Lancet editors miss bogus reference on Japanese longevity and salt intake


Is it too much to ask of medical journal editors to verify references for key claims? After all, just because a study author footnotes a claim, should that act automatically enshrine the claim with credibility?

If you want to know how lazy editors can help launch diet and health myths, you need look no further than a new article in The Lancet entitled, “What has made the population of Japan healthy?

The study’s media release stated,

[Japanese] life expectancy increased rapidly throughout the 1950s and 60s as first infectious disease mortality dropped markedly, which was swiftly followed by stroke mortality falling. High blood pressure was also controlled through salt reduction campaigns and increased use of antihypertensive drugs and better health technologies. [Emphasis added]

Curious about the salt reduction claim, I read the full article which spotlighted it in a summary box entitled “Key Messages”:

The control of blood pressure improved through population-based interventions such as salt reduction campaigns…

The text of the article went on to read,

A reduction in dietary salt intake has been very important for the health improvement of the Japanese population. Average salt intake among middle-aged men decreased from 30 g/day in the 1950s to 14 g/day in the 1980s…

Two factors that might be important in contributing to the falling trend in blood pressure in the population are the increased coverage of antihypertensive drugs in patients with hypertension and improved lifestyles that include reduced dietary salt intake.38

“Two factors that might be important”? I though the article said that blood pressure was controlled by salt reduction. So I went to check out footnote 38, which directed me to the following study,

Ikeda N, Gakidou E, Hasegawa T, Murray CJ. Understanding the decline of mean systolic blood pressure in Japan: an analysis of pooled data from the National Nutrition Survey, 1986–2002. Bull World Health Organ 2008; 86: 978–88.

It didn’t take long thereafter for The Lancet article’s claim to begin to teeter. The abstract in Ikeda et al. stated,

Declining mean systolic blood pressure (SBP) in Japan between 1986 and 2002 was partly attributable to the increased use of antihypertensive medications, especially in the older population, and lowered mean BMI in young women. However, a substantial part of the decline was left unexplained and needs to be investigated further. A still greater decline in SBP would be expected through improvements in body weight management, salt and alcohol intake, and treatment and control of hypertension. [Emphasis added]

So lower blood pressure was linked with medications, not reduced salt intake, which only merited a hopeful “would be expected.”

Adding detail to this observation, the Ikeda et al. study stated,

Reduced mean daily salt intake contributed [in a statistically significant manner] to the decline of mean SBP by −0.4 to −0.2 mmHg in all age groups in both sexes.

But SBP is meaningless on a population level, and fractional mmHg changes in SBP are miniscule and likely not even detectable on a clinical basis for an individual — after all, “ideal” SBP is on the order of 120 mmHg. It’s no wonder that Ikeda et al. go on to acknowledge that,

Lifestyle-related factors such as physical activity, alcohol drinking and dietary salt intake made only limited contributions to the decline of mean SBP in this study.

And even that assertion is an overstatement as there is no evidence that reducing dietary salt intake even made a “limited” contribution.

So The Lancet article makes a prominent claim that is actually debunked, as opposed to sustained, by its reference.

The added bizarre twist, here, is that Ikeda is the lead author of the article in The Lancet. So Ikeda debunked his own claim before he made it, but made it anyway, and then had the nerve to cite his prior debunking as support for the new claim.

I guess The Lancet‘s editors were too busy rushing the article to publication to actually “edit” it. The Lancet‘s editors were also apparently too busy in 1998 to uncover the scientific misconduct behind the study that fraudulently linked the MMR vaccine with autism — a study that launched anti-vaccine hysteria.

We’ll see if and how the media plays Ikeda’s new article. But if you ever hear someone bloviating about how low-salt diets help the Japanese live longer, you’ll know where the myth came from and how bogus it is.