Mild cognitive impairment (MCI) is the stage before the diagnosis of dementia. Although the primary caregiver or the patient complains of subjective memory deterioration, there is no significant difficulty in performing daily activities.1 Since there are individual differences in the degree of cognitive decline depending on the time of diagnosis, other cognitive functions along with memory may also deteriorate; 1 to 2 out of 10 individuals recover their cognitive abilities.2, 3 However, it is highly likely to progress to dementia if left untreated because the pathological progression of brain cells has already begun.2 Dementia occurs due to irreversible damage to brain cells that impairs cognitive function, making daily life challenging and distressing for older adults and their caregivers.1,4 Approximately 23.8%–46% of older adults with MCI aged 65 years or above progress to dementia within three years of onset.5, 6 Therefore, it is essential to prevent the early onset of dementia in people with MCI.

Researchers have conducted studies on cognitive improvement interventions and the management of cognitive decline risk factors to prevent the progression of MCI to dementia in older adults.7, 8 In particular, research emphasized non-pharmacological interventions to enhance cognitive function in older adults with MCI because there is insufficient evidence to demonstrate the efficacy of pharmacological interventions.1,9 Studies found that among the risk factors for cognitive decline in MCI, the prevalence of sleep disturbance is between 60.3% and 70.1%, which is higher than that of cognitively healthy individuals.10, 11, 12 Furthermore, studies have reported sleep quality to be low in over 60% of older adults with MCI.12 If low sleep quality persists for more than two years, the transition to dementia occurs three times faster due to brain atrophy and beta-amyloid accumulation.13, 14 Therefore, it is essential to actively manage sleep disorders among older adults with MCI.

There are reports that when older adults with MCI continually exercise—the non-pharmacological intervention to be verified in the present study—this lowers the risk of progression to dementia15 and more effectively improves cognitive function than prescription drugs.16 Additionally, exercise is effective in improving the quality of sleep among older adults.17 If they do not exercise consistently, cognitive decline will continue,15 and sleep problems are likely to occur.18 Accordingly, evidence for a more effective exercise method is required because continuous exercise is essential for older adults with MCI.

To date, meta-analyses of exercise therapy, including various exercise types in older adults with MCI, have been conducted by researchers.19,20 Subgroup analyses of these meta-analyses revealed that only aerobic exercise had a consistent effect on improving cognitive function, and the effects of resistance exercise differed. In addition, resistance exercise may not be easily accessible for older adults due to the use of weight loads, and issues such as injuries and fractures may occur when performing strengthening exercises with various equipment.21 On the other hand, the aerobic exercise we want to review can be easily performed by older adults because it is widely available, low cost, and low risk.22 Furthermore, aerobic exercise affects cognitive function by strengthening the cardiopulmonary system; increasing cerebral blood flow, the size of the hippocampus, and neuroplasticity; and enhancing the secretion of neurotransmitters.23,24

Prior meta-analyses of aerobic exercise alone25,26 also reported positive effects on improving cognitive function in older adults with MCI. However, these meta-analyses focused on differences in measurement instruments and did not analyze the effects of type, time, and frequency of aerobic exercise. Therefore, the present systematic review and meta-analysis aims to evaluate the effects of aerobic exercise on cognitive function and sleep in older adults with MCI, and to investigate specific exercise methods.