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You don't hear a whole lot about homocysteine these days but ten or fifteen years ago it was quite the buzzword in nutrition and preventive medicine circles–and a cash cow for nutritional supplement sellers.

A little background on the homocysteine hypothesis

Population studies (aka epidemiological studies) showed that people with high levels of homocysteine in their blood had a higher risk of heart disease. Homocysteine is an amino acid which is an normal byproduct of protein metabolism. Ideally, it is further converted into another amino acid, methionine. However, if this "recycling"  breaks down, homocysteine can build up in the blood. 

When the link between high homocysteine and heart disease risk was noticed, researchers theorized that homocysteine might irritate the blood vessel lining, leading to injury, inflammation, and the formation of arterial plaques.

Certain B vitamins (B6, B12, and folic acid) act as co-factors in the conversion of homocysteine to methionine. Further research confirmed that those with high homocysteine tended to be low in one or more of these nutrients. Taking the next step, it was established that supplementing with these nutrients reliably reduced elevated homocysteine levels. It seemed all but certain that this would in turn lower heart disease risk.

Hold that thought

However, the homocysteine hypothesis recently took a big hit, in the form of a meta-analysis of eight studies involving some 24,000 subjects. The upshot? The authors found “no evidence that homocysteine-lowering interventions, in the form of supplements of vitamins B6, B9 or B12, given alone or in combination, at any dosage compared with placebo or standard care, prevents myocardial infarction, stroke, or reduces total mortality in participants at risk or with established cardiovascular disease.”

Ouch.

Those in the business of selling nutritional supplements are crying foul, claiming that the conclusions are "misleading."  Read responses from the Health Food Manufacturers’ Association (HFMA) and the International Alliance of Dietary/Food Supplement Associations (IADSA).

It's possible that those with very high homocysteine levels have more to gain than those with only mildly elevated levels–and that the meta-analysis obscures this reality. The meta-analysis also failed to evaluate whether B vitamins could prevent healthy people from developing heart disease. But, coming from organizations who profit from sale of dietary supplements, I find this argument less compelling.

I'm curious: How many of you have had your homocysteine levels tested? How many of you take B vitamins specifically to manage homocysteine levels? Share your comments below.