The findings also indicate future risk for cardiovascular disease, as homocysteine in the blood is thought to be a marker for elevated risk of the disease.
It is unclear if the differences between races are due to diet, lifestyle or heredity, said the researchers, but the findings offer further evidence that several factors, including race, need to be taken into account for dietary requirements. Since high homocysteine levels have been linked to diets low in folic acid and vitamins B6 and B12, it may be necessary to increase folic acid intake among blacks. These vitamins help break down homocysteine.
Preeclampsia affects around 5-8 per cent of all pregnancies, according to the Preeclampsia Foundation, and can endanger the lives of mothers and babies.The onset of the disorder is detected by an increase in blood pressure and can cause protein in the urine - a sign of potential kidney damage and severe water retention resulting in swelling in the hands and feet.
"There is a higher incidence of preeclampsia in black women and we know that when black women experience the disorder they are more likely to have a more severe form that shows up as early as six months into pregnancy," said lead author Thelma E. Patrick from the University of Pittsburgh School of Nursing.
Researchers examined 85 white women and 78 black women who gave birth at Magee-Womens Hospital. 34 white women and 26 black women had preeclampsia.
The researchers report in Hypertension (10.1161/01.HYP.0000126580.81230.da) that homocysteine levels were higher in both black and white women with preeclampsia compared to those with uncomplicated pregnancies. Black women with preeclampsia had the highest homocysteine levels: 8.7 micromoles per liter; while the levels were 7.6 umol/L for black women with normal pregnancy; 7.5 umol/L for white women with preeclampsia and 5.5 umol/L for white women without preeclampsia.
"There were no differences in folic acid or B12 levels within racial groups, but there were differences in those levels between races. Folic acid was higher in white women compared to black women, whereas B12 was higher in black women compared to white women," Patrick said. "That finding is intriguing because both folic acid and B12 are needed to break down homocysteine.
"I had assumed folic acid and B12 tracked until this," she said. "In searching the literature, I found a study of postmenopausal women that found the same thing: homocysteine was elevated in black women and their folate was down but their B12 was increased."
"We need to test this further either through supplementation or by controlling diet or weight to see if the same thing happens," she added.
Other trials have investigated deficiency of selenium and vitamin C as possible risk factors for preeclampsia.
The US, Canada and Chile currently require folic acid fortification of flour to protect women from the risk of birth defects in their babies, shown to be at higher risk if the mother is deficient in this vitamin.