[Review of the role of hyperhomocysteinemia and B-vitamin deficiency in neurological and psychiatric disorders--current evidence and preliminary recommendations].

Elevated concentration of total homocysteine (Hcy) in plasma (> 12 micromol/l) is a risk factor for several diseases of the central nervous system. Epidemiological studies have shown a dose-dependent relationship between concentrations of Hcy and the risk for neurodegenerative diseases. Hcy is a marker for B-vitamin deficiency (folate, B12, B6). Hyperhomocysteinemia (HHcy) causes hypomethylation which is an important mechanism that links Hcy to dementia. Supplementation with vitamins B aims at reducing the risk of neurodegenerative diseases. Current evidence suggests that Hcy-lowering treatment has a positive effect for the secondary and primary prevention of stroke. HHcy is very common in patients with Parkinson disease particularly those who receive L-dopa treatment. Furthermore, a positive association has been reported between HHcy and multiple sclerosis. Moreover, HHcy and vitamin B deficiency are reported to have a causal role in depression, and epilepsy. In addition several anti-epileptic drugs cause secondary HHcy. Therefore, sufficient intakes of the vitamins are recommended for patients who have already developed neuropsychiatric diseases. Vitamin B deficiency should be suspected in children with development disorders, failure to thrive and unexplained neurological manifestations. Elderly people are also an important at-risk group where vitamin B deficiency and HHcy have been linked to neurodegenerative diseases. Treatment with folate, B12, and B6 can improve cerebral function. Preventive vitamin B supplementation and sufficient intake seem very important for secondary and primary prevention of neuropsychiatric disorders, especially in subjects with a low intake or status of the vitamins.