A case series presented online in Nutrition Journal revealed that adding the amino acid N-acetylcysteine to a regimen of B vitamins administered to cognitively impaired patients with high homocysteine levels resulted in improvement in all patients. High levels of plasma homocysteine have been linked with an elevated risk of vascular disease and dementia, and have been reported in patients with mild cognitive impairment and Alzheimer's disease.

Andrew McCaddon of Wales College of Medicine in Wrexham, North Wales presented seven cases of older individuals with memory loss and/or confusion who had high plasma levels of homocysteine. "Although plasma levels of homocysteine are largely determined by vitamin B12 and folate status," Dr McCaddon writes, "Antioxidant therapy might also be required for optimal reduction in neurovascular tissue."

The five women and two men were given 600 milligrams N-acetylcysteine per day, along with treatment with oral or injectable vitamin B12 and, for most of the patients, 5 milligrams folic acid.

All seven patients experienced subjective improvement in their cognitive function after a varying amount of weeks. Objective improvement, as assessed by cognitive function test scores, was noted in five patients. One patient who underwent magnetic resonance imaging prior to receiving supplementation showed cessation of the progression of small vessel disease upon re-examination after one year of supplementation.

Dr McCaddon observed that the mechanism underlying the association with elevated homocysteine could be its adverse effects on neurovascular tissue combined with neurotransmitter synthesis impairment caused by defects in methyl group metabolism. The responses to N-acetyl cysteine demonstrated in the case series suggests that homocysteine could be a marker for the effects of oxidative stress in brain tissue.