IHN Database

Natural folates poorly absorbed

DUBLIN, IRELAND. There is now substantial evidence that folic acid is very important for human health. A deficiency has been implicated in a wide variety of disorders from Alzheimer's disease to atherosclerosis, heart attack, stroke, osteoporosis, cervical and colon cancer, depression, dementia, cleft lip and palate, hearing loss, and of course, neural tube defects. Folic acid (folinic acid, folacin, pteroylglutamic acid) is essential for the synthesis of adenine and thymine, two of the four nucleic acids that make up our genes, DNA and chromosomes. It is also required for the proper metabolism of the essential amino acid methionine that is found primarily in animal proteins. A folic acid deficiency has been clearly linked to an elevated level of homocysteine, a sulfur-containing amino acid. High homocysteine levels, in turn, have been linked to cardiovascular disease and a host of other undesirable conditions.

It is, unfortunately, estimated that 88% of all North Americans suffer from a folic acid deficiency. Obviously, the standard diet does not supply what we need. This has led to the fortification of cereals and other foodstuffs to try to ensure a minimum daily intake of 0.4 mg/day. Although beans and green vegetables like spinach and kale are good sources of folic acid, relatively few people eat lots of vegetables and cooking destroys most of the folate anyway. Realizing the poor availability from the diet many medical researchers now advocate daily supplementation with folic acid.

A group of researchers at Trinity College in Dublin recently completed a study to see just how poorly folic acid is absorbed from foods and whether a folic acid supplement increases serum level substantially more than an equivalent amount contained in food. Their randomized, placebo-controlled blind study included 74 healthy men who were assigned to one of eight treatment protocols for 30 days. Prior to the start of the study all participants had received 1.6 mg/day of vitamin B6 and 1.5 micrograms/day of vitamin B12 for 4 weeks to ensure that they were not deficient in these vitamins, which are required for folic acid to carry out its functions effectively. The supplementation with vitamins B6 and B12 was continued throughout the study period.

The 8 treatment protocols were as follows:

  • Folate-depleted meal + placebo
  • Meal fortified with spinach + placebo
  • Meal fortified with yeast + placebo
  • Folate-depleted meal + 200 mcg folic acid
  • Mid-morning drink with no folate + placebo
  • Mid-morning drink with spinach + placebo
  • Mid-morning drink with yeast + placebo
  • Mid-morning drink + 200 mcg folic acid

The meals and drinks fortified with spinach or yeast were all formulated to contain enough spinach or yeast to provide 200 mcg of folate. All study participants provided blood samples at the beginning and end of the study. Analysis of these samples showed that the bioavailability of folic acid from spinach and yeast was significantly lower than the bioavailability from the supplement. Overall, the bioavailability of folate from spinach was 30% of that observed for pure folic acid and the bioavailability from yeast was 59% of that observed for pure folic acid. The folic acid supplement increased the average serum level of folate by about 26% (from 17.2 nmol/L to 21.6 nmol/L) and reduced the plasma homocysteine level by 12% (from 11.5 to 10.1 micromol/L). The corresponding values for spinach was a folate increase of 13% and homocysteine reduction of 3.3%.
Hannon-Fletcher, MP, et al. Determining bioavailability of food folates in a controlled intervention study. American Journal of Clinical Nutrition, Vol. 80, October 2004, pp. 911-18

Editor's comment: This clinical trial clearly shows that supplementation with folic acid is required in order to ensure an adequate daily intake. About 400 micrograms/day is an adequate and safe dosage and is the amount contained in most multivitamin pills.

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