The Key to Life Nutrition Program: results from a community-based dietary sodium reduction trial

Hypertension increases the risk for CVD, stroke and kidney disease. Reduction of salt in the diet for the prevention and treatment of hypertension predates the availability of drug therapy for the treatment of hypertension. Exclusion of salt from the diet of hypertensives was recommended as early as 1905(1). Allen and Sherrill recommended salt restriction for treatment of hypertension in 1905 and subsequently in 1922(1). The dietary treatment of hypertension received a big boost with the introduction of the rice diet by Kempner in 1944(1). Grollman documented that the low salt level of the diet was the primary determinant for the decrease in blood pressure. In the 1950s, it was recognized that in spite of the benefits of reducing salt intake on blood pressure levels, it was difficult to implement such a diet and there was substantial variation in response to reduced salt intake(2). Furthermore, it was recognized that measurement of the dietary intake of Na was very difficult and that only 24 h urinary excretion provided a reasonable estimate of dietary intake(2,3). Dahl noted that the average daily US intake of salt in the 1950s was between 5 and 15 g. He estimated that human consumption only needed to be between 100 and 400 mg NaCl/d(4). Na is an essential nutrient in the human body used for maintaining cell homeostasis by regulating extracellular fluid. A small amount of natural Na is found in virtually all foods, with greater amounts added during processing or during the cooking process. On average, Americans consume much higher amounts than is physiologically needed. Minimum daily requirements to replace necessary losses have been estimated at 115 mg; however the recommended safe minimum level for adults is set at 500 mg to accommodate varying levels of activity and environmental conditions(5,6). Excess dietary Na causes retention of Na and water, an increase in venous tone, peripheral resistance and central (but not total) blood volume, and higher blood pressure; it also increases left ventricular mass and cardiovascular morbidity(7–9). For decades, there has been sufficient evidence from clinical trials demonstrating that non-pharmacological interventions including Na reduction are effective not only in decreasing blood pressure and preventing hypertension, but also in decreasing left ventricular mass(10) and reducing cardiovascular morbidity(11–17). The 2005 Dietary Guidelines for Americans and the Institute of Medicine recommended an Na intake of ≤2300 mg/d for ‘normal’ individuals and ≤1500 mg/d for individuals considered at increased risk (individuals with hypertension, blacks, middle-aged and older adults)(18,19). Consuming Na in greater than recommended amounts is considered a risk factor for increasing blood pressure(20–23). Past trials comparing behavioural interventions have provided scientific evidence that lifestyle modifications such as reducing dietary Na intake to recommended levels can result in blood pressure reduction and prevention of hypertension(12–16,24). The Dietary Approaches to Stop Hypertension (DASH) trial was a landmark study for Na intervention in which participants were randomly assigned to one of three diets, each containing 3000 mg Na/d with a 500 mg daily discretionary Na allowance. Participants had a mean age of 44, 45 and 44 years for the control diet, the fruits and vegetables diet and the combination DASH diet, respectively(24,25). The DASH diet is high in fruits, vegetables, low-fat dairy products, whole grains, poultry, fish and nuts. This diet is also low in saturated fats, red meat, sweets and sugar-containing beverages(25). All foods were provided for the 11-week intervention and participants were advised not to consume any ‘outside’ foods. All three groups experienced blood pressure reduction. The DASH diet group showed the greatest average reduction in systolic blood pressure (SBP; 6 mmHg) and a 3 mmHg reduction in diastolic blood pressure (DBP). This reduction was even greater when stratified for persons with stage 1 hypertension (average reduction in SBP and DBP of 11 mmHg and 6 mmHg, respectively)(24). Accurately capturing dietary Na intake from all sources poses a considerable challenge. Collecting dietary Na intake through food questionnaires is often riddled with under-reporting(26,27). The preferred methodology involves the use of 24 h urinary Na excretion to obtain reliable values. Under normal conditions, approximately 93 % of dietary Na is excreted through the urine, with minimal losses through faeces and sweat. Daily Na retention is approximately 3·4 % or 7·4 mmol(28,29). Salt reduction is often recommended for older individuals, especially those with hypertension, congestive heart failure and renal disease. There is, however, little objective evidence of the success of reducing salt intake, especially in the long term, as measured by changes in urinary Na excretion among free-living individuals. How much of a reduction in Na in the urine is obtainable in the community by providing nutritional counselling as compared with the reduction that may be obtained in a more rigorous, clinical trial setting? To answer this question, we examined the effects of implementing prevention guidelines for older individuals, the ‘10 Keys’™ to Healthy Aging. We evaluated the effects of the dietary recommendations to reduce salt intake among hypertensives. The study did not measure the effects on blood pressure nor compare individuals who did or did not receive the dietary advice. Clinical trials have clearly documented the benefits of salt reduction on blood pressure levels and therefore it would be redundant to repeat this, as such trials have also compared the effects of the dietary intervention v. no intervention. The present study was restricted to individuals living in their homes in the community. Many of the participants were either widows or widowers or had a disabled spouse who would be ineligible for the study.