Today's Boston Globe has a balanced article on the ongoing controversy about the health aspects of dietary salt. Unlike many journalists, however, Globe reporter Judy Foreman focuses on the right question: "Is lowering salt consumption important for health." After the obligatory quoting of an anti-salt advocate, in this case Dr. Lawrence Appel of Johns Hopkins who pointed out 1) lowering salt can reduce blood pressure and, 2) loweirng dietary salt is "easier for morst people than ... making other dietary changes", Foreman states that "lowering blood pressure by salt reduction may not translate to a survival advantage, quoting Dr. Hillel Cohen of New York City's Albert Einstein College of Medicine who explained the most recent study: "people who reduced salt actually had a 37 percent greater risk of death than those who didn't." Foreman makes it clear that "The Salt Institute did not pay for the study." Actually, Foreman neglects to mention, the data Dr. Cohen analyzed is from the federal government's own NHANES II database.
Congratulations to the Globe and Ms. Foreman for recognizing that the proper question is the health outcome of any intervention (e.g. survivability or, in this case, it might be incidence of heart attacks) not impact on an intermediate variable like blood pressure. There are many metabolic changes that occur when a person reduces dietary salt. Blood pressure is one. Dangerously increasing insulin resistance is another. Yet another is stimulation of the renin-agiotensen system; high plasma renin activity has been shown to produce dramatically higher rates of heart attacks. Next time someone tells you that reducing salt can lower your blood pressure (it can, though in a minority of the population), remind them that none of the 13 reported studies of whether reducing dietary salt actually improves health outcomes, none, has suggested a lower salt diet is healthier. None.
After a busy spate, I'm catching up. Perhaps you saw articles published last week (for example, in the Boca Raton News , June 15) discussing a recent study by the National Academy of Sciences on teh question of whether teh flavanol in cocoa reduces the incidence of cardiovascular events.
Boca Raton News writer Nicol Jenkins, interviewed eminent Harvard researcher Norm Hollenberg who had published earlier work in this area in 2003 and 2004 , describing the study results:
Researchers provided participants with a cocoa drink that was either high or low in certain cocoa flavanols. Only the group consuming the flavanol-rich cocoa experienced increased blood vessel relaxation.
"Pinpointing specific nutrients responsible for the observed cardiovascular effects, as we are seeing here with (-) epicatechin, opens up new possibilities for the development of dietary or therapeutic interventions for cardiovascular disease," said co-author Norman Hollenberg, MD, PhD, professor of medicine at Harvard Medical School.
To assess the long-term benefits of a flavanol-rich diet, the researchers further studied two populations of Kuna Indians of Panama. A previous study has shown that hypertension is rare among the indigenous Kuna Indians living on the islands compared to those living on the mainland. The island-dwelling Kuna Indians traditionally consume large quantities of flavanol-rich cocoa (an average of 3-4 cups daily), while those who live in the suburbs of Panama City consume very little cocoa. This supported the idea that cocoa flavanols may be responsible for lower blood pressure in the island dwellers.
Every time I read about Hollenberg's research on the Panamanian Kuna Indians, my mind recalls his findings that so clearly resolved a long-standing contention of the anti-salt crowd that when primitive peoples migrate from their customary isolated, rural homelands to settle in urban centers their blood pressure increases. Of course, they conclude, this is because their primitive diet was low in sodium and their city-dwelling diet is substantially higher. And usually that is the salt consumption pattern of migrants. But, of course, one could argue that many things change in the migration. Instead of avoiding snakes, they have to dodge taxis and buses; instead of a relatively simple and slower-paced lifestyle, they have to function in high-energy and fast-paced urban settings. Even in the diet, a lot changes, not just salt.
So what did Hollenberg do regarding these Kuna Indians? He studied two groups, one that stayed at home on their remote, isolated islands and another group that migrated to Panama City and published his findings in a 1997 article in the American Heart Association's Hypertension magazine . What did he find? Migrants had a significant increase in hypertension when they moved from their home islands to Panama City -- so what? That's what other migrant studies have found. What is different about the Kuna is that, at home on their isolated island homes, they consume salt in about the same amounts as Americans do. Thus, it is some other aspect of their personal urbanization that contributes to their increased blood pressure -- not salt! Perhaps rush hour traffic? Job stresses? Simple adjustment to a lot of new things? No one knows, but we know it wasn't higher salt intake levels. For the record, Hollenberg doesn't buy the "stress " theory either.
Thanks for making that clear, Dr. Hollenberg.
A recent article in the Medical Journal of Australia should have received more US media attention than it has.
On June 5, the MJA ran an article "Media reporting on research presented at scientific meetings: more caution needed" (HTML PDF ). Dartmouth Medical School professors Dr. Lisa Schwartz write that because "the public has a strong appetite for medical news and scientific meetings provide the media with an easy source of provocative material" oral presentations (and the news releases that accompany them) usually omit key disclaimers and key study facts. For example, one-third did not report the study size and 40% did not quantify the main result, only 6% of animal studies noted that the results might not apply to humans and only 2 or 175 stories admitted that the data were not (peer reviewed or) published.
It's easy to fault honest researchers and reporters for failure to disclose the limits of these studies. What is more bothersome, and unmentioned in the article, is the practice of research project sponsors like the National Heart, Lung and Blood Institute which, for example, put out a news release the day before its funded researchers supported the DASH-Sodium Study. NHLBI has stated that they have no access to the underlying data, yet their news release claimed the study showed every American would benefit by reducing dietary sodium. Reporters called me for reaction and, in fact, I did attend the presentation of the paper at the American Society of Hypertension meeting the next day, but what could I "react" to? The paper was not only not peer-reviewed or published, it hadn't even yet been presented! Not only that, but now that the data have dripped out over the past couple years, it shows that in six of eight subgroups (collectively including well over three-fourths of the population) there was no statistically significant association at all. So don't just blame resume-sensitive researchers or headline-hunting reporters.
The fish-based, high-salt, low-fat Japanese diet, probably the saltiest in the world due to massive amounts of seafood, soy sauce and pickled vegetables, is credited with a major role in making the Japanese the world's longest-lived population.
Researchers at Tohoku University recently reported to the Japanese Society of Nutrition and Food Science in Shizuoka the superiority of Japanese fare to that ingested by Americans.
More than four in five Americans believe if the federal government pays for health-related research the results should be freely availalbe both to other medical researchers and to the general public according to a Harris Poll announced May 31.
Yet a week earlier an editorial in Kidney International criticized the Salt Institute for employing the Data Quality Act with its requirement that data disseminated by federal agencies had to be available for independent review and verification. In this case, the data in question were from a federally-funded study and used by the federal government to make policy and issue public health guidelines.
Perhaps we should simply conclude that HHS is thumbing its nose at the public in sitting on these data. But perhaps another well-known phenomenon is taking place. When pollsters ask the public their opinion about Congress, not only this year, but generally over the past generation, Congress scores poorly (lower than George W., and that's not good), but when asked whether they think their own Congressman is doing a good job, most say "yes." It's a question of the trees and the forest.
Perhaps the public hasn't focused on the fact that when a bureaucrat locks up federally-funded research, the question should be on access, not on whether the individual being polled agrees with the opinion of the bureaucrat on what the undisclosed data really mean.
When six of eight subgroups of the DASH-Sodium study show no statistically significant relationship of salt and blood pressure -- and don't address at all the paramount question of whether a health benefit is realized -- then we all are losers when HHS refuses to abide by the Data Quality Act and allow independent verification of its interpretation that "every American" benefits by cutting back salt.
The public "gets it" on the macro level. Now we need to get down to cases.
