By William C. Haas III, MD, MBA

Integrative Medicine Fellow, Department of Family and Community Medicine, University of Arizona, Tucson

Dr. Haas reports no financial relationships relevant to this field of study.

SYNOPSIS: Peak levels of cardiorespiratory fitness are positively correlated with enhanced cognitive function among older adults.

SOURCE: Freudenberger P, Petrovic K, Sen A, et al. Fitness and cognition in the elderly: The Austrian Stroke Prevention Study. Neurology 2016;86:418-424.

Despite overwhelming evidence supporting the benefits of regular physical activity, relatively few older adults achieve the minimum recommended amount of weekly physical activity.1 The trend toward increasing physical inactivity among the elderly raises concern, especially in light of research suggesting that physically active adults have a lower risk of cognitive decline and dementia compared to inactive adults.2 Efforts to slow cognitive decline and dementia are paramount given the lack of effective treatment options in addition to the associated social and economic burdens.

The precise neuroprotective mechanism resulting from enhanced physical activity remains unclear. One prevailing hypothesis suggests improved cardiovascular fitness reduces cerebrovascular disease.3 Cardiovascular fitness, defined as the body’s maximal capacity for oxygen consumption (VO2max), is an important variable for consideration, as cardiovascular fitness declines with age, but can increase with regular physical activity.

Drawing patients from the original Austrian Stroke Prevention Study, Freudenberger et al conducted a follow-up cohort study to clarify the connection between cardiorespiratory fitness and cognitive function. The primary purpose of the study was to determine the effect of VO2max on global and domain-specific cognitive function. Researchers also attempted to determine whether the effect of VO2max on cognitive function was mediated by signs of brain aging seen on MRI.

The authors recruited 877 patients from the Austrian Stroke Prevention Study to participate. The original prevention study was a community-based cohort study that evaluated the effects of vascular risk factors on brain structure and function in elderly patients without a history of stroke or dementia. Participants recruited for the follow-up study underwent additional testing, including cognitive testing, exercise ECG, and MRI. Cognitive testing consisted of a battery of validated tests involving memory, motor skills, and executive function. Exercise ECG was performed to estimate VO2max based on the formula: 15 x (maximum heart rate/resting heart rate). Researchers performed an MRI to quantify lacunar infarct burden, white matter lesions, and atrophy. The authors also assessed vascular risk factors and included cigarette smoking, hypertension, cholesterol, type 2 diabetes mellitus, and body mass index.

With regard to the main outcome, VO2max displayed a positive linear trend for enhanced memory, executive function, and global cognition. The differences in effect size between the lowest and highest quartile of VO2max were 0.298 for memory (P = 0.001), 0.117 for executive function (P = 0.005), and 0.260 for global cognition (P = 0.001). Interestingly, the differences displayed by individuals in the highest vs. lowest quartile of VO2max corresponded to an age difference of four, six, and seven years for global cognition, memory, and executive function, respectively. Finally, with regard to secondary outcomes, the effect of VO2max on cognition was not mediated by the presence of lacunar infarcts, white matter lesions, or atrophy.

COMMENTARY

Before forming clinical recommendations based on these results, it is important to revisit the purpose of the study. The researchers specifically attempted to determine whether greater cardiorespiratory fitness was associated with better cognitive function based on protection of cortical and subcortical brain structures. Although researchers did not find evidence to support their neuro-structural protection hypothesis, they established a positive correlation between VO2max and cognitive performance. In fact, participants with the highest VO2max demonstrated a significantly younger cognitive age compared to participants with the lowest VO2max.

Despite positive correlations between VO2max and cognitive performance, advise caution when recommending vigorous physical activity to elderly patients based solely on the results of this study. VO2max represents the ability of the cardiopulmonary system to uptake, transport, and use oxygen during bouts of maximal physical exertion. It is a measure of peak cardiorespiratory fitness and is not synonymous with general physical fitness. Although consistent exercise at sub-maximal exertion levels can improve VO2max, such vigorous exercise is unlikely advisable for the majority of elderly patients. It is also important to note that up to 65% of VO2max may be attributed to non-modifiable genetic factors.4

Also consider a few inherent limitations of the study. The cross-sectional nature reflects correlations only at a moment in time. Clinicians can only infer the ability to improve cognitive function with improvements in VO2max. Additionally, one of the main variables, VO2max, was estimated and not directly measured, which could alter actual results.

This study shines light on the important topic of preserving cognitive function with aging. Cardiorespiratory fitness appears to function as a protective factor against cognitive decline. However, the study falls short of establishing a connection between improvements in cardiorespiratory fitness and improvements in cognitive function. Until additional studies are performed with regard to optimizing cognitive function, clinicians should continue counseling their patients on age-appropriate exercise given the many other well-known health benefits.

REFERENCES

  1. Elsawy B, Higgins KE. Physical activity guidelines for older adults. Am Fam Physician 2010;81:55-59.
  2. Hamer M, Chida Y. Physical activity and risk of neurodegenerative disease: A systematic review of prospective evidence. Psychol Med 2009;39:3-11.
  3. Ainslie PN, Cotter JD, George KP, et al. Elevation in cerebral blood flow velocity with aerobic fitness throughout healthy human ageing. J Physiol 2008;586:4005-4010.
  4. Bouchard C, Rankinen T, Timmons JA. Genomics and genetics in the biology of adaption to exercise. Compr Physiol 2011;1:1603-1648.