Saturday, June 26, 2010
After posting a brief note on facebook the other day i thought it time to expand on this topic. Seeing the number and variation of responses to my facebook post i realised there is a lot of information out there about low sodium levels. And when i did some investigation myself, i found there are plenty of dramatic stories, particularly in the athletics field, of deaths due to hyponatremia.
But firstly, the background, and the good news. I recently completed a 19-day water fast. I did not get blood tests prior to commencing the fast so there is no baseline on which to compare data. Seven days after the fast, a blood test was done. Two major anomalies were discovered that may or may not be inter-related.
Firstly, Sodium levels were 128 mmol/L (normal range is 135-145). Secondly Ferritin levels were 634 ug/L (normal range is 30-150). The focus of this post is low sodium, also known as hyponatremia. Will get to the elevated ferritin in a later post as more information comes to hand.
So what is hyponatremia? It is, put quite simply, an imbalance between the sodium and water levels in the blood. This can come about in three different ways[*]:
• hypervolemic hyponatremia - excess water dilutes the sodium concentration, causing low sodium levels. Hypervolemic hyponatremia is commonly the result of kidney failure, heart failure or liver failure.
• euvolemic hyponatremia - normal water levels are combined with low sodium levels. This condition is commonly due to chronic health conditions, cancer or certain medications.
• hypovolemic hyponatremia - water and sodium levels are both low. This can occur, for example, when exercising in the heat without replenishing your fluid electrolytes or with marked blood loss.
Hyponatremia is considered severe at a blood serum level of below 125. At this point an acute case of hyponatremia can cause seizures, coma or death.
Wikipedia points out that "Hyponatremia can ... affect athletes who consume too much fluid during endurance events, people who fast on juice or water for extended periods and people whose dietary sodium intake is chronically insufficient."
But what causes it? Depending on the type (see dot points above), a number of causes have been postulated. Of particular interest are the following:
• Chronic, severe vomiting or diarrhea. This causes the body to lose fluids and electrolytes, such as sodium.
• Dehydration. In dehydration, the body loses fluids and electrolytes.
• Diet. A low-sodium, high-water diet can disturb the proper balance between sodium and fluids in the blood. Excessive intake of diuretics, including beer or coffee, can have the same effect.
• Consuming excessive water during exercise (exertional hyponatremia). Because sodium is lost through sweat, drinking too much water during endurance activities, such as marathons and triathlons, can dilute the sodium content of blood.
Though my sodium intake is very low compared to the general population (i use no added salt whatsoever in food and this has been my practice for more than 10 years) i would not classify that as insufficient. My last blood test (June 2009) showed no sign of low sodium levels.
Having just completed a water fast, followed by more than 10 days of chronic diarrhea it is my guess that this has contributed to the low sodium levels. I would note that when the blood test was taken (seven days after breaking the fast), i had been experiencing diarrhea for only 2-3 days. Was i dehydrated? How could i be sure? That would depend on whether i was hypovolemic, or hypervolemic. the symptoms look the same.
So a bigger question might be why diarrhea after breaking a fast?
Now for the good news. Re-tested three weeks later, blood tests now show a sodium level of 137. Low, but within "normal" range. The diarrhea ceased after about 12 or so days. Though i started to consume more water, i also increased the amount of exercise. It is the middle of winter, so hardly likely to be losing water (and electrolytes) via excessive sweating.
And yes, there's even a facebook page dedicated to hyponatremia. Posted on this page is the story about the Kokoda Trail deaths. Read about a follow-up study here.