Dr. Ron’s Research Review – January 20, 2015

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This week’s research review focuses on bias on salt research.

Thomas Frieden, the director of the CDC, titled a 2010 paper in the prestigious Annals of Internal Medicine: “We can reduce dietary sodium, save money, and save lives.” Indeed, Frieden called reducing sodium intake in our diet “the most cost effective intervention to control chronic disease” after tobacco control—a conclusion that underpins the CDC’s current nationwide strategy to reduce the public’s consumption of salt.
Researchers Niels Graudal and Gesche Jürgens wrote the following year in the British Medical Journal: “It is surprising that many countries have uncritically adopted sodium reduction, which probably is the largest delusion in the history of preventive medicine.”
Three years later, the Institute of Medicine (now called the National Academy of Medicine) “determined that evidence from studies on direct health outcomes is inconsistent and insufficient to conclude that lowering sodium intakes below 2,300 mg per day either increases or decreases risk of CVD [cardiovascular disease] outcomes (including stroke and CVD mortality) or all-cause mortality in the general U.S. population.”
As the field has grown over the past several decades, the polarities have deepened, and the two camps have all but stopped talking to each other. Papers that aim to review the full field instead summarize one side or another— giving us not one but two bodies of knowledge, each firmly aiming to prove only its own thinking.

 

Dr. Ron


 

Articles

This Is Why You Can't Always Trust Data
            (Galea, 2015) Link Download
Even academic studies can get distorted by researchers’ biases. For a telling example, consider the decades-old debate over whether too much salt in the diet is bad for your health.

There is more to salt than just a pinch of sodium.
            (Gasowski and Cwynar, 2013) Download

Salt intake and cardiovascular disease: why are the data inconsistent
            (O'Donnell et al., 2013) Download
Effective population-based interventions are required to reduce the global burden of cardiovascular disease (CVD). Reducing salt intake has emerged as a leading target, with many guidelines recommending sodium intakes of 2.3 g/day or lower. These guideline thresholds are based largely on clinical trials reporting a reduction in blood pressure with low, compared with moderate, intake. However, no large-scale randomized trials have been conducted to determine the effect of low sodium intake on CV events. Prospective cohort studies evaluating the association between sodium intake and CV outcomes have been inconsistent and a number of recent studies have reported an association between low sodium intake (in the range recommended by current guidelines) and an increased risk of CV death. In the largest of these studies, a J-shaped association between sodium intake and CV death and heart failure was found. Despite a large body of research in this area, there are divergent interpretations of these data, with some advocating a re-evaluation of the current guideline recommendations. In this article, we explore potential reasons for the differing interpretations of existing evidence on the association between sodium intake and CVD. Similar to other areas in prevention, the controversy is likely to remain unresolved until large-scale definitive randomized controlled trials are conducted to determine the effect of low sodium intake (compared to moderate intake) on CVD incidence.


 

References

Galea, S. (2015), ‘This Is Why You Can’t Always Trust Data’, Fortune Magazine, PubMedID:
Gasowski, J and M Cwynar (2013), ‘There is more to salt than just a pinch of sodium.’, Hypertension, 62 (5), 829-30. PubMedID: 23980071
O’Donnell, MJ, et al. (2013), ‘Salt intake and cardiovascular disease: why are the data inconsistent’, Eur Heart J, 34 (14), 1034-40. PubMedID: 23257945