Meatless eating typically improves cardiovascular health, but new research suggests that a dietary shortage of a crucial vitamin leads to an overabundance of the amino acid homocysteine in some vegetarians, which could pose a risk to their hearts.
A high homocysteine concentration in blood is associated with an elevated risk of heart disease. In past studies, people who have a homocysteine concentration of 15 micromoles per liter (mol/l) in their blood while fasting have a 60 to 80 percent greater risk of cardiovascular disease than do study volunteers with 10 mol/l, a more typical concentration.
Metabolic processes continually derive homocysteine by converting another amino acid, methionine, and also reconvert homocysteine into methionine. The latter reaction requires several essential nutrients, including vitamins B6 and B12. Deficiencies of these vitamins, therefore, can result in a buildup of homocysteine.
Since these B vitamins are abundant in many animal products but not in fruits or vegetables, vegetarians may not get enough of them unless they eat vitamin-fortified foods or take dietary supplements.
To test whether some vegetarians come up short on B vitamins, a team of eight researchers from three Taiwanese universities measured concentrations of several vitamins and amino acids in the blood plasma of 90 women–half of them vegetarians–from Hualien, Taiwan.
The vegetarians had an average plasma-homocysteine concentration of 11.2 mol/l when fasting, compared with a value of 8.64 mol/l among the women who regularly ate animal products. The vegetarians also had only about half as much vitamin B12 in their blood as the others did.
Vitamin B12 deficiency was highly predictive of elevated plasma homocysteine among the vegetarians. The researchers, led by Hsu-Fang Chou of Tzu-Chi University in Hualien, report their findings in the February Journal of Nutrition.
A proper vegetarian diet could remedy any potential deficiencies, suggests Ella Haddad of Loma Linda University in California. She and her colleagues previously reported that American vegetarians have lower, not higher, plasma homocysteine than their omnivorous counterparts. Haddad attributes this, in part, to the fact that U.S. vegetarians and vegans, who avoid all animal products, “consume more vitamin B12 [from fortified foods] and generally show higher blood levels of the vitamin” than the Taiwanese study participants do.
Nevertheless, says Haddad, the new finding emphasizes that “vegetarians should make sure they eat a regular and reliable source of vitamin B12, either from fortified food, supplements, or both.”