[Nutrient supplements--possibilities and limitations: part 2].

Pregnant women are at greater risk of an insufficient vitamin and mineral supply. Based on hemodynamic, endocrine and metabolic changes due to pregnancy, the body weight and blood volume increase. These changes result in an increased requirement of most vitamins and minerals while the energy requirement increases by about 10%. Besides iodine (recommended intake as supplement 150 microg/d), iron (recommended intake 30-40 mg/d), vitamin D (recommended intake as supplement 20-50 microg/d), and docosahexaenoic acid (recommended intake 200 mg/d), folic acid is one of the critical micronutrients during pregnancy. Food folate and synthetic folic acid differ in their bioavailability. About 50% of the food folate is absorbed whereas almost 100% of folic acid from supplements is bioavailable. The contents are thus indicated as folate equivalents. In the form ofTHF, folic acid functions as coenzyme for the transfer of C1 units in the metabolism of amino acids, purines and pyrimidines. Folic acid (isolated or in combination with other vitamins and minerals) reduces the total risk for neural tube defects by 72%. For primary prevention it is recommended that all women who are planning to become pregnant take 400-800 microg synthetic folic acid along with a diet rich in folate. The additional intake should be continued at least until the end of the first trimester. For secondary prevention of neural tube defects an intake of 4 mg/d is recommended.