Homocysteine
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Homocysteine.PNG
The metabolic intermediate homocysteine is an amino acid created by the single carbon chemistry of S-adenosyl-methionine. It can be converted back to methionine, or converted to cysteine or taurine via the transsulfuration pathway.
The chemical structure of homocysteine is shown on the right.
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Cardiovascular risks
A high level of blood serum homocysteine is considered to be a marker of potential cardiovascular (risk factor for heart attack and stroke) disease. Note that as a consequence of the chemistry in which homocysteine is involved, deficiencies of the vitamins folic acid, pyridoxine (B6), or cobalamin (B12) can lead to high homocysteine levels. A current area of research is whether high serum homocysteine itself is a problem or merely an indicator of extant problems.
Although homocysteine can be converted back to methionine, there is no indication that dietary homocysteine contributes any homocysteine nutritionally to humans.
Elevated homocysteine
Elevations of homocysteine occur in the rare hereditary disease homocystinuria and in methyl-tetrahydrofolate-reductase deficiency. The latter is quite common and usually goes unnoticed, although there are reports that thrombosis and cardiovascular disease occurs more often in people with elevated homocysteine.
Bone weakness
Elevated levels of homocysteine have been linked to increased fractures in elderly persons.
In a study published in 2004, blood concentrations of homocysteine were compared to incidents of hip fracture. The study found that men in the upper quartile of homocysteine concentrations were four times more likely than men in lower quartile to break a hip. Women in the upper quartile were twice as likely as women in the lower quartile to suffer a hip fracture. (McLean, et al., 2004)
In another study, men and women with the highest concentrations were twice as likely to experience a fracture as those with the lowest levels. (van Meurs, et al., 2004)
Homocysteine does not appear to have any effect on bone density. Instead, it appears that homocysteine affects collagen by interfering with the cross-linking between collagen fibers and the tissues they reinforce.
Countering the effects of homocysteine on bone weakness
Vitamin supplements could counter the effects of homocysteine on collagen. Folate and B12 are both known to lower concentrations of homocysteine in blood. U.S. food processors have been adding folate to flour since the late 1990s. B12 is inefficiently absorbed from food by elderly persons. They could gain a greater benefit from taking multivitamin supplements.
References
- McLean RR, Jacques PF, Selhub J, Tucker KL, Samelson EJ, Broe KE, Hannan MT, Cupples LA, Kiel DP.Homocysteine as a predictive factor for hip fracture in older persons. N Engl J Med 2004;350:2042-9. PMID 15141042.
- van Meurs JB, Dhonukshe-Rutten RA, Pluijm SM, van der Klift M, de Jonge R, Lindemans J, de Groot LC, Hofman A, Witteman JC, van Leeuwen JP, Breteler MM, Lips P, Pols HA, Uitterlinden AG. Homocysteine levels and the risk of osteoporotic fracture. N Engl J Med 2004;350:2033-41. PMID 15141041.
Further Information
- Methionine and Homocysteine (http://www.thorne.com/altmedrev/fulltext/meth1-4.html)
- Structure, Properties, and metabolism of Homocysteine (http://www.diabetesforum.net/cgi-bin/display_engine.pl?category_id=8&content_id=232)de:Homocystein