Link between homocysteine levels and certain foods remains complex. (Risk & Recovery).

elevated levels of homocysteine, an amino acid in the blood, are linked to cardiovascular disease, stroke and most recently Alzheimer's disease (see Running & FitNews, May 2002). Levels are kept at a healthy minimum by ensuring that your diet contains sufficient amounts of vitamins B-9 (folic acid), B-12 and B-6, maintaining a healthy body weight, remaining physically active, eating plenty of fiber, managing hypertension and limiting alcohol consumption. But two additional factors that previously were linked to high concentrations of homocysteine in the blood are under re-examination.

While it is still clear that coffee is somewhat responsible for elevated blood levels of homocysteine, all of the compounds within it that contribute to this have eluded researchers. A recent study analyzed the caffeine in coffee and found that it was only partly responsible for high levels of homocysteine in subjects. Consumption of caffeine in capsule form increased homocysteine concentrations in healthy subjects, but the pill form of the drug had only 25 to 50% of the homocysteine-raising effect of paper-filtered coffee with a similar amount of caffeine. And coffee, unlike caffeine, affected homocysteine concentrations in the participants within hours after intake. Thus compounds in coffee other than caffeine must be additionally responsible for the homocysteine-level raising effect of coffee.

Another factor that has been associated with high levels of homocysteine in the blood is high protein intake. The results of a six-month prevention study on 65 overweight subjects suggest that this relationship may be somewhat tenuous. The researchers state that increasing dietary protein intake from 12% to 220/o of total energy, with a corresponding increase in methionine intake, does not increase plasma homocysteine concentrations." (Methionine is another amino acid associated with human growth.) The findings are in agreement with a larger 1997 study that found an inverse association in homocysteine blood levels with intakes of folate and B-6 and B-12 vitamins, but not with intakes of methionine and protein. The sources of protein in the 2002 study were primarily of animal origin and consequently had a high methionine content. Whether this was a factor in the body's ability to break down homocysteine is not presently known.

The researchers suspect that the acute effects of protein intake may differ significantly from the chronic effects over as long as a six-month period. They observed that the statistical relevance of both vitamin B-12 intake and weight loss after three months was diminished after a six-month period. They hypothesize that an adaptation to a high protein and/or methionine intake induces a more efficient homocysteine metabolism, thereby maintaining a normalized concentration of the substance in the plasma. Another factor may be that the largely meat-, dairy- and fish-based diet also provided a high intake of vitamins that could have counterbalanced any effect the heightened levels of protein and methionine could have had on homocysteine concentrations.

(Am. Journ. Clinical Nutrition, 2002, Vol. 76, No. 6, pp. 1202-1206, pp. 1244-1248, pp. 1279-1289)