What Does Eating Plants Do For Hypertension? (Part One)

“There are two kinds of cardiologists – those that are vegan and those that haven’t read the data”.

Dr. Kim Williams, cardiologist and the president of the American College of Cardiology 2015 & 2016

High blood pressure (hypertension) is the number one risk factor for death in the world. Statistics tell us that 1 out of every 6 people worldwide have high blood pressure and that 9 out of 10 adults who live to the age of 80 will develop high blood pressure at some point in their lives. These numbers are expected to increase rapidly over the next decade. Hypertension contributes to death from heart attacks, heart failure, aneurysms, strokes and kidney failure. Although it affects most of us as we age, hypertension is not an inevitable result of aging. In fact we have known since the 1920s that blood pressure does not have to rise with age. Researchers measured the blood pressure of over 1000 people from Kenya and discovered that not only did they not have high blood pressure but their pressures actually decreased as they aged (1). Another study completed in 1937 found blood pressures in rural Chinese people hold steady around 110/70 for their entire lives (2). Both the Kenyans and the Chinese people in these studies ate diets centered around whole plant foods with meat eaten only on special occasions.

What is blood pressure?

Blood pressure is the force of blood pushing against the artery walls as it flows through the bloodstream. Blood pressure varies throughout the day but, when it stays high most of the time, it is called hypertension. Measurement of blood pressure results in a double number. The first number is the systolic blood pressure which is the force of the blood on artery walls when the heart beats or contracts. The second number, the diastolic blood pressure, is the force of the blood on artery walls between heart beats. Normal blood pressure is usually considered to be 120/80. When systolic blood pressure is over 140 mmHg or diastolic blood pressure is over 90 mmHg, hypertension is diagnosed. These numbers are quite arbitrary and even people with blood pressures of 120/80 can benefit from lower pressures (4). The blood pressure below which there is no further health benefit is actually 110/70 (5).

Hypertension is known as “The Silent Killer” because over half of people affected do not know they have it. It does not produce noticeable symptoms. If you’re lucky, your first inkling that you have hypertension may be when your doctor measures your blood pressure during your regular physical examination. If you’re not so lucky, the first sign of hypertension may be death from a heart attack or stroke.

Diet and blood pressure

The largest study to compare blood pressures among people eating different diets was an Adventist Health Study that included 89,000 Seventh Day Adventists in California (3). As diets became more and more plant based, blood pressures decreased in a step-wise fashion.

Flexitarians (those eating meat about once a week) had blood pressures 25% lower than non-vegetarians.
Pescovegetarians (those who eat no meat except fish) had blood pressures 38% lower than non-vegetarians.
Lacto-ovo vegetarians (those who eat dairy and eggs but no meat) had blood pressures 55% lower than non-vegetarians.
Vegans (those eating only plants) had blood pressures 75% lower than non-vegetarians.

Experimentally it has been shown than if vegetarians eat meat their blood pressure will increase (6). If you remove meat from people’s diets, blood pressures go down (7).

Canadian Diabetes and the American Heart Association both recommend the DASH diet to reduce high blood pressure. (DASH means Dietary Approaches to Stop Hypertension). The DASH diet is predominantly plant-based. It emphasizes whole grains, fruits and vegetables but also includes some low-fat dairy and lean meats. Why is it not completely plant-based? The chair of the diet design committee was Frank Sacks, the author of several studies elucidating the blood pressure lowering effects of vegetarian diets (8,9). He was well aware of the wealth of scientific evidence on the power of plants for blood pressure reduction. But he and his committee just did not believe that the public would be willing or able to make such a significant dietary change. They therefore crafted the DASH diet to capture the benefits of the blood pressure-lowering power of a vegetarian diet while including enough animal products to make it palatable, a compromise that they hoped would actually be followed. It is just this sort of thinking that needs to be turned around. Why not tell people the truth and let them make their own educated decision about what they want to eat? Studies show that if people understand the potent benefits of eating only plants, they are very willing to eat the healthiest diet to enjoy those benefits (10,11).

What about sodium?

Part of the reason that plant-based diets work is that they are naturally low in sodium, a significant factor in the development of high blood pressure. For the first 90% of our evolution our diets were extremely low in salt and our bodies evolved into salt-conserving machines. In these modern times salt is ubiquitous in our diets. We eat excessive amounts of processed foods that are often very high in salt, salt is added to many meats to draw in water in order to increase the product’s selling weight and we add salt to our food as we cook it and at the table as we eat it. All this results in our ingestion of ten times more salt than our bodies are designed to handle. Sodium is an essential nutrient but too much of it causes water to be retained in body tissues. The extra fluid not only increases the pressure within our blood vessels but also sets up a cascade of inflammation that can damage blood vessels and cause stiffening of the arteries. During the 1940s, before the invention of blood pressure-reducing drugs, patients with extremely high blood pressure were deemed untreatable. A physician by the name of Dr. Walter Kempner gathered up some of these unfortunate patients and treated them with an exclusively rice and fruit diet, a plant-based diet extremely low in salt, fat, protein and calories. His patients experienced extreme drops in blood pressure, with some dropping from 240/150 down to 105/80 using dietary changes only and no medications, demonstrating beyond doubt that a low salt diet works (12). This effect is confirmed by studies on cultures such as the Yanomamo people who live deep in the Amazon rainforest of Brazil. Their diet is plant-based and contains no added salt at all. Their lifetime blood pressures are 100/60 on average. Virtually none of the Yanomamo population has high blood pressure while people living elsewhere in Brazil suffer hypertension at the rate of 38% of the population (13,14,15).

