A new study in JAMA found higher salt consumption strongly associated with less death from heart disease. The association with total mortality (more salt, less death) was almost significant. To grasp the strength of the evidence, see this. Yes, it’s a correlation, but I don’t know of any examples of such a strong correlation reversing (so that more salt is now correlated with more death) when now-unknown confounders are taken into account. In 1998, Gary Taubes argued that the benefits of salt reduction were greatly overstated. The new study did find more salt correlated with higher systolic blood pressure but in the big picture (mortality) that didn’t matter. If all those warnings about salt had any effect, the new study suggests their effect was negative.
Perhaps people who eat less salt are more credulous (they believed the experts) — and this damages them in other ways? Perhaps they rely on doctors more, for example. It is hard to interpret this finding in a way that makes mainstream health care look good. A New York Times article about the study points out that “the new study is not the only one to find adverse effects of low-sodium diets.” And it reports what someone at the Centers for Disease Control said:
Dr. Peter Briss, a medical director at the centers, said that the study was small; that its subjects were relatively young, with an average age of 40 at the start; and that with few cardiovascular events, it was hard to draw conclusions.
Dr. Briss fails to understand statistics. Ordinary statistical calculations take sample size and number of events into consideration when indicating the strength of the evidence. That’s the one of the main purposes of those calculations. As for “relatively young,” I know of nothing to suggest that the effects of sodium reverse with age — so it is irrelevant that the subjects were relatively young. That someone at the CDC is so clueless is remarkable.
The link to JAMA goes to a registration page; here’s the abstract to the paper from PubMed:
https://www.ncbi.nlm.nih.gov/pubmed/21540421
Is there a cost effective way to measure your own blood sodium concentration for daily tracking?
Is there a cost effective way to measure your own blood sodium concentration for daily tracking?
Sodium in blood or urine is easy to measure in a medical lab – the analysis takes under a minute – but in this study they would have measured 24-hour urine excretion, which involves collecting all urine over a day. Not very convenient.
Also, blood concentrations of sodium are tightly regulated in healthy people, so presumably blood levels wouldn’t give the required information.
I bet the mechanism is iodine up-regulating the thyroid. If the coastal Japanese are any example, humans can experience health benefits from very high iodine levels. Many of the patients I see in my practice suffer from low thyroid hormone. Yet another national health problem inflicted on us by public health advice.
Question – it seems to me the correlation != causation bias here is strong.
What if people who already regulate the sodium intake are doing it consciously and deliberately? And what if they’re doing it because of pre-existing health concerns?
That would explain a higher mortality rate.
The authors did not consider this idea. They merely say their results are not consistent with current recommendations. The health of the three groups (low, middle, high tertile of salt intake) appears about the same. However, those in the highest tertile drink more than those in the other two tertiles. Drinking (alcohol) seems to reduce heart disease mortality. Perhaps that has something to do with these results.
A better thing to do is test whether salt affects your blood pressure.
A small minority of people are sensitive to salt. You can determine if you are one of those people by doing what I did.
One week before your salt free diet, take daily blood pressure readings. Then go on a salt free diet for a week and take daily blood pressure readings. Compare the two weeks of readings, if there is no decrease in blood pressure during the salt free week, you are not sensitive to salt.
I saw no change in my blood pressure so I ignore all salt free propaganda.
Re correlation and causation, in many studies the healthy user effect causes spurious correlations, e.g. people who eat more vegetables are healthier in part because they’re already healthier and they’re smart and likely to pay attention to diet. I think it can be ruled out here because the healthy users would be more likely to lower their salt consumption. It was the “unhealthy users” who had lower mortality.
I remember Robb Wolf making a comment in a podcast that salt consumption will lower cortisol levels via aldosterone.
what i’ve understood is that some people excrete salt better than others (related to renal function), and that those who excrete salt poorly have a link between heart disease and salt intake. further, it’s not clear that it’s mediated through directly raising blood pressure – it could be indirect. if someone is sensitive to salt in this way, it weakens their heart over time, which causes blood pressure. so @jake, i don’t think your test is meaningful.
