COMMENTARY

Salt, Salt, Salt -- Plus Sleep and Job Stress: More Data to Share With Your Patients

Linda Brookes, MSc

Disclosures

September 09, 2009

In This Article

New position papers and research data from the American Society of Hypertension (ASH) and the American Dietetic Association highlight the role of patients' diets, especially salt intake, in controlling high blood pressure, the starting point for cardiovascular disease, the number 1 cause of mortality in the world today. And it's not just the patients -- over and over the deleterious role of societal forces (especially advertising) is also stressed by the researchers as a major negative factor in the overall health picture. The new data provide details about the effects of these factors in women, blacks, and other minorities; about the physiologic substrates (fluid retention, sleep deprivation); and about the hypertensive effect of job stress (managerial vs professional, differentiated by gender) -- it doesn't go away with retirement!

Dietary Approaches to Lower Blood Pressure

New ASH Position Paper on Diet and Blood Pressure

ASH issued its latest position paper, which summarizes the evidence for the effects of diet-related factors in lowering blood pressure and presents recommendations for healthcare providers.[1] The lead author is Lawrence J. Appel, MD, MPH (Johns Hopkins University, Baltimore, Maryland), who was a co-author of previous policy documents on dietary approaches to prevention and treatment of hypertension issued by the American Heart Association[2] and the federal government.[3]

The authors of the position paper note that a substantial body of evidence has implicated several aspects of diet in the pathogenesis of elevated blood pressure. Well-established risk factors include excess salt intake, low potassium intake, excess weight, high alcohol consumption, and a "suboptimal" dietary pattern. Blacks are especially sensitive to the blood pressure-raising effects of excess salt intake, insufficient potassium intake, and suboptimal diet. Thus, according to the authors, dietary changes have the potential to substantially reduce racial disparities in blood pressure and its consequences.

In view of the age-related rise in blood pressure in both children and adults, the direct, progressive relationship of blood pressure with cardiovascular-renal diseases throughout the usual range of blood pressure, and the worldwide epidemic of blood pressure-related disease, the paper's authors recommend reducing blood pressure in nonhypertensive as well as hypertensive individuals. They point out that in nonhypertensive individuals, dietary changes can delay or even prevent hypertension. In uncomplicated stage I hypertension, dietary changes serve as initial treatment before drug therapy and in hypertensive individuals already on drug therapy, lifestyle modifications can further lower blood pressure.

ASH diet-related recommendations to lower blood pressure are:

  • Maintaining or aiming for normal weight (nonoverweight should not go over a body mass index [BMI] of 25 kg/m2; overweight/obese: lose weight and maintain BMI < 25 kg/m2);

  • Lower sodium intake as much as possible (goal in general population ≤ 2300 mg/day; goal in blacks, middle- and older-aged persons, persons with hypertension, diabetes, or chronic kidney disease: ≤ 1500 mg/day);

  • DASH-style dietary pattern (fruits and vegetables 8-10 servings/day; reduce saturated fat and cholesterol, with fat-free or low-fat dairy products 2-3 servings/day; increase potassium intake with a goal of 4.7 g/day; and

  • Moderate alcohol intake: (men ≤ 2 alcoholic drinks per day; women ≤ 1 alcoholic drink per day -- 1 drink defined as 12 oz of beer, 5 oz of wine, or 1.5 oz of spirits).

The original DASH (Dietary Approaches to Stop Hypertension) diet[4] has been shown to lower blood pressure in both men and women, blacks and non-blacks, and hypertensives and nonhypertensives.[5,6] The ASH authors note that some variants of the DASH diet produce lesser decreases in blood pressure, but the 3 studied in the OmniHeart trial (diets rich in carbohydrates, in protein, or in unsaturated fat, respectively),[7] are as effective as the original. Of note, people with chronic kidney disease should not follow these diets because of the high potassium, phosphorus, and protein content. There is insufficient evidence to recommend certain other dietary approaches, including omega-3 polyunsaturated fatty acid supplements, other fats (total fat, omega-6 polyunsaturated fatty acids, and monounsaturated fat), dietary fiber, calcium, and magnesium.

The authors state, "By example and through advice, physicians have a powerful influence on their patients' willingness to make dietary lifestyle changes." While acknowledging that "ultimately, people select the types and volume of food they eat and the amount of physical activity they perform," the authors note the adverse effect of cultural forces, societal norms, commercial interests, and the scope of the blood pressure epidemic and call for an effective public health strategy involving the government, food industry, and employers.

American Dietetic Association Position Paper

The American Dietetic Association has also issued a position statement on diet and blood pressure, with a review of a vegetarian diet.[8] The statement describes all the health advantages of vegetarianism. A large cohort study reported that non-meat eaters, especially vegans, have a lower prevalence of hypertension than meat eaters, although largely because of differences in body mass index.[9] The results of other studies that compared blood pressure in vegetarians with that in nonvegetarians produced mixed results. The authors of the position statement suggest that the beneficial effects of plant components, such as potassium, magnesium, antioxidants, dietary fat, and fiber, could result in lower blood pressure. The authors point out that a vegetarian diet is associated with a lower risk for death from ischemic heart disease and that vegetarians also appear to have lower levels LDL cholesterol and lower rates of type 2 diabetes than nonvegetarians. They also note that vegetarians tend to have a lower BMI, which might account for the differences in blood pressure and lower overall cancer rates.

Dietary and Lifestyle Risk Factors Associated With Incident Hypertension in Women

Adhering to low-risk dietary and lifestyle factors -- including maintaining normal weight, daily vigorous exercise, a DASH-style diet, restricting consumption of alcohol and use of analgesics, and taking a folic acid supplement -- has been shown to reduce the risk for hypertension among women by up to almost 80%, according to a study published in JAMA.[10]In an analysis funded by the American Heart Association, John P. Forman, MD (Brigham and Women's Hospital and Harvard Medical School, Boston) and colleagues analyzed data from 83,882 women aged 27-44 years who participated in the second Nurses' Health Study (NHS2), part of the long-running NHS, which is funded by the National Institutes of Health. At NHS2 baseline in 1991, none of these women had cardiovascular disease, diabetes, or cancer and all reported normal blood pressure (systolic blood pressure [SBP] ≤ 120 mm Hg and diastolic blood pressure [DBP] ≤ 80 mm Hg). They were followed for incident hypertension for 14 years through 2005, during which 12,319 new cases of hypertension were reported.

The 6 modifiable factors leading to low risk for hypertension were defined as:

  • BMI < 25;

  • Daily mean of 30 minutes of vigorous exercise;

  • High score on the DASH diet based on responses to a food frequency questionnaire;

  • Modest alcohol intake ≤ 10 g/day;

  • Use of nonnarcotic analgesics less than once per week; and

  • Intake of ≥ 400 μg/day of supplemental folic acid.

The DASH score was determined based on high intake of fruits, vegetables, nuts, and legumes; use of low-fat dairy products and whole grains; and low intake of sodium, sweetened beverages, and red and processed meats.

All 6 risk factors were independently associated with the risk of developing hypertension during follow-up after adjusting for age, race, family history of hypertension, smoking status, and use of oral contraceptives. By calculating the hypothetical population attributable risk, an estimate of the percentage of new hypertension cases that hypothetically could have been prevented according to the number of low-risk factors present, Dr Forman's group found that in women who were at low risk for all 6 factors (only 0.3% of the population), 78% of hypothetical cases of hypertension were prevented. The population attributable risks were 72% for 5 low-risk factors (0.8% of the population); 58% for 4 low-risk factors (1.6% of the population); and 53% for 3 low-risk factors (3.1% of the population).

BMI alone was by far the most powerful predictor of hypertension, with a BMI of ≥ 25 having an adjusted population attributable risk of 40% compared with a BMI < 25. "Although speculative, if these associations were causal and independent, then lifestyle modification could have the potential to prevent a large proportion of new-onset hypertension occurring among young women," the researchers suggest.

They also found that although multiple (4-5) low-risk factors were significantly associated with a lower risk of developing hypertension among normal weight and overweight women, there was no association in women who were obese (BMI ≥ 30). "These findings imply that in the context of hypertension risk, obese women might not benefit from other low-risk behaviors unless weight loss is also addressed," the researchers say. "Because obesity is common (approximately one third of the US population), this finding has important consequences, particularly because, in the absence of calorie restriction and additional physical activity, adherence to the other 5 low-risk factors may not reduce weight."

Comment. In an accompanying editorial,[11] Véronique L. Roger, MD, MPH (Mayo Clinic, Rochester, Minnesota), says that the lifestyle choices that appear to protect against hypertension in the study relate to both individual and society, with the societal climate interacting with individual choices to enable or inhibit these choices. "Thus, the approach to cardiovascular disease prevention and treatment is characterized by the interplay between individual and society and between clinical and societal factors." She believes that public health policy must play a central role in disease prevention, since "there is an element of societal disingenuity to require of individuals personal choices that oppose societal trends." She suggests improving the quality of school-based meals, "which still do not meet national dietary recommendations for good health," as the most obvious action to take, along with "the conceptualization and restructuring of the environment to promote physical activity."

Significant Blood Pressure Decrease With Modest Dietary Salt Reduction in Asians and Blacks

A modest reduction in salt ingestion produces a significant decrease in blood pressure in black and Asian individuals as well as in whites, according to the results of a large clinical trial published in Hypertension.[12] Researchers at St George's and King's College, University of London, UK, also showed that salt reduction reduces urinary albumin and improves large artery compliance. For the study, funded by the UK Food Standards Agency, Feng J. He, PhD and colleagues tested the effect of salt reduction in 169 people, including 71 whites, 69 blacks (59% black Africans, 40% black Caribbeans, and 1% mixed ethnic origin), and 29 Asians (94% South Asian, 3% Chinese, and 3% mixed ethnic origin). The 113 men and 56 women, average age 50 years, all had untreated mild hypertension defined as SBP 140-170 mm Hg or DBP 90-105 mm Hg. Average sitting SBP was 147 mm Hg and average DBP 91 mm Hg. After 2 weeks on a reduced-salt diet, participants were randomly assigned in double-blind fashion to take either 9 slow-release sodium tablets (10 mmol sodium per tablet) or 9 placebo tablets daily for 6 weeks, after which they crossed over to take the opposite tablets for 6 weeks. Participants remained on the reduced salt diet throughout the trial.

Moving from slow-release sodium to placebo, mean 24-hour urinary sodium was reduced from 165 to 110 mmol/24 hours, equivalent to 9.7-6.5 g/day of salt. This reduction in salt was accompanied by a significant decrease in blood pressure from an average of 146/91 mmHg to 141/88 mm Hg (P < .001). In whites, blacks, and Asians, mean 24-hour urinary sodium was reduced by 3.5, 2.7, and 4.0 g/day, respectively. With these reductions in salt intake, there were significant falls in blood pressure of 4.6/2.5, 4.8/2/2, and 5.4/2.2 mm Hg, respectively. Significant reductions were also seen in all 3 groups in urinary albumin, albumin/creatinine ratio, and carotid-femoral pulse wave velocity. Subgroup analysis showed that the reductions in blood pressure and urinary albumin/creatinine ratio were significant in all groups, although the decrease in pulse wave velocity was significant in blacks only. Plasma renin activity and aldosterone showed significant increases in whites, but no significant changes in blacks and Asians.

"A lower salt intake, in the long-term, could play an important role in the prevention of cardiovascular disease, renal disease, and osteoporosis," said Dr. He. "Our study provides further support for the current UK public health recommendation to reduce salt intake to less than 6 g/day." The recommendation for salt intake in the United States is also 6 g/day.

Senior investigator Graham A. MacGregor, MD, PhD, added, "About 80% of salt intake in developed countries comes from sodium added by the food industry. The best strategy to reduce salt intake in the population is to persuade the food industry to make a gradual and sustained reduction in the amount of salt added to food in a structured program across the whole of the food industry. This is now happening in the United Kingdom and the average salt intake has already fallen from 9.5 to 8.6 g/day, and will continue to fall as more salt is taken out of all foods, with the saving of many lives. Even a small reduction in blood pressure in the whole population would have a large impact on reducing the number of people suffering and/or dying from strokes, heart attacks, and heart failure." (Prof. MacGregor is chairman of both Consensus Action on Salt and Health [CASH] in the UK and World Action on Salt and Health [WASH]).

Comment. In an accompanying commentary in Hypertension,[13] Brent M Egan, MD (Medical University of South Carolina, Charleston), adds that despite previous concerns about possible adverse effects associated with universal salt restriction, this trial showed no marked activation of the renin-angiotensin system with long-term moderate sodium reduction, even in white men. He notes that the beneficial effects of moderate sodium reduction on urinary albumin excretion and arterial pulse-wave velocity could not be separated from the blood pressure effects in the trial. Nonetheless, the pleiotropic benefits of moderate salt reduction may help explain the reported relationships between salt intake and cardiovascular and all-cause mortality.

High Salt Intake Causes Excess Fluid Retention Leading to Resistant Hypertension

High salt dietary intake is an important cause of resistant hypertension, mainly due to excess fluid retention that persists despite thiazide diuretic use, according to results of a small study funded by the National Heart, Lung, and Blood Institute and published in Hypertension.[14] Resistant hypertension is usually defined as hypertension that remains uncontrolled despite the use of ≥ 3 blood pressure-lowering drugs of different classes, including a thiazide-type diuretic, at optimal doses. Researchers at the University of Alabama at Birmingham examined the effects of dietary salt restriction on office and 24-hour ambulatory blood pressure in subjects with blood pressure > 140/90 mm Hg but < 160/100 mm Hg as determined at ≥ 2 clinic visits. Patients with a history of heart attack or stroke in the previous 6 months, congestive heart failure, or diabetes on insulin treatment were not included in the study. Twelve subjects were entered into a randomized crossover evaluation of low sodium (50 mmol/24 hours) and high sodium (250 mmol/24 hours) diets for 7 days each separated by a 2-week washout period. They were taking an average of 3.4 antihypertensive medications including hydrochlorothiazide (HCTZ) 25 mg daily and an angiotensin converting enzyme inhibitor or an angiotensin receptor blocker, and continued on these medications throughout the study.

The researchers found that with the low-salt diet, office SBP and DBP were significantly reduced by 22.7 and 9.1 mm Hg, respectively, compared with the high-salt diet. Ambulatory blood pressure monitoring also showed significant reductions in daytime SBP and DBP by 20.7 and 9.6 mm Hg, nighttime SBP and DBP by 20.3 and 9.9 mm Hg, and in 24-hour SBP and DBP by 20.1 and 9.8 mm Hg, respectively. These blood pressure reductions were much larger than those previously observed in unselected hypertensive subjects, the researchers note. "It suggests that patients with resistance are particularly salt sensitive and emphasizes the importance of low dietary salt intake in the clinical management of resistant hypertension." The researchers suggest that the enhanced salt sensitivity in these subjects could be explained by longer-term administration of renin-angiotensin system blockers.

During low salt intake, plasma renin activity increased, whereas brain natriuretic peptide and creatinine clearance decreased, consistent with reduction in intravascular volume, thus supporting the hypothesis that persistent fluid retention is due at least partly to excess dietary salt, the researchers say. These changes occurred despite all subjects' receiving HCTZ 25 mg/day, which may not be sufficient to overcome sodium-induced fluid retention, the researchers suggest. All participants in the study had been advised to lower their dietary salt intake and thought they had done so, but none achieved it. "The degree of salt restriction needed to overcome resistance to pharmacological therapies . . . is unlikely to be accomplished without expert dietary consultation," the researchers stress.

Comment. In an accompanying commentary,[15] Dr Lawrence J. Appel admits that he was surprised by the "huge" blood pressure reduction, "which was roughly the equivalent of adding 2 antihypertensive medications." He suggests that in managing cases of resistant hypertension, physicians should substitute long-acting chlorthalidone for short-acting HCTZ, and if possible refer patients to a dietitian for counseling. "Although clinicians commonly focus on the next drug and sometimes a device, a renewed and aggressive emphasis on lifestyle modification, specifically sodium reduction, is warranted in patients with resistant hypertension and uncontrolled blood pressure," he urges.

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