Lately a battle of sorts has been raging among scientists and salt-related businesses regarding the extent to which elevated salt consumption contributes to death and disease. Much of this controversy stems from a study published in the American Journal of Hypertension in 2014 suggesting a U-shaped curve on a graph of salt intake where too little sodium intake is just as bad for health as too much (23). Issues have been discovered in the data used for this study that have resulted in flawed conclusions (24,25). Problems include using data that was not designed to assess the sodium/health relationship, making inaccurate estimates of sodium intake and not taking into account the overall health of the participants in the study.

We need to look at trials that are properly conducted, using the more accurate method of actual 24-hour data collections from healthy people. These results show a continuous decrease in cardiovascular disease events (such as heart attacks and strokes) as sodium levels decrease (24,25). To look at the picture the other way around, for every gram of sodium intake a day there is a 17% increase in cardiovascular disease risk (26).

Strong scientific evidence for the life-saving benefit of reducing salt is abundantly available, so much so that nearly all nutrition experts and government bodies recommend drastically reduced salt consumption (16,17,21,22). The average daily sodium consumption in North Americans at present is 3500 mg. Health Canada recommends a level closer to 1500 mg with a maximum of 2300 mg. Those defending the salt industry describe this as extreme and claim that very few people can actually get their salt consumption this low (18,19,20). Salt is big business for the processed food and meat industry and their defense of salt is vocal and powerful. Never forget that those who have a financial stake in a product will fight back using whatever tactics are at hand. Nonetheless the scientific evidence cannot be ignored – reducing salt saves lives.

Nitric oxide plays its part in preventing hypertension

We’ve talked about sodium but what about other factors of a whole-food plant-based diet that lead to lower blood pressure. As we learned in “What Does Eating Plants Do For Your Blood Vessels”, nitric oxide produced in the endothelium (the lining of our blood vessels), plays a very important part in the ability of our blood vessels to relax. Relaxed blood vessels are blood vessels under less pressure. So eating to increase nitric oxide levels makes sense for lowering blood pressure. Nitric oxide is produced by the endothelium but there are also foods that are high in nitrates that can be valuable. Both the saliva in our mouth and the microbes in our gut convert nitrates into nitric oxide. The best food sources of nitrates are beets, celery, cabbage, endive, fennel, rhubarb and leafy greens such as swiss chard, cilantro, lettuce, parsley and arugula. Other lesser sources include dark cocoa, spinach, chervil and capsaicin from red peppers. A meta-analysis of the science surrounding the effects of consuming beet juice showed significant drops in both systolic and diastolic blood pressure, an effect that lasts on into the next day (27). Eating nitrate rich foods and encouraging more nitric oxide production in our endothelium through eating lots of fruits and vegetables and regular exercise will help keep blood pressure down. Be aware though that excess mouthwash use destroys friendly, nitric oxide producing bacteria in the mouth (28).

You may be wondering why nitrates and nitrites from meat are bad for you while those from vegetables are not. Sodium nitrate is used for preserving meats. Once it interacts with the bacteria in meat it converts to sodium nitrite, a chemical that inhibits the growth of dangerous bacteria. Nitrites react with secondary amines under acidic conditions (such as those in the human stomach) and produce a dangerous compound called nitrosamine. Nitrosamine also forms during the curing process for meat and when meat is heated. Often the meat we eat contains nitrosamines even before it makes it to our mouths. The IARC (International Agency for Research on Cancer) denotes nitrosamines to be “probably carcinogenic to humans” (Group 2A). Happily plants do not produce nitrosamine. They have the advantage of natural phytonutrients and antioxidants that block nitrosamine formation (29).

SOURCES:

1 Donnison, C. Blood Pressure in the African Native. Its bearing upon the Aetiology of Hyperpiesia and arterio-sclerosis. The Lancet, 1929; 213(5497), 6-7.

2 Morse, W., & Beh, Y. Blood Pressure Amongst Aboriginal Ethnic Groups Of Szechwan Province, West China. The Lancet, 1937; 229(5929), 966-968.

3 Le, L.T., Sabaté, J. Beyond meatless, the health effects of vegan diets: findings from the Adventist cohorts. Nutrients. 2014 May 27;6(6):2131-2147.

