Healthy young adult participants scored lower on spatial
orientation tests after 8 days on a high-aspartame diet
than they did after the same period on a low-aspartame
diet, supporting previous evidence of neurobehavioral
effects of aspartame (Wurtman, 1983, 1987). Harte and
Kanarek (2004) also reported that participants who drank
sucrose-sweetened beverages performed better on spatial
memory and attention tasks than those who consumed
aspartame-sweetened beverages. In another study, recall,
reaction time, and spatial memory scores were better
among those who consumed glucose compared to aspar-
tame-sweetened beverages (Sunram-Lea et al., 2002).
However, working memory, as measured by Sternberg's
Item Recognition Test, did not differ in our participants, as
found by Brandt, Sunram-Lea, and Qualtrough (2006)
Table 2. Within-Subject Differences in Neurobehavior
Scores After High and Low Aspartame Intake (N¼28)
Variable M SD Paired t-test p
Spatial orientation
High-aspartame 14.1 4.2 2.4 .03 ?
Low-aspartame 16.6 4.3
Working memory
High-aspartame 730.0 152.7 1.5 N.S.
Low-aspartame 761.1 201.6
Mood (irritability)
High-aspartame 33.4 9.0 3.4 .002 ??
Low-aspartame 30.5 7.3
Depression
High-aspartame 36.8 7.0 3.8 .001 ??
Low-aspartame 34.4 6.2
? p<.05.
?? p<.01.
Research in Nursing & Health
190 RESEARCH IN NURSING & HEALTH
when comparing the impact of aspartame and glucose on
memory.
A high dose of aspartame caused more irritability and
depression than a low-aspartame dose consumed by the
same participants, supporting earlier study findings by Wal-
ton et al. (1993), whose work was not completed because
of adverse reactions in some of the vulnerable study partic-
ipants. The amount of aspartame served to participants in
Walton's study was 30mg/kg body weight/day, which was
only slightly higher than the amount in our high-aspartame
diet. Additionally, three participants in our study scored in
the clinically depressed category while consuming the high-
aspartame diet, despite no previous histories of depression.
These results contrast with another study, in which mood
did not differ significantly when overweight women con-
sumed a beverage sweetened with aspartame or a
sucrose-sweetened beverage over a 5-week period and
self-reported prospective food and drink intake, mood, and
daily activities in 2-hour increments (Reid et al., 2010).
Headaches were rare in our sample, so we were unable to
support or refute those of Jacob and Stechschulte (2008),
who proposed a link between aspartame and migraine
based on a clinical case study of six individuals.
Limitations of our study included the small homoge-
neous sample, which may make it difficult to apply our con-
clusions to other study populations. Also, our sample size
of 28 participants resulted in a statistical power of .72,
which is on the lower end of the acceptable range. A wash-
out period before the baseline assessments and using food
diaries during the between-treatment washout period to ver-
ify that aspartame was not consumed would have strength-
ened the design.
Conclusions
Aspartame intake affected certain aspects of neurobehavio-
ral performance. Spatial orientation was weaker and irritabil-
ity and depression were more frequent after high-
aspartame consumption than low aspartame consumption
when subjects served as their own controls. Furthermore,
seven participants experienced clinically significant neuro-
behavioral conditions following the higher level of aspar-
tame consumption. A diet high in aspartame did not
influence working memory or headaches.
Investigators who previously had explored the neuro-
behavioral effects of aspartame consumption did not control
the effects of non-study food and beverage intakes in their
participants' diets or administered single-dose treatments,
such as aspartame-sweetened beverages or capsules, fol-
lowed by cognition, mood, and/or depression testing. Our
study represents an advance over this previous work.
Nonetheless, because there are relatively few clinical stud-
ies of the neurobehavioral aspects of short-term aspartame
consumption and the results of these are conflicting, addi-
tional research is warranted to assess the safety of aspar-
tame consumption and its implications for health.