Few studies have investigated the effects of the nutrient in terms of disease prevention because food composition databases were not available until only recently.

The new study has taken advantage of these databases and reports that people with increased intake of choline, and its oxidation product betaine (found naturally in vegetables such as spinach), have lower levels of homocysteine.

The amino acid homocysteine has been linked by epidemiological studies to an increased risk of cardiovascular disease. A meta-analysis in the British Medical Journal (Vol. 325, pp. 1202-1208) of genetic and prospective studies reported that a 3 micromole per litre decrease in homocysteine levels was associated with a decrease in the risk of ischemic heart disease of 16 percent.

The Harvard study, published in the American Journal of Clinical Nutrition (Vol. 83, pp. 905-911), analysed the dietary intake of 1960 volunteers (1040 women) with an average age of 54 using a validated 130-item food frequency questionnaire.

Choline and betaine intake was calculated using the Harvard University Food Composition Database, the US Department of Agriculture's choline database, and values published in 2003 in the Journal of Nutrition (Vol. 133, pp. 1302-1307).

The researchers found that the highest choline intake (401 milligrams per day) was associated with a nine per cent lower plasma concentration of homocysteine, compared to the lowest intake group (234 milligrams per day).

When betaine was counted along with choline, a similar reduction in homocysteine level was observed (9.2 per cent) when comparing the highest intake groups (689 milligrams per day) with the lowest intake group (383 milligrams per day).

The results took into account possible complicating factors such as age, sex, smoking, alcohol, hypertension, and intakes of B-vitamins.

Increased intake of B-vitamins, and particularly folate/folic acid, has been reported to reduce homocysteine levels, and protect against heart disease.

“Intakes of choline and betaine predicted plasma homocysteine concentrations independent predictors, including intakes of folate and B vitamins,” said the researchers.

The mechanism behind the benefits is proposed to be the oxidation of choline to betaine, which then donates a methyl group to homocysteine to form methionine. This mechanism, say the researchers, is confined to the kidney and livers.

This also suggests, said Cho, that even if folate intake is low, homocysteine levels can be reduced by having an adequate intake of choline and betaine.

Recommended daily intakes of choline were set in 1998 at values of 550 milligrams per day for men and 425 milligrams a day for women. The mean intake of the entire study population was found to be 313 milligrams a day, indicating this study population were not consuming adequate amounts of the micronutrient.

The results appear to be in line with intervention studies using high dose betaine or choline supplementation, which have reported homocysteine reductions of up to 20 per cent (betaine, 1.5 to 6 grams per day).

Red meat was reported to be the richest source of choline, giving about 14 per cent of the daily intake. Spinach was reported to be the participants' richest source of betaine, accounting for over 25 per cent of the daily intake.