Reducing Sodium Content in the American Diet

[摘要]

Cardiovascular diseases are responsible for 40 percent of all deaths in the United States. Each year, more than 725,000 Americans die of heart disease and more than 160,000 die of stroke.¹

Elevated blood pressure levels are a major cause of these diseases. The relationship between blood pressure levels and risk of developing cardiovascular diseases is strong, continuous, graded, consistent, independent, and etiologically significant.^2-3

More than 50% of adults in the U.S. have blood pressure levels which are higher than optimal (defined as < 120 mm Hg systolic and 80 mm Hg diastolic), thereby putting them at significantly increased risk of developing these diseases.^4-5 For example, the estimated 23 million persons with high normal blood pressure (130-139 mm Hg systolic and/or 85-89 mm Hg diastolic) have a 1.5 to 2.5 times greater risk of having a heart attack, a stroke, or heart failure in 10 years than those with optimal blood pressure levels.⁶

Hypertension, defined as a systolic blood pressure ≥ 140 mm Hg, a diastolic blood pressure ≥ 90 mm Hg, affects about 43 million U.S. adults and presents the highest risk.^4-5 The prevalence of hypertension rises dramatically with increasing age; by age 80, more than 70 percent of the population is hypertensive.⁴ Blacks suffer from even higher rates of hypertension and its deleterious effects than whites.⁴ The majority of hypertension is uncontrolled.⁷ The Healthy People 2000 objective of 50 percent of hypertensives having their blood pressures controlled to a level less that 140/90 mm Hg was not met⁸; instead, only about 25 percent of adults with hypertension had their blood controlled to this extent.⁷

Hypertension is a largely preventable risk factor.⁹ The National High Blood Pressure Education Program guidelines recommend five nutritional/lifestyle approaches to prevent hypertension: (1) reduction of sodium intake, (2) weight reduction in the overweight, (3) regular physical activity, (4) moderation of alcohol intake, and (5) an eating plan that is rich in fruits, vegetables, and low-fat dairy products and reduced in saturated fat, total fat and cholesterol.^9-10 These same nutritional approaches are also highly effective in treating hypertension and can significantly reduce the need for medications.⁶

Because of the high prevalence of elevated blood pressure levels and their sequelae in the United States, effective public health interventions which will lead to population-wide reductions in blood pressure are needed. Reduction in sodium intake represents an important public health opportunity and challenge in this regard.

There is a clear relationship between habitual sodium intake and blood pressure levels.¹¹ The evidence is sufficiently strong to warrant recommendations for the public to reduce dietary sodium intake. A meta-analysis of 32 randomized clinical trials concluded that if a population decreases its sodium intake by 2,300 mg, this would lower blood pressure by 5.8 mm Hg systolic/2.5 mm Hg diastolic in hypertensives, and by 2.3 mm Hg systolic/1.4 mm Hg diastolic in nonhypertensives12 A 3 mm Hg reduction in systolic blood pressure for the general U.S. population would result in 11 percent fewer strokes, 7 percent fewer coronary events, and 5 percent fewer deaths.¹³

A small number of researchers have disputed the link between sodium intake and blood pressure¹⁴ However, randomized clinical trials have now definitively demonstrated that reducing sodium intake decreases blood pressure in people with and without high blood pressure. The recent Dietary Approaches to Stop Hypertension (DASH)-Sodium study showed that a salt-reduced diet alone lowered blood pressure by 8.3/4.4 mm Hg in hypertensives and by 5.6/2.8 mm Hg in normotensives compared to the usual high-sodium American diet.¹⁵ The lower the sodium intake in the diet, the greater was the fall in blood pressure. These findings reaffirm the benefit of continuing to recommend that sodium be limited to no more than 2400 mg per day and suggest that limiting sodium intake further to 1500 mg per day is feasible and provides additional blood pressure lowering without adverse effects.

Higher sodium intake has adverse effects beyond those of increasing blood pressure. An intake of sodium higher by 2300 mg per day is associated with an increase in risk of coronary heart disease mortality of 61 percent, stroke mortality of 89 percent, and all-cause mortality of 39 percent over a 19-year period among adults who are overweight after adjusting for blood pressure, age, BMI, and other important variables.¹⁶ Higher sodium consumption is also associated with an increased risk of developing urinary stones and osteoporosis.^17-18

The average American adult ingests nearly 4,000 mg of sodium daily, far exceeding the current recommendation to consume no more than 2400 mg per day (approximately 6 grams of sodium chloride)19 Between 2/3 and 3/4 of the daily sodium intake of the U.S. population comes from salt in processed foods, the remainder coming from salt added while cooking or at the table.^20-21 Thus, in the U.S. and other western societies, a high dietary salt intake is due to a large portion of daily calories consisting of processed foods.

