People with high blood pressure are usually advised to lower their sodium intake. Can you instead excercise more to sweat off the sodium, or would the sodium loss be negligible compared to what you can accomplish with your diet? How many grams of salt do you lose if you, say, ride a stationary bike for half an hour? (I know it depends on numerous parameters, but I’m just looking for order of magnitude answer here)
Also, we are sweating constantly whether the skin is wet with sweat or not. Is sodium being secreted in that case as well? Or are the electrolytes staying in the cells and water evaporating directly through the membranes?
Hmm. Exercising to help with high blood pressure? Gee, sounds like a good idea. Not necessarily for the sodium loss, but because it’s the healthy thing to do.
I don’t know much about actual sodium loss, but I can tell you than when I run for extended periods of time (say an hour and a half), I have lots of salt residue on my skin (face mostly). I rarely have much residue when I run for less than an hour, so I suspect 30 minutes on a bike won’t get you much. Unless you’re pedalling like the dickens. But YMMV probably.
As for sweating, you can be “sweating” but not realize it, depending on your environment. In dry climates, you’ll sweat, but it evaporates so fast you may not even know it. When it’s humid, you feel like you sweat a lot. But really, it’s just not evaporating, and the water is staying on your skin.
All in all, I’d advise moderately reducing sodium, as well as exercising. That’s probably the healthier way to do things. But, as usual, IANAD.
If you want to reduce sodium levels through exercise, you’ll have to run a marathon. Despite what Gatorade et al tell you, you don’t start to get significant mineral depletion until you’ve been involved in aerobic exercise for about an hour and a half.
Now I’m not saying you shouldn’t exercise, just that it’s not a practical way to control sodium levels. Regular exercise on it’s own will help with high blood pressure, but you will have to reduce sodium intake in your diet.