4 Mihaylova, B., Emberson, J., Blackwell, L., Keech, A, et al. Cholesterol Treatment Trials: The effects of lowering LDL cholesterol with statin therapy in people at low risk of vascular disease: Meta-analysis of individual data from 27 randomised trials. (2012). Lancet. 2012 Aug 11; 380(9841):581-590.

5 Law, M.R., Morris, J.K., Wald, N.J. Use of blood pressure lowering drugs in the prevention of cardiovascular disease: meta-analysis of 147 randomised trials in the context of expectations from prospective epidemiological studies. BMJ. 2009 May 19; 338:b1665

6 Donaldson, A.N. The Relation of Protein Foods to Hypertension. Cal West Med. 1926 Mar; 24(3):328-331.

7 McDougal, J., Thomas, L.E., McDougall, C. et al. Effects of 7 days on an ad libitum low-fat vegan diet: the McDougall Program cohort. Nutr J. 2014 Oct 14; 13:99.

8 Sacks, F.M., Kass, E.H. Low blood pressure in vegetarians: effects of specific foods and nutrients. Am J Clin Nutr. 1988 Sep; 48(3 Suppl):795-800.

9 Sacks, F.M., Campos, H. Dietary Therapy in Hypertension. N Engl J Med 2010; 362:2102-2112.

10 Lea, E.J., Crawford, D., Worsley, A. Public views of the benefits and barriers to the consumption of a plant-based diet. Eur J Clin Nutr. 2006 Jul; 60(7):828–837.

11 Tuso, P.J. Nutritional Update for Physicians: Plant-Based Diets. Perm J. 2013 Spring; 17(2): 61–66.

12 Kempner, W. Treatment of heart and kidney disease and of hypertensive and arteriosclerotic vascular disease with the rice diet. Ann Intern Med. 1949 Nov; 31(5):821-56, illust.

13 Mancilha-Carvalho, J., Souza e Silva,N.A.. The Yanomami Indians in the INTERSALT Study. Arq Bras Cardiol. 2003 Mar;80(3):289-300.

14 Mancilha-Carvalho, J.J., Crews, D.E. Lipid profiles of Yanomamo Indians of Brazil. Prev Med. 1990 Jan; 19(1):66-75.

15 Oliver, W.J., Cohen, E.L., Neel, J.V.. Blood pressure, sodium intake, and sodium related hormones in the Yanomamo Indians, a “no-salt” culture. Circulation. 1975 Jul; 52(1):146-151.

16 MacGregor, G.A., Markandu, N.D., et al. Double-blind randomised crossover trial of moderate sodium restriction in essential hypertension. Lancet. 1982 Feb 13; 1(8268):351-355.

17 Neal,B. Dietary salt is a public health hazard that requires vigorous attack. Can J Cardiol. 2014 May; 30(5):502-506.

18 Mente, A., O’Donnell, M.J., Yusuf, S. The population risks of dietary salt excess are exaggerated. Can J Cardiol. 2014 May; 30(5):507-512.

19 Bayer, R., Johns, D.M., Galea, S. Salt and public health: contested science and the challenge of evidence-based decision making. Health Aff (Millwood). 2012 Dec; 31(12):2738-2746.

20 MacGregor, G., De Wardener, H.E. Commentary: Salt, blood pressure and health. Int. J. Epidemiol. (2002) 31 (2): 320-327.

21 Batuman,V. Salt and hypertension: why is there still a debate? Kidney International Supplements (2013) 3, 316–320.

22 Feng, J.H., MacGregor, G.A. Reducing Population Salt Intake—Time for Global Action. The Journal of Clinical Hypertension Volume 17, Issue 1, pages 10 -13,

23 Graudal, N., Jurgens, G., Baslund, B., Alderman,M.H. Compared with usual sodium intake, low- and excessive-sodium diets are associated with increased mortality: a meta-analysis. Am J Hypertens. 2014 Sep; 27(9):1129-1137.

24 Cook, N.R., Appel, L,J., Whelton, P.K. Lower levels of sodium intake and reduced cardiovascular risk. Circulation. 2014 Mar 4; 129(9):981-989.

25 Whelton, P.K., Appel, L.J.. Sodium and cardiovascular disease: what the data show. Am J Hypertens. 2014 Sep; 27(9):1143-1145.

26 Cappuccio, F.P. Cardiovascular and other effects of salt consumption. Kidney Int Suppl (2011). 2013 Dec; 3(4): 312–315.

27 Siervo, M., Lara, J. et al. Inorganic Nitrate and Beetroot Juice Supplementation Reduces Blood Pressure in Adults: A Systematic Review and Meta-Analysis. J. Nutr. June 1, 2013; 143(6): 818-826.

28 52 Ahluwalia, A., Gladwin, M., Coleman, G.D. et al. Dietary Nitrate and the Epidemiology of Cardiovascular Disease: Report From a National Heart, Lung, and Blood Institute Workshop. J Am Heart Ass. 2016;5: e003402.

29 http://www.cbc.ca/natureofthings/m/features/background-nitrosamines

30 https://monographs.iarc.fr/ENG/Monographs/vol94/mono94.pdf