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Home > Vitafriendspku > Your pku journey > What Impact Does Elevated Phe Levels Have On My Health?

What Impact Does Elevated Phe Levels Have On My Health?


As an adult with PKU you may have been told as a child or a teenager that you no longer needed to follow a low protein diet.

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This is because, it used to be thought that high blood phe levels had minimal impact once the brain was fully developed and it was thought the brain was fully developed once you were a teenager. However more recent research and findings has led to the recommendation of Diet for Life.

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Although some adults say they don’t feel any different to their norm when they have high phe levels, others do report problems when their phe levels are high and it is thought that the variability in cognitive outcomes in adults with PKU is linked to the variability in dietary adherence.

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Research has shown that cognitive performance is linked with present and past phe levels. It is thought that high phe levels in adulthood have more of an effect on parts of the brain that develop later such as executive function which includes speed of processing and the ability to sustain attention. You will hear people referring to a feeling of ‘brain fog’ when phe levels are high. You may feel a bit muddled when doing tasks and your friends, family and colleagues may notice you’re not quite yourself. Having a poor executive function may hinder you when you’ve got a packed schedule or if you are starting a new job.

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In Australia, Newborn screening for PKU began in the 1960’s. Therefore, the oldest individuals being treated for PKU are into their 60’s. It is generally well-accepted in Australia; the recommendation is Diet Treatment of PKU for Life.  

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Those not treated for life risk the following complications associated with high phe levels - 

  • depression and anxiety
  • tremors (the shakes)
  • stiff or weak legs
  • headaches
  • eczema
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Additional Concerns

Unfortunately, unplanned pregnancies do occur. Uncontrolled PKU (high blood Phe) in pregnant woman can have devastating effects on the unborn baby. 

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Therefore, it is essential blood phe levels are controlled prior to becoming pregnant, and throughout the pregnancy. High phe levels do not tend to occur in isolation. If an individual has high phe levels due to no longer taking their protein substitute  they are also at risk of not fully meeting their requirements for several vitamins that are added to the protein substitute.

The recommendation is Diet for Life but if an adult feels very strongly that they want to come off diet, they should discuss it with their Specialist Metabolic team. Although the team will respect and seek to support that individual’s choice, they will also want to monitor their health and well-being to ensure that coming “off diet” has no ill effects. Part of that monitoring will be ensuring that the diet is well balanced and providing all the nutrients required for good health.  

If somebody simply stops taking their protein substitute whilst remaining on a severely restricted protein intake, they are putting themselves at risk of protein malnutrition and vitamin and mineral deficiencies. 

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