I was wondering the reason for this as well. Apparently one suspected cause is blood being shunted to the core to avoid excessive heat loss. This causes an increase in blood pressure and in response the kidneys pull more water out of the blood.
Source: Google and a handful of urology websites.
Iāve not had a problem with having to stop on 3-5 hour rides, however nobody has mentioned this so Iāll simply add that if you are looking for more control then search the Internet for āKegel for menā
Typed out some thoughts on this but either felt I was oversimplifying it to the point that someone would call me out or getting too deep into the weeds of the physiology.
Instead, here is a video that discusses urine production and relates things like cardiac output (increases with heart rate) and sodium.
Mine was good for 6 hours today but the pub stop 10miles from home burst the dam. Fortunately I was home when it did 
I asked the AI in the news
One reason why people need to pee more in the winter is because of the colder temperatures. Colder temperatures cause the body to reduce its production of a hormone called vasopressin, which helps balance the fluids in the body and helps with water retention. With less vasopressin, the body needs to expel more fluid and this can lead to an increased frequency of urination.
Have you (or anyone else) used one? Happy with the results?
I used one. Hard to say how accurate but for the money Iāll do it again and the results were sort of what I expected so, yeah. Pretty neat.
Silly question perhaps, but do you just add a little table salt to your drinking bottle? Does it dissolve in cold water?
Sodium Citrate is recommended and generally most things mix better in warmer water.
Should be measured based on how many mgās of sodium. For sodium citrate 1 tsp is roughly 1000mg. But for table salt, it would be half that.
Iām 57 years old and the frequency that I need to pee seems to be increasing as I age. I wonder if thereās more to it than adding more salt for aging athletes.
What is āWhy Iāll never sleep through the night againā?
There is, but sodium definitely helps.
train those kegels!
Iām 72 and have to pee 2 times in the night.
Extra salt does nothing to help.
Iām the heavy sweating type of person.
40F in the garage on trainer with fan on full blast and Iām dripping.
On rides here in Texas I got used to having to drink tons along with extra electrolytes. I use premade caps. They are easy. I do take them before the ride and during. If itās going to be 100 miler I start taking them 2 days before with extra water.
Now in winter, I still feel the need to drink a lot. In the cold I probably pee once an hour on the bike. On warm days the frequency goes away.
I know! I want to try it for sleep now too! Iām wondering how this will impact blood pressure over night though.
Salt causes more fluid to be released into the blood stream and stored in tissues. This raises blood pressure. Potassium works just the opposite. Too much or too little of either causes problems. Long term you need a balance.
What to do when all/most of the on-bike nutrition comes via drink mix? I drink about 3-4 90gr carb bottles on a 3-4 hour ride and often have to pee 2-3 times, often at a fixed distance (i.e. same route, is same pee location). Also increase the sodium in the bottles or switch to more gels/chews?
You are drinking more water than your body wants/needs. Have 1 bottle of concentrated mix and the other bottles water. This way you can regulate your water intake as needed and itās not tied to carb intake. Then just sip from your carb bottle every 15-20 mins spreading it across how many hours you ride. For 4+ hour rides on my MTB, smaller bottle then on my road bike, Iāll use 2 carb bottles and 2 clear and consume 1 concentrated carb bottle every 2 hours then swap.
Increasing sodium does help. It doesnāt fully solve, but it helps.