The first day I tried to measure my salt consumption was one of the hottest we have had this summer in St. Louis with the thermometer reaching the high 90s and the heat index well over 100. In the midst of this heat I rode my bike to my local gym, worked out on the elliptical for about 35 minutes then rode home. Although the distance i rode was not far (maybe 3 miles) I was sweating profusely.
This profuse sweating was not the norm for me but it clearly was changing my salt “balance” for the day. The optimal amount of salt to consume may be controversial but clearly the more you sweat the more salt you should consume to replace the lost sodium.
Even the AHA , which continues to stand by its ultra low 1.5 gram per day salt limit for everyone recognizes this factor and states
“The recommendation for less than 1500 mg/day does not apply to people who lose large amounts of sodium in sweat, such as competitive athletes and workers exposed to extreme heat stress (for example, foundry workers and fire fighters)”
I was back on my elliptical today (after a bike ride that resulted in no sweating) and watched the men playing the round of 16 in The US Open Tennis Tournament on the large TV screens conveniently placed to entertain me. Temperatures have been unusually high In NYC this week and the players have been suffering as a result. The men play best of 5 sets and matches routinely last longer than 3 hours played in the heat of the day with full sun exposure.
Scientists have studied professional tennis players and measured their sweat loss to be as high as 2.5 L/ hour while playing singles in hot circumstances. A liter of sweat contains around 920 mg of sodium.
That means these guys are losing 2.3 grams of sodium per hour of tennis played! This happens to be one teaspoon of salt and equal to the more moderate limit on sodium consumption (compared to the AHA) of the USDA. Clearly, consumption of salt on the order of 8 grams/ day would be needed in these circumstances to maintain salt balance and acceptable sodium levels in the blood.
How much are more normal individuals losing daily and how much does that vary depending on activity, ambient temperature and humidity?
The simple answer has to be that no authority knows the amount of salt each individual loses daily. Sweating and salt loss vary widely between individuals and over time in the same individuals.
It is common for my patients to note that during the summer months their blood pressure drops when they spend time gardening or if they have a job that requires heavy exertion in hot conditions. Often a downward adjustment in blood pressure medications is needed to account for this (especially if a diuretic is one of their BP drugs).
These variations in salt loss in the context of large variations in cardiovascular physiology and blood pressure regulation between individuals is further support for abandoning the ultra-low salt limits suggested by the AHA and the USDA.
Moderation may not be best for all things in diet (processed foods and added sugar come to mind) but for salt consumption moderation appears best.