Guanidinoacetic acid (GAA) is the natural biosynthetic
precursor of creatine, in a metabolic reaction that requires only a methyl
group transfer. The use of GAA as a food additive for restoring creatine load
in human tissues is rather unexplored and data on efficacy and safety are
limited. In particular, an increase in serum homocysteine after GAA
administration can be regarded as critical and should be prevented. The present
study evaluated the effects of orally administered GAA with and without methyl
group donors on serum and urine creatine concentrations, and the occurrence of
adverse events during an intervention in healthy human subjects. A total of
twenty male and female volunteers were randomised in a double-blind design to
receive either GAA (2.4 g/d) or GAA with methyl donors (2.4 g/d of GAA and 1.6
g/d of betaine HCl, 5 mug/d of vitamin B12, 10 mg/d of vitamin B6 and 600 mug/d
of folic acid) by oral administration for 8 weeks. Serum and urine creatine
increased significantly from before to after administration in both groups
(P< 0.001). The proportion of participants who reported minor adverse events
was 33.3 % in the GAA group, and 10.0 % in the GAA with methyl donors group (P=
0.30). Hyperhomocysteinaemia was found in 55.6 % of participants supplemented
with GAA, while no participant experienced hyperhomocysteinaemia in the group
supplemented with GAA and methyl donors (P= 0.01). In summary, both
interventions strongly influenced creatine metabolism, resulting in a
significant increase in fasting serum creatine. The concomitant supplementation
of methyl donors along with GAA largely precluded the elevation of serum
homocysteine caused by GAA administration alone.
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- Stuart Craig
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