Sleep Patterns Affected
The low blood glucose levels caused by the alcohol in your body can have a serious effect on sleep patterns too. REM sleep is disturbed and this is the sleep cycle where you consolidate and commit to long-term memory everything that happened during the day.
Antidiuretic hormones which normally prevent too much urine being created are reduced in the body when you drink alcohol, the resulting effect being excess urine production, dehydration... and of course several trips to the bathroom in the night which compound your already disturbed sleep!
Dehydration continues well after alcohol consumption and since as little as a 2-percent decrease in body water weight can have a significant impact on performance this is certainly going affect your Strava time the following day.
Muscle Growth is Affected
Lack of sleep not only turns me into the human equivalent of a caged tiger being poked with a big stick but the double whammy here is that less sleep equals less HGH being produced by the body. What does HGH do? Exactly what the name Human Growth Hormone suggests—builds muscles. Reducing what is naturally produced in the body to build muscle is clearly a performance decreasing strategy.
Cortisol Production Increases
Cortisol (a useful "fight or flight" hormone which increases with stress levels) increases when you drink alcohol. While you may be having a merry old time while you're in the pub, the aftermath on your system can be dramatic. Increased cortisol negatively affects testosterone levels and being in a prolonged and unnecessary state of "I'm ready to flee from an attacking rhinoceros" can't be good for anyone.
Testosterone Production is Reduced
Studies have shown that consuming alcohol leads to a dip in testosterone (i.e. post-riding drinking could really affect that period of muscle growth after a training ride). And don't be fooled by thinking testosterone is only a guy issue. Sadly this isn't the case; girls need it too for muscle development.
Oh dear, this really is kind of depressing isn't it? So, what's the answer? Never letting a drop pass your lips again? Maybe—but remember life's for having fun and sometimes the mood-enhancing benefits of a few drinks with good friends can far outweigh the physical downsides. I'm a great believer in "all things in moderation" and while I can't claim that drinking is going to improve performance most of us aren't competing at a pro level and the odd drink or two isn't going to ruin our lives.
More: Fluid Facts for Athletes