In a British study, they had everyone from barely drinking coffee to about 25 cups of coffee a day.  During this study, they found that coffee does not stiffen the blood vessels and arteries of the people who drink coffee.  Caffeine is a natural stimulant.  It peaks an hour after consumption but eliminates about half of it between 4-6 hours.  Caffeine reactions vary depending on the person.  You should try not to consume no more than 400 mg of caffeine a day which is about 4 cups of coffee or 10 cups of black tea.  These numbers are if you have had no current heart issues.  If you have had a heart attack or possible other heart complications you should keep your intake to about half of that.  

Caffeine is an antagonist of adenosine which is the receptor that promotes sleepiness.  Caffeine can make it hard to sleep at night depending on how late you drink it and how your body will react and how much you consume.  It could delay the timing of your body clock which will reduce your total time of sleep.  There is one study that found consuming caffeine 6 hours before bedtime can reduce your sleep by 1 hour.  It can cause insomnia because of the lack of sleep when caffeine is consumed too close to bedtime.  Some people may experience more frequent wakings, shortened deep sleep, and REM is less affected.

Blue rays can affect sleep which can overall affect your weight loss goals.  Adults should try and get about 7 hours of uninterrupted sleep.  This may be hard but people should try and aim for it.  Inefficient sleep can affect circulation, memory, and possibly social relationships.  A good amount of sleep can aid in weight loss.  Sleeping less than 6 hours you could experience less waist loss circumference than people who get 7-9 hours of sleep.  Sticking to a consistent sleep and wake cycle will protect your daily circadian rhythm and will help encourage natural melatonin production.  Less REM sleep happens when you stare into blue light later at night.  People should try to include a one to the two-hour cutoff of blue light before bedtime.  If that is not possible dim the brightness or change to warm colors on the screen.  Also, try and use dim lights in your bedroom instead of blue lights.  

Blue light exposure does affect your weight loss as well.  Blue light reduces melatonin production, throws your rhythms out of sync, and inhibits sleep.  It also reduces sleep and makes you more restless at night.  The disruptive sleep with blue light can aid in weight gain because of the amount of sleep you are not getting.  That being said blue light can also lead to later bedtimes which can also include weight gain, and late-night snacking.  When people snack late at night they usually will pick the more high-calorie foods.  People who are also sleep-deprived usually tend to crave more junk food or not want to cook anything so go the easy way out.  One night of bad sleep can lead to hunger hormones spiking which will increase your appetite.  Shortened sleep can create stress or stress can also be the reason which can lead to stress eating which is also usually not the healthiest of options people pick.  Sleeping in a cooler room can help you fall asleep faster, wake up less often, burn more calories, and stimulate your metabolism.  If you can shoot for your room to be between 62-68 degrees Fahrenheit.