According to a study published in Physiology & Behavior, rats with a sodium chloride deficiency shy away from activities they normally enjoy, results that were interpreted as a sign of depression.
"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," said Kim Johnson.
The research may go someway to explaining why people add extra salt to food, or seek out salt-rich foods, despite warnings from numerous scientists and health professionals convinced that high salt intake is responsible for increasing blood pressure (hypertension), a major risk factor for cardiovascular disease (CVD).
“Our preference for sodium is often so compelling that patients with hypertension or CHF have difficulty adhering to a low sodium diet due to issues with palatability (e.g., food becomes bland and unappetizing) despite the recognized health benefits of doing so,” wrote the researchers.
Salt is of course a vital nutrient and is necessary for the body to function, but campaigners for salt reduction, like the Consensus Action on Salt and Health (CASH) consider the average daily salt consumption in the western world, between 10 and 12g, far too high.
The pressure has been mounting on food manufacturers to reduce the salt content of their foods and the UK's food standards agency (FSA) recommendation of six grams of salt per day for the general population is understood to be more a realistic target than the ideal healthy limit recommended by WHO/FAO.
Commenting on the study, Wendy Jarrett, spokesperson for CASH, said: "Our bodies need a very small amount of salt to function, but nothing like the quantities that most of us eat.
"This research may help us to understand why some people still eat too much salt, even though they know it's bad for them.
"I personally have never felt depressed by not eating too much salt: I think it would be far more depressing to have a heart attack or stroke that could have been avoided by not eating so much salt."
Feeling good about over-consumption
Johnson and co-workers added a note of caution that the depressive symptoms did not prove ‘full-blown depression’ since the condition is complicated, but the idea that salt is a natural mood-elevating substance could help explain why people are so tempted to over-consume it, even though it's known to contribute to high blood pressure, heart disease and other health problems.
“Rats depleted of sodium multiple times show a neurochemical profile similar to that seen following sensitization to drugs of abuse and demonstrate a craving for sodium as exhibited by an increased breakpoint in a progressive fixed ratio operant task,” wrote the UI researchers.
“These findings suggest that changes in sodium status can alter the chemistry and anatomy of putative reward pathways in the brain, the same pathways impacted by drugs of abuse and potentially involved in maintaining addiction.
“Our preference for sodium is often so compelling that patients with hypertension or CHF have difficulty adhering to a low sodium diet due to issues with palatability (e.g., food becomes bland and unappetizing) despite the recognized health benefits of doing so,” they added.
Industry moves
Moves by national agencies and food manufacturers to reduce the salt content of their products have been increasing, with the UK widely seen as leading the way. While reformulating and reducing salt in existing formulations has been one approach, a second approach has been to launch low-salt alternatives to established favourites.
There has also been an increase in the number of new low-salt products on the market. According to Mintel’s Global New Products Database (GNPD) there were 428 such launches in the US in 2006, followed by 542 in 2007, and 533 in 2008. In Europe, 451 new low-salt products were launched in 2006, followed by 733 in 2007, and 536 last year.
Mintel’s numbers are for new products and don't include all incremental reformulations, unless they are very prominent on-pack.
However, CASH’s Jarrett told FoodNavigator that the organisation’s stance has always been for food manufacturers to reduce the salt content of their foods, rather than produce low salt alternatives as an alternative.
“For a long time the food industry argued that, for instance, low salt baked beans were on the market, so there was no need to remove any salt from standard baked beans,” she said.
“Of course, if you are trying to reduce salt intake on a population level, then the best way to do it is to remove small amounts from across the board, on a gradual basis over a long period of time.
“That way people do not notice any difference in the products they buy and don't even know that their risk of cardiovascular disease is being reduced!”
Source: Physiology & Behavior Volume 94, Pages 709-721, DOI: 10.1016/j.physbeh.2008.04.008“Salt craving: The psychobiology of pathogenic sodium intake” Authors; M.J. Morris, E.S. Na, A.K. Johnson