Physical Function and Alzheimer's - Cause or Effect?

Summarized by Robert W. Griffith, MD
July 28, 2006

Summary

In older people, lower levels of physical function are associated with an increased risk of subsequent dementia, including Alzheimer's disease.

Introduction

It's been demonstrated that, in older people, physical performance is linked with cognitive (i.e. mental) performance. Is it possible that the brain damage of Alzheimer's and other dementias is accompanied by damage in the parts of the brain responsible for muscle movements? And if this is so, is deterioration in physical performance a sign of impending Alzheimer's? University of Washington researchers have examined this possibility in a study reported in the Archives of Internal Medicine, and we summarize their findings here.

What was done

The subjects of the study were 2288 people aged 65 or older living in the Seattle area that did not have dementia. At entry they underwent screening with the Cognitive Ability Screening Instrument (CASI); a CASI score corresponding to Mini-Mental State exam score of 25-26 was used as the cut-off for diagnosing dementia. Physical function was assessed using 4 tests: time to walk 10 feet; time to stand from a seated position in a chair to a standing position, repeated 5 times; standing balance; and grip strength in the dominant hand. Each test was scored from 0 to 4 points, so the total score possible was 16.

Other measures at baseline included age, sex, years of education, family history of Alzheimer's, APOE e4 genotype (a risk factor for Alzheimer's), depression, exercise taken, and cardiovascular disease history.

CASI was repeated every two years; those scoring below the cut-off underwent a standard exam to diagnose or exclude dementia. The average follow-up period was 5.9 years.

What was found

The average age at baseline was around 75; 60% of the subjects were women, and 90% were white. Three hundred and nineteen participants developed dementia during the follow-up period (221 had Alzheimer's and 43 had other types of dementia, chiefly vascular).

The incidence of dementia expressed in person-years was 53.1 cases for those who did poorly on the physical function testing at baseline (i.e. 10 or below out of 16 points). For those scoring better than 10 on the physical function tests, the incidence was only 17.4 cases per 1000 person-years. Those with lower levels of physical performance at baseline were clearly less likely to remain dementia-free than those at higher levels.

Analyses showed that these findings were similar after adjusting for all possible variable factors measured, e.g. age, gender, education level, family history of dementia, and so on.

What these results mean

This study shows that older people found to have poor physical function in 4 tests are at increased risk of developing dementia and have an increased rate of mental decline during the 6 years following their assessment.

In more detailed analysis, poor standing balance was linked to an increased risk of dementia in those without apparent mental impairment, and poor walking speed was linked in thosewithand without mental decline. Poor gait has previously been associated with increased vascular dementias, but here the link was with both vascular and Alzheimer's. The findings suggest, therefore, if confirmed, that gait slowing and poor balance are early markers, and poor handgrip a later marker for developing dementia.

If this is the case, how can physical exercise improve mental functioning, as has been shown a number of times? Indeed, physical fitness is associated with a lower risk of developing dementia. The fact that a connection between the two, even if not fully explained, should be sufficient to encourage people to exercise more as they get older.

Source

• Performance-based physical function and future dementia in older people. L. Wang, EB. Larson, JD. Bowen, G. van Belle, Arch Intern Med, 2006, vol. 166, pp. 1115--1120

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