New evidence published in the online journal Open Heart suggests that added sugars probably matter more than dietary sodium for risk of hypertension and cardiovascular disease.
Cardiovascular disease is the number one cause of premature mortality in the developed world, and hypertension is its most important risk factor.
Hypertension was implicated as a primary or contributing factor in more than 348,000 deaths in the US in 2009, with costs to the nation in excess of $50 billion annually. Controlling hypertension is a major focus of public health initiatives, and dietary approaches to address hypertension have historically focused on sodium.
Nonetheless, the potential benefits of sodium reduction are debatable; studies have shown that the reduction in blood pressure achieved by restricting salt is slim.
Recent data encompassing over 100,000 patients indicates that sodium intake between 3-6 g/day is associated with a lower risk of death and cardiovascular events compared with either a higher or lower level of intake. "Thus, guidelines advising restriction of sodium intake below 3 g/day may cause harm," the authors write.
Processed foods happen to be major sources of not just sodium, but also of highly refined carbohydrates: that is, various sugars and the simple starches that give rise to them through digestion. The researchers comment:
"Compelling evidence from basic science, population studies, and clinical trials implicate sugars, and particularly the monosaccharide fructose, as playing a major role in 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."
Sucrose, or table sugar, is a disaccharide composed of two monosaccharides: glucose and fructose. Sucrose is a common ingredient in industrially processed foods, but not as common as another sweetener: high-fructose corn syrup (HFCS). Whereas sucrose is equal parts fructose and glucose, HFCS has more fructose (usually 55%) than glucose (the remaining 45%) and is the most frequently used sweetener in processed foods - particularly in fruit drinks and sodas.
Ingesting one 24-ounce soft drink has been shown to cause an average maximum increase in blood pressure of 15/9 mm Hg and heart rate of 9 bpm.
The researchers indicate "sugar may be much more meaningfully related to blood pressure than sodium, as suggested by a greater magnitude of effect with dietary manipulation."
Higher sugar intake significantly increases systolic (6.9 mm Hg) and diastolic blood pressure (5.6 mm Hg) in trials of 8 weeks or more in duration. This effect is increased to 7.6/6.1 mm Hg, when studies that received funding from the sugar industry are excluded.
Those who consume 25% or more calories from added sugar have an almost threefold increased risk of death due to cardiovascular disease, according to the research.
Even moderate doses of added sugar for short durations may cause harm
Current US per capita intake of added sugars is approximately two to eight times higher than current recommendations by the American Heart Association (AHA) and the World Health Organization (WHO). Considering adolescents specifically, current consumption might be as much as six to 16 times higher.
An increase in sympathetic tone from the overconsumption of fructose is one likely mechanism for the sugar's ability to increase heart rate, cardiac output, renal sodium retention and vascular resistance, all of which may interact to elevate blood pressure and increase myocardial oxygen demand.
However, ingestion of sugars - including fructose - in their naturally occurring biological contexts (i.e. as whole fruits) is not harmful and is likely beneficial.
Just as most dietary sodium does not come from the salt shaker, most dietary sugar does not come from the sugar bowl. Dr James DiNicolantonio, from the Department of Preventive Cardiology at Saint Luke's Mid America Heart Institute on Kansas City, MO, concludes:
"Reducing consumption of added sugars by limiting processed foods containing them, made by corporations would be a good place to start."
The evidence shows that even moderate doses of added sugar for short durations may cause substantial harm.
Medical News Today recently reported that regularly drinking high levels of sugar-sweetened soda could lead to the premature aging of immune cells, leaving the body vulnerable to chronic diseases in a similar manner to the effects of smoking.