Sodium is an important mineral that is essential for proper functioning of the human body -- however, the American diet contains dangerously high amounts of sodium, almost 80 percent of which comes from processed and restaurant foods.[1] The human diet, for millions of years, did not contain any added salt -- only the sodium present in natural foods, adding up to only about 1000 mg sodium per day. The dietary intake of sodium in the U.S. today is about 3500 mg/day. [2]
Excess dietary salt is most notorious for increasing blood pressure. Americans have a 90 percent lifetime probability of developing high blood pressure -- so even if your blood pressure is normal now, if you continue to eat the typical American diet, you will be at risk. Elevated blood pressure accounts for 62 percent of strokes and 49 percent of coronary heart disease. [3] Notably, the risk for heart attack and stroke begins climbing with systolic pressures (first number in the blood pressure reading) above 115 mm Hg -- considered "normal" by most standards.[4] Even if you eat an otherwise healthy diet, and your arteries are free of plaque, hypertension late in life damages the delicate blood vessels of the brain, increasing the risk of hemorrhagic stroke.
The American Heart Association, recognizing the significant risks of high blood pressure, has recently dropped their recommended maximum sodium intake from 2300 mg to 1500 mg.[5]
But did you know that salt has additional dangerous effects that are not related to blood pressure?
Cardiovascular disease.
In the 1990s, it was found that the relationship between salt intake and stroke mortality was stronger than the relationship between blood pressure and stroke mortality; this result suggested that salt may have deleterious effects on the cardiovascular system that are not related to blood pressure. [6] Further research determined that long-term excess dietary sodium promotes excessive cell growth leading to thickening of the vessel wall and altered production of structural proteins leading to arterial stiffening. [7-10]
In one recent study, higher sodium intake was associated with greater carotid artery intima-media thickness (IMT) -- an accurate predictor of future cardiovascular events -- in people without high blood pressure. Thickening indicates atherosclerotic plaque formation, and therefore increased risk of heart attack or stroke. [11] I use this test to assess cardiovascular risk and track patients' progress in my medical practice.
Dietary salt has also been associated with endothelial dysfunction (the inability of endothelial cells to properly regulate blood pressure), which is one of the initiating events of atherosclerosis. [12] In fact, endothelial function is suppressed within a mere 30 minutes following a high salt meal. [13]
Kidney disease.
Hypertension is an important risk factor for kidney disease, but dietary sodium has other damaging effects on the kidneys. High salt intake drives the production of oxygen radicals, leading to oxidative stress in kidney tissue. [10] In the Nurses' Health Study, high dietary sodium was associated with a decline in kidney function over an 11-year follow-up period. [14] In patients who already have kidney disease, high salt intake promotes fibrosis of kidney tissue, contributing to kidney injury. [15]
Osteoporosis.
High salt intake is a risk factor for osteoporosis because excess dietary sodium promotes urinary calcium loss, leading to calcium loss from bone and therefore decreased bone density. Daily sodium intakes characteristic of Americans have been associated with increased bone loss at the hip, and sodium restriction reduces markers of bone breakdown. [16] Even in the presence of a high calcium diet, high salt intake results in net calcium loss from bone. [17]
Although postmenopausal women are most vulnerable to these calcium losses [18], high salt intake in young girls may prevent the attainment of peak bone mass during puberty, putting these girls at risk for osteoporosis later in life. [10]
Ulcers & gastric cancer.
Salt is the strongest factor relating to stomach cancer -- sodium intake data from 24 different countries were significantly correlated to stomach cancer mortality rates. [19] Additional studies have found positive correlations between salt consumption and gastric cancer incidence. [20] A high salt diet increases growth of the ulcer-promoting bacteria H. pylori in the stomach, which is also a risk factor for gastric cancer.[10]
Asthma.
In asthma patients, high dietary sodium may increase severity of the disease. [10]
Avoid added salt!
Reducing dietary salt is not only important for those who already have elevated blood pressure -- limiting added salt is essential for all of us to remain in good health. It is also important to note that expensive and exotic sea salts are still salt. All salt originates from the sea -- it contains over 98 percent sodium chloride, and it is not health-promoting. Sea salts may contain small amounts of trace minerals, the amounts are insignificant compared to those in natural plant foods. A high-nutrient, vegetable-based diet with little or no added salt is ideal.
