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Salt and Cardiovascular Mortality

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Getting the science right on the health outcomes of salt reduced diets

Getting the science right on the health outcomes of salt reduced diets

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  • 1. Sodium intake and mortality Perspectives on the evidence from the U.S. National Health and Nutrition Examination Surveys (NHANES) Hillel W. Cohen, MPH, DrPH Associate Professor of Epidemiology and Population Health Albert Einstein College of Medicine, Bronx NY
  • 2. The Sodium Hypothesis Higher Sodium (Na) Intake Elevated Blood Pressure (BP) Excess Cardiovascular Disease (CVD) Events
  • 3. Blood pressure: a demonstrated, modifiable risk factor of CVD Elevated Blood Pressure Excess CVD Events Consistent evidence Meaningful effect
  • 4. How strong is the association between higher Na and BP? Elevated Blood Pressure Higher Sodium Intake Data suggest the magnitude of the association is modest
  • 5. Sodium and BP: a modest association
    • In a cross sectional analysis of NHANES III:
    • ALL dietary factors combined, including sodium, contributed about 2% variability SBP
    • In comparison, age contributed about 35.3% variability SBP
    *Hajjar et al., Arch Intern Med, 2001
  • 6. Sodium and BP: a modest association
    • NHANES Follow-up: Dietary sodium did not predict hypertension 1
    • Health Professionals (male): Dietary sodium did not predict hypertension 2
    1) Ford & Cooper, Hypertension 1991. 2) Ascherio et al. Circulation 1992
  • 7. Sodium and BP: a modest association
    • Clinical Trials – Cochrane Reviews: Mean BP Decline in Intervention Trials ( N )
    • Jurgens & Graudal – short and long term Normal BP subjects (N=57) , BP decline: 1.3/0.5 mmHg Elevated BP subjects (N=58) , BP decline: 4.2/2.0 mmHg
    • He & MacGregor - duration >= 4 weeks Normal BP subjects (N=11), BP decline: 2.0/1.0 mmHg Elevated BP subjects (N=17) , BP decline: 5.0/2.7 mmHg
    • Brunner et al. - duration >= 3 months - 3 yrs. All subjects (N=23), BP decline: 2.1/1.6 mmHg
  • 8. Sodium and BP: a modest association
    • Clinical Trials – Cochrane Reviews cont.:
    • Hooper et al. – Duration >= 6 months - 7 yrs 11 Trials: (3 normal, 5 untxt and 3 txt hypertensives) Interm. follow-up: BP decline: 2.5/1.2 mmHg Late follow-up: BP decline: 1.1/0.6 mmHg
    • DASH-Sodium consistent with meta-analyses sodium decline within diet Control Diet 3.5 g to 2.3 g BP decline: 2.1/1.1 mmHg Dash Diet 3.5 g to 2.3 g BP decline: 1.3/0.6 mmHg
  • 9. What is the relationship of sodium intake with CVD events? A mount B P sodium ? B P C vd A mount C vd sodium Does association of BP with both Na and CVD answer the question?
  • 10. A correlation exercise:
    • If A is correlated with B , say: r 1 =0.5
    • and B is correlated with C , say: r 2 =0.6
    • What is a reasonable estimate of the correlation of A with C : r 3 = ?
    • a) .6 b) .5 c) .3 d) don’t know
    • Answer: d) Can’t tell if r 3 > 0
    • Only if both correlations are >= 0.75 can one make a reasonable inference that r 3 > 0 (r 1 2 + r 2 2 >= 1)
  • 11. To estimate the relationship of Na with CVD events
    • Direct Evidence is Necessary
    Even though Na is associated with BP and BP is associated with CVD… To determine if Na is associated with CVD:
  • 12. Diet and CVD clinical outcome trials
    • CVD and mortality outcome trials difficult
    • Large sample sizes needed
    • Long follow-up needed
    Hooper et al. * : Few studies had clinical outcome data and these had few events. 17 Deaths recorded, evenly divided between intervention and control. *Hooper et al. The Cochrane Database of Systematic Reviews 2004.
  • 13. Na and CVD: cohort studies MRFIT* Outcome: All-cause mortality Population: males Median urinary sodium ~ 117 mmol/d Results: no association *Cutler JA. ASH 1997 (presentation).
  • 14. Na and CVD: cohort studies Hawaiian Japanese Men* Outcome: Stroke Population: men, Japanese ancestry, n=7895 Median dietary sodium: approx. 2000 mg/d Results: no association *Kagan et al. Stroke, 1985.
  • 15. Na and CVD: cohort studies Worksite Hypertension Program* Outcome: Myocardial Infarction Population: Treated hypertensives n=2937 Median urinary sodium (mmol/d): Men: 126 mmol Women 97 mmol Results: Inverse association for men No association for women *Alderman et al. Hypertension, 1995.
