Dietary Sodium & Diabetes- “You can go with this or you can go with that…”
My Personal Journey with Dietary Sodium
My boss is a really smart endocrinologist who has to be in the 99th percentile of MDs in terms of his nutrition knowledge. He reads the literature and understands it well. Accordingly, I was a little concerned the other day when he asked me what we are telling our patients about dietary sodium. I responded to his question that according to the 2010 Dietary Guidelines for Americans, we are telling our patients with diabetes to limit their sodium to 1500 mg/day. He responded to me that I might want to take a look at the literature because there have been some recent studies published that indicate that people with lower intakes of dietary sodium seem to have increased mortality when compared to individuals with higher intakes of sodium.
In part, my boss was yanking my chain because he knows that I am very passionate in sharing my opinion that as a population we eat too much sodium. Just like an annoying friend or relative who has “found religion” in the form of a new diet, supplement, or workout regimen, eight years ago I jumped on the low sodium bandwagon when I learned at an annual physical that my blood pressure was 142/72. At the time my doctor started to outline the prospective BP medications that could be used to treat my hypertension.
As a registered dietitian who doles out nutrition advice for a living, I asked my PCP for some time to work on this with some lifestyle changes before starting medication. Being very familiar with the results from the Dietary Approaches to Hypertension Sodium study (DASH Sodium); I proceeded to rid my diet of excess sodium and increased my intake of fruits and vegetables to 9 servings per day.
Boosting my intake of fruits and vegetables was not too tall of a task. Cutting my sodium was another story. I basically needed an “intervention”as I used to drink a quart of Gatorade everyday at lunch, top everything but my ice cream with peperoncini hot peppers, and devour multiple boxes of Cheez-It crackers on a weekly basis. It was hard, but I kicked my sodium habit and got my intake down to about 1500 mg per day. Today my BP consistently runs in the low 120s over 70, and I have turned a couple of my hypertensive buddies on to the eating pattern, and they in turn have lowered their BPs as well.
So, what’s good for the goose is good for the gander, right? Well, in my opinion, for the general population probably; for the population with diabetes, maybe yes, or maybe no. Much to my chagrin there is literature out there that seems to fly in the face of conventional wisdom relative to dietary sodium intake.
The Case for Reducing Dietary Sodium Intake across Populations
I will start with what is known and pretty well accepted when one looks at general populations and sodium intake:
- The lifetime probability of developing HTN in the US approaches 90%.
- Across populations, the level of BP, the incremental rise in BP with age, and prevalence of HTN are directly related to Na intake.
- Populations with average daily Na intakes less than 1265 mg have low blood pressure and little or no increase in blood pressure with age.
- Excess dietary Na, independent of its effect on BP has other harmful CV effects including: being an independent predictor of left ventricular mass, increasing platelet reactivity, impacting arterial compliance, and contributing to aortic stiffness.
- In Finland a successful campaign to decrease the ratio of dietary Na to K was initiated in 1972. This campaign is associated with an average population decrease in DBP of 10 mm Hg, with a corresponding decrease in deaths from stroke and ischemic heart disease of 60% among 30 to 59-year-old men and women.
- In the US, secular trends show a 55% increase in Na intake since the early 1970's to 2000, as well as a corresponding increase in age-adjusted HTN of 50%.
- In 2005 the National Academy of Sciences established the following daily dietary Na guidelines: 1500 mg for 9 to 50-year-olds ; 1300 mg for 51 to 70-year-olds; and 1200 mg for people > age 71.
- Although MD's can and should educate pts about reducing Na intake, even highly motivated individuals will find it difficult because 80% of Na intake is derived from salt added by food processors and restaurants.
The Case against Making Universal Dietary Sodium Recommendations
Now for some interesting results from studies related to sodium intake and co-morbidity risk in people with diabetes:
- Any restriction in dietary sodium intake is associated with activation of the sympathetic nervous system and the rennin-angiotensin-aldosterone system, as well as increased LDL cholesterol.
- Some studies indicate that salt restriction reduces insulin sensitivity in patients with type 2 diabetes.
- A recently published longitudinal study in Finland showed that although blood pressure levels were higher in individuals with high sodium intake, individuals with the highest daily urinary sodium excretion, as well as the lowest excretion had reduced survival rates. Additionally, individuals with the lowest sodium excretion had the highest incidence of ESRD.
So what’s a Clinician to Do?
OK, so maybe a universal sodium restriction is not warranted for the entire population. Just when you think you have your arms around a topic, a plethora of confounding information shows up. Ugg!
I’ll finish with another personal story. My first professional outpatient job was as a renal dietitian at a hemodialysis center when I was in graduate school. Although HD is a tough road to hoe for everyone involved with it, I really enjoyed my work there because I had a chance to see the patients on a regular basis and get to know them. What was striking to me about my patients was that hardly anyone had straight forward kidney disease. What almost all of the patients had in common was a long history of diabetes and/or hypertension that appeared to have been poorly controlled over an extended period of time.
Moving forward I will humbly set down off of my sodium soapbox, and do my best to evaluate each patient’s situation individually. However, it is going to take a few more well designed and well executed studies to convince me that paying careful attention to sodium intake is not in most of my patients’ best interest.
References
Appel, LJ, et al. Compelling evidence for public health action to reduce salt intake. NEJM 2010, 362 (7): 650-652.
Dickenson, B D, et al. Reducing the population burden of cardiovascular disease by reducing sodium intake: a report of the council on science and public health. Arch Int Med 2007, 167 (14): 1460-1468.
Grassi, G., et al. Short and long-term neuroadrenergic effects of modulate dietary sodium restriction in essential hypertension. Circulation 2002, 106: 1957-1961.
Graudal, N. A., et al. Effects of sodium restriction on blood pressure, rennin, aldosterone, catecholamines, cholesterols, and triglyceride: a meta-analysis. JAMA 1998: 279: 1383-1391.
Havas, S., et al. The urgent need to reduce sodium consumption. JAMA 2007, 298 (12); 1439-1441.
Petrie, J. R., et al. Dietary sodium restriction impairs insulin sensitivity in noninsulin-dependent diabetes mellitus. J Clin Endocrinol Metab, 1998, 83: 1552-1557.
Svetkey, L. P., et al. The DASH diet, sodium intake and blood pressure trial (DASH-Sodium). Journal of the American Dietetic Association, 1999, 99 (8): S96-S104.
Thomas, M. C., et al. The association between dietary sodium intake, ESRD, and all-cause mortality in patient with type 1 diabetes. Diabetes Care 2011; 34: 861-866.
United States Department of Agriculture & US Department of Health & Human Services. Dietary Guidelines for Americans, 2010.