Let me throw in some inarticulate skepticism about drawing any conclusions. It’s just too hard to interpret, given that so much of our other knowledge that is supposed to help us control for confounds is itself shaky and based on correlation — and it controls for confounds based on other shaky knowledge. It’s a guessing game based on knowledge drawn from other guessing games…
Seth: Regarding light/moderate alcohol consumption and its health benefits — there is correlational evidence from a 2009 study that people who drink a lot also exercise a lot, which throws a monkey wrench into the benefits of alcohol.
A summary of the data:
“Light, moderate, and heavy drinkers worked out 5.7, 10.1 and 19.9 minutes more per week, respectively. Also, drinking resulted in a 10.1 percent increase in the probability of vigorous physical activity.”
(https://www.livescience.com/7910-exercisers-drink-alcohol.html)
The study was published here.
(https://www.healthpromotionjournal.com/publications/journal/ib2009-09.htm)
Q:
My test is meaningful. If salt is going to give you problems the first place it is going to show up is in a blood pressure rise. There may be other effects but blood pressure will always be affected.
“But among the study’s other problems, Dr. Briss said, its subjects who seemed to consume the smallest amount of sodium also provided less urine than those consuming more, an indication that they might not have collected all of their urine in an 24-hour period.”
This seems to me like a pretty important (possible) flaw in the study.
Ashish, such a difference (“less urine”) between subjects would not produce differences between groups on other measures, unless being careless is somehow health-promoting. It’s hard to see why that would be. If Briss is saying that subjects in the lowest-sodium group probably ate more sodium than recorded, that makes the results more impressive (because a smaller difference in sodium was correlated with the same heart disease difference) rather than less impressive.
Hunter-gatherers seem to have eaten very little sodium. That puts a heavy burden of proof on those who would claim that high sodium intake is healthful, a burden that I would say this one study doesn’t come within a mile of meeting.
Cakeb Cooper’s comment about iodine might well be the explanation for the study’s results.
This reminds me of your article on Salt and Lyme disease, where the author claimed that salt kills parasites within the body. Do you think there is a connection?
I agree with Taubes but there can be problems with small sample sizes. If a small sample size test is found to be “statistically significant” that necessarily means that the effect found is going to be pretty large. Maybe there is a large effect, but a lot of times this large effect disappears when they get around to doing a large sample size test.
Hi Seth,
I wondered if I could pick your brains (please!);
I’ve been trying to use the SLD theory to inform my food choices – I understand that less flavour will mean a weaker flavour/calorie association, but I was wondering about salt.
If I’m trying to lose weight – would salt not contribute to the strength of the association? I hope not!
Also – just to clarify – if I ate a potato – would it be better to have it without any spices added – just have it plain – and this would help to lower my set point? ( due to its blandness), or maybe I could have it with spices but vary the spices each day.
I was also wondering how far apart you could eat a food before the flavour/calorie association would kick in – so if you had something with a certain flavour/calorie combination once a week – would that be enough for the brain to start to recognise it and raise the set point when you ate it?
thankyou!
Seth: 1. I don’t think salt has any effect on flavor-calorie associative strength. 2. I found that eating bland foods doesn’t work very well. Don’t think that eating potatoes without spices is going to do much. 3. Yes, you can certainly learn a flavor/calorie association if you eat that food once/week.
Thanks for answering my questions!
I have another question about food and was wondering if you might know the answer or be interested in it yourself.
I found it totally interesting in your book – the thing about adding water to food making it more fattening.
Was wondering about soup though, cos I’ve read loads of evidence for soup being really good for filling you up.
Just wondered – is soup somehow different to bread because the water is incorporated in a different way?
Seth: I remember a study where just having soup for lunch instead of something else caused weight loss. Surprising. I don’t know why soup has this effect.
Hi Seth,
just to let you know, in case you were wondering…
I found a study; ‘Water incorporated into a food, but not served with food decreases energy intake in lean women’
It found that when the food was eaten as a soup; energy intake was about 1209kj, when the food was eaten not as a soup but with water served alongside; energy intake was about 1657kj and with no extra water served, about 1639kj was consumed.
So eating foods as a soup has quite a significant effect on calorie intake.
Been thinking about how best to eat in the SLD way – and it seems as though eating low energy dense foods is one of the most important ways that we can eat to feel full on fewer calories.
Do you think eating low energy dense foods somehow lowers the set point by creating a weaker flavour calorie association?
Seth: Yes, that is a reasonable possibility.