To The Editor


To the editor, I write to express concern about the inclusion of tuna in the latest FDA guidelines for fish intake in pregnancy, and to advocate a precautionary approach to choosing which fish to eat.  Briefly, the following considerations apply. 

  1. We have an epidemic of childhood neurodevelopmental, behavioral and learning disorders (including autism, and ADD), impacting at least one in six children, according to the America Academy of Pediatrics. 
  2. Mercury is an extremely potent neurotoxin, which passes readily through the placenta and breast milk.  While the causes of these childhood disorders are complex and poorly understood, mercury, along with PCB’s and lead, is at the top of the list of concerns.  In fact, because of these concerns, Oregon has led the country in mercury abatement efforts. 
  3. The EPA NHANES study in 2000 showed 8% of women of childbearing age had mercury levels high enough to be a threat to the developing fetus, and levels were threefold higher in women who ate fish vs non-consumers. 
  4. According to FDA analyses, mercury levels in tuna range from undetectable to 1.8 ppm, while average levels in the four species we are advised to avoid (shark, Mexican tilefish, swordfish, and king mackerel), ranged from 0.7 ppm to 1.5 ppm. 
  5. An 130 pound woman who consumes six ounces of tuna with the high end concentration of mercury will receive a mercury dose more than fifty times the EPA recommended limit dose (of 0.1 mcg mercury/kg body weight) per day.  If she consumes the recommended serving of canned light tuna, which has an average mercury concentration of 0.13 ppm, she will receive a dose more than three times EPA limit dose per day.  And if she consumes albacore light tuna, with average mercury at 0.35 ppm, she’ll receive a dose ten times EPA safety level.  I suspect the inclusion of tuna in the latest FDA guidelines is based on averaging the weekly exposure to mercury, assuming that the overdose on one day will be eliminated before the next tuna meal a week later.  This assumption has not been tested rigorously. 
  6. By contrast, canned salmon has 1/8 the mercury concentration of canned light tuna. 
  7. Omega three oils are an essential nutrient for the developing brain, and fish are one of the richest sources (also found in flax seed, chia seed, walnuts, but therein requiring further conversion to the beneficial long chain omega threes).  (8) Clean and economical sources of omega three oils from fish are readily available as supplements from many suppliers, and so there are good and safe alternatives to eating tuna.  In fact, one six ounce serving of canned light tuna provides less omega three oils than one capsule of purified fish oil, which costs about ten cents.

The Precautionary Principle in toxicology states that we should assume a substance is toxic until proven otherwise.  The neuro- and immuno-toxicity of mercury is well established,  and so the remaining question regarding tuna is whether its mercury dose is safe or not.  Shall our incubating fetuses be the testing ground?  As shown above, some tuna samples are very clean, and others are extremely high, even exceeding the fish we’re advised to avoid.   And we cannot ascertain the mercury level of a serving of tuna by inspection, taste, or interviewing the fisherman.   Applying the Precautionary Principle, it makes best sense that pregnant women should avoid all forms of tuna, and instead obtain their essential omega three oils from distilled fish oil supplement flax seeds, chia seeds, and walnuts.  I’ll be happy to provide references for the data listed.

– John A Green III MD

Table 5. Percent of women aged 16 to 49 years with blood MeHg > 5.8 µg/L, by NHANES
survey release
Survey Release Percent THg >5.8 µg/L (SE) Percent MeHg >5.8 µg/L (SE)
Overall 3.45 (0.36) 3.14 (0.34)

  • 1999-2000 7.13 (1.78) 6.77 (1.77)
  • 2001-2002 3.67 (0.72) 3.14 (0.71)
  • 2003-2004 2.40 (0.82) 1.70 (0.70)
  • 2005-2006 2.67 (0.60) 2.33 (0.58)
  • 2007-2008 2.49 (0.60) 2.42 (0.56)
  • 2009-2010 2.30 (0.41) 2.14 (0.36)