Industrialisation and poor farming practices has meant access to nutrient-rich food and fresh water (with a balanced mineral content) is becoming harder to obtain. 

In addition, there are many external factors in our modern world that can leach valuable trace elements from the cells of the body faster than we can replace them from diet alone: 

Pollution:  

Heavy metals and pesticides found in our food, water and the air

Medicines:  

e.g. Streptomycin (antibiotic) removes Magnesium and Manganese

Supplements:

Incorrect use of herbal medicines or food supplements

Stress:

When the body is under any form of stress the requirement for trace elements increases.