Very often scientific research studies produce findings that contradict one another. This leads to significant confusion especially when the findings influence policy and national health campaigns. This post will consider the current attention dietary salt intake has received in the media due to recently published studies.
Federal health officials recommend daily sodium intake of ~2,300mg for normotensives and
1,500mgs for vulnerable populations (2). Yet, the average American consumes >3,000mgs of sodium daily (2). High salt intake has long been considered a major contributor to cardiovascular (CV) conditions including hypertension, congestive heart failure, stroke, and heart disease. (Photo: dailyfitnessmagz.com)
However, a recent Huffington Post article explored interesting findings by a group of researchers who reported no ties to the food or salt industries. Graudal et al. (2011) analyzed 167 studies that assessed low to high sodium diets on at least one of these parameters:
-systolic and diastolic blood pressure
-plasma or serum levels of several hormones and proteins
Data for normotensive and hypertensive individuals of Caucasian, Black, and Asian backgrounds were analyzed. Notably they found that sodium reduction resulted in significant increase in plasma renin, 2.5% increase in cholesterol, and 7% increase in triglyceride (4). These researchers identified an inverse relationship between decreasing sodium intake and increasing total cholesterol, and considered the potential CV risks that occur as a result.
Approximately two weeks later Health.com posted an article that highlighted a recent study that confirms the high sodium high-risk relationship that dominates discourse and research on this issue. O’Donnell et al. (2011) set out to clarify the optimal daily intake amount as it pertains to patients at risk for CV disease. Their study population included 28, 880 individuals with high CV risk from two pharmaceutical sponsored clinical studies for heart disease drugs. They measured sodium and potassium intake indirectly by estimating excretion levels (5). While the study by O’Donnell et al. demonstrated a J curve relationship indicating risk at both ends of the salt intake spectrum, they emphasized the high sodium high cardiovascular risk dynamic as significant and underplayed the low sodium high-risk relationship (5).
While study designs, methodology, populations, and location can all contribute to the discrepancies in findings, Folkow (2011) argues that another significant player is bias. In a recent editorial review, he highlights room for conflict of interest and proposes three alternative potential contributors to the salt-cholesterol relationship as opposed to what we consume (3):
-mental stateà mental stress can elevate plasma cholesterol levels more than eating eight eggs would
-influence of exerciseà effects metabolism, organ structure and function, “mental state, sympathetic activity, [and] immune functions”
-placebo effectsà participants “are aware of whether they are targets or controls”
Failure to fully disclose data, especially that which contradicts the original hypothesis, also contributes to bias.
Most data suggests that for normotensive individuals maintaining moderate sodium intake is optimal. However, more research needs to be conducted on larger sample populations to clarify the effects of low-sodium intake on individuals at risk for CV conditions to ensure that while trying to solve one problem we aren’t creating another one.
(1) “Study Confirms Sodium-Related Heart Risks” Online article, 11/23/11
http://news.health.com/2011/11/23/sodium-heart-risks/ Accessed 11/25/11
(2) “Low-Salt Diet Benefits Questions in New Study” Online article, 11/9/11
http://www.huffingtonpost.com/2011/11/09/low-salt-diet-cholesterol-study_n_1084611.html?ref=healthy-living-health-news Accessed 11/25/11
(3) Folkow, B. On bias in medical research; reflections on present salt-cholesterol controversies. Scandinavian Cardiovascular Journal, 2011; 45: 194-197
(4) Graudal N.A., Hubeck-Graudal T., Jurgens G. Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride. Cochrane Database of Systematic Reviews 2011, Issue 11. Art. No.: CD004022. DOI: 10.1002/14651858.CD004022.pub3.
I believe that there is a need for a reduction in our nation’s consumption of salt in that it is a precursor for heart disease in that it increases blood pressure. But what I found most startling in a study done at Harvard’s School of Public Healthy was that nation’s average salt consumption of 3600 mg a day has stayed consistent over the past 50 years. This suggests less causation for the increase in heart disease and diabetes inflicted on American’s. We would think that salt is the culprit in the increase of heart disease but in fact the finger can be pointed more towards the increase in obesity. There though is a definite link between a high sodium diet and obesity, which could explain this increase disease. Salt intake leads to dehydration, increasing liquid consumption. The drink of choice has become soda and coffee, for its high levels of sugar and caffeine give a rush of energy. Sugary, carbonated beverage intake has increase by 135% since 1977 in the US, suggesting a positive correlation with the increase in blood pressure leading to heart disease. So salt has actually indirectly affected our health.
ReplyDeleteJulia Vantine, HealthDay. Americans’ salt intake unchanged for 50 years. http://www.usatoday.com/yourlife/food/diet-nutrition/2010-11-22-salt_N.htm
University of Helsinki (2006, November 1). Salt Intake Is Strongly Associated With Obesity. ScienceDaily. Retrieved November 28, 2011,
It is interesting how sodium can affect hypertension so much. I wonder how it affects athletes and other individuals that are constantly using sodium and other electrolytes and in turn losing them rapidly during exercise. Some studies have shown that it is not universal about how sodium effects blood pressure but rather it depends on preexisting conditions or individual health/fitness levels. A study funded by the American Heart association showed that excessive sodium induced hypertension was only relevant in individuals that already were expressing borderline hypertension, while individuals that showed normal blood pressure had no effect with excessive amounts of sodium (Mark et al. 1975). The group that was borderline hypertensive expressed elevated forearm vascular resistance, neurogenic vasoconstriction, and arterial pressure. The study suggests that the reason this may be is not related to renin-angiotensin-aldotestorin systems. Another study from Hofman et al looked at sodium intake in newborns and the relationship it has with blood pressure. The study found that, in newborn infants less sodium intake leads to lower blood pressure (Hofman et al. 1983). Clearly depending on age and body condition sodium intake, whether excessively high or excessively low, can play a different effect on the body to lower or raise blood pressure.
ReplyDeleteAL Mark, WJ Lawton, FM Abboud, AE Fitz, WE Connor and DD Heistad (1975). Effects of high and low sodium intake on arterial pressure and forearm vasular resistance in borderline hypertension. A preliminary report. Circulation Research, Vol 36, 194-198
A Hofman, A Hazebroek, H Valkenburg (1983). A Randomized Trial of Sodium Intake and Blood Pressure in Newborn Infants. JAMA 1983;250:370-373