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Na = Not Appropriate: Salt, CVD, and CVA
Abstract & Commentary
By Russell H. Greenfield, MD, Editor
Synopsis: Dietary salt intake around the world is very high, especially in certain regions, and this finding is associated with higher rates of stroke (CVA) and cardiovascular disease (CVD) in those areas. Salt is both readily visible on dinner tables and also hidden among a mass of ingredients used in prepared foods and present on food labels. The data provided here strongly suggest that a modest decrease in salt intake translates into a markedly effective preventive strategy against vascular disease, and can be taken to imply that assessment of salt intake be considered yet another vital sign, one that can be altered in a positive way through relatively simple means education.
Source: Strazzullo P, et al. Salt intake, stroke, and cardiovascular disease: A meta-analysis of prospective studies. BMJ 2009;339:b4567.
The authors of this systematic review and meta-analysis investigated the documented relationship between salt intake and CVA or total CVD outcome in adults. Culling data from Medline, Embase, AMED, CINAHL, Psychinfo, and the Cochrane Library, multiple analyses were performed on the prospective studies identified (13 studies reflecting data on 19 independent cohort samples with more than 175,000 subjects), including measures of heterogeneity and evidence of publication bias (regarding the latter, none was found). To be included in the analysis, studies had to not only be prospective in nature, but also assess salt intake at baseline and follow subjects for at least 3 years.
As might be expected, it is difficult to accurately assess a given population's total salt intake. Some studies employed 24-hour dietary recall, others used a food-frequency questionnaire, while a small number measured 24-hour urine excretion. Follow-up in the various studies ranged from 3.5 to 19 years. In light of the variance in the studies, the researchers concede they likely underestimated total daily salt intake among the subjects. This makes their findings all the more sobering.
They found that the higher the salt intake, the greater the pooled risk for CVA (relative risk [RR], 1.23) and CVD (RR, 1.14). The longer the period of follow-up, the greater the risk of CVA (but not CVD) associated with high salt intake was.
The authors conclude that high salt intake is associated with a significantly increased risk of CVA and total cardiovascular events. High salt intake, a readily modifiable risk factor, translates into the loss of millions of lives worldwide due to vascular disease.
Practitioners have long advised their healthy patients to minimize salt intake in the hope of stemming the tide of increasing rates of hypertension, and among those with existing CVD to help prevent worsening of their clinical conditions. After all, nearly half of all CVAs and acute coronary events are believed to be secondary to hypertension. Standard recommendations include avoidance of added salt, looking for low-salt options at restaurants, and choosing low-salt foods at the market. Even so, after all the years of caution, it is the sheer amount of sodium ingested daily by people around the world as reported here that is mind-boggling, as well as the size of the estimated positive health impact that a moderate diminution in salt intake could have.
The authors suggest that taking all sources of salt into account, most people ingest about 2 teaspoons (10 g of salt, or almost 5 g of sodium) a day. They convincingly show that the higher the salt intake of a given population of people, the higher the rates of CVA and heart disease. They also suggest that cutting the average daily salt intake by half could prevent a significant amount of vascular disease, cutting the risk of stroke by 23% and heart disease by 17%. These are extraordinary numbers.
Generally, daily sodium intake should not exceed 2 g per day (some authorities recommend no more than 1,200-1,500 mg/d). Keeping in mind that one teaspoon (5 g) of salt contains approximately 2.4 g of sodium, it's plain to see how easily sodium intake can exceed recommended levels. Some people continue to reach for the salt shaker, but many simply don't recognize how salt-laden restaurant-variety and processed food can be, and even more have no idea how to read a food label. In addition, the traditional menu of some cultures emphasizes salt (think Chinese food).
Prevention, of course, works best, yet most people still believe that they are destined to develop vascular disease. It's simply not true, as numerous studies show that dietary and lifestyle factors trump genetics when it comes to health matters. Re-emphasizing the importance of healthy food choices, educating our patients (including children) on how to properly read food labels, and providing a sense that we can, in large part, be masters of our future health may go a long way toward keeping our patients well for years to come. Thus, nutritional guidance, in this case regarding safe levels of salt intake from all available sources, becomes a mandatory and cost-effective part of the compact between practitioner and patient.