High dietary folic Acid and high plasma folate in children and adults with phenylketonuria.

BACKGROUND

PKU patients on a strict low protein diet get most of their folic acid intake from protein substitute. Several protein substitutes contain high amounts of this vitamin. Concern has been raised about the safety of high levels of folic acid, especially in relation to cancer risk.

METHODS

This cross-sectional study included 34 children and 22 adults with PKU. A dietary interview was performed and intake of folic acid and vitamin B12 from protein substitute was calculated for patients compliant with their protein substitute. Intakes of folic acid and vitamin B12 were compared with plasma levels of folate, vitamin B12, and homocysteine.

RESULTS

Children aged 2-9 years had the highest intake of folic acid according to RDI (449 %), and children aged 7-10 years had the highest intake of folic acid according to UL (155 %). Median plasma folate level in PKU children was two times the upper reference level and in PKU adults well above. Children between 10 and 13 years had the highest level of plasma folate. Young children had both a high intake and high plasma levels of vitamin B12. Homocysteine levels were low or in the lower part of the normal reference range in most patients.

CONCLUSION

Children with PKU are at a particular risk of receiving folic acid high above RDI and many children with PKU receive doses above the UL. Many PKU patients have a very high level of plasma folate related to a very high content of folic acid in many of their protein substitutes.