Homocystinuria

Mildly elevated total homocysteine (tHcy) is associated with an increased risk of cerebrovascular, peripheral vascular, and cardiovascular diseases. Once homocysteine is formed, it is either remethylated to form methionine, requiring vitamin B-12, folate, and riboflavin, or undergoes a transsulfuration to form cysteine, which is dependent on pyridoxal-P (PLP). Vitamin B-6 has been used for years to successfully treat homocystinuria caused by cystathionine B-synthase deficiency; however its role in the prevention or treatment of mild hyperhomocysteinemia is unclear. There is inconclusive evidence in younger populations regarding the effectiveness of vitamin B-6 in reducing homocysteine concentrations. To date no vitamin B-6 intervention has been performed in elderly persons although it is well established that vitamin B-6 status declines with age and plasma tHcy concentrations increase with age.

The goal of a recent study was to investigate the effect of low-dose vitamin B-6 supplementation on fasting tHcy concentrations in healthy elderly persons after exclusion of those deficient in vitamin B-12 and after optimization of folate and riboflavin status. Twenty-two healthy, elderly individuals were recruited as subjects. They were randomized into a double-blind, placebo-controlled trial for 12 weeks. Prior to starting the vitamin B-6 intervention, all subjects received supplementation with riboflavin for 12 weeks followed by a combination of folic acid and riboflavin for an additional six weeks. Folic acid and riboflavin supplementation continued throughout the vitamin B-6 intervention period. Fasting blood samples were drawn immediately prior to the intervention. Subjects were then supplied with either vitamin B-6 (1.6 mg) or a placebo tablet daily. Subjects were asked to maintain their usual diet and refrain from initiating any form of vitamin supplementation during the intervention. Current dietary intake was assessed using a four-day food record following comprehensive instruction on how to complete food records from a trained nutritionist. Blood was analyzed for tHcy, plasma PLP, red blood cell folate, serum folate, and serum vitamin B-12 concentrations.

It was found that folic acid supplementation lowered fasting tHcy by 19.6%. Two-way analysis of variance demonstrated that the significant improvement in vitamin B-6 status in response to vitamin B-6 supplementation was reflected in a significant reduction in plasma tHcy of 7.5%.

It appears that low-dose vitamin B-6 effectively reduces fasting plasma tHcy in healthy, elderly individuals who are both folate and riboflavin replete. Researchers suggest that any program with the goal of treating or preventing hyperhomocysteinemia should include vitamin B-6 supplementation.

M. McKinley, H. McNulty, J. McPartlin, et al. Low-dose vitamin B-6 effectively lowers fasting plasma homocysteine in healthy elderly persons who are folate and riboflavin replete. Am J Clin Nutr 73:759-764 (April 2001) [Correspondence: H. McNulty, Northern Ireland Centre for Diet and Health, University of Ulster, Coleraine BT52 1SA, UK. E-mail: h.mcnulty@u1st.ac.uk.]

COPYRIGHT 2001 Technical Insights, a divison of John Wiley & Sons.
COPYRIGHT 2001 Gale Group