MCI diagnosis, death, emigration or the end of 2013. Adults with ADHD (diagnosed at any age), dementia or MCI (diagnosed at age ≥50 years) were identified through medical records and prescription reports. The presence of comorbidities was also considered. The results obtained were compared with those of adults without ADHD.

Within the study cohort, 9532 (0.3%) adults had a confirmed diagnosis of ADHD, or prescribed medications for ADHD; a total of 5168 (54.2%) were male, and the overall median age at diagnosis was 52 years (interquartile range [IQR] 48–57). By the end of the follow-up, 55,194 (1.5%) and 23,507 (0.6%) adults had developed dementia or MCI, respectively. Adults with ADHD were younger than adults without ADHD when diagnosed with dementia (median [IQR] age at diagnosis, 61.5 [56–70.5] years vs 72 [67–76] years) or MCI (median [IQR] age at diagnosis 59 [53–66] years vs 69 [62–74] years), and showed increased risk of developing either dementia (hazard ratio [HR] 2.92, 95% confidence interval [CI] 2.40–3.57) or MCI (HR 6.21, 95% CI 5.25–7.35).

Comorbidities such as metabolic and sleep disorders had a minimal influence on the associations of ADHD with dementia (HR 2.81, 95% CI 2.30–3.43 for metabolomic disorders; HR 2.73, 95% CI 2.23–3.33 for sleep disorders) and MCI (HR 5.81, 95% CI 4.91–6.87 for metabolomic disorders; HR 4.81, 95% CI 4.06–5.69 for sleep disorders), as opposed to psychiatric disorders, which significantly attenuated the observations (HR 1.62, 95% CI 1.32–1.98 for dementia; HR 2.54, 95% CI 2.14–3.01 for MCI). Furthermore, the study showed that women with ADHD had a 42% lower chance of developing dementia compared with men, but that they shared the same probability of developing MCI.

Regarding limitations associated with this study, misdiagnosis of ADHD was possible, because early symptoms of dementia, such as poor attention or memory problems, might overlap with those of ADHD. This issue was partially addressed in the study; however, the authors suggested that further studies are required to validate MCI and adult ADHD classification criteria in Swedish registries. Furthermore, the relatively young age of the study cohort at the end of the follow-up (median age of 63 years) may suggest that the study only captured cases of early-onset dementia and MCI, and may have influenced the observed rates of dementia between men and women. It was also not possible to account for the associations between ADHD and subtypes of dementia, or for other health behaviours, such as diet, exercise or smoking habits.

The study showed that there is an increased risk for adults with ADHD to develop dementia and MCI compared with those without ADHD, although the risk significantly attenuates after controlling for psychiatric disorders, and that the association with dementia is stronger in men than in women. However, the researchers suggested that further studies should address the limitations of the current study and provide a more accurate picture of these associations.

Read more about the relationship between ADHD and dementia here

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