Salt reduction and stroke: A special need for a special population

Heart disease and stroke are the first- and third-leading causes of death in the United States in the 21st century.

In 2006, CVD accounted for 31.7% of all deaths, with 26% from heart disease and 5.7% from stroke. The Healthy People 2010 objective of reducing the death rate for stroke to 50 deaths per 100,000 was met in 2004. Unfortunately, the target death rate for stroke was not achieved in the black subpopulation. In 2006, the age-adjusted mortality rate for stroke was 32.3% higher in blacks than in whites (61.6 vs. 41.7 per 100,000, respectively). The premature death rate was also noted to be higher in blacks, with approximately 39% of black women who died of stroke having a stroke before age 75 years and 60.7% of black men who died of stroke having a stroke before age 75 vs. 17.3% of white women and 31.1% of white men, respectively.

Wallace Johnson

The Healthy People 2020 initiative has four main goals: to eliminate preventable disease, disability, injury and premature death; to achieve health equity, eliminate disparities and improve the health of all groups; to create social and physical environments that promote good health for all; and to promote healthy development and healthy behaviors across every life stage. One key intervention that will at least partially address all four goals is to achieve a population-based sodium consumption of less than 1,500 mg/day, and an integral part of the success of that intervention will be to target high-risk special populations early.

Worldwide, the increased consumption of highly processed food has resulted in an average salt intake of 9 to 12 g/day (namely, 50 times more than our evolutionary salt intake) in many countries, including the US. Excess salt intake has been proved to have both BP-dependent and BP-independent adverse CV effects. Blacks in particular have an excessive prevalence of hypertension; disproportionate prevalence of severe hypertension (>180/110 mm Hg); inadequate BP control in the long term; and a high frequency of comorbid conditions, all of which support the special need for reducing salt in this population.

Linking salt to hypertension

The link between excess sodium intake, hypertension and adverse CV events has been noted in animal studies, epidemiological studies, clinical trials and meta-analyses of these trials. More than 50 randomized trials have evaluated the effects of sodium reduction on BP in adults.

A 2002 meta-analysis of the available randomized trials revealed that a modest salt reduction (which corresponds to a median urinary sodium reduction of 1,800 mg/day) lowered systolic/diastolic blood BP by 2/1 mm Hg in normotensive patients and by 5/2.7 mm Hg in hypertensive individuals. In patients with more severe, resistant hypertension, a recent trial noted a sodium reduction of 4,600 mg/day lowered systolic/diastolic BP by 22.7/9.1 mm Hg. Despite the large body of data, some investigators still question the validity of the link between sodium and adverse CV events because large randomized clinical trials with hard clinical outcomes are lacking.

Large randomized clinical trials could provide more data, although conducting these trials is difficult due to financial, logistic and political constraints. One recent publication also suggested that sodium reduction may even be harmful, based largely on inferences from cohort studies that contained major methodological limitations.

Globally, high BP accounts for 54% of stroke and 47% of CHD events, thereby indicating that about half of these events occur in those without documented hypertension. Excess salt intake appears to have a key role in the pathophysiology of hypertension, especially in blacks.

Importantly, an increased sodium intake can lead to left ventricular hypertrophy, ventricular fibrosis, diastolic dysfunction, renal injury and gastric cancer, which are effects that appear to be independent of the BP increases. Sodium loading has also been shown to increase oxidative stress, promote endothelial dysfunction and induce mitogenic responses (fibrosis in the heart, kidneys and arteries), which result in cardiac and vascular remodeling. This may have special significance for many stroke patients because the underlying vascular pathology of many lacunar strokes is lipohyalinosis.

Salt reduction initiatives

Any large-scale campaign to reduce stroke must include an initiative to reduce sodium intake on a national level. Although some sodium intake, namely 1,500 mg/day, is required to assure nutritional adequacy, most Americans are at little risk of “salt deficiency” due to the large amount of the dietary salt that comes from the sodium contained in processed foods.

In 2010, the scientific advisory group of the US Dietary Guidelines Committee recommended adopting a target sodium intake goal of 1,500 mg/day for all US adults, instead of allowing a daily intake of less than 2,300 mg/day in the younger, healthy adult population. Cooperation from the food industry is essential because more than 75% of the average US dietary sodium intake comes from processed foods.

The success of Finland and England in reducing sodium intake has been the stimulus behind the National Salt Reduction Initiative, a New York City-led partnership of cities, states and national health organizations that was unveiled in January. The initiative organizers have consulted with food industry leaders to develop specific targets to help companies reduce salt levels in 61 categories of packaged foods and 25 classes of restaurant food. Some popular food products have already met these targets — a clear indication that sodium reduction in consumer products will not automatically result in tasteless, unpopular food.

The goal of the National Salt Reduction Initiative is to cut the salt content of packaged and restaurant food by 25% in 5 years. This would reduce the nation’s salt intake by 20% and prevent thousands of premature deaths. One investigator group quantified the effects of reducing sodium intake by 1,200 mg/day and noted that this reduction should result in 30,000 to 66,000 fewer strokes, 60,000 to 120,000 fewer CHD events and a savings of between $10 billion and $24 billion in health care costs.

Salt reduction for blacks

Those who are black tend to have a higher prevalence of salt-sensitivity, hypertension and stroke events than whites, and as a result, we feel this subpopulation needs an aggressive salt reduction initiative. Blacks will certainly benefit from the previously mentioned National Salt Reduction Initiative, but only an overly aggressive health campaign in this population will have a significant effect on the well-known racial health disparity in CVD.

We suggest targeting black communities with an educational intervention aimed at the churches, hair salons, schools, professional organizations and community leaders. Getting buy-in from the local food industry businesses in low-income black communities will take a different approach because many of the food vendors are small storefront entities. Prior research has indicated that blacks are less trustful of large government initiatives, so cultural sensitivity will be especially important. Targeting a high-risk subpopulation early will provide a good benchmark for approaching other lower-risk subpopulations in the future.

Wallace Johnson, MD, is an assistant professor of medicine at the University of Maryland School of Medicine in Baltimore.

For more information:

• Appel L. Circulation. 2011;123:1138-1143.
• CDC. CDC Health Disparities and Inequalities Report — United States, 2011. MMWR Morb Mortal Wkly Rep. 2011;60(suppl):1-113.
• Flack J. Hypertension. 2010;56:780-800.
• He F. J Hum Hypertens. 2008;22:4-11.