  • 16. Na and CVD: cohort studies Scottish Heart Health Study* Outcome: All CHD, CHD & All-Cause Mortality Population: Scottish adults n= 11,629 Mean urinary sodium mmol/d males ~ 186 mmol females ~ 136 mmol Results Males: Indirect assoc., All-Cause Mortality Females: Direct assoc., All CHD No assoc. for other outcomes, either sex *Tunstall-Pedoe et al., BMJ 1997.
  • 17. Na and CVD: cohort studies Finland study* Outcome: CHD; CHD, CVD & All Mortality Population: Finish adults n= 2533 Median urinary sodium mmol/d males = 206 mmol females = 155 mmol Results: Direct associations *Tuomilehto et al. Lancet, 2001.
  • 18. Na and CVD: cohort studies Takayama Study* Outcome: Stroke Mortality Population: Japanese adults n= 39,079 Mean dietary sodium ** males = 5.7 gm females = 5.2 gm Results: Direct association with stroke *Nagata et al. Stroke, 2004. **Mean Na for middle tertile
  • 19. Na and CVD: cohort studies TOHP (Trials of hypertension prevention)* Outcome: All CVD; All cause mortality Population: 3126 U.S. adults 30-54 y.o. Diastolic 80-89 mmHg; BMI ≥25 in >90% participants Results for lower Na group: Significant (p=.044) protection for all CVD Not significant (p=.35) for all mortality *Cook et al. BMJ 2007
  • 20. The NHANES Experience National Health and Nutrition Examination Surveys Representative samples of non-institutionalized adults in the U.S. Outcome follow-up added after. Sodium and calories from 24-hr dietary recall. Baseline surveys conducted NHANES I 1971-1975 NHANES II 1976-1980 NHANES III 1988-1994
  • 21. The NHANES Experience NHANES I (a) * Outcome: CVD and All-Cause Mortality Population: U.S. adults n= 11,346 Mean dietary sodium: (mg/d) Men: 2515 mg Women 1701 mg Results: Inverse association for Na Direct association for Na/Cal *Alderman et al. Lancet, 1998.
  • 22. The NHANES Experience NHANES I (b) * Outcome: Stroke, CVD & All-Cause Mortality Population: U.S. adults n= 9,485 BMI <27.8 kg/m 2 n=6797 BMI > 27.8 n=2688 Results: Direct associations in Overweight (28%) No associations in Non-overweight (72%) *He et al. JAMA, 1999.
  • 23. The NHANES Experience NHANES II* Outcome: CVD and All-Cause Mortality Population: U.S. adults ages 30-74 at entry n= 7154 representing 78.9 million Mean dietary sodium: 2718 mg/d Median: 2360 mg/d *Cohen et al. Sodium intake and mortality in the NHANES II Follow-up Study. American Journal of Medicine (2006) 119: 275.e7-275.e14.
  • 24. NHANES II * CVD and all-cause mortality *Cohen et al. AJM, 2006 . ** rates without weighting;RR with weighting Age-sex adjusted rates**
  • 25. NHANES II * Adjusted CVD Mortality Hazard Ratios *Cohen et al. AJM, 2006 . Adjusted for age, sex, race, smoking, alcohol, SBP, BP-txt, BMI, education, physical activity, dietary K, Hx diabetes, cholesterol, (calories) .03 0.80, 0.99 0.89 Na per 1000 mg .04 1.01, 1.49 1.22 Na <residuals adjusted median .03 1.03, 1.81 1.37 Na < 2300 mg .008 0.68, 0.94 0.80 Na mg per calorie P 95% CI H.R. Sodium
  • 26. NHANES II * All-Cause Mortality Hazard Ratios *Cohen et al. AJM, 2006 . Adjusted for age, sex, race, smoking, alcohol, SBP, BP-txt, BMI, education, physical activity, dietary K, Hx diabetes, cholesterol, (calories) .06 0.87, 1.00 0.93 Na per 1000 mg .13 0.97, 1.30 1.12 Na <residuals adjusted median .003 1.10, 1.50 1.28 Na < 2300 mg .05 0.79, 1.00 0.89 Na mg per calorie P 95% CI H.R. Na
  • 27. Adjusted hazard ratios of CVD mortality for Na intake <2300 mg in 27 selected subgroups estimated by Cox models
  • 28. Adjusted hazard ratios of CVD mortality for Na intake <2300 mg in 27 selected subgroups estimated by Cox models
  • 29. The NHANES Experience NHANES III
    • Third in the series
    • Widely used to characterize US dietary intakes, including sodium
    • This is the first presentation of these data, linking baseline sodium to mortality
    • Just published online ahead of print: Sodium Intake and Mortality Follow-Up in the Third NHANES Cohen HW, Hailpern SM, Alderman MH Journal of General Internal Medicine, 2008 DOI 10.1007/s11606-008-0645-6
  • 30. NHANES III* Population: U.S. adults age >30 at entry Exclusions: CVD at baseline or on low salt diet for BP Remaining n = 8699 (representing about 100 million) Mean dietary sodium: 3207 ± 1608 mg/d Median: 2922 mg/d (IQR: 2060, 4048) *Cohen et al. Sodium intake and mortality follow-up in the Third National Health and Nutrition Examination Survey (NHANES III), JGIM 2008.
