4
VOLUME 11 NUMBER 1 • MARCH 2014
REVIEW
SA JOURNAL OF DIABETES & VASCULAR DISEASE
The effects of acute hypoglycaemia on cognitive function
in type 1 diabetes
BERET INKSTER, BRIAN M FRIER
Abstract
T
hroughout life with type 1 diabetes mellitus people
with the condition are exposed to multiple episodes
of hypoglycaemia associated with insulin therapy.
Hypoglycaemia affects several domains of cognitive function.
Studiesinnon-diabeticadultsandinpeoplewithtype1diabetes
have shown that almost all domains of cognitive function
are impaired to some degree during acute hypoglycaemia,
with complex tasks being more greatly affected. The specific
cognitive functions of attention and memory are both
profoundly impaired during hypoglycaemia.
These cognitive processes are fundamental to the
performance of many day to day tasks. Their impairment
disrupts everyday life and raises safety concerns for the
pursuit of activities such as driving.
Mood and emotion are also negatively affected by
hypoglycaemia, resulting in tense tiredness, whilemotivation
is reduced, and anger may be generated in some individuals.
Hypoglycaemia can cause embarrassing social situations,
and may lead to chronic anxiety and depression in people
with type 1 diabetes.
At present few therapeutic measures can modify or
ameliorate the effects of hypoglycaemia on cognitive
function, so instigation of measures to prevent exposure
to hypoglycaemia is of major clinical importance, while
preserving good glycaemic control.
Keywords:
hypoglycaemia, cognitive function, mood, memory,
attention, type 1 diabetes
Introduction
Cognitive function refers to all aspects of thinking and intellectual
activity. This encompasses many mental processes: abstract
thinking, reasoning, judgement, language, memory, attention
and concentration, motor performance, constructional ability,
speed of information processing and perception. Earlier studies of
Correspondence to: Dr Berit Inkster
Department of Diabetes, Royal Infirmary, 51 Little France Crescent,
Edinburgh, EH16 4SA, Scotland, UK.
Tel: +44 (0) 131 242 1378; Fax: +44 (0) 131 242 1484
e-mail:
Brian M Frier
The Queen’s Medical Research Institute, University of Edinburgh, Scotland,
UK.
Previously published in:
Br J Diabetes Vasc Dis
2012;
12
(5): 221–226.
S Afr J Diabetes Vasc Dis
2014;
11
: 4–8
hypoglycaemia that used tests of general cognitive function found
that most were affected adversely (Table 1).
1
Simple cognitive tasks such as finger tapping and simple reaction
time are not significantly affected by hypoglycaemia,
1
but the speed
at which tasks are performed is often diminished, while accuracy
or absolute ability are preserved.
1,2
More recent research has tried to
isolate specific cognitive processes, but this is difficult to achieve as
most psychometric tests and everyday tasks require a combination
of cognitive skills, so attempting segregation into separate cognitive
domains is difficult and artificial.
Testing cognitive function during hypoglycaemia has several
limitations, and many studies differ too much in design and
methodology to permit comparison of results.
2
Target blood
glucose levels vary from 2 to 3 mmol/l, and measures of cognitive
function include a wide range of tests and some neurophysiological
measures such as sensory evoked potentials. Study design may be
inadequate through lack of a euglycaemia control arm, an absence
of power calculations and heterogeneity of study cohorts. It is
often difficult to extrapolate experimental outcomes to real life
scenarios where blood glucose excursions may be more rapid and
hypoglycaemia less prolonged. Exposure to hypoglycaemia is not
confined to the young and healthy, who are the usual participants
in research studies; older people may respond differently or
experience greater magnitudes of dysfunction.
Table 1.
Cognitive domains and functions that are impaired
during acute hypoglycaemia, as demonstrated by specific tests.
Adapted from Deary.
1
Test
Trail making
Digit symbol
Reaction time (especially
involving a decision)
Mental arithmetic
Verbal fluency
Stroop test
Grooved pegboard
Pursuit rotor
Letter cancellation
Delayed verbal memory
Backward digit span
Story recall
Cognitive functions tested
Attention, visual scanning, mental
flexibility, planning, motor speed
Sustained attention, speed of
response, visual scanning, mental
efficiency
Attention, discrimination, psychomo-
tor speed, speed of decision making
Working memory, short-term
memory
Retrieval from semantic memory,
letter fluency, category fluency,
category switching
Selective attention, mental tracking,
ability to inhibit conflicting inputs
Fine manual dexterity
Hand-eye co-ordination, vigilance,
motor control
Attention, distractibility
Verbal learning, delayed recall
Attention, short-term memory,
working memory
Short-term memory
