test scores and mood contained just
4 to 9 milligrams of caffeine. “That’s only
about a tenth as much as you’d find in a
cup of coffee,” Kennedy points out. “So
guarana was doing something that wasn’t
attributable to its caffeine” — although
his team doesn’t yet know what.
He and colleagues have also been
investigating other natural products that
might elevate energy, attention and mental performance. Among these: Chinese
ginseng (Panax ginseng). Young adults
scored better on a battery of mental
tests— including serial subtraction of
numbers in their heads— and exhibited
less mental fatigue after getting this
herbal supplement rather than a placebo.
How Chinese ginseng may improve
performance is unknown, but Kennedy
suspects the effect might have to do
with ginseng’s ability to moderate blood
sugar levels. At least at the 200-milligram
dose used by his group, this supplement
caused a drop in blood-glucose levels one
hour after consumption.
Researchers report that American
ginseng (P. quinquefolius) also shows
promise. Compared with a placebo, all
doses improved some aspect of cognition, Swinburne’s Andrew Scholey
and colleagues report in October in
Psychopharmacology. One difference:
This herbal supplement had no effect
on blood glucose.
The Northumbria researchers are
also exploring the idea that some natural products bolster brain function by
affecting blood flow. For instance, if
they dilate vessels, the products might
allow more fuel — glucose — in to power
brain activities. Kennedy and colleagues
tested the idea by giving 30 students a
cup of cocoa on three mornings. Each
day’s formulation contained a different amount — 46, 520 or 994 milligrams
per serving — of cocoa flavanols, natural
agents that have antioxidant and sometimes heart-healthy properties.
The cocoa packages used in the study
were prepared by Mars, a candy company
that has been exploring health attributes
of some chocolate products.
Both higher-dose formulations,
especially the middle one, improved
performance during mentally challeng-
ing tests involving math and the visual
processing of information, the scientists
report. At the same time, the college stu-
dents receiving the middle dose reported
a reduction in mental fatigue. Maxi-
mum benefits showed up two hours into
testing, which roughly corre-
sponds to the expected peaks
in concentrations of flavanols
in the blood and in blood flow
to the brain, Kennedy’s team
reported in the October Jour-
nal of Psychopharmacology.
s h.e. Gorby, a.M. Brownawell and M.c.
Falk. “Do specific dietary constituents and supplements affect mental
energy? review of the evidence.”
Nutrition Reviews, December 2010.
February 26, 2011 | science news | 29