Salt and (fill in the blank)
Is the "silly season" of US elections spilling over into anti-salt advocacy? Latest news release: longstanding anti-salt zealots in Finland assert that salt is responsible for the burst in global obesity.
In an article in Progress in Cardiovascular Diseases , Drs. Heikki Karppanen and Eero Mervaala assert that their study "refutes the frequently repeated claims that a comprehensive salt reduction would not produce any overall health benefits, or would even increase diseases and shorten the life span."
The Salt Institute has made the argument frequently (and, apparently, someone is listening!) that observational studies of health outcomes fail to identify population health benefits at levels common in the North American diet -- and advocating a controlled trial of reduced salt diets to determine whether they decrease heart attacks and cardiovascular mortality.
We still think that's the right question, but this claim that low-salt diets "would be a powerful means against obesity" is just over the top. Of course, if we made foods so unpalatable as to stop people from eating as much (as has been done with less-than-happy results in geriatric institutions) we might be able to link salt and body mass, but to assert that
The increased intake of salt, through induction of thirst with increased intake of high-energy beverages has obviously remarkably contributed to the increase of obesity in the United States.
with no evidence adduced to support the allegation is irresponsible.
The authors specifically cited Salt Institute statistics of U.S. salt sales saying that salt intake had increased "more than 50%" over a recent 15 year period. In response, I wrote Dr. Karppanen:
Your concern with increased salt intakes is obviously misplaced. While salt intakes in the U.S. have increased in the past 15 years, they track population increases. The U.S. population is 300 million today. We've added 50 million in population in those years. I know population growth is something a bit foreign to your part of the world, but we've experienced a lot of immigration and natural population growth. Even so, our latest figures show food salt sales growth up 41%, not "over 50%" and while greater than the population growth, this does not account for US food salt which is exported in US processed foods, salt used in food processing and wastage. The better metric, as I'm sure you agree, is 24-hour urines and those in study after study show that baseline salt intakes per capita are unchanging generation after generation.
Of course, correlation is not causation, but to correlate salt intake with the rise in obesity ignores evidence that those on higher salt diets are actually leaner than other Americans. Just as obviously, the longest-lived national population in the world, the Japanese, have much higher salt intakes than Americans. Your "obvious" correlation of salt intake and thirst and obesity makes interesting headlines, but sorry science.
The Finns claim salt reduction is responsible for increasing the life span of their compatriots by 7-8 years over the past one-third century. Let's keep in mind, Romans lived to an average age of 28. The Yanomamo people of the Brazilian jungles who are touted as low-salt-consuming models for our diet live only into their 30s. A century ago, Americans lived only 48 years on average while a century later we live 77 years on average. If Finland's medical and nutrition improvements parallel Americans, 7-8 years additional longevity over the past 30 years is just average, nothing to crow about -- nor to try to assign causation when none can be adduced from ecologic data.
Unfortunately, while preposterous charges amongst American politicians will likely abate after November 7th, there is no apparent reprieve from the anti-salt crowd.
