Effects of myo-inositol ingestion on human brain myo-inositol levels: a proton magnetic resonance spectroscopic imaging study.

BACKGROUND: Cerebrospinal fluid levels of myo-Inositol (m-Ino) are reported to be decreased in patients with affective disorder, and dietary supplements of m-Ino have been shown to reduce the symptoms of major depression. Myo-Inositol transport across the blood-brain barrier is mediated by a low capacity, saturable system. This study tests whether dietary m-Ino increases brain m-Ino or changes brain metabolism of m-Ino, possibly explaining the ability of this compound to alter mood. METHODS: Using proton magnetic resonance spectroscopic imaging, we measured m-Ino levels in occipital gray and parietal white matter of seventeen healthy subjects. Magnetic resonance spectroscopic imaging was performed twice at baseline as well as at day 4 and day 8 while subjects ingested 6 g of m-Ino twice a day. RESULTS: Following 4 days of m-Ino, m-Ino/Cr was 20% higher than baseline levels in occipital gray matter (p < 0.04) and 8% higher in parietal white matter (p = ns). By day 8, m-Ino/Cr ratios had returned to baseline values. CONCLUSIONS: Brain m-Ino levels initially increase during m-Ino administration and subsequently return to baseline levels. The time-limited increases observed for brain m-Ino may reflect homeostatic mechanisms, possibly associated with the role of m-Ino as a cerebral osmolyte, or with changes in brain phosphoinositide metabolism.