I've see races that offer runners salt packets right before the gun and I’ve read about the performance benefits of dosing up on baking soda in days before a race.
I don’t know if it was the baking soda, heat or direct sun at the most recent Chicago Marathon but I felt REALLY thirsty. I also wonder if I was drinking too much at the water stations.
What is your suggestion on how to best utilize sodium (in training or before a race) and how to prevent hydration issues?
There are a few races that hand out salt packets at the start of the race with the intention of raising sodium levels and preventing exertional hyponatremia. This is not an evidence-based strategy and is probably misguided. Nearly all hyponatremia associated with marathon races is a result of ingesting too much free water with a temporary abnormal water clearance (inappropriate ADH secretion). Drinking to thirst or knowing your sweat rate and replacing below that level are more appropriate preventive measures.
Using bicarbonate as a performance enhancing substance has been studied at short distances, but there is no data to support using baking soda for the marathon or other longer duration activities. This will not help your hydration profile in long distance running nor will it decrease your risk of cramping. Lactic acid will build within the exercising muscle as a waste product of glucose metabolism and is not related to bicarb ingestion for marathon running.
It did get warm on race day in Chicago this year. Nothing to rival the 2007 race, but warm enough that you probably felt it; in part because you had lost some of the heat acclimatization that you built up during the summer months. You probably felt thirsty because you lost enough body water through sweating and evaporation to trigger your thirst mechanism. I am not sure if the baking soda had anything to do with your thirst during the race.
My suggestion for sodium is to eat your normal diet. If you lose a lot of salt in your sweat during workouts or races (your clothes and skin are caked with salt), you should add a little extra table salt to your food or eat salty foods. Most runners decrease their sweat salt losses as they train and maintain very normal body sodium levels during races and workouts. If you are having trouble with your hydration, I would suggest you weigh yourself before and after workouts over a period of weeks to see how much you lose per hour at your usual pace. That would be an estimate of your sweat rate and if you replace about a pint for every pound, you will stay well hydrated. If you feel the water sloshing around in your stomach, stop taking fluids until that sensation is cleared. A simpler strategy for slower runners is to drink when you feel thirsty; although this may leave you a tad dehydrated, you will not get overhydrated.
Hope this helps.