In that brain functioning naturally declines with age, a number of previous studies submit that folic acid and vitamin B12 serve to maintain healthy brain function, suggesting that low levels of these nutrients may lead to a more rapid deterioration of cognitive function. Janine G Walker, from Australia National University (Australia), and colleagues completed a randomized controlled trial conducted over two years, in which a subset of participants consumed a daily oral dose of 400 micrograms of folic acid plus 100 micrograms of vitamin B12, with the remainder of the subjects administered a placebo. The team examined changes in cognitive functioning at 12 and 24 months via two standardized assessment tests. At 24 months, the combination of folic acid with B-12 improved delayed recall scores, as compared to placebo. Whereas no significant changes were evident in orientation, attention, semantic memory, processing speed, or self-reported observations, the study authors conclude that: "Long-term supplementation of daily oral 400 [micrograms of folic acid plus 100 micrograms of] vitamin B-12 promotes improvement in cognitive functioning after 24 [months], particularly in immediate and delayed memory performance.”