Thursday, 8 September 2011

Don't touch those salty balls


I, like a few people went through the 'South Park' phase quite a few years ago, watching the often crude exploits of Stan, Cartman and Kenny (and Mr Hankey) week on week. It was toilet humour, of this there is no doubt and I do wonder how many hours of my life I wasted on that show. Chef was also a prominent character in the early days of the show; remembered also for his number 1 hit song 'Chocolate salty balls'. It is hard to believe that sandwiched between the Spice Girls and Steps in late 1998, Chef was number one in the UK singles chart. This tenuous link (I should perhaps rename this site that) brings me to this post on salt and our evolutionary addiction.

The September 2011 edition of Chemistry World carries an interesting article on some research linking our ancient appetite for salt to our modern day societal addiction to drugs of abuse such as cocaine and opiates. The paper in question is this one by Wolfgang Liedtke and colleagues* recently published in PNAS. In it they claim to have identified the mechanism controlling our evolutionary appetite for salt and suggest that such a mechanism might be utilised by other addictive compounds, thus potentially explaining our societal fascination with some drugs of abuse.

I can't pretend to understand all the intricacies of the study by Liedtke and co, but the interpretation provided in the Chemistry World journal does make things a little easier. It is with this in mind that I draw a few details from said publication, properly referenced**, save any charges of plagiarism being levelled at me.

Evolutionary-wise salt is pretty vital to human existence. Indeed so vital was it to us that we built our cities near to deposits and wars have been fought over it. As with many things nowadays, you hear about salt being the bad guy in modern health and the onwards implication that we should halt our consumption. Maybe I am being a little melodramatic there because I don't think anyone actually thinks that salt should not be included in our diet; rather that we follow the tenet: everything in moderation. Certainly in these times, moderation is not necessarily a word at the forefront of consumption.

Anyhow, in the current study the genes activated by salt appetite in the hypothalamus were identified; some of those genes being the same as those regulated by drugs of abuse. After withholding salt from mice (sorry!), giving them a diuretic and increasing their salt appetite by administering the stress hormone ACTH, the researchers found that the hunger for salt made another area of the hypothalamus more susceptible to the effects of dopamine, hence making the mouse brain really, really happy when salt was eventually given. Dopamine has some pretty consistent relationships with drugs of abuse as per its reward hormone status.

Obviously this was another mouse study and one has to be careful about the interpretation. Indeed in light of some new research*** on laboratory vs. 'dirty' mice, perhaps very careful. There are a few avenues of interest from this research. The primary being that salt at higher concentrations might in certain people allow them to become addicted to overeating with the biological end-point as cocaine or morphine. With the right genes and the right environmental factors (low salt diet followed by high salt foods and stress) should salt also be called a drug of abuse?

To end, dare I post it.. take it away Isaac Hayes..

* Liedtke WB. et al. Relation of addiction genes to hypothalamic gene changes subserving genesis and gratification of a classic instinct, sodium appetite. PNAS. July 2011

** Senthilingam M. Appetite for salt linked to drug addiction. Chemistry World. 8(9) September 2011

*** Boysen P. et al. Natural killer cells in free-living Mus musculus have a primed phenotype. Molecular Ecology. September 2011.