High brain lactate is a hallmark of aging and caused by a shift in the lactate dehydrogenase A/B ratio.
Ross JM, Öberg J, Brené S, Coppotelli G, Terzioglu M, Pernold K, Goiny M, Sitnikov R, Kehr J, Trifunovic A, et al. Proc Natl Acad Sci U S A. 2010 Nov 16; 107(46):20087-92. Epub 2010 Nov 1.