On a windy cloudy day it is fun to lay on your back and watch the clouds go by. They change shapes and with a little imagination one can see lions that become cars and then turn into Leonardo DiCaprio eating an ice cream cone. This is somewhat reminiscent of the story of folate in the last decade. Just when you think you recognize the shape of things, the wind picks up and what you thought was a beautiful healthy diet turns into a toxic overdose.
We are going to address the question of how young women, particularly vegetarian women, can reduce their risk of bearing a child with neural tube defects (NTD) by consuming a diet high in folate. Science has supported this precaution for nearly a decade but the story keeps changing. We are going to start by taking a quick trip from the early 90s to today to review this morphing story of folate. Then when we have cleared away a few weeds, we will find the folate in the foliage.
Folate was one of the last vitamins discovered in part because it does not have a dramatic deficiency disease like scurvy or rickets. It is also fairly unstable and difficult to purify. Folate was so ubiquitously distributed in green leafy foods that it was named after its foliage sources. It quietly took its place in the pantheon of water-soluble B vitamins until the early 90s when a well-designed clinical trial showed that women given a multivitamin pill including 800 mg/day of folic acid (the synthetic version of natural folate) had a significant decrease in NTD births. In 1992 the CDC recommended that women capable of becoming pregnant should take 400 mg/day of folic acid in addition to a healthy diet with food sources of folate. Since half of all pregnancies are unintended and the vitamin needs to be consumed at least a month before conception, the recommendation was not limited to women who were intending to get pregnant. This amount was well above the 200-250mg/day consumed on average by American women.
At about this same time the folate "cloud" split and the new half turned into a fighter of heart disease. Researchers found that high blood levels of homocysteine, an amino acid by-product, presaged impending heart disease by several years. Homocysteine levels build up when tissue levels of folate and other B vitamins are low. Subsequent studies have since shown that small additions of folate (either in foods or in pills) can reduce homocysteine. A definitive study showing that increased dietary folate will reduce heart disease has not yet been done.
For these and other reasons the Food and Nutrition Board in 1998 recommended a new RDA for folate of 400 mg/day for both men and women. They reaffirmed the recommendation that at-risk women take an additional 400 mg pill daily. They also determined that an intake of 320 mg/day was about what the average adult required and that 1000 mg/day was the tolerable upper limit of intake, the toxic threshold. Based on previous bioavailability studies they determined that synthetic folic acid was 70% more digestible and absorbable than the natural folate. This has important implications when trying to calculate actual intakes of the vitamin from a varied diet.
Also in 1998, food fortification with folic acid became required by the FDA for a variety of grains, flour, and baked goods. The goal was to increase the average American's intake by about 100 mg/day (or the equivalent of 170 mg of natural folate). Several studies since have demonstrated the success of this policy in raising American blood folate levels and decreasing blood homocysteine levels.
The final cloud shape we will discuss is a report last year in which a group of FDA scientists tried to carefully combine all of this information into a new analysis of how much folate Americans are now getting in their diets. The answer was a shocking increase to about 700 mg/day, a 3-fold rise. But no one popped champagne corks and declared the folate war over and won. Why not? Only a small, and unspecified, amount of this "increase" was the additional amount from fortification. The rest was from the 70% better bioavailability of the synthetic folic acid that was already in the diet (from fortified foods like breakfast cereals and from vitamin pills) but were not previously counted in the total. Besides, there are two downers in the news. Only about 30% of women were heeding the auspicious advice of the Feds and taking their folic acid pills daily. The rest were getting less than half the recommended amount.
The other downer was like a fluffy cloud teddy bear turning into a dark grizzly bear thunderstorm: toxicity. If a woman consumes the usual 250 mg/day of natural folate and then adds 400 mg of synthetic folic acid, now adjusted for bioavailability, she is consuming the equivalent of 930 mg/day, dangerously close to the tolerable upper limit of safety. Here is where the thunderstorm breaks and we all run for cover. What is a woman to do? If she does not take the vitamin pill she risks her baby and if she does then she is apparently risking herself and maybe the baby too.
The threat of NTD is small (about 1 in 1000 live births) but real and serious. All the studies show consistent beneficial effects of folate in preventing NTD; even over the levels that we are now suppose to consider toxic. However, this toxicity level should not be interpreted in the usual manner. It is more like saying, "Don't bother to consume more than this amount. It probably doesn't help that much more and it might complicate things."
I believe there is a real live vegetarian alternative to this dilemma. We need to return to the foliage from which folate first came. A recent study by a Dutch group determined that a diet rich in citrus fruit, citrus juice and green vegetables (spinach, green peas, broccoli, Brussels sprouts, and green beans) could give a daily intake of 560 mg. This did not include the approximately 170 mg/day in fortification now present in all our diets and the other great plant-based sources in legumes like chickpeas, lentils, split peas, kidney bean, etc.
Think about this. Doesn't this really define a healthy piece of a great vegan diet, legumes, greens, and fruit? Nobody is asking you to actually calculate your folate intake everyday but a healthy varied diet that includes plenty of these foods, leaving the whole "5-a-day" thing in the dust, should have no trouble. For the woman who wants to make sure her bases are covered, maybe a folic acid pill every other day would be safe and efficacious.
The clouds clear and we have a reasonable solution: a variety of legumes, greens, and citrus, and for that special woman, maybe a pill every couple of days. And remember, the folate is in the foliage.
Marty Root has a PhD in Nutrition from Cornell University, and works as a Senior Research Scientist at BioSignia, Inc. in Chapel Hill, NC. His work involves making statistical models that predict the onset of chronic diseases such as heart disease and the cancers. A frequent contributor to VegSource.com, Dr Root is married and has three children.