Salt also deadens the taste buds -- this means that when you avoid highly salted and processed foods, you will regain your ability to detect and enjoy the subtle flavors in natural foods and actually experience heightened pleasure from natural, unsalted foods.
Dr. Fuhrman is a best-selling author, nutritional researcher and board certified family physician specializing in nutritional medicine. Visit his informative website at DrFuhrman.com, and his blog at DiseaseProof.com.
References:
1.Jacobson, M.F. Salt: The Forgotten Killer. Center for Science in the Public Interest, 2005.
2.Bernstein, A.M. and W.C. Willett, Trends in 24-h urinary sodium excretion in the United States, 1957-2003: a systematic review. The American journal of clinical nutrition, 2010. 92(5): p. 1172-80.
3.He, F.J. and G.A. MacGregor, A comprehensive review on salt and health and current experience of worldwide salt reduction programmes. J Hum Hypertens, 2009. 23(6): p. 363-84.
4.Lewington, S., et al., Age-specific relevance of usual blood pressure to vascular mortality: a meta-analysis of individual data for one million adults in 61 prospective studies. Lancet, 2002. 360(9349): p. 1903-13.
5.Appel, L.J., et al., The Importance of Population-Wide Sodium Reduction as a Means to Prevent Cardiovascular Disease and Stroke: A Call to Action From the American Heart Association. Circulation, 2011.
6.Perry, I.J. and D.G. Beevers, Salt intake and stroke: a possible direct effect. J Hum Hypertens, 1992. 6(1): p. 23-5.
7.Simon, G., Experimental evidence for blood pressure-independent vascular effects of high sodium diet. Am J Hypertens, 2003. 16(12): p. 1074-8.
8.Sanders, P.W., Vascular consequences of dietary salt intake. Am J Physiol Renal Physiol, 2009. 297(2): p. F237-43.
9.Safar, M.E., et al., Pressure-independent contribution of sodium to large artery structure and function in hypertension. Cardiovasc Res, 2000. 46(2): p. 269-76.
10.de Wardener, H.E. and G.A. MacGregor, Harmful effects of dietary salt in addition to hypertension. Journal of human hypertension, 2002. 16(4): p. 213-23.
11.Lorenz, M.W., et al., Prediction of clinical cardiovascular events with carotid intima-media thickness: a systematic review and meta-analysis. Circulation, 2007. 115(4): p. 459-67.
12.Dickinson, K.M., J.B. Keogh, and P.M. Clifton, Effects of a low-salt diet on flow-mediated dilatation in humans. Am J Clin Nutr, 2009. 89(2): p. 485-90.
13.Dickinson, K.M., P.M. Clifton, and J.B. Keogh, Endothelial function is impaired after a high-salt meal in healthy subjects. The American journal of clinical nutrition, 2011.
14.Diets High In Sodium And Artificially Sweetened Soda Linked To Kidney Function Decline. ScienceDaily, 2009.
15.Jones-Burton, C., et al., An in-depth review of the evidence linking dietary salt intake and progression of chronic kidney disease. American journal of nephrology, 2006. 26(3): p. 268-75.
16.Devine, A., et al., A longitudinal study of the effect of sodium and calcium intakes on regional bone density in postmenopausal women. The American journal of clinical nutrition, 1995. 62(4): p. 740-5.
17.Teucher, B., et al., Sodium and bone health: impact of moderately high and low salt intakes on calcium metabolism in postmenopausal women. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research, 2008. 23(9): p. 1477-85.
18.Heaney, R.P., Role of dietary sodium in osteoporosis. Journal of the American College of Nutrition, 2006. 25(3 Suppl): p. 271S-276S.
19.Sonnenberg, A., Dietary salt and gastric ulcer. Gut, 1986. 27(10): p. 1138-42.
20.Tsugane, S. and S. Sasazuki, Diet and the risk of gastric cancer: review of epidemiological evidence. Gastric Cancer, 2007. 10(2): p. 75-83.