The findings of the Norwegian Vitamin trial (NORVIT), presented yesterday at the European Society of Cardiology Congress in Stockholm, comes on the back of 15 years of research into the effects of folic acid (vitamin B9) and vitamin B6 in preventing heart disease and stroke.
It is particularly remarkable as it is said to be the first to examine whether high doses of B vitamins prevent recurrent heart disease in patients who have had a myocardial infarction (heart attack), and its findings seem to contradict the beneficial link indicated by the earlier research.
The theory has been put forward that the vitamins lower the blood level of the amino acid homocysteine, high levels of which may damage the lining of arteries, increase clotting of the blood, and cause blockages in the arteries.
"The results of the NORVIT trial are important because they tell doctors that prescribing high doses of B vitamins will not prevent heart disease or stroke," said lead researcher Professor Kaare Harald Bønaa of the University of Tromsø, Norway. "B vitamins should be prescribed only to patients who have B vitamin deficiency diseases."
In the United States all flour and grain products with at least 20 percent of the RDA of folic acid per serving (between 0.43 and 1.4 mg per pound) since 1998 in an effort to address the incidence of pregnancies affected by the neural tube defects, caused by folic acid deficiency in the mother.
Despite evidence showing the effectiveness of the policy on birth defects, European countries have chosen not to follow suit since it exposes all sectors of the population to elevated levels of the B vitamin.
It is feared that fortifying flour and grain products may complicate the diagnosis of other deficiency-related conditions, like pernicious anemia in elderly patients. This latest study may provide further fuel to the policy's detractors.
The Office of Dietary Supplements cites a number of other important functions for vitamin B6, including protein metabolism, red blood cell metabolism, the effective functioning of the nervous and immune systems and the conversion of tryptophan to niacin.
The three-year trial involved 3749 patients at 35 hospitals in Norway, who were divided into four groups: one group received 0.8mg of folic acid per day; one received 40mg of vitamin B6; one received both 0.8mg of folic acid and 40mg of B6; and one received a placebo. All four groups took the supplements in addition to standard treatments after a heart attack.
Professor Bønaa and his team found that the patients who took either the folic acid or the B6 alone had a small increase in the risk of cardiovascular disease. But those who took both vitamins had a 20 percent increased risk.
The increased risk was particularly seen in patients who had high levels of homocysteine at the start of the trial, those with impaired renal function, and those who were using other vitamin supplements as well as those included in the study.
Interestingly, the homocysteine levels of the patients taking the B vitamins were lowered by as much as 30 percent. But despite the putative link between homocysteine and cardiovascular disease, this did not translate into a lower risk.
The American Heart Association estimates that 7.1 million people in the US experience myocardial infarction each year.
According to the Norwegian research team, one in three patients who has a heart attack suffers another or a stroke within three years - even those receiving the best medical care.