Is there a way to make an educated guess of how much sodium is lost during hot racing situations? Also what are the side effects of excess sodium intake during a race?
This is a req for an average salt loss sweat rate. Some people are much higher. A good sign your higher is after a couple hour ride you helmet straps and jersey are crusted in salt.
Once you know your fluid intake under various conditions, then you can estimate your sodium requirements. Sodium intake is estimated proportionally to fluid intake, not to riding time. How much sodium you need depends on how much fluid (sweat and urine) you’re losing and also on the sodium concentration in the fluid you’ve lost. During exercise, urine has approximately the same sodium concentration as sweat. A liter of sweat contains, on average, 50 meq sodium which equals 1000 mg sodium/quart of sweat (see Table 2).
Example: You consume a 20 oz. water bottle of a sports drink. Since one quart equals 32 oz., you need 20/32 x 1000 = 625 mg sodium. The sports drink gives you 440 mg/quart, or 275 mg. To complement the fluid intake you still need about 350 mg sodium, which you can get from food or a salt capsule.
The volume of blood plasma increases by about 10% on the first day of hot weather riding, even if you are already fit. You need more sodium when you are acclimating to heat. For a 154 lb athlete, that extra plasma requires about 2.5 g salt (~ 1000 mg sodium) to be brought up to normal sodium concentration. Do this by increasing the ratio of salt capsules to fluid intake, by eating more salty snacks and/or adding more table salt to food.
Withholding sodium won’t “teach” your body to conserve sodium. The trigger for sodium conservation appears to be core temperature, not sodium concentration. You produce as much of the sodium-conserving hormones on your first day of heat acclimatization as on the last day; what changes is theorized to be the sensitivity of the kidneys and sweat glands to those hormones.
Competing in hot weather after you’ve trained in cool weather should be treated like the first few days of heat acclimatizing: increase your sodium intake.
Acclimatization decreases the sodium-in-sweat concentration. Studies of unfit subjects have shown as much as a 60% reduction of sodium-in-sweat as a consequence of acclimatization. So, you need somewhat less sodium when you are acclimatized to heat.
Now one thing to be said about the extra sodium need to acclimate. Unless you are a picky/healthy eater your diet probably has enough. The typical american diet is really high in salt.