Can drinking coffee especially in office hours increse your productivity? It is normal practice in many offices to drink coffee. Can caffeine increse your productivity? Some people suggest drink water and not coffee. Can sugary substances cause sleep?
According to a recent study (here's an article about it on the Guardian), people who drink caffeine aren't any more alert than those who don't:
At best, a habitual coffee drinker gets to the same level of alertness as a non-drinker after drinking coffee. The article also says that when a non-coffee drinker drank coffee, they got more headaches than usual but didn't feel any more alert. So despite being served and consumed in most workplaces, coffee doesn't increase productivity at all—except in the sense that if you already are a habitual coffee drinker, you'll be less productive when you don't drink coffee.
As for sugary foods, they tend to cause a temporary increase in blood sugar followed by a big dip (the Wikipedia article on blood sugar has a nice graph comparing blood sugar after sugar-rich versus starch-rich foods). During such a dip people tend to experience symptoms like drowsiness and impaired cognitive function. So yes, sugary foods can cause drowsiness, and for the sake of productivity it's probably best to stick to foods with a lower glycemic index.
I can tell you, from my personal experience, that some coffee may make you more alert, but if you overdo it, you may become agitated and have more difficulty focusing and articulating your ideas.
It always pays to know yourself and your body and listen to its signals.
It's said that overtime is a symptom of poor project management. It is effective in the short run and easily correlated with productivity, but you're better off using techniques that avoid it in the long run.
I'm starting to think that caffeine acts in a similar manner. Most research will correlate caffeine with productivity. But it doesn't necessarily mean that you should constantly use it.
Caffeine works by tricking your body/brain into panic mode. Most of us are familiar with those moments where we put out a month of work in the last two days before a deadline, under pressure. Caffeine will produce that feeling every day.
However, there are some other techniques which are better at creating that kind of imminent panic, such as timeboxing and Pomodoro. Unlike caffeine, you can easily shut down the panic mode from these when necessary.
I'd speculate that being able to 'panic yourself' on demand will give you better productivity in the latter part of the day, because you're not wearing yourself out as quickly.
Waking us up
I'd say the best use of coffee is waking you up in the morning.
On the other hand, if you are not naturally waking up and feeling refreshed in the morning, it's a strong sign that you're not getting enough sleep. You might get improved focus with a strong dose of coffee, but not necessarily improved long term memory storage.
There will be moments when you do need a boost of coffee to get you up (jet lag, late crunch time work), but it should not be the norm.
Caffeine has a half life of 6 hours, so it will most likely give you insomnia if used later in the day. This may cause insomnia, which requires more caffeine to fix.
Caffeine has its moments and patches many problems. But it should be the exception, not the norm. Besides, it is well known that drinking caffeine constantly weakens its effects, so you'll probably get a better result by using it sparingly.
I don't think drinking coffee in itself makes you any more alert but taking a break and walking to the coffee machine may help you work more efficiently. The same effect is created consciously by using for example the pomodoro technique with its 5 minute break every half hour. And the added health issues with extensive coffee drinking is avoided.
In my opinion one thing can help you increase productivity in a long run is taking a break regularly so that you can relax a bit and try to refresh sanity. If drinking a coffee is your own way of taking a break then, I think it can also help. However, when taking coffee every now and then it would also affects the body.