I always love it when two examinations of the identically same data set come to opposite conclusions. It shows how easy it is to go wrong when relying on statistics. In today's pair of studies, one group of researchers decided that lowering sodium makes no difference in cardiovascular health. The other group found that lowering sodium did improve cardiovascular health. They also gave a good explanation of how the first study slipped up. And they emphasized the importance of the sodium potassium ratio.
Previously we discussed a different pair of contradictory studies that used the same data set here. In that particular case one way of looking at the data set showed vegans did better than non-vegetarians. Another way of dividing the identically same data set gave a different result. It showed that those vegetarians who also ate fish, or consumed milk and eggs, did better than vegans.
The Sodium Potassium Ratio
The researchers in today's pair of studies used the sodium potassium ratio instead of the potassium sodium ratio. The sodium potassium ratio is used more commonly in the medical literature than the potassium sodium ratio. It is simply the inverse of the potassium sodium ratio.
I prefer the potassium sodium ratio because as the number gets larger, you are doing better and better. With the sodium potassium ratio as the number gets larger, you are doing worse and worse. I prefer for a larger number to mean that you are doing better. For most games and sports a larger number is better. Whole numbers are easier to remember than fractions. Going from 0.5 to 0.1 doesn't seem like much. But going from 2 to 10 does.
The First Study
In 2008 (1), the researchers looked at data in the Third National Health and Nutrition Examination Survey (NHANES III). They included 8699 people over the age of 30 that they recruited between 1988 and 1994 in their study. Based on a single 24 hour dietary recall questionnaire, they divided the people into 4 groups according to sodium intake.
The researchers then determined how many in each group had died by the year 2000 from cardiovascular disease, or from any cause. They concluded that those who took in more sodium had fewer deaths. They did not study potassium at all.
The Second Study
In 2011 (2), a different set of researchers used the same data set (NHANES III), but included 12,267 participants over the age of 20. The researchers also obtained a second 24 hour dietary recall in 8% of the participants. They used this second questionnaire to better estimate sodium and potassium intake in the entire group.
They then looked at the sodium potassium ratio and deaths through 2006. This gave an average follow-up period of 14.8 years. They found the sodium potassium ratio had a significant association with death. The association applied to cardiovascular death, and to death from any cause.
They also found an association of sodium with cardiovascular death for people with a normal blood pressure, but a reverse association if they were hypertensive. The researchers concluded that the reason for low sodium seeming to be harmful in the first study was that the low sodium group had many hypertensive patients. The hypertensive patients may have been put on a reduced sodium diet. This is commonly done by doctors for their heart patients.
Which Study Is Right?
A commentary after the 2011 study sums up the two studies well (it is after the citations at the same link). It states that the methodology in the 2011 study was superior. The 2011 study also concurs with the basic science of the cell. The sodium potassium ratio is critical to cellular function.
How can you tell which study is right when two contradictory studies are reported? It seems that every week there are news reports with a new contradictory result. Sadly, you need to have a bit of knowledge about the subject. Hill's criteria are a good place to start.
Two of Hill's criteria are the most important. You should have enormous differences between the test group and the control group. And basic science studies should be consistent with the results.
When you are improving your potassium sodium ratio realize that the importance of the ratio is not based on just a few observational studies. There is a huge underpinning of basic science studies supporting the importance of the potassium sodium ratio to cardiovascular health at the cellular level.
Tables Of Sodium And Potassium In Food
Looking to improve your potassium sodium ratio? Find a listing of tables with the potassium and sodium content of thousands of foods by clicking the “Links to Food Potassium Tables” tab at the top of the page.
1. Sodium intake and mortality follow-up in the Third National Health and Nutrition Examination Survey (NHANES III). Cohen HW, Hailpern SM, Alderman MH. J Gen Intern Med. 2008 Sep;23(9):1297-302. doi: 10.1007/s11606-008-0645-6. Epub 2008 May 9.
2. Sodium and potassium intake and mortality among US adults: prospective data from the Third National Health and Nutrition Examination Survey. Yang Q, Liu T, Kuklina EV, Flanders WD, Hong Y, Gillespie C, Chang MH, Gwinn M, Dowling N, Khoury MJ, Hu FB. Arch Intern Med. 2011 Jul 11;171(13):1183-91. doi: 10.1001/archinternmed.2011.257.