I’m a bit of a science geek. I love reading about running science. I haven’t done much running this past week because of a bad cold so I thought I’d try writing about an ultra-running science article that caught my eye. I’ve heard the lead author, Dr Martin Hoffman, talk at a Wilderness Medicine Conference and that’s partly why it caught my eye, plus like I said I’m a science geek and found the title interesting!
Is Sodium Supplementation Necessary to Avoid Dehydration During Prolonged Exercise in the Heat?
The use of salt tablets by ultra-runners is very common. But are they necessary in ultra- marathons? Is it dogma?
A recent study published in the Journal of Strength and Conditioning Research adds to the accumulating evidence saying supplemental salt tablets aren’t needed.
Here’s the pdf-Endurance-article
The setting for this study was the Western States Endurance Run (161 Km ultra-marathon)in 2014.
Many ultra-runners reading this will know the race and will probably have heard of the lead author Martin Hoffman who has published a lot of studies on ultra-endurance science.
The authors’ previous work showed that adequate hydration was maintained without taking in sodium supplements and by drinking to thirst. For this study they sought to add to that data. They also sought to examine the relationship between the quantity of sodium consumed in supplements and change in body weight.
The authors measured the body weights of participants before, during and after the race. Hydration status was determined using weight change from that immediately before the start of the race. If a runner had a 1% or greater weight gain then they were overhydrated. If they had a 4% or more weight loss then they were dehydrated. Anything in-between was normal hydration (“euhydration”)
The authors say previous work has shown the anticipated “normal” weight loss in an event like Western States is 4% (This 4% loss is loss from breakdown of muscle and liver glycogen and fat stores). Of note, this 4% weight loss maintains normal hydration.
After the race, the authors collected self-reported data from participants on how much supplemental sodium they took in during the race. This was then correlated with body weight change.
A summary of the data:
- There was a greater intake of sodium supplements in those who were overhydrated than those who were dehydrated.
- Those using sodium supplements never lost more than an average of 2.5% body weight.
- Those not using sodium supplements had a more appropriate weight loss ie closer to the 4% anticipated.
- 93% of runners used sodium supplements!
The authors concluded:
- “The use of sodium supplements tends to be associated with inadequate weight loss and it is not a determinant of hydration status.”
- “Sodium supplementation is not necessary to maintain proper hydration during prolonged continuous exercise in a hot environment.”
- “This work provides further support that appropriate hydration status can be maintained during prolonged endurance exercise under hot conditions without the use of sodium supplements and by drinking to thirst.”
I’ve never used salt supplements in my ultras. However, having read quite a lot on the subject I’m aware that there is some evidence that salt ingestion may improve performance. This improved performance may be through a centrally acting brain effect. Salt, fat and sugar are 3 addictive foodstuffs and that may be the link to the acute change in performance with salt.
You probably know Dr Tim Noakes is a well-known name when it comes to the subject of sodium and fluid intake in endurance sport. Check out the review of his book “Waterlogged” on irunfar. Dr Noakes certainly agrees that for the vast majority of people in the vast majority of ultra-marathons sodium supplementation is unnecessary outside of daily intake.
If I get to the end of my 100 miler in July – I sure hope I do! – I will be sitting down to a big plate of food with lots of addictive salt, fat and sugar!