gms | German Medical Science

According to the World Health Organization, 37 million people worldwide live with dementia, the majority due to Alzheimer's disease (AD). With the ageing of populations, this figure is projected to increase rapidly over the next 20 years [Ref. 1]. Despite distinct pathophysiology, common risk factors for Alzheimer's disease and vascular dementia have been reported. From a public health point of view, there is growing interest in the epidemiology of impaired cognitive function as a multifactorial disease, regardless of disease type.

Physical inactivity is seen as a major risk factor for cardiovascular diseases [Ref. 2], [Ref. 3]. Recent evidence indicates that even low physical activity with a moderate intensity can be beneficial and lower the risk of cardiovascular disease [Ref. 2]. A study conducted in Germany also stresses the important role of leisure-time physical activity for reduction of risk factors of cardiovascular disease in the general population [Ref. 4].

The American Heart Association suggests regularly performed low-intensity activities for persons of every age (from 40% to 50% of maximum ventilatory oxygen uptake [Ref. 2]) performed daily to lower the risk of cardiovascular diseases. Further they suggest to include short periods of 5 to 10 minutes of moderate intensity (60-75% of maximal capacity) to a total of 30 minutes daily and a moderate to high resistance training for a minimum of 2 days per week (10 to 15 repetitions on each muscle group) [Ref. 2].

To our knowledge there are only a few studies about the influence of physical inactivity on cognitive function. Oswald et al. [Ref. 5] observed a reduction of symptoms of dementia related to a combined psychomotor and memory training over nine months (n=309). A moderate correlation between changes in grip strength, speed, and memory (n=425) was reported by Christensen et al. [Ref. 6], indicating that these variables have a tendency to move together over time.

Our objective was to examine the association between lack of physical activity and cognitive function in the elderly.

The HeiDE-study („Heidelberger Langzeitstudie zu Risikofaktoren und Diagnose chronischer Erkrankungen") is an ongoing population-based cohort study. All HeiDE participants had a 10-year follow-up (FU) in 2002-2003. The follow-up essentially consisted of a self-administered questionnaire on life style factors, including detailed information on physical activity (hours per week of activities not sufficient and sufficient to work up a sweat, respectively) during lifetime, and a self-report of incidence of physician diagnosed chronic diseases [Ref. 7]. According to recommendations of the American Heart Association [Ref. 2], we defined cut points for a lack of physical activity not strenuous enough to work up a sweat as less than 3.5 hours per week (equivalent to 30 minutes daily), and a lack of physical activity strenuous enough to work up a sweat as less than 2 hours per week.

Total hours of physical activity per week were calculated by adding hours of activities not strenuous enough to work up a sweat and hours strenuous enough to work up a sweat. Lack of total physical activity was defined as less than 3.5 hours of total physical activity per week.

Of all participants still alive at the 10-year follow-up (4857), 4010 (83%) sent back the questionnaire and gave written informed consent for future contact and follow-up. From January to December 2003, all 740 participants of HeiDE aged 70 years or more who had returned the follow-up questionnaire were eligible for a telephone interview on cognitive function. Validated instruments to assess cognitive function, including the Telephone Interview of Cognitive Status (TICS), were translated into German.

We first used multivariable linear regression with the TICS score as dependent variable and then dichotomized the TICS score at the 25^th percentile of values into impaired function (below 25^th percentile) and normal function and used multivariate logistic regression to estimate the association between lack of physical activity and impaired function on TICS test as dependent variable.

All models were controlled for age, gender, smoking, alcohol consumption, body mass index (BMI, weight in kg divided by squared height in m), educational level, and depressive symptoms to estimate mean differences in cognitive function scores and odds ratios (OR) of a low score (lack of physical activity below the defined cut points) and their 95% confidence intervals (CI) for participants with lack of physical activity compared to physical more active participants. In a second multivariable regression analysis we additional controlled for comorbidity.

Out of 473 participants interviewed (64.9% of all eligible), 52 reported a lack of physical activity not strenuous enough to work up a sweat like biking, and walking defined as less than 3.5 hours per week (11.8%). More than half (55.7%) of all participants (246) did not perform physical activities strenuous enough to work up a sweat for more than 2 hours a week. Overall, 37 participants (8.4%) reported less than 3.5 hours of total physical activity per week.

There was a trend towards lower performance on the TICS score for participants with lack of physical activity not strenuous enough to work up a sweat who scored lower on the TICS than participants who were physically active (crude mean difference: -1.0; 95% CI: -1.9 to -0.1, and multivariate-adjusted mean difference: -0.8; 95% CI: -1.6 to 0.1). The adjusted OR for impaired cognitive function in participants with lack of physical activity was 1.9 (95% CI: 0.9 - 4.1).

There was also a trend of lower performance on the TICS score for participants with less than 2 hours per week of physical activity strenuous enough to work up a sweat. They scored lower on the TICS than participants exercising more or equal than 2 hours per week (crude mean difference: -0.6; 95% CI: -1.2 to -0.1, and multivariate-adjusted mean difference: -0.7; 95% CI: -1.3 to -0.2). The adjusted OR for impaired cognitive function in participants with less than 2 hours per week of physical activity strenuous enough to work up a sweat was 1.3 (95% CI: 0.8 - 2.3).

Participants with a total physical activity per week of less than 3.5 hours scored again lower on the TICS than participants with more or equal than 3.5 hours (crude mean difference: -1.6; 95% CI: -2.6 to -0.5, and multivariate-adjusted mean difference: -1.2; 95% CI: -2.2 to -0.2). The adjusted OR for a low score in less physical active participants was 2.2 (95% CI: 0.9 - 5.0).

These trends were essentially unchanged by further adjustment for comorbidity.

The main limitation of our study is the cross-sectional design. Impaired cognitive function may result in physical inactivity rather than vice-versa. Individuals with a diagnosis of Alzheimer´s Disease have been shown to suffer from various extrapyramidal dysfunctions, e.g. spontaneous decreased movements in a study conducted among 467 participants [Ref. 8].To address this problem, we will analyze the effect of lifetime physical activity in addition to current physical activity.

We conclude that cognitive function could be successfully assessed by telephone interview in elderly participants of an ongoing population-based cohort study. Lack of physical activity was associated with a lower cognitive performance as measured by the TICS.