Monday, September 8, 2008

Water - how much do you need?

I've had posts in the past which have thought about water. There is an oft repeated prescription that we need 8 glasses a day, a prescription that has been shown to be a myth . Drinking too much can actually be dangerous. The basic idea I think is to drink according to thirst - not an earth-shattering idea but an important one.

Be that as it may, it is still important to drink. Way back I posted a study which said that not having enough water in your system limits strength, power and high-intensity endurance.

Here is another study which says the same sort of thing and more:

If you don't have enough water in your system you are likely to have

  • more stress hormones - (cortisol and norepinephrine)
  • less testosterone
  • altered carbohydrate and lipid metabolism

The implication seems to be that if you want to promote muscle growth and minimise muscle breakdown, then you need to be adequately hydrated. I'd need to read the whole paper to get more, but this is certainly interesting stuff.

Effect of hydration state on resistance exercise-induced endocrine markers of anabolism, catabolism, and metabolism

Hypohydration (decreased total body water) exacerbates the catabolic hormonal response to endurance exercise with unclear effects on anabolic hormones. Limited research exists that evaluates the effect of hypohydration on endocrine responses to resistance exercise; this work merits attention as the acute postexercise hormonal environment potently modulates resistance training adaptations. The purpose of this study was to examine the effect of hydration state on the endocrine and metabolic responses to resistance exercise. Seven healthy resistance-trained men (age = 23 ± 4 yr, body mass = 87.8 ± 6.8 kg, body fat = 11.5 ± 5.2%) completed three identical resistance exercise bouts in different hydration states: euhydrated (EU), hypohydrated by 2.5% body mass (HY25), and hypohydrated by 5.0% body mass (HY50). Investigators manipulated hydration status via controlled water deprivation and exercise-heat stress. Cortisol, epinephrine, norepinephrine, testosterone, growth hormone, insulin-like growth factor-I, insulin, glucose, lactate, glycerol, and free fatty acids were measured during euhydrated rest, immediately preceding resistance exercise, immediately postexercise, and during 60 min of recovery. Body mass decreased 0.2 ± 0.4, 2.4 ± 0.4, and 4.8 ± 0.4% during EU, HY25, and HY50, respectively, supported by humoral and urinary changes that clearly indicated subjects achieved three distinct hydration states. Hypohydration significantly 1) increased circulating concentrations of cortisol and norepinephrine, 2) attenuated the testosterone response to exercise, and 3) altered carbohydrate and lipid metabolism. These results suggest that hypohydration can modify the hormonal and metabolic response to resistance exercise, influencing the postexercise circulatory milieu.


Methuselah said...

Hi - thanks for this article. The links to your other posts and external sites helped me fill in some gaps on this subject.

I tend to drink beyond my thirst on the basis that I'd rather be safe than sorry, and alsmost never get to the point where I am thirsty. It seems that although there is no evidence that we need 8 glasses per day, equally there is no evidence that 8 glasses, per se, is too much. My impression from your posts and the studies is that there is evidence for harm in excessive consumption, but that 8 glasses would probably not come into the category of 'excessive consumption'...would you agree?

Pay Now Live Later

Chris said...

I don't think 8 glasses a day will do harm, but it isn't convenient or necessary. Sometimes it becomes just another thing to stress over. Plus it adds more toilet visits. So yeah, no problem, but not necessary.

Janer said...

Hi Chris - thanks for your blog. It's a great resource. I have access to the PDF of this article but not sure how to get it to you ...

Chris said...

hi Janer

thanks for the offer, but someone has already sent it.

you can get me by email: chris at forwards things....