Monday, December 10, 2012

How Fast Can You Walk?

As infants, we learn to crawl before we walk.  As toddlers, we advance from walking to running.  So perhaps it's not so ironic to use gait speed as a determinant of health & predictor of mortality.  After all, the sicker or less healthy we are, the less likely we are to be able to ambulate quickly.  The bigger issue is, of course, proving this hypothesis, especially in the older old, those >85yo, who are typically under-represented in most studies.  And so with much serendipity, I stumbled upon a prospective population-based study published in the American Journal of Medicine this month in which the authors looked for predictors of survival (inverse of mortality).

Specifically, the authors of the Leiden 85-plus Study followed for 12yrs 599 participants age 85yo at baseline.  They noted that less than 10% of this group of the oldest old could walk faster than 0.8m/s, much less 1m/s.  On the other side of the bell shaped curve, slow gait of <0.4m/s for women and <0.45m/s for men was associated w/greater all-cause mortality after just 2yrs and definitely by 12yrs.  Unfortunately, confounders led to loss of statistical significance.  

But what if you can't walk at all for whatever reason?  Then how do you predict mortality?  Remember your Instrumental Activities of Daily Living?  The formal IADLs are the ability to use the telephone, shopping, food preparation, housekeeping, laundry, mode of transportation, responsibility for own medications, and ability to handle finances.  The authors abstracted from this definition and graded competence in doing light housework, doing heavy cleaning, washing & ironing clothers, cleaning & making bed, preparing a hot meal, climbing stairs, getting around outdoors, shopping, and attending to feet & toenails.  Complete independence in an activity rated 1 point while relying completely upon someone else rated 4 points, for a total score ranging from 9 up to 36.

It turns out that poor ability in IADLs as demonstrated by a score >25 was associated w/increase risk of mortality (and thusly, a decrease rate of survival), even after taking other variables into account.  Bottom line, if you can walk, faster gait is better than slower.  But even if you can't walk, greater independence in IADLs is associated w/lower mortality and greater survival.

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