Salt Sensitive…or not?

Slowing aging is partly about reducing the odds of sudden death. Stroke and heart attack are two of the leading causes of sudden death in the world, so I am pretty concerned about them. I figure any way I can reduce the chances of stroke or heart attack will improve my chances for living longer. High blood pressure greatly increases my chances of having a stroke or heat attack.

My blood pressure has been higher than it should be for several years now. My Thai and Sri Lankan doctors are not concerned because it is not in the hypertension range, and they tell me that my blood pressure is within the normal range for someone my age (134/84). But that is now considered high by doctors in the US, who have recently upgraded their recommended maximum blood pressure to 120/80 (if you are over this you are considered hypertensive; before you weren’t considered hypertensive unless your BP was 140/90). By this new definition I am definitely hypertensive.

I have tried a lot of things to keep my blood pressure low over the years without much success. I have tried losing weight; exercise; meditation; mostly following the Dietary Approaches to Stop Hypertension (DASH) diet; reducing stress; going for long walks; . The approaches that worked the best for me were losing weight and exercise. The DASH diet seemed to help a bit but not a lot. Other things did not have much, if any, impact. One thing I have not tried until now was to get my salt intake down under an average of 1,500 mg a day. While I have occasionally gotten my daily consumption below that, only very seldom have I managed to get my weekly average below 1,500 mg of sodium a day.

Sodium is a critical nutrient, and in prehistoric times it was hard for people to get enough of it. Most animals still have trouble, which is why salt licks are so popular with a lot of herbivores (carnivores probably get enough salt from the meat they eat). The theory goes that it tastes good to encourage us to find salty foods to assure we get enough in our diet. Unfortunately it is also a good preservative since salt inhibits bacteria, so most processed foods like canned food or lunch meats have a lot of salt in them.

Salt is made of up of a sodium atom (Na, which weights 33 grams per mole) and a chloride atom (which weighs 35 grams per mole). So a mole of salt is 58 grams, about 40% sodium by weight. When you put 100 mg (100 milligrams is about 1/33 of an ounce, or a pinch) of salt on your eggs, you will get almost 40 mg of sodium and around 60 mg of chlorine (which isn’t important to us here as it is usually easily excreted). This isn’t much, but when you look at how much sodium is in a cup of mashed potatoes you are eating about a gram of salt, or 600 mg of sodium. That is almost 25% of your recommended daily allowance (RDA) for sodium, or 40% of the DASH diet sodium goal! This makes it difficult to eat very much mashed potatoes without risking exceeding your RDA.

Nutrient levels in a person is based on flows. Inflows from food, air and water. Outflows through urine, feces, sweat air and surface loss (skin, hair and nails). For sodium the most significant loss is through urine and sweat. To have the right amount of sodium in your body your consumption needs to balance excretion. Your primary source for sodium is salt in your diet. You lose the most salt through your urine or your sweat, with insignificant amounts lost from breathing (the water vapor that leaves in your breath contains a small amount of salt) and in your feces. Loss through sweating is highly variable and depends on how much water you sweat. Because everyone has a different skin area, has different temperatures at which they sweat at and probably a lot of other factors it can become very difficult to calculate. But if you weigh yourself before and after a hard sweaty exercise you can get an idea. Your sweat has about 500 mg of sodium per pound of sweat. I estimate when I am sweating hard I loose a bit over 2 pounds of sweat per hour (this is how much weight I loose in an hour of hard exercise). So when I am sweating hard I estimate I lose about 1200 mg of sodium salt an hour.

The DASH (Dietary Approaches to Stop Hypertension) diet recommends consuming less than 1,500 mg of sodium a day. Since salt is made up of sodium and chloride, 1,000 mg of salt contains 396 mg of sodium. To get below 1,500 mg of sodium I have to eat less than 3,800 mg (or less than 4 g) of salt a day. This seems like a ton of salt to me. But when you start eating processed food this isn’t very much. A 3 ounce serving of Canadian bacon, for instance has 3 grams of salt! Since I log all my food I know my sodium consumption is a lot higher than the diet recommends, so I have always tried to keep my diet low in salt by not putting salt on any food except. Unfortunately, this is not enough; my normal foods I eat already has too much sodium. Bread has a lot of salt, as do meats and most processed foods. Not just a little either; just 1 slice of bread has 10% of your DASH diet sodium for the day, and 3 ounces of smoked salmon has nearly half, a can of chicken soup 2/3!

