The original paleo diet included seafood with 22 times the safe limit of toxic metals, study finds

  • Stone Age humans may have consumed toxic amount of heavy metals in their seafood, according to a recent study.
  • Researchers found levels of lead 3-4 times in cod and seal were higher than considered safe by today's standards. Levels of cadmium, another heavy metal, were 15-22 times higher than considered safe, high amounts of mercury were also found.
  • These results suggest that natural food sources may have been unsafe for our ancestors, in part due to climate change. 
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When most people think of the paleo diet, they picture a simple, back-to-basics eating style full of real food like grass-fed meats, sustainable seafood, and some fruits, veggies, seeds, and nuts.

What they don't imagine is a bunch of toxic metals, including lead and mercury — but that's exactly what researchers found in a new study on the seafood diet of early humans in Norway, published January 28 in Quaternary International. 

Researchers from the Arctic University of Norway and Stockholm University looked at 40 samples of skeleton remains of Atlantic cod and harp seal, both food sources for prehistoric humans, from eight archaeological sites in a region called Varanger in northeastern Norway. The bones were between 3,800 to 6,200 years old, representing a period of the Stone Age where humans in that region ate mostly seafood, along with some reindeer, beaver, hare, and occasionally some species of birds.

They found that evidence that both species contained toxic heavy metals cadmium and lead, in dangerous quantities. The amount of cadmium was between 15-22 times higher than what today considered safe for human consumption; the amount of lead was between three and four times higher than considered safe.

Researchers also found elevated levels of mercury, another toxic heavy metal, although not beyond what is currently regarded as safe. 

High levels of toxins made Stone Age seafood 'unhealthy if not unsafe,' researchers concluded

All three types of heavy metals found in the seafood remnants are linked to human health issues. Exposure to cadmium can cause kidney, bone, and liver problems, while both lead and mercury can cause brain damage and even death, according to the Centers for Disease Control and Prevention (CDC). 

Researchers concluded, based on these findings, that "marine food during the Younger Stone Age in Varanger was unhealthy if not unsafe," according to the study. 

However, it's not clear from the data in this study what the health effects of eating contaminated seafood may have been, or even if our Stone Age ancestors lived long enough to suffer the side effects of the toxins. 

Climate change may have played a role in the level of toxins in seafood

In trying to account for these results, researchers found a correlation between the surprisingly high levels of toxins and markers of climate change such as sea surface temperature and shoreline levels. They found that the higher levels of metals, at least in Atlantic cod, were linked to rising sea levels and sea temperatures, potentially due to erosion and/or volcanic activity. 

However, this study was relatively small, so more research is needed, across more bone samples and a broader region, to better understand how changing temperatures and rising seas may have affected our ancestors' food sources and health. 

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