She discovered that the body has a limited ability to absorb the most common form of folic acid (vitamin B11), thus compounding the fact that the average Dutch person consumes too little of this vitamin anyway. Folic acid is not just something that pregnant women should take to reduce the chance of a child with spina bifida. There are now indications that folic acid can also reduce the risk of cardiovascular diseases.
The researchers state that the amount of folic acid in the blood could be increased by means of nutritional advice or new products that contain either more folic acid or a more easily absorbable form of folic acid. Up until now, Dutch law has forbidden the enrichment of products with folic acid. However, plant breeding might provide a solution to this problem.
In cooperation with the National Institute of Public Health and the Environment (RIVM), the researchers analysed the food intake of 2435 people aged 20 to 65 years. Although the recommended daily intake of folic acid has recently been increased to 300 micrograms per day, the average intake was found to be about 250 micrograms per day. Two-thirds of this amount was in the polyglutamate form.
Folic acid occurs in two different forms: bound to a polyglutamate or to a monoglutamate. The small intestine first of all has to convert the polyglutamate form of folic acid into the monoglutamate form, before the body can absorb the vitamin. The researchers wanted to establish whether this extra conversion step meant that the polyglutamate form was less well absorbed than the monoglutamate form.
To determine this they divided 180 healthy volunteers, aged 50 to 70 years, into three groups. Every day, the first group received a capsule containing a small quantity of monoglutamate folic acid, the second group a capsule containing polyglutamate folic acid and the third group a capsule containing a placebo. After 12 weeks, the researchers compared the concentrations of folic acid in the blood plasma and red blood cells. The increase in the concentration of folic acid in the polyglutamate group was only 66% of that in the monoglutamate group.
Using this data the researchers estimated the extent to which the poorly-absorbed form affected the overall absorption of folic acid. An example: a daily intake of 240 micrograms of folic acid contains 80 micrograms in the monoglutamate form and 160 micrograms in the polyglutamate form. Therefore, in total the blood absorbs 80 x 100% + 160 x 66% = 186 micrograms. This is about three-quarters of the original amount.
The researchers also established that in addition to the normal nutritional requirements, about 400 micrograms of folic acid per day is needed for an optimal reduction of the so-called homocysteine level. A high level of this substance is associated with cardiovascular diseases. However, it has yet to be demonstrated that a reduction in this level decreases the risk of cardiovascular diseases.
For further information please contact Dr Alida Melse-Boonstra (Division of Human Nutrition and Epidemiology Wageningen University), tel. 31-317-48-5639, e-mail: alida.melse@wur.nl. The doctoral thesis was defended on 3 September 2003. Dr Melse-Boonstra's supervisors are Prof. F.J. Kok and Prof. C.E.West.
The research was funded by the Netherlands Organisation for Scientific Research.