Summary
High plasma levels of homocysteine are the results of the interplay between congenital
and environmental factors. In the last two decades, a growing amount of interest has
focused on mild-to-moderate hyperhomocysteinemia as a risk factor of thromboembolic
diseases. Case-control and cross-sectional studies clearly indicated that mild-to-moderate
hyperhomocysteinemia is associated with heightened risk of both arterial and venous
thrombosis. On the other hand, prospective studies did not unequivocally show that
hyperhomocysteinemia is associated with a high thrombotic risk. Therefore, additional
studies are needed to define whether hyperhomocysteinemia is a risk factor for thrombosis,
especially of the venous circulation. Among these, prospective cohort studies will
clarify better the temporal relationship between high homocysteine levels and the
thrombotic event. Most importantly, however, randomized, placebo-controlled, double-blind
trials of the effects of homocysteine-lowering vitamins on the thrombotic risk are
urgently needed. Not only will they help in defining whether the relationship between
hyperhomocysteinemia and thrombosis is causal, they will also have a potential dramatic
impact in the prevention of thromboembolic events.