Diabetics and Reaction Times: Cause for Concern
Edited excerpts from the article “A comparative study of reaction times between
type II diabetics and non-diabetics” by Samantha J Richerson, Charles J Robinson
and Judy Shum
Editing and Commentary by Dr. Don Rose, Writer,
Life Alert
--
An
article of mine found elsewhere on this Senior Protection site discusses falls
among seniors. In it, I hope to convey some of the common causes of falls, and their
prevention. One of the causes is slower reaction times that develop in the elderly.
In the
article by Richerson, Robinson and Shum (excerpted below), the authors detail
a study comparing Type II diabetics and non-diabetics. One of their conclusions
is that slips and falls are more likely to occur among the diabetic group, due to
increased reaction times. Since an increasing number of Americans are developing
Type II diabetes, often due to obesity, there is much cause for concern. Seniors
who are diabetic are doubly at risk, since they are in two risk groups for slower
reaction times.
However, knowledge is power. Use the information below as motivation, and ammunition,
to take the steps needed to
prevent or even reverse Type II diabetes. The cascade
of beneficial effects will be enormous. --Dr. Don Rose
--
Introduction and Background
Aging slows reflexes and increases the time to react to a number of external stimuli
of different modalities. What has escaped extensive examination has been the effect
of Type II diabetes on these same reaction times and the comparison of modalities
across the various sensory inputs. Only two studies have tested older individuals
with diabetes. These have demonstrated increased reaction times to visual and auditory
stimuli. Mohan, et al. found a 30 ms difference in auditory reaction times between
those with diabetes (approximately 210 ms) and a control group (180 ms). Dobrzanski,
et al. found a doubling of visual reaction time in diabetics (473 ms) versus that
measured in healthy individuals (216 ms). In addition to the measured effects in
these two studies, diabetes has also been shown to affect peripheral nerves in the
somatosensory and auditory system, slows psychomotor responses, and has cognitive
effects on those individuals without proper metabolic control, all of which may
affect reaction times.
One of the largest implications that an increased reaction time may have is in the
area of slips and falls. Falls are incurred by one third of the elderly population
and are a common source of morbidity and mortality. Evidence that older subjects
have an increased incidence of slips and falls when compared to healthy young adults
have been attributed to increase in sway as seen by center-of-pressure or center-of-gravity
(COP, COG), or head and hip variability. Diabetics have been shown to have a higher
incidence of postural instability and reduced peripheral sensations, thus leading
to an even higher incidence of falls resulting from slips than their healthy elder
counterparts. These changes in balance metrics due to both normal aging and diabetes
have been well measured, but never accurately explained. It is our contention that
the postural instability may be due to slower input of information to the central
nervous system, which does not allow the nervous system to react to stimuli as quickly,
producing a higher incidence of slips and falls.
The aim of this study was to measure and compare reaction times to plantar (sole
of the foot) touch, auditory tone, and whole body lateral movement in subjects over
50 years old with and without diabetes, as well as a group of healthy younger adults
under 25 years of age. Subjects with diabetes were expected to have reaction times
longer than those of the age-matched controls, while the aged controls were in turn
expected to have reaction times greater than those seen in the younger adult group.
The implications of the changes in reaction time will be discussed with respect
to the central and peripheral nervous system.
Methods
Subjects
Subjects included 37 mature adults over 50 yrs old. Thirteen had a clinical diagnosis
of type II diabetes made by their primary physician (group PN, mean = 60.6 ± 6.5
yrs, 7 Female/ 6 Male) and 23 did not (group NI, mean = 59.4 ± 8.0 yrs, 11 Female
/ 12 Make). Reaction times from these groups were compared to a younger adult group
(age <25, N = 9, mean = 22.9 yrs, 4 Female/ 5 Male).
Screening
Subjects recruited for this study were relatively healthy individuals with no current
or past history of severe heart, circulation, or breathing problems; chronic lower
back pain or spasms; deformities of the spine, bones or joints (including advanced
arthritis); cerebral stroke, spinal cord injuries or other damage to the nervous
system; non-healing skin ulcers; advanced diabetes; current drug or alcohol dependence;
or repeated falls.
Diabetic individuals targeted for this study were those with very early and mild
Type II Diabetes. The subject's primary care physician undertook the diagnosis of
diabetes. Targeted recruits had all been diagnosed within the last 10 years. All
subjects with diabetes were using either diet or oral medication to manage blood
sugar levels.
Plantar sensory tactile thresholds were measured on each sole for all subjects using
Semmes-Weinstein Monofilaments. Tactile force perception thresholds on the glabrous
skin of the feet were determined for the right and left feet using these monofilaments.
A certified audiologist carried out air conduction auditory threshold testing on
all mature subjects (but none of the younger adults due to their health). Both mature
adult groups underwent testing at 1, 2, 4, and 8 kHz in both ears. Average threshold
level was recorded in decibels.
Reaction Time Protocol
Reaction time was defined as the time between a stimulus onset and a signaled response
of the subject. Three different stimuli were presented – touch, tone and platform
movement.
Results
Tactile Thresholds from Semmes-Weinstein Monofilament Tests
The study examined the average force necessary for detection of each group tested
at each location on the foot sole. None of the diabetics in this study had significant
plantar sensory loss. No significant differences were found in thresholds between
right and left legs for the metatarsal and toe in any group. Data from the right
and left legs were then pooled. For both plantar locations, young adults had significantly
lower thresholds than the other groups. The diabetic and healthy adult groups did
not differ significantly.
