Background

I probably eat a lot of salt. Is that bad? To get some answers, I ran a search on Google Scholar for meta analyses on the effects of sodium intake. I found a very recent meta analyses (Graudal et al. 2014) that compares usual sodium intake (defined as the actual mean sodium intake +/- two standard deviations) with low and high intakes. The results show that there may be an increased risk for dying (All Cause Mortality, ACM) but the results are not large (maybe a 15% risk increase), nor statistically significant (this may be due to a small sample size). The risk of disesases of the heart and blood circulation, e.g. strokes, heart attacks etc. (Cardiovascular Diseases, CVD) increases by something like 20% - but this result’s statistical significance completely depends on one single study (the p value changes from 0.48 to 0.0003, see table 1 in the study). Intrigued, I looked it up.
Yang et al. (2011) has very clear results: eat less sodium, eat more potassium, make sure that the ratio of sodium to potassium does not get high (the biochemical background is that sodium and potassium often act together, especially moving sodium in and out of cells requires potassium in an equal amount). The study used data from a huge study of a representative sample of the US population, the National Health And Nutrition Examination Survey III (NHANES III), run by the Centers for Disease Control (CDC). The data is probably as good as it gets and provides a large sample (more than 30,000 participants). The only downside is that it is not a prospective study, but rather a simple cross-sectional design, i.e. each participant was questioned and examined once in time. This happened in two waves from 1988 to 1994. To analyze the risk of dying, the CDC provides data on mortality for the study participants, with the last update done in 2011. Because Yang et al. (2011) gave only aggregates, I decided to take a look at the data myself.
The NHANES III data (the “III” denotes that this was the third such study. Nowadays, the NHANES study is a continuous excercise and the data are published every two years) are available publicly (Disease Control, National Health, and Nutrition Examination Survey Data. Hyattsville 1997) as well as the linked mortality files (Disease Control, National Health, and Nutrition Examination Survey Data. Hyattsville 2011).

Sources

Disease Control, Centers for, Prevention (CDC). National Center for Health Statistics (NCHS). National Health, and MD Nutrition Examination Survey Data. Hyattsville. 1997. “NHANES III Data.” http://www.cdc.gov/nchs/nhanes/nhanes3/data_files.htm; U.S. Department of Health and Human Services, Centers for Disease Control and Prevention.

———. 2011. “2011 Public Use Linked Mortality Files (for NHANES III).” http://www.cdc.gov/nchs/data_access/data_linkage/mortality/data_files_data_dictionaries.htm; U.S. Department of Health and Human Services, Centers for Disease Control and Prevention.

Graudal, Niels, Gesche Jürgens, Bo Baslund, and Michael H Alderman. 2014. “Compared with Usual Sodium Intake, Low-and Excessive-Sodium Diets Are Associated with Increased Mortality: A Meta-Analysis.” American Journal of Hypertension. Oxford University Press, hpu028.

Yang, Quanhe, Tiebin Liu, Elena V Kuklina, W Dana Flanders, Yuling Hong, Cathleen Gillespie, Man-Huei Chang, et al. 2011. “Sodium and Potassium Intake and Mortality Among US Adults: Prospective Data from the Third National Health and Nutrition Examination Survey.” Archives of Internal Medicine 171 (13). American Medical Association: 1183–91.