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Beer and rehydration after sport and exercise
Ron Maughan
St Andrews University
THE 8TH EUROPEAN BEER AND HEALTH SYMPOSIUM
Recovery after exercise
Exercise causes:
Why is hydration important?
Dehydration, if sufficiently severe, can cause:
Sweat loss
Effective recovery requires replacement of losses Reduced exercise performance
Reduced blood volume
Increased heart rate
Reduced skin & muscle blood flow
Impaired thermoregulation Increased perception of effort
Headache, nausea, insomnia
Impaired mental function
Increased risk of heat illness
Symptomatic responses
Effects of fluid restriction A number of subjective responses were measured by questionnaire
Shirreffs et al, 2004
pm
0
am
pm
am
90
13
24
37
80
70
60
-1
50
Thirst
Change in body mass (%)
In one trial, fluid intake was restricted for 36 h and normal drinking was allowed in the other trial
0
-2
40
30
20
Fluid restriction
Control
10
0
-3
-3
-4
-5
-6
-7
pm
am
13
24
37
24
37
80
0
-2
am
90
Fluid restriction caused a loss of 2.7% of body mass in 36 hours
-1
pm
0
1
Change in plasma volume (%)
To assess some of the effects of hydration on mood and brain function, 15 healthy adults participated in 2 trials: 0
13
24
70
37
Mouth dryness
Depletion of glycogen (carbohydrate) stores 60
50
40
30
20
10
0
0
13
1
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Symptomatic responses
75
Ability to concentrate
65
Alertness
Driver error accounts for about 68% of all vehicle crashes in the UK (Department of Transport, 2011)
80
70
60
55
50
45
Fluid restriction
Control
40
35
70
60
50
40
30
20
30
0
13
24
37
pm
am
pm
am
0
13
24
37
75
45
70
65
40
60
55
30
50
45
40
35
Driver fatigue causes up to 20% of accidents on monotonous roads (e.g. motorways and A roads)
These accidents are 3 times more likely to be fatal
35
Headache
Tiredness
Driver Error and Road Accidents
25
20
15
10
5
30
0
0
13
pm
am
24
37
pm
am
0
13
24
37
Hydration and Driving Errors
60
Number of errors
50
HYD
FR
40
Water and electrolyte losses in athletes
* P < 0.05
*
*
*
30‐60
60‐90
90‐120
30
20
10
0
0‐30
Effects of a short period of fluid restriction, on performance during a 120 minute monotonous driving task. Watson et al Physiol Behav
2015, 147, 313‐318
Sodium
50.816.5
Potassium
4.81.6
Calcium
1.30.9
Magnesium
0.50.5
Chloride
46.613.1
Baseline measures:
Sweat electrolyte content (mmol/l) [mean  SD]
Shirreffs & Maughan, 1997
Post‐exercise rehydration protocol
Dehydration measures
Blood, urine samples
30‐90 min rehydration period
Performance test
Sweat rates can reach 2‐3 l/h
Recovery of fluid and electrolyte balance after exercise
blood samples, urine samples, body mass etc
Water and electrolyte losses
4 ‐ 6 hour recovery period
20‐90min
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Volume and Composition (1)
Urine excretion during recovery
Interaction of volume of fluid consumed and sodium concentration on the efficacy of rehydration after sweat loss of 2% of body mass
Two subject groups:
Low (23 mmol/l) sodium
High (61 mmol/l) sodium
Four Volume trials:
50% of weight loss
100% of weight loss
150% of weight loss
200% of weight loss
Shirreffs et al, 1996
Whole body fluid balance status
50%
Unless sufficient volume is consumed after dehydration, the body remains in net negative fluid balance

100% 
150%
CONCLUSION

If the electrolyte (sodium) content of drinks is low, positive fluid balance is not maintained, even when the volume consumed is large
200%
Positive fluid balance is achieved when both volume and sodium content of drinks are high. It is probably necessary to drink about 1.5 litres for each litre of sweat loss
Shirreffs et al Med Sci Sports Ex.1996; 28: 1260‐1271
Shirreffs et al, 1996
Alcohol and Rehydration
Alcohol has a diuretic action, stimulating urine formation by suppression of vasopressin (ADH) secretion
It was estimated by Eggleton (1942) that ingestion of 1 gram of alcohol increases urine output by 10 ml
Eggleton (1942) also showed that small amounts of alcohol did not impair rehydration in subjects
who were already dehydrated
Eggleton MG (1942) J Physiol 101 172‐191
Alcohol and fluid balance
Alcohol in high doses has a clear diuretic action
Example 1: pint of beer
Alcohol content
11 g
Volume
564 ml
Excess urine loss
110 ml
The diuretic effect has been estimated at 10 ml of excess fluid loss per gram of alcohol
Net fluid balance + 454 ml
Drinks with an alcohol content of less than about 10% should result in positive fluid balance
Alcohol content
10 g
Volume
25 ml
Excess urine loss
100 ml
BUT there have been few studies of the effects of high alcohol doses ‐
Ethics Committees do not like these studies
Example 2: nip of whisky
Net fluid balance ‐75 ml
Note that there will be a volume diuresis with beer!
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Urine excretion during recovery
Alcohol and Rehydration
500
Drinks contained 0, 1, 2 or 4% alcohol
400
0%
1%
2%
4%
20
15
10
Urine volume (ml)
25
350
300
250
200
150
100
5
50
0
Blood and urine samples were collected for a further 6 hours
0%
1%
2%
4%
450
Blood ethanol concentration (mmol/l)
6 volunteers were dehydrated by 2% of body mass (approximately 1.4 litres) by intermittent exercise in the heat and then consumed, over 60 min, a volume of drink equal to 1.5 times the volume of sweat lost Pre
Post
0
1
2
4
6
0
Post
Time after rehydration (h)
0
1
2
4
6
Time after rehydration (h)
Urine excretion “delayed” with the 4% drink
Shirreffs & Maughan JAP (1997) 83, 1152‐1158
Whole body fluid balance status
1000
0%
1%
2%
4%
Net fluid balance (ml)
500
Post
0
1
2
4
Diuretic effect of Alcohol
1. The diuretic action of alcohol may be overplayed when advising against its consumption after exercise
0
Pre
Shirreffs & Maughan, 1997
6
-500
-1000
2. Alcohol has a negligible diuretic effect when consumed in a dilute solution by hypohydrated individuals
Time after rehydration (h)
-1500
Shirreffs & Maughan, 1997
-2000
No difference in whole body fluid balance status between trials
Shirreffs & Maughan, 1997
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A randomized trial to assess the potential of different beverages to
affect hydration status: development of a beverage hydration index
Am J Clin Nutr doi: 10.3945/ajcn.115.114769
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A low alcohol beer with added sodium offers a potential compromise between a beverage with high social acceptance and one which avoids the exacerbated fluid losses observed when consuming full strength beer.
The electrolyte concentration of low alcohol beer
appears to have more significant impact on post exercise fluid retention than small changes in alcohol content
Thank you
Cheers
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