What happens if you aren’t getting enough? Sodium is needed by your body for proper neuron function, ion balance in your cells and many other things. If you are low on sodium one symptom I came across as a sign you are low on sodium was muscle cramping…but that is caused by many other things too. With our modern diet the odds of being low on salt are tiny. Sodium is key to neuron signaling, so another symptom is nerve related issues.

Too much sodium can lead to a number of problems. It can cause high blood pressure, it is hard on your kidneys and can cause your hands and/or feet to swell. My big issue is high blood pressure so while I am on this cruise around the world I thought I would try to reduce my salt consumption to see if my blood pressure responded. My kidney tests have always been good, and I drink plenty of water, so I think if I have an issue with sodium it is my blood pressure.

Even though I only put salt on eggs (and seldom have eggs), my diet seems to perpetually have more salt than recommended. More recently with all the good food on the cruise I am on right now it has been occasionally getting up over 4,000 mg. My daily average over the last 3 years has been around 3,400–see graph–or almost 1,000 mg more than US Na over 3 yearsFDA’s recommendation of 2,300 mg [1]. I have been thinking about cutting out salt to get it below the DASH limit for some time so when someone blogged about not being sensitive to salt so I wrote and asked how they knew. They replied that they just reduced their salt for a week, then increased their salt for a week all the while recording their blood pressure. If there was a change then they were sensitive, if there were no change then they weren’t. My sodium intake is definitely on the high side. The question is whether it impacts my health.

A couple of weeks ago I decided to see if I were salt sensitive. It was nearing the end of May and I was up for my monthly 3 day fast where I don’t eat anything for 72 hours, so I figured that would be a good time to start (perhaps…when you lose fat you may gain some salt from the fat, though I am hoping the normal salt loss was greater). I also decided to increased my water consumption to help flush salt out of my system.

After my fast I was more careful about what I ate, keeping things that have salt to a minimum and logging all my foods (which I do anyhow) to monitor salt intake. Thus by 7 days into my trial my average daily sodium intake had fallen below the DASH recommendation of 1,500 mg a day. This is the log of my salt consumption, blood pressure and other notes I recorded:

5/30 0 mg Na (fasting). Blood pressure 134/84.
Drank 1,230 g of water today. I set up a spreadsheet to track my weekly average salt consumption. To set it up and give me a starting point I went back a week, so my starting level was an average of 3,350 mg/day for the week before I started my trial. I am not sure what the half-life of salt is in a person, but that is really the number I should be using, but this is probably a really good approximation and I use it for all my nutrients.

5/31 0 mg Na (fasting). Blood pressure 134/88.
I drank 585 g of water today. My blood pressure is usually up a bit when I fast, so this was not a surprise.

6/1 1,361 mg Na. Blood pressure 138/91.
I drank 1,294 g of water today. After 3 days (72 hours since my last dinner Wednesday evening) of fasting I had dinner. I was not very careful of what I ate so in this meal alone I had 1,361 mg. The thing I ate with the most salt at 310 mg of sodium for half a cup was mashed potatoes, though the thing with the most per gram consumed was the salad dressing. The things with the least salt were the raw fruits and vegetables.

6/2 1,140 mg Na. Blood pressure 132/81.
I was really careful to avoid foods with salt today, and as a result actually ate less all day than I’d eaten the evening before. The thing with the most salt were the pancakes, with almost 400 mg of sodium for an 8″ pancake. Again the foods with the least salt was the raw fruits and vegetables. Pears actually had 0 salt.

6/3 2,508 mg Na. Blood pressure 127/86.
I missed my goal today, eating too much salt, mostly through eating too much food (2487 kcal). The worst things were the oatmeal provided 330 mg; 2 T ranch salad dressing had 200; the bread that I ate (2 slices plus a dinner roll) added up to 490. The best were, again, fruits and vegetables with 0 mg in the orange I ate. However even though I fell off my goal I was off the ship (I am on a cruise ship going around the world as I do this test) and I spent 2.5 hours just pouring off sweat because I was walking around in 97 F (36 C) degree heat and high humidity, so I hope that I managed too offset some of my high salt consumption. However this is the first day my 7 day average fell below 1,500 mg (my goal), at 1,377 mg (see graph).

6/4 2,073 mg Na. Blood pressure 123/84.
Today I tried to be careful, but did not manage to keep it down where it should be. In spite of this my average salt consumption stayed below my goal of 1,500 mg (mostly from fasting for 3 days).