Audiology Thresholds
Significant differences were found both between groups and among frequencies. Diabetics
had significantly higher thresholds at 8 kHz (median = 35.0 dB) and the healthy
adult group had significantly higher thresholds at 4 and 8 kHz (median = 25.0 dB
and 35.0 dB respectively). Additionally, there was no significant difference
between the diabetics and non-diabetics at 4 and 8 kHz, but there was
a significant difference at 1 kHz, and trend toward significance at 2 kHz.
Reaction Time Measurement
Reaction times to platform movement, plantar touch, and a bell tone were measured
in all subjects. Measurements for reaction times were taken as the time between
the beginning of the stimulus and the button press indicating subjects detected
the stimuli. Averages were taken from all trials that were detected.
For platform movements, reaction times of all groups are significantly different
from each other, with reaction times in the adults with diabetes being longest (mean
= 777.8 ms), followed by aged matched adults (mean = 623.9 ms). Young adults had
the shortest reaction times (mean = 431.0 ms) to movements.
For the touch modality, reaction times for adults with diabetes are significantly
longer than both other groups (mean = 353.1 ms). However, reaction times to foot
sole touch between young (mean = 216.0 ms) and healthy mature adults (mean = 331.5
ms) were not significantly different.
For the tone modality, no significant differences in reaction times were found between
groups (diabetic mean = 282.6 ms; healthy adult mean = 276.9 ms; younger adult mean
= 218.0 ms). For all groups, movement reaction times were significantly longer than
the other two modalities (plantar touch and auditory tone), which did not differ
significantly.
Discussion
At this point, it is instructive to review the results and call out the various
findings to build a specific hypothesis. The key results follow:
1) Subjects with controlled type II diabetes all had mild, but measurable peripheral
neuropathies in at least one nerve in the lower limb, while those without diabetes
over the age of 50 had no measurable evidence of neuropathy.
2) Subjects with diabetes had increased reaction times to all three test modalities.
Touch and Tone reaction times were slightly, but not significantly, higher, while
platform reaction time was significantly higher.
3) Older adults, whether diabetic or not, had longer reaction times to platform
moves and to foot sole touch (all locations) than did younger adults, and reaction
times to the bell tone did differ between groups, even though those with diabetes
had higher auditory air conduction thresholds at every frequency tested (except
8 kHz) than their non-diabetic counterparts.
4) Reaction times to platform movement are 200 to 300% longer in all groups when
compared to reaction times to touch and tone.
Implications
Individuals with diabetes often have neurological side effects that affect the peripheral
nervous system. However, the increase in whole body movement reaction time seen
in adults with diabetes in this study can not solely be related to peripheral nervous
system changes due to diabetes. Even when motor nerve conductions slow from 50.0
m/s to 40.0 m/s (as seen in nerve conduction testing here), signal transmission
time for a 1 m long nerve increases only 5 ms, which does not account for a 200
ms increase in movement reaction time. An additional slowing has to be occurring
in the processing of the signals by the central nervous system.
Deficits in the central nervous system (CNS) of those with diabetes may also be
seen in cognitive deficits. Dey, et al. found no correlation between the duration
of diabetes and cognitive function in those with non-insulin-dependent diabetes
less than 18 years old. They hypothesized that in order to see the decline in cognitive
function and other central nervous system effects seen by other researchers, a longer
duration of disease state must be present. However, in our study, diabetics (all
with less than 10 years disease duration) had a significantly higher reaction time
to movement, which could be interpreted to indicate that not only are central effects
present, but they manifest themselves early in the disease. These increases in movement
reaction times among the mature adults with diabetes may also have an effect on
posture and gait. The longer reaction times of a slipping diabetic subject will
thus increase the probability of a fall. Diabetics have been shown to have a higher
incidence of postural instability, longer reaction times, and reduced peripheral
sensations thus leading to a higher incidence of falls resulting from slips.
Reaction times to plantar surface touch indicate the extent of peripheral neuropathy
in the population of diabetics. The fact that the mature adults with diabetes had
increased reaction times to plantar touch is another indication that peripheral
neuropathy was present in these subjects.
Auditory reaction times measured here for diabetics and age-matched controls do
roughly concur with the one reaction time study that includes diabetics. Although
no significant differences in auditory reaction times were seen between mature adults
with and without diabetes and their young adult counterparts, a sensorineural hearing
loss was seen in the mature adults with diabetes at the mid- and high-frequencies.
Conclusion
From this study we can conclude that diabetes does affect reaction times, although
the type and severity of the slowing may be related to the difficulty of the task
and the prevalence of central and peripheral nerve deficits seen as side effects
of diabetes. Auditory reaction times, the simplest of the tasks here with the shortest
path between peripheral and central nervous system, did not show any differences
in reaction times. When using a test that has a significantly longer path in the
peripheral nervous system, such as the reaction time to plantar touch, slightly
longer reaction times are seen in the adults with diabetes. When a more complicated
task including detecting movement, signal transmission and interpretation, and response
was required from the body, as in the platform movement reaction time test, a significant
difference in reaction times were seen among all groups. This test takes more fully
into account the peripheral nervous system signaling as well as the central nervous
system processing and thus is a better overall test to determine deficits in healthy
aging and aging individuals with diabetes.
We have presented here, in addition to normal auditory and touch reaction times,
lateral whole body reaction time, which has been shown to be the most sensitive
indicator of differences between healthy young, healthy mature adults, and mature
adults with mild diabetes among the modalities tested here. In other studies, we
have found that adults with diabetes have substantially higher thresholds than healthy
adults to detecting whole body motion. This, in addition to the increased whole
body reaction times, indicate that mild diabetes has profound effects on one’s ability
to detect and react to motion, which leads to insights on their ability to detect
and prevent
slips and falls.
This article is based on the research article entitled,
“A comparative study of
reaction times between type II diabetics and non-diabetics” by Samantha J Richerson,
Charles J Robinson and Judy Shum. The article on this
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