Having more than 8 mercury amalgam fillings is associated with dangerously high blood mercury levels.

Dental amalgam fillings are a combination of mercury, silver, tin and other metals. They have always been a controversial topic, but according to research they can significantly contribute to chronically elevated mercury levels in the body if you have enough of them. More than 8 appears to be the dangerous level.

The research analyzed data from almost 15,000 individuals and is the first to demonstrate a clear relationship between dental fillings and mercury exposure. The results will be published in the journal Ecotoxicology and Environmental Safety.

According to professor John Yu, one of the study’s authors, "This study is trying to provide the most accurate levels of exposure, which will form the scientific basis to make future risk assessment." This study was the first to control for age, education, race, gender, ethnicity, smoking and seafood consumption. Seafood consumption in particular is a known big contributor to mercury levels in the body.

The researchers also analyzed exposure by which specific types of mercury were present in the blood. They found a significant increase in methyl mercury (the most toxic form of mercury) in people with multiple dental fillings. Dental amalgam has been the most widely used dental filling material for more than 150 years. Mostly because it's affordable and durable. The reality is, around half of the compound contains mercury. At high levels, it can cause brain, heart, kidney, lung and immune system damage. More recent research shows that methyl mercury might cause damage even at low levels.

If you choose to have your mercury fillings removed, make sure you visit a dentist who is experienced at this procedure, as if done incorrectly, it can expose you to even greater levels of mercury. Selenium, zinc and lipoic acid all help with removal of mercury from the body.

Reference: