A Little DASH of Common Sense

Abstract & Commentary

By Barbara Phillips, MD, MSPH, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips reports no financial relationship to this field of study.

Synopsis: Middle-aged women who followed the DASH diet had a lower risk of stroke and coronary heart disease over a 24-year-period than comparable women who did not.

Source: Fung TT, et al. Adherence to a DASH-Style Diet and Risk of Coronary Heart Disease and Stroke in Women. Arch Intern Med. 2008;168(7):713-720.

This study is the report of an observation of 88,517 women who were part of the Nurses' Health Study. This analysis included participants for whom adequate dietary information was available and who had no history of coronary heart disease, stroke, or diabetes at baseline. Participants in this study were not instructed or counseled to use any particular diet, but the investigators retrospectively assessed their spontaneous use of the Dietary Approaches to Stop Hypertension (DASH) diet.1 This was done by using analysis of food frequency questionnaires (FFQ), focusing on 8 components: high intake of fruits, vegetables, nuts and legumes, low-fat dairy products, and whole grains, and low intake of sodium, sweetened beverages, and red and processed meats. DASH scores ranged from 8 to 40, with higher scores indicating closer adherence to the diet. The participants were divided into quintiles based on DASH scores. The authors collected data on incident coronary heart disease (nonfatal myocardial infarction [MI] or fatal CHD) and stroke for the next 24 years after the return of the first FFQ questionnaire in 1980. To reduce random within-person variation and to best represent long-term dietary intake, the investigators used cumulative means of the DASH score from the repeated FFQ administrations. For example, the DASH score in 1980 was used to predict risk from 1980 to 1984, and the mean DASH score from 1980 and 1984 was used to predict risk from 1984 to 1986. Cox proportional hazard modeling was used to assess the association between the DASH score and risk of CHD and stroke. Analyses were adjusted for age, smoking, BMI, menopausal status, postmenopausal hormone use, energy (calorie) intake, multivitamin intake, alcohol, family history of CHD, physical activity, and aspirin use. Most subjects also gave blood for measurement of C-reactive protein (CRP), interleukin 6 (IL-6) levels, total cholesterol, fasting triglycerides, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol.

During the 24 years of follow-up, there were 2317 cases of CHD, and 2317 cases of stroke (1242 of these were ischemic). Women with higher DASH scores tended to use multivitamins, exercise more, and consume more fiber and omega-3 fatty acids but less saturated fat, trans fat, and total energy. They were also less likely to be current smokers but more likely to report a history of hypertension.

There was an inverse association between the DASH score and incident CHD and stroke. After statistical adjustment for confounders, women in the top quintile of the DASH score had a reduced relative risk (RR) of 0.76 (P < .001) for both fatal and nonfatal CHD compared with those in the lowest quintile. Further statistical adjustment for hypertension and high cholesterol did not change this finding. For stroke risk, those in the top quintile DASH score group had a lower relative risk of 0.82 (P = .002) compared with those in the bottom quintile, and the relationship was not affected by additional adjustment for hypertension and or diabetes. Of note, the inverse association between the DASH score appeared to be stronger among smokers (P = .09 for interaction) and those with hypertension (P = .05 for interaction) for the risk of stroke.

For those who had serum biomarkers of inflammation measured, a higher DASH score was associated with lower CRP and IL-6 levels but not for blood lipid levels.

Commentary

This report received some attention in the lay press ("Blood pressure diet cuts heart, stroke risk"),2 and your patients may ask you about it. While the findings of this study are not particularly surprising, what is new about this report is the duration of time over which the women were followed (nearly a quarter of a century!), and the ability to link improved cardiovascular outcomes to a specific named diet, the DASH diet. Because a randomized clinical trial of the DASH diet on cardiovascular end points is unlikely to occur, this study is probably about as good as it is going to get in terms of defining the long-term benefits of the DASH diet in the primary prevention of CVD among healthy subjects. It is notable that this study suggested people with hypertension (and thus at increased risk for stroke) seemed particularly likely to benefit from adherence to the DASH diet in terms of reduction in stroke.

The DASH diet has previously been reported to reduce both systolic and diastolic blood pressure among both those with hypertension and those without.1 It has also been shown to reduce low-density lipoprotein cholesterol levels,3 and is recommended by the National Heart, Lung, and Blood Institute (NHLBI) for the prevention and treatment of hypertension.4 The total DASH score depends on including some things (fruits, vegetable, nuts) and excluding others (salt, sodas, red meat). Different components of the DASH score have been linked to lower blood pressure. Plant foods have been associated with lower blood pressure.5-7 On the other hand, meat intake has been associated with higher blood pressure.8 The DASH diet is not difficult to follow, and is available on the internet for your patients who are interested in lifestyle approaches to good health.9 A typical daily DASH diet might include:

— At least 8 servings of fruits and vegetables (a serving is a ½ cup of cooked or a full cup of raw plant food, or a piece of fruit).

— One serving of nuts or legumes (a serving is a handful of nuts or half-cup of legumes).

— At least 2 servings of whole grains (a serving is a slice of bread, a cup of cereal, or ½ cup of cooked pasta or rice).

— About 2 servings of low-fat dairy products. (A serving is one cup).

— One-half serving of meat (a full serving is the size of a deck of cards).

References

1. Appel LJ, et al. N Engl J Med. 1997;336(16):1117-1124.

2. Lexington Herald Leader, April 15, 2008

3. Obarzanek E, et al. Am J Clin Nutr. 2001;74(1):80-89.

4. United States Department of Health and Human Services, National Institutes of Health, National Heart Lung, and Blood Institute. Your Guide to Lowering Your Blood Pressure With DASH. http://www.nhlbi.nih.gov/health/public/heart/hbp/dash/

5. Alonso A, et al. Fruit and vegetable consumption is inversely associated with blood pressure in a Mediterranean population with a high vegetable-fat intake: the Seguimiento Universidad de Navarra (SUN) Study. Br J Nutr. 2004;92(2):311-319.

6. Alonso A, et al. Arch Med Res. 2006;37(6):778-786.

7. Miura K, et al. Relation of vegetable, fruit, and meat intake to 7-year blood pressure change in middle-aged men: the Chicago Western Electric Study. Am J Epidemiol. 2004;159(6):572-580.

8. Steffen LM, et al. Associations of plant food, dairy product, and meat intakes with 15-y incidence of elevated blood pressure in young black and white adults: the Coronary Artery Risk Development in Young Adults (CARDIA) Study. Am J Clin Nutr. 2005;82(6):1169-1177.

9. www.nhlbi.nih.gov/hbp/prevent/h_eating/h_e_dash.htm