Sugar added to processed foods may be a more important contributor to hypertension than salt, researchers found.
In a review, two researchers who study the impact of diet on cardiovascular risk wrote that the emphasis on lowering dietary sodium in guidelines aimed at reducing hypertension is misguided and not evidence-based.
"Added sugars probably matter more than dietary sodium for hypertension, and fructose in particular may uniquely increase cardiovascular risk by inciting metabolic dysfunction and increasing blood pressure variability, myocardial oxygen demand, heart rate, and inflammation," James J. DiNicolantonio, PharmD, of Saint Luke's Mid America Heart Institute, Kansas City, Missouri and Sean C. Lucan, MD, MPH, of Montefiore Medical Center in New York City wrote in the BMJ journal Open Heart.
DiNicolantonio, who is an associate editor of Open Heart, said in an interview with MedPage Today that the sodium restriction guidelines are "the greatest con in preventive nutrition in human history."
"The studies tell us that 3 to 4 grams of sodium (daily) is the level associated with the lowest risk for cardiovascular disease and all-cause mortality, so why do the guidelines all tell us to consume fewer than 2.4 grams (2,400 milligrams) of sodium a day?" he said.
AHA/ACC Guidelines Stress Diet, Not Salt
The latest version of the American Heart Association/American College of Cardiology lifestyle guidelines aimed at reducing cardiovascular risk, published last July, advise adults who would benefit from blood pressure lowering to consume no more than 2,400 mg of sodium a day, with further reductions to 1,500 mg a day recommended to achieve greater reductions in blood pressure. The strength of the recommendation was graded "moderate."
Following a DASH or Mediterranean diet-style diet was also recommended in the guidelines as a strategy for lowering blood pressure, and the strength of this recommendation was rated "strong." Both diets call for eating plenty of vegetables, fruits, and whole grains, along with low-fat dairy products, poultry, fish, legumes, nuts and certain vegetable oils, with very limited intake of sweets, sugar-sweetened beverages, and red meat.
Robert H. Eckel, MD, who co-chaired the AHA/ACC guidelines writing panel said they were both evidence-based and well founded.
Eckel is a professor of medicine at the University of Colorado Denver and a spokesman for the American Heart Association.
""The most rigorous clinical trials -- those where meals were provided or food intake was monitored very closely -- show that when sodium is restricted to the level of 2,400 mg from the usual intake somewhere in the range of 3,500 to 4,000 mg, blood pressure goes down," he told MedPage Today
In their analysis of the scientific evidence examining the impact of both salt and sugar consumption on hypertension, DiNicolantonio and Lucan noted that there is little debate about where most sodium in the average American's diet comes from.
"While there is no argument that recommendations to reduce consumption of processed foods are highly appropriate and advisable, the arguments in this review are that the benefits of such recommendations might have less to do with sodium -- minimally related to blood pressure and perhaps even inversely related to cardiovascular risk -- and more to do with highly-refined carbohydrates," they wrote.
Blood pressure reductions associated with reduced sodium intake were shown in one study to be at most around 4.8 mmHg systolic and 2.5 mmHg. The researchers said it is not clear if this level of reduction is associated with a health benefit.
DiNicolantonio said there is also evidence linking reduced sodium intake to worse clinical outcomes and even greater all-cause mortality, including a study in diabetics and several studies in patients with congestive heart failure.
'Americans' Sodium Intake Stable'
The Food and Drug Administration is currently drafting guidelines asking the food industry to voluntarily lower sodium levels in its products, but the researchers noted that the mean intake of sodium in Western populations (approximately 3.5-4 g/day) has remained roughly the same for the past 5 decades despite the dramatic rise in the consumption of processed foods.
"Such stability in intake suggests tight physiologic control, which if indeed the case, could mean that lowering sodium levels in the food supply could have unintended consequences," they wrote. "Because processed foods are the principal source of dietary sodium, if these foods became less salty, there could be a compensatory increase in their consumption to obtain the sodium that physiology demands."
They wrote that "compelling evidence from basic science, population studies, and clinical trials" has linked sugars, and particularly the monosaccharide fructose, to the development of hypertension. Moreover, evidence suggests that sugars in general, and fructose in particular, may contribute to overall cardiovascular risk through a variety of mechanisms.
Feeding sucrose to rats has been shown in at least one study to stimulate the sympathetic nervous system (SNS), which leads to increases in heart rate, renin secretion, renal sodium retention, and vascular resistance. All of these effects interact to elevate blood pressure, and feeding sucrose to rats has been shown in other studies to increase blood pressure.
"A couple of hundred years ago hypertension basically didn't even exist, and as soon as sugar consumption started to increase so did hypertension, gout, obesity, and diabetes," DiNicolantonio said.
Sugar Linked to Higher BP in Some Studies
The researchers cited a study by Yang et al. published last spring in JAMA showing that compared with patients who consume less than 10% of their calories from added sugars, those who consumed 10.0% to 24.9% of their calories from added sugars have a 30% increased risk of mortality from CVD, and those who consume 25% or more calories from added sugars have an almost threefold increased risk.
Data from the National Health and Nutrition Examination Survey (NHANES 2003 to 2006) suggests that the mean intake of fructose among Americans is 83.1 g/day.
They also cited a recent meta-analysis of randomized, controlled trials showing that higher sugar intake significantly increases systolic (6.9 mm Hg, P<0.0001) and diastolic blood pressure (5.6 mmHg, P=0.0005) versus lower sugar intake in trials of 8 weeks or more in duration. When studies that received funding from the sugar industry were excluded from the analysis, the magnitude of blood pressure elevation was even more pronounced (7.6 mmHg systolic, 6.1 mm Hg diastolic on average).
The researchers noted that some trials suggest fructose may be uniquely detrimental to the cardiovascular system. In a randomized crossover study in young healthy adults (21 to 33 years old), ingestion of a fructose solution (60 g) increased systolic blood pressure (6.2±0.8 mmHg). A similar increase in blood pressure was not seen with ingestion of a glucose solution, but both drinks significantly increased heart rate and cardiac output.
In a randomized trial of 74 adult men, a high fructose diet for just 2 weeks not only significantly increased 24 hour ambulatory blood pressure (+7/5 mmHg, P<0.004 and P=0.007, respectively) and increased pulse rate by 8% (4 bpm), but also increased triglycerides, fasting insulin and homeostatic model assessment index (a measure of insulin resistance and beta-cell function).
'AHA/ACC Guidelines Don't Ignore Sugar'
"Just as most dietary sodium does not come from the salt shaker, most dietary sugar does not come from the sugar bowl; reducing consumption of added sugars by limiting processed foods containing them, made by corporations would be a good place to start," DiNicolantonio and Lucan concluded, adding that reducing processed-food consumption would be consistent with existing guidelines already in place that "misguidedly focus more on the less-consequential white crystals -- salt."
Not surprisingly, Eckel did not agree that the AHA/ACC guidelines are misguided.
"The DASH diet lowers blood pressure and there is very little sugar in this diet or in the Mediterranean diet," he said. "We are certainly not advocating eating a lot of sugar or ignoring sugar consumption."
Eckel said while some studies suggest that sugar consumption has a direct impact on blood pressure, the association is not proven.
"Blood pressure lowering can be accomplished by following a heart-healthy diet and further by restricting sodium to around two and a half grams a day," he said.
Resources from AACE
The reviewers reported no funding source and no relevant relationships with industry.