6/5 2,457 mg Na. Blood pressure 134/85.
Today I really failed to keep my consumption of salt down, but the ship was in Dubai today, and again I spent a certain amount of time too hot and sweating, though probably not enough to offset my higher salt consumption. Even so I managed to keep it under the RDA, if not below the DASH diet recommendations.

6/6 0 mg Na. Blood pressure 137/88.
Thursdays are a fast day for me, so my salt consumption was 0.

6/7 1,426 mg Na. Blood pressure 133/86.

At an initial evaluation, 3 days after my average salt consumption fell below 1,500 I see that my 7 day average systolic blood pressure is down about 2 points, from 134 to 132. However, my average diastolic is up about 1.5 points! From about 84.5 to 86. So, I decided to extend the test out for a few more days to evaluate if this was a real reaction or just normal variation, since my average intake has only been below the DASH diet recommendations for 3 days; a week would be better. Then comes the other half of the test, where I try to eat a lot of salt.

6/8 658 mg Na. Blood pressure variable, probably around 129/79.
Because I am traveling and I wanted to keep as much of my weight allowance as possible for books (I brought a lot of books about aging with me for this cruise) so I brought my wrist blood pressure cuff instead of my arm one. Unfortunately this sometimes causes problems like today when I just could not manage to get a good reading:
Systolic Diastolic Pulse
119 66 60
131 83 54
138 77 50
119 82 59
I finally sort of fudged the numbers around a bit and settled on a blood pressure of 129/79. No idea if this is correct or not but it is the best I can do. I am hoping the 9th I will get a better reading so I can know if this drop in pressure is real or not. I had planned to stop the trial at this point, but because there is a sudden sharp drop (assuming these numbers are correct) I shall continue this trial until at least Sunday.

My 7 day average blood pressure before today was 132/86. So 129 is a drop of 3 points on the systolic and 79 is a drop of 7 points on the diastolic. If the numbers continue to slide, or even stay this low, I will consider salt a successful ‘biohack’ for me.

Because this is such a sharp drop I decided to keep my salt consumption down for a while longer to see if I got a further response. Because I measure my blood pressure in the morning (before eating) the low salt today has no bearing on today’s blood pressure reading.

salt consumed over 1st half of experiment

6/9 1,369 mg Na. Blood pressure was variable again, estimated at 127/80.
My 3 day fast is starting to fall off the weekly averages, and because of that my average salt consumption for the week ending yesterday was creeping up. By reducing my consumption of salt yesterday I managed to push the weekly average down below 1,500 to 1,466.

Because sweating is a means to losing sodium I decided to start logging how long I spend sweating each day. While this is usually based on exercise it can also result from being too hot. We spent 2.5 hours walking around in high heat (95 F, 35 C) and humidity while were in Muscat, Oman on June 3. So I logged 150 minutes of sweating hard that day. 2 days later in Dubai it was also really hot, but not as humid and we spent the majority of the 6 hours we were ashore inside air conditioned buildings so I only count 20 minutes of sweating. The other days I referred to my exercise log to determine how much time I spent sweating.

ave BP


I am trying to post one blog a week, but this experiment has a long way to go, so I am going to publish it in 2 parts. Part 2 will come along in about a month, after I have time to finish this experiment! Since my blood pressure seems to be responding to lower salt I will probably continue a low salt diet for quite a bit longer (2 weeks?) to assure it is not a measuring artifact. When I feel my blood pressure has either leveled off at a lower value or it goes back to the original and stays there for awhile I will do the 2nd half of the experiment: increasing my salt intake. See if my blood pressure goes up in response.

References & more reading

Sodium consumption
[1] US Food & Drug Association salt recommendations
[2] CDC

Click to access sodium_dietary_guidelines.pdf

Dash diet
[3] Great explanation from the Mayo Clinic about the DASH diet
[4] Dash Diet [this is mostly just an ad to buy the book]
[5] DASH eating plan from the U.S. National Institute of Health
[6] Ideas for starting the DASH diet from WebMD
[7] US news article about the DASH diet

Salt regulation
[8] National Institure of Health
[9] Journal article about how high salt affects sodium output of the kidneys
[10] Sodium loss in sweat
[11] Sodium lack from Mayo Clinic
[12] Sweat produced per hour
[13] Scientific article about sweating

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