Heavy metal and the blues

Most people are unaware of the scale of pollutants that exist in our atmosphere. Yet these pollutants - the by-product of modern industry and lifestyle - are having an effect on human health that is only just being understood.

In a paper just published in “BMJ Open”, researchers from Deakin’s IMPACT Strategic Research Centre have found that higher levels of cadmium within the body are linked to a higher incidence of depression.

People with elevated levels of cadmium were almost twice as likely to display symptoms of depression, compared to those with lower cadmium levels.

However, the news is not all bad. Some other heavy metals and persistent organic pollutants (POPS) were found not to be associated with depression – as had been feared by the researchers. 

Surprisingly, higher mercury was associated with a lower risk for depression. This unexpected finding was explained by fish consumption, a source of mercury. This suggests that the protective effect of fish consumption may have outweighed any potential noxious effect of mercury.

Using the US-based National Health and Nutrition Examination Survey (NHANES), the study assessed over 15,000 people across three different time waves. NHANES is a program of studies designed to assess the health and nutritional status of adults and children in the United States.

Given the ubiquitous nature of persistent organic pollutants, the results could be taken as representative of cadmium levels within people in all countries.

“Cadmium is a not uncommon persistent organic pollutant that is a by-product of all kinds of industrial processes, including mining, and it is commonly used in metal plating, batteries and plastics,” said Professor Michael Berk, the Director of IMPACT.

“It is one factor thought to increase the risk of depression, along with social factors, stress, diet, personality, childhood abuse and genetics.”

“The connection with depression shows that we need to look more closely at how cadmium is coming into the environment and ensure that we dispose of it safely.”

He explained that previous research has shown a number of adverse health effects from persistent organic pollutants, particularly in the area of developmental and brain problems.

“For instance, several perfluorinated compounds (PFCs) found in food packaging, clothing, fabrics, carpets, dust and human milk, affect brain systems,” he said.

PFCs are used by manufacturers to make products resistant to stains, grease, and water. They are often used in paper food containers such as microwave popcorn bags and fast food wrappers. Yet the consequences of their use are not fully understood. They are classified as persistent organic compounds because they resist chemical or biological degradation and exposure to light in the environment.

Professor Berk explained that one of the problems for researchers is that persistent organic pollutants have a ubiquitous presence in the atmosphere across the globe. They are transmitted by air and water - far from their original source. This means that there is nowhere on the planet that can be used for control purposes.

“Many POPS can accumulate and magnify in human and animal tissues, becoming more concentrated up the food chain,” he said.

“Exposure to these pollutants can have neurobiological effects and lead to a range of diseases and illnesses, especially when exposure is in utero or early childhood.”

 “Our research shows that we need to study the effect of POPs and heavy metals further, to investigate the role of various agents in the pathophysiology of depression and other diseases.”

• Read about this research in “BMJ Open”
• The 7.30 Report