Salt reduction - benefits beyond blood pressure

Transcription

1 Salt reduction - benefits beyond blood pressure Jennifer Keogh Associate Professor Sansom Institute for Health Research University of South Australia

2 Intersalt study 1 Epidemiological study of electrolyte excretion & BP 10,079 men & women 20-59yr in 52 centres Na excretion ranged from 0.2 mmol/24 h (Yanomamo Indians, Brazil) -242 mmol/24 h (north China) 4 centres found very low Na excretion, low BP, and little or no upward slope of BP with age. In 48 centres Na was significantly related to the slope of BP with age +ve associations seen between BP and 24 hr Na excretion BMI & alcohol intake ve associations between BP and K excretion. Public health policy that sodium potassium intake with in obesity & alcohol consumption could bring important public health benefits 2 1. BMJ Jul 30;297(6644): Elliott et al Clin Exp Hypertens A. 1989;11(5-6):

3 Salt in the diet today: Intake National target UL 100 mmol sodium 1 Recommendations to reduce chronic disease risk 70 mmol sodium/day Hobart Salt Study Beard 2 6g/day, 36% women, 6% men Average salt intake 7-10 g/day. Sodium excretion overweight volunteers in CSIRO studies n=274 3 Men (n=85) 181 ± 95 mmol urinary sodium/24hrs Women (n=189) 136 ± 61 mmol urinary sodium/24hrs 1. NH&MRC 2005; 2. Beard et al Med J Aust Apr 21;166(8):404-7; 3 Keogh & Clifton Med J Aust Nov 3;189(9):526.

4 Other studies CSIRO study 62 Women 24hr Na excretion ± 43.0 mmol/day ~7.6g salt 1 76 women 24 hr urine Salt intake of 6.4±2.6g/day 2 Bread and cereals (27%) Dressings/sauces (20%) Meat/egg-based dishes (18%) Snacks/desserts/extras (11%) Milk and dairy products (11%). Half reported using salt in cooking or at the table Discrepancies demonstrate need for population data 1. Lassale et al J Hum Nutr Diet Dec;22(6): Charlton et al Aust N Z J Public Health Aug;34(4):

5 Why worry? intake by 3g/day would new cases of CHD by 60,000, stroke by 32,000 MI by 54,000 deaths by 44,000/yr in the US 1 Based on US adults consuming ~10g salt/day Strategy 1: Collaboration with industry that Na intake by 9.5% averts 513,885 strokes and 480, 358 MIs over the lifetime of adults aged years alive today compared with the status quo QALYs by 2.1 million & saves $32. 1 billion in medical costs 2 Strategy 2: A tax on sodium that Na intake by 6% QALYs by 1.3 million and saves $22. 4 billion over the same period 2 1. Bibbins-Domingo et al N Engl J Med Feb 18;362(7): Smith-Spangler et al Ann Intern Med Apr 20;152(8):481-7, W170-3.

6 Intervention? Follow-up of the Trials Of Hypertension Prevention (TOHP) found the risk of a cardiovascular event was 25% in the low sodium group and 30% after adjustment for baseline sodium excretion and weight after years Sodium was only 44 mmol/24 hours in TOHP 1 and 33 mmol/24 hours in TOHP 11 Cook et al BMJ Apr 28;334(7599):885-8.

7 Is the BP response to salt removed by weight loss? Obesity strongly associated with high BP Obese participants Weight ~9% 12 weeks SBP 9 mmhg DBP 7 mmhg Salt load caused the same in BP before and after weight loss Ho et al Horm Metab Res Sep;39(9):694-9.

8 Salt and resistant hypertension Subjects with resistant hypertension Randomised cross over design 50 vs 250 mmol Na/24 hours 7 days Subjects on 3 BP medications Low- compared to high-salt diet office SBP & DBP by 23 and 9 mm Hg Pimenta et al Hypertension Sep;54(3):

9 Effects of salt beyond BP Left ventricular hypertrophy which mortality due to cardiovascular disease is closely related to salt intake 1,2 Pulse wave velocity, a measure of vascular compliance, is improved by salt 3,4 1. Hu et al Curr Hypertens Rep Feb;4(1): Coca & De la Sierra Adv Exp Med Biol. 1997;432: Avolio et al Arteriosclerosis Mar-Apr;6(2): Todd et al Am J Clin Nutr Mar;91(3):

10 Not only but also. Osteoporosis? Urine excretion of Na & Ca linked 2,300 mg (approx 100 mmol/d) of Na takes out about 40 mg of Ca in the urine 2-y study of bone density in 124 postmenopausal Na excretion -ve correlated with changes in bone density at the hip in bone loss achieved by an of 891 mg Ca can also be achieved by halving daily Na excretion No bone loss occurred at the total hip site at a calcium intake of 1768 mg/d or a urine sodium excretion of 2110 mg/d (approx 92 mmol/d) Devine Am J Clin Nutr Oct;62(4):740-5.

11 Flow-mediated Dilatation (FMD) High-resolution ultrasound to assess endothelium-dependent FMD following reactive hyperaemia after occlusion of the brachial artery - Non-invasive FMD relies on NO produced from the endothelium in response to shear stress Low brachial artery FMD seen in patients with risk factors CVD e.g. obesity, diabetes, hypertension, smokers, hypercholesterolaemia

12 Effects on FMD of reduced salt vs. usual salt 3g salt/day compared with 9 g/day Crossover design - 2 weeks on each diet Obese participants Results 1.5% greater (improved) FMD compared with the usual salt diet i.e. 45% greater change after the low salt diet than after the usual salt diet Dickinson et al Am J Clin Nutr Feb;89(2):

13 Benefit? Improvement similar to that seen with atorvastatin 1 Greater than that seen with other interventions such as ACE inhibition 2 or folate supplementation 3 1. Hoshiga 2010; 2. Bots 2007; 3. Title 2000

14 Finally. Public Health action to salt in food supply to population salt intake People at risk of CVD e.g. with diabetes need targeted education Salt reduction reduces calcium requirements and may ameliorate bone loss Need population Na excretion data Food industry has an important role