March 2009 - Research from the University of Iowa published in Physiology &
Behavior suggests that over-consumption of and craving for salt may be explained by its mood-enhancing qualities.
Researchers found rats deficient in sodium chloride (common table salt) avoided activities they normally enjoy.
Psychologist Kim Johnson said:
"Things that normally would be pleasurable for rats didn't elicit the same degree of relish, which
leads us to believe that a salt deficit and the craving associated with it can induce one of the key symptoms
associated with depression."
The researchers explain that experiencing a loss of pleasure in normally enjoyable activities is an
important feature of psychological depression. The notion that salt may be a natural mood-elevating substance could
help explain over-consumption despite its known association with high blood pressure, heart disease and other
health problems.
Previous studies have shown that the worldwide average for salt intake per individual is about 10
grams per day compared to the U.S. Food and Drug Administration recommended intake of 6 grams, and exceeding what
the body actually requires by more than 8 grams.
The researchers explain that processed and restaurant food currently contain high levels of salt
accounting for 77 per cent of daily intake. Discovery of its food-preserving properties in about 2000 B.C. was
associated with massive increases in consumption and cost. Roman soldiers' were paid in salt; the word salary
being derived from the Latin for salt. When refrigeration was introduced in the 19th century, excessive consumption
continued because people liked the taste and the cost had fallen.
The researchers conclude that the evolution of humans from creatures inhabiting salt water
environments might have played an important part in the desire for salt. Perspiration removed sodium in the
African climate. Salt was scarce because early man lived in the continental interior and relied on a
vegetable-rich diet. Nonetheless, salt is essential; sodium and chloride play a key role in transit of fluids
in and out of all cells in the body and in transmission of information via nerve cells.
Kim Johnson commented:
"Most of our biological systems require sodium to function properly, but as a species that didn't
have ready access to it, our kidneys evolved to become salt misers."
The researchers also conclude that behavior came to play a key role in ensuring the body is not deficient
in salt. Humans have evolved a taste system designed to detect salt and a brain that remembers the location of salt
sources. A pleasure mechanism in the brain is activated when salt is consumed.
However, salt also has some of the qualities of an addictive substance. For example, continued use
even when it is known to be harmful. Many people told to reduce consumption find it difficult because they like the
taste and find low-sodium foods bland. Another feature of addiction is the development of intense craving when a
drug is withheld. Researchers identified similar changes in brain activity when rats were exposed to drug or salt
deprivation.
Kim Johnson concluded:
"This suggests that salt need and cravings may be linked to the same brain pathways as those related to drug addiction and abuse."