  • 31. NHANES III* Outcomes: CVD deaths: 436 (236 CHD, 82 CVA, 118 other) All-Cause Mortality: 1150 deaths Mean follow-up time: 8.7 ±2.3 years Hazard ratios adjusted for age, sex, race/ethnicity, education, smoking, diabetes, cancer, SBP, alcohol, physical activity, dietary K, weight, cholesterol, txt for hypertension and calories *Cohen et al. Sodium intake and mortality follow-up in the Third National Health and Nutrition Examination Survey (NHANES III), JGIM 2008.
  • 32. NHANES III * Adjusted CVD Mortality Hazard Ratios *Cohen et al. JGIM, 2008. Adjusted for age, sex, race/ethnicity, education, smoking, diabetes, cancer, SBP, alcohol, physical activity, dietary K, weight, cholesterol, txt for hypertension (calories for 1 st row) .07 0.77, 1.01 0.88 Na per 1000 mg .07 0.77, 1.01 0.88 Na residuals adjusted per 1000 mg .40 0.72, 1.14 0.91 Na mg per calorie P 95% CI H.R. Sodium
  • 33. NHANES III * Adjusted All-Cause Mortality HRs *Cohen et al. JGIM, 2008. Adjusted for age, sex, race/ethnicity, education, smoking, diabetes, cancer, SBP, alcohol, physical activity, dietary K, weight, cholesterol, txt for hypertension (calories for 1 st row) .11 0.88, 1.01 0.94 Na per 1000 mg .11 0.88, 1.02 0.95 Na residuals adjusted per 1000 mg .94 0.88, 1.12 1.00 Na mg per calorie P 95% CI H.R. Sodium
  • 34. NHANES III* 99% CI for Hazard Ratios per 1000 mg Na CVD mortality: (.73, 1. 06 ) All cause mortality: (.86, 1. 04 ) Very small probability of meaningful increased risk of mortality per 1000 mg Na *Cohen et al. Sodium intake and mortality follow-up in the Third National Health and Nutrition Examination Survey (NHANES III). JGIM, 2008.
  • 35. NHANES Limitations and Strength
    • Observational studies subject to confounding; causal inferences not possible
    • Single 24-hour dietary recall may not reflect “usual diet” over time
    • 24-hour recall may not be accurate
    • However: 24-hour recall more closely resembles how individuals would calculate Na intake if trying to meet guidelines
  • 36. NHANES Strengths
    • Large, representative sample
    • Prospectively collected outcomes
    • Mortality outcomes (especially all-cause) have high validity
    • Public access data: analyses can be replicated
    • Results consistent in last 2 surveys
  • 37. Potential mechanisms for adverse effects of lower sodium diet
    • Lower Na can elevate plasma renin and aldosterone levels
    • For some, lower Na may stimulate sympathetic nervous system
    • For some, lower Na may reduce insulin sensitivity
    • Lower Na may be marker for problematic levels of other nutrients or other individual characteristics
  • 38. Heterogeneity of effects likely
    • Modest BP effect of Na restriction not likely to benefit large % of individuals who
    • Have normal BP and/or normal weight
    • Have healthy kidneys
    • Are not “salt-sensitive”
    • Need BP medication and achieve lower pressures
  • 39. No strong evidence for either benefit or harm of sodium restriction With regard to clinical outcomes of morbidity and mortality:
  • 40. U. S. PREVENTIVE SERVICES TASK FORCE - 2003
    • Nonpharmacologic therapies, such as reducing dietary sodium intake, potassium supplementation, increased physical activity, weight loss, stress management, and reducing alcohol intake, are associated with a reduction in blood pressure, but their impact on cardiovascular outcomes has not been studied .
    • There is insufficient evidence to recommend single or multiple interventions or to guide the clinician in selecting among nonpharmacologic therapies
    U.S. Preventive Services Task Force. Screening for High Blood Pressure: Recommendations and Rationale . July 2003. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/clinic/3rduspstf/highbloodsc/hibloodrr.htm
  • 41. Should government restrict sodium in processed food? With little and contradictory evidence regarding benefit or harm, does the rationale of “can’t hurt” apply?
  • 42. Potential problems from “law of unintended consequences”
    • Will industry substitute sugar, fat or untested chemical additives to improve taste or prolong shelf-life?
    • Will lower salt increase food-borne illness?
    • Will “heart-healthy” labels and advertising based on lowered Na lead to higher calorie consumption?
    • Is sodium restriction the most effective area for intervention?
  • 43. Summary
    • Strong recommendations for universal sodium restriction
    • are not supported by strong evidence.
  • 44. Acknowledgements
    • Michael H. Alderman
    • Jing Fang
    • Susan M. Hailpern
    • Judy Wylie-Rosett
  • 45.
    • THANK YOU!
  • 46. Contact information: Dr. Hillel W. Cohen Dept. of Epidemiology and Population Health Albert Einstein College of Medicine Bronx, NY 10461, USA 718-430-3745 [email_address]

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