Alarm Over Folic Acid Based on Weak Evidence
By Alan R. Gaby, MD
Healthnotes Newswire (December 16, 2004)—It seems these days that whenever a negative study appears about a vitamin or herb, no matter how weak the evidence, it makes the news. This week the media publicized a report in the British Medical Journal (2004;329:1375–6) suggesting that women who take a folic acid supplement during pregnancy have an increased risk of dying from breast cancer 35 years later. Although the authors of the study acknowledged that their results were preliminary and could easily have been due to chance, media reports included such alarmist headlines as “Study uncovers folic acid cancer link,” and “Folic acid linked to breast cancer.”
The new study was a long-term follow-up of some 3,000 women who had been pregnant between June 1966 and June 1967. During pregnancy they were randomly assigned to take a folic acid supplement (0.2 or 5 mg per day) or placebo. By September 2002, the percentage of women who had died of breast cancer was 1.6% in the high-dose folic acid group, 1.3% in the low-dose folic acid group, and 0.9% in the placebo group. Compared with the placebo group, the mortality rate from breast cancer was 51% higher in the group taking 0.2 mg of folic acid and 92% higher in those taking 5 mg of folic acid. The total number of breast cancer deaths was small, however, and none of the differences between the three groups was statistically significant. The risk of death from heart disease was about 10% lower in the folic acid groups than in the placebo group, but those differences were not statistically significant either.
Researchers use statistics to determine the likelihood that their findings are real, as opposed to a chance occurrence. For example, if one was to flip a coin six times, and heads came up four times, one would not necessarily conclude the coin was weighted, even though there were twice as many heads as tails. Such wide variations in outcome also occur randomly in research studies, particularly when the total number of “events” (in this case, breast cancer) is small. Previous studies in humans have suggested that increasing intake of folic acid is associated with a reduction, not an increase, in breast cancer risk.
Taking folic acid around the time of conception has clearly been shown to reduce the risk of neural tube defects, and supplementation during pregnancy also lowers the incidence of certain pregnancy complications and of having a low-birthweight baby. Because of these benefits, public health officials recommend that women of childbearing age take a supplement providing 0.4 mg (400 mcg) of folic acid per day, both before and during pregnancy. That amount of folic acid is similar to what one would obtain from a healthful diet.
While there is no evidence of an adverse effect of folic acid in this dosage range, there is not much information on the long-term safety of 5 mg per day. Supplementing with large doses of folic acid can decrease the absorption of zinc, a nutrient that enhances immune function and helps prevent cancer. It is theoretically possible, therefore, that taking a large dose of folic acid during pregnancy could have negative consequences for some women. Fortunately, the average woman does not need to take a large dose of this vitamin during pregnancy to realize its benefits.
Alan R. Gaby, MD, an expert in nutritional therapies, testified to the White House Commission on CAM upon request in December 2001. Dr. Gaby served as a member of the Ad-Hoc Advisory Panel of the National Institutes of Health Office of Alternative Medicine. He is the author of Preventing and Reversing Osteoporosis (Prima, 1994), and co-author of The Natural Pharmacy, 2nd Edition (Healthnotes, Three Rivers Press, 1999), the A–Z Guide to Drug-Herb-Vitamin Interactions (Healthnotes, Three Rivers Press, 1999), Clinical Essentials Volume 1 and 2 (Healthnotes, 2000), and The Patient’s Book of Natural Healing (Prima, 1999). A former professor at Bastyr University of Natural Health Sciences, in Kenmore, WA, where he served as the Endowed Professor of Nutrition, Dr. Gaby is the Chief Medical Editor for Healthnotes, Inc.
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