Mild cognitive impairment and dementia: the importance of modifiable risk factors

Abstract

Background: Mild cognitive impairment (MCI), a common condition among the elderly, is defined as a deterioration of memory, attention, and cognitive function that exceeds what would be expected for the individual's age and level of education, yet does not interfere significantly with the activities of daily living. MCI may be a precursor of dementia; the rate of transition from MCI to dementia is 10% to 20% per year. The role of somatic diseases and modifiable risk factors in MCI and dementia needs further study.

Methods: We analyzed pertinent original articles and reviews published 1990 up to December 2010 that were retrieved by a selective search in PubMed and the Cochrane Library.

Results: MCI and dementia are associated with many somatic disorders and modifiable risk factors. MCI has biologically plausible associations with hypertension, diabetes mellitus, and hyperlipidemia, although the interventional trials performed to date have yielded negative results. Recently, chronic renal failure has also been recognized as a risk factor. Insufficient evidence supports a putative benefit on MCI from the substitution of vitamin B12, vitamin D, or testosterone (when these substances are deficient), the treatment of hyperhomocysteinemia or subclinical thyroid dysfunction, or hormone replacement therapy after menopause. Epidemiological data suggest that a Mediterranean diet, physical activity, and moderate alcohol consumption protect against MCI, while cigarette smoking promotes it and should be stopped.

Conclusion: Modifiable risk factors for MCI should be sought (at the very latest) in persons who already have MCI, as their optimal treatment may improve these patients' cognitive performance or keep the existing deficits from progressing.

Figure 1

Changes in various parameters during development of dementia (modified from e91). This greatly simplified depiction of the development over time of biomarkers (decreasing levels of amyloid ß1–42 in cerebrospinal fluid, increase in level of tau protein in cerebrospinal fluid as indicator of neurofibrillary degeneration), the findings of nuclear medicine (PET amyloid imaging with increasing cerebral deposition of amyloid ß1–42, FDG-PET with changes in cerebral metabolism) and structural imaging (increasing atrophy on CT or MRI), and clinical symptoms (impairment of cognition and daily function) in patients with dementia clearly shows the importance of early diagnosis and treatment. MCI, mild cognitive impairment

Figure 2

The association between chronic renal failure and cognitive impairment: findings of large (> 900 participants) cross-sectional (blue) and longitudinal (red) studies. CI, Confidence interval

Figure 3

The association between exercise and cognitive impairment: findings of large studies (> 1000 participants). CI, Confidence interval