The J-shape controversy

Facts

High blood pressure (BP) contributes to strokes, heart attacks, heart and kidney failures, and dementia.

A moderate reduction in salt intake in a population, through a reduction in BP, is associated with a reduction of all CVDs.

The collective evidence from prospective longitudinal studies as well as randomized controlled clinical trials indicates that a lower salt intake is associated with a lower incidence of fatal and non-fatal cardiovascular events, in particular stroke.

Based on the evidence accrued over the past 40 years, in 2013, Member States of the World Health Organization adopted the Global action plan for the prevention and control of non-communicable diseases 2013-2020, to take coordinated action at all levels, to attain nine voluntary global targets, including a 30% relative reduction in mean population intake of sodium by 2025 with a goal of <2000mg/day (equivalent to 5g of salt per day).

Oppositions

Recommendations have been opposed by sectors of the food and beverages industry for decades.

High sodium consumption is a source of profit by increasing preference for salty foods, enhancing water binding in meat products to increase weight and therefore price before packaging, and making cheap and unpalatable food edible at minimal cost.

High sodium intake also causes thirst and high demand for beverages, including those such as sugar-sweetened beverages manufactured by some of the same industries that produce salty foods.

This mechanism would contribute to the epidemic of obesity, particularly in children and adolescents.

A reduction in BP would reduce the prevalence of hypertension and the use of anti-hypertensive medications, preventing CVD, and reducing costs for the health-care system.

Controversy

Notwithstanding the compelling evidence, some studies have reported contradictory results on the association between sodium consumption and health outcomes.

The studies report that, rather than there being a linear rise in CVD as sodium intake rises, CVD declines as sodium levels declines from high levels, with the benefit then leveling off and CVD increasing for lower sodium levels (describing a J-shaped curve).

These results cast doubt on the wisdom of global policies recommending a moderate reduction in the consumption of sodium for individuals and populations to help reduce the burden of CVD, which is the leading cause of illness, disability, and death worldwide.

This claim has generated controversy, heated debates, headlines in main stream and social media, and general confusion for clinicians, health professionals, policy makers, and the public because the results are in stark contrast to the evidence.

Scientific critiques have raised serious concerns about the quality of the methods used and refuted those conclusions.