Poor absorption of folic acid is compounding a low intake among people in the Netherlands, suggest researchers, who advise that a more bioavailable form of the B vitamin be included in foods.
A study found that the average Dutch person consumes around 85 per cent of the recommended daily intake of folic acid. Furthermore, our bodies do not absorb up to a quarter of this daily intake, according to Alida Melse-Boonstra, carrying out doctoral research at the Wageningen Centre for Food Sciences and Wageningen University in the Netherlands.
Folic acid, promoted especially for use by pregnant women to reduce the risk of spina bifida in newborns, could also reduce the risk of cardiovascular disease, recent research has shown. But it appears that the body has a limited ability to absorb the most common form of folic acid (vitamin B11).
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 in the Netherlands 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.
The body must convert this into the monoglutamate form before it 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 per cent of that in the monoglutamate group, they report.
The team estimate that a daily intake of 240 micrograms of folic acid contains 80 micrograms in the monoglutamate form and 160 micrograms in the polyglutamate form. If only 66 per cent of the polyglutamate form is absorbed, the body only gains around 186 micrograms, or three-quarters of the original amount, of folic acid.
And besides the normal nutritional requirements, about 400 micrograms of folic acid is needed everyday for an optimal reduction of the so-called homocysteine level, added the researchers. A high level of this substance is associated with cardiovascular diseases, although it has yet to be demonstrated that a reduction in this level decreases the risk of cardiovascular diseases.
The Dutch team concluded that nutritional advice or new products that contain either more folic acid or a more easily absorbable form of folic acid could help to increase intake of the nutrient. Fortification of foods with folic acid faces considerable resistance by European authorities however. While the process has been in place for some years in the US, Canada and Chile, with success demonstrated by recent studies, agencies such as the UK's Food Standards Agency claim that not enough is known about the potential adverse effects of such an initiative.
For further information on the study contact Dr Alida Melse-Boonstra.