The National High Blood Pressure Education Program Coordinating Committee, the National Academy of Sciences, and the American Heart Association officially support the public health strategy of reducing Americans’ daily dietary sodium intake to no more than 2,400 mg and indicate that this would reduce the mean blood pressure of the U.S. population.^22-24 Healthy adults living in a temperate climate can maintain a normal sodium balance with as little as 115 mg of dietary sodium per day.²⁵ Given the wide variation in Americans’ physical activity and climatic exposure, a level of 500 mg of sodium intake per day has been recommended as safe.²⁶ Animal experiments, epidemiologic studies, and randomized clinical trials have found no long-term adverse effects associated with habitual sodium intake ≤ 2,400 mg per day.^9-10

Healthy People 2010 has established an objective to increase the proportion of the population who meet this standard (≤ 2400 mg per day) from 21 percent to 65 percent by the year 2010.²⁶ Gradually reducing the amount of sodium added in the manufacturing and commercial preparation of food is a prudent and safe public health intervention, and the single most effective means of attaining this goal. Such a reduction will also make a substantial contribution to meeting the Healthy People 2010 objective of 50 percent of hypertensives having their blood pressure under control and the Healthy People objectives of a 20 percent reduction in mortality rates from heart disease and stroke by the year 2010.²⁶

The APHA:

• urges partnerships with the National Heart, Lung, and Blood Institute’s National High Blood Pressure Education Program Coordinating Committee and other organizations to work with the food manufacturers and preparers to meet a goal of reducing the sodium content of processed foods by 50% over the next 10 years. 
• urges working with the National High Blood Pressure Education Program Coordinating Committee, state and local health departments, other professional organizations, food manufacturers, supermarkets, and the restaurant industry in educating consumers to choose lower sodium foods, especially fresh fruits and vegetables instead of high-sodium canned fruits and vegetables.
• urges working with public health agencies in other countries such as the United Kingdom and France which are focusing on reducing sodium in their food supplies.²⁷
• urges working with the National High Blood Pressure Education Program, state and local health departments, and other organizations to make hypertension prevention and control a high priority throughout the United States so that the Healthy People 2010 objectives for improving control of high blood pressure, reducing sodium consumption, and reducing mortality from heart disease and stroke can be met.

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References

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8. Healthy People 2000, Volume 1, Chapter 15: Heart Disease and Stroke. Washington, DC: U.S. Dept. of Health and Human Services, 1990.
9. National High Blood Pressure Education Program Working Group Report on Primary Prevention of Hypertension. Arch Intern Med 1993;153:186-208.
10. National High Blood Pressure Education Program Working Group. Whelton PK, He J, Appel LS. Cutler JA, Havis S, Kotchen P et al. Report on Primary Prevention of Hypertension. Clinical and Public Health Advisory on the Primary Prevention of Hypertension 2002. Submitted for publication JAMA.
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14. Taubes G. The (Political) Science of Salt. Science 1998; 281:898-907.
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16. He J, Ogden LG, Vupputuri S, Bazzano LA, Loria C, Whelton PK. Dietary sodium intake and subsequent risk of cardiovascular disease in overweight adults. JAMA 1999; 282:20-27-2034.
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18. Devine A, Criddle RA, Dick IM, Kerr DA, Prince RI. A longitudinal study of the effect of sodium and calcium intakes on regional bone loss. Am J Clin Nutr 1995; 62:740-745.
19. U.S. Department of Agriculture, Agricultural Research Service 1997. Data tables: Results from the USDA’s 1994-96 Continuing Survey of Food Intakes by Individuals and 1994-96 Diet and Health Knowledge Survey. On: 1994-96 Continuing Survey of Food Intakes by Individuals and 1994-96 Diet and Health Knowledge Survey. CD-ROM, NTIS Accession Number PB98-500457.
20. James WP, Ralph A, Sanchez-Castillo CP. The dominance of salt in manufactured food in the sodium intake of affluent societies. Lancet 1987;1:426-9.
21. Mattes RD, Donnelly D. Relative contributions of dietary sodium sources. J Am Coll Nutr 1991; 10:383-393.
22. Kraus RM, Eckel RH, Howard B, Appel LJ, Daniels SR, Deckelman RJ et al. AHA Dietary Guidelines Revision 2000: A statement for healthcare professionals from the Nutrition Committee of the American Heart Association. Circ 2000;102:2284-2289.
23. Chobanian AV, Hill M. National Heart, Lung, and Blood Institute Workshop on Sodium and Blood Pressure: a critical review of current scientific evidence. Hypertension 2000; 35:858-63. 
24. National Research Council. Recommended Dietary Allowances, 10th ed. Washington, DC: National Academy Press; 1989. 
25. Healthy People 2010 Conference Edition, Volume 1, Chapter 12: Heart Disease and Stroke, Section 12-10. Washington, DC: U.S. Dept. of Health and Human Services, 2000.
26. “Salt Reduction at Sainsbury’s” online posting, retrieved January 18, 2002 from the World Wide Web http://www.sainsburys.co.uk/food_issues/.

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[发布日期] 2002-11-13

[学科分类] 医学（综合）