On National Coffee Day, it's good to reflect how closely work and coffee go together. Heaven knows workers spend enough on it: an estimated average of $1,092 a year . An office without coffee would be a far less productive workplace -- or so we think. Here, Fortune takes a look at what research proves to be true about coffee at work. 
 
 Coffee heightens your powers of perception. Really. 
 
 
 
 If you ever wondered whether your sense of being more alert after a cup of coffee was scientific fact or your own fancy, researchers from the London School of Hygiene & Tropical Medicine say you were right all along. Caffeine "improved concept formation and reasoning … orientation and attention … and perception." But there was no improvement in verbal functioning and language schools, other than the ability to order, without a trip of the tongue, that " grande, quad, nonfat, one-pump, no-whip mocha ." 
 
 Drinking coffee can stiffen your moral fiber. 
 
 According to University of North Carolina researchers, sleep deprived people are more susceptible to social influences , like a boss who wants you to step over ethical lines. Caffeine can serve to give you backbone, "strengthening your self-control and willpower when you’re exhausted," according to co-author Michael Christian. 
 
 You're probably drinking coffee at the wrong time of day. 
 
 
 
 Having a cup the minute you roll out of bed is a mistake . Between 8am and 9am -- and noon and 1pm, as well as 5:30pm and 6:30pm -- most people have a spike in their level of cortisol, which helps the body metabolize and use sugar and fat for energy. In other words, you’re already revving up. A jolt of caffeine reduces production of cortisol, which is what you really need, and almost makes you more reliant on increasing caffeine intake, starting a vicious circle. So target the caffeine jolt to between 9:30 am and 11:30am, and if you want to keep sailing through the day, have another cup of java between 1:30 to 3:30. If you're an early bird or sleep in later, just wait an hour after waking before your first coffee. 
 
 Take a break with coworkers. 
 
 
 
 A study by Massachusetts Institute of Technology researchers found that communal coffee breaks can increase productivity . The "strength of an individual’s social group was positively related to productivity," according to the study, and that "giving employees breaks at the same time we increased the strength of an individual’s social groups." But isn't shmoozing over coffee just a waste of time? No, another study by Emily Hunter, Ph.D., and Cindy Wu, Ph.D., associate professors of management in Baylor University’s Hankamer School of Business, found that when workers take breaks doing something they enjoy, like drinking coffee, it also improved their job satisfaction. 
 
 If you're stressed out, don't drink coffee. 
 
 
 
 If a bad day at work is pushing you over the mental and emotional edge, put down the cup of coffee. A study out of Duke University Medical Center makes it clear that caffeine can elevate your blood pressure and adrenaline levels. When you're stressed out, there are other ways to find your happy place. ||||| Tons of businesses around the country are offering free and discounted cups of joe for National Coffee Day. (Photo: Shutterstock) 
 
 Let’s be real: Pretty much every day is National Coffee Day in America. Americans love their coffee — a lot. The average American drinks 2.1 cups a day, and 49 percent of coffee drinkers say they’d rather give up their cell phone for a month than coffee. We import more than $4 billion dollars’ worth of the stuff every year, and it accounts for 75 percent of American caffeine consumption. And just in case you’re fretting over the health ramifications of all of that brew, the government’s 2015 dietary guidelines say that drinking 3-5 cups of coffee a day is perfectly safe (as long as you’re not pouring in the cream and sugar.) 
 
 
 
 However, Sept. 29 — the official National Coffee Day — is the one day a year you can get your caffeine fix for free at many shops around the country. Here are some of the deals and steals to keep an eye out for: 
 
 Dunkin’ is offering guests a free cup of Dark Roast coffee. (Photo Courtesy of Dunkin Donuts) 
 
 Dunkin’ Donuts 
 
 Though “donuts” is in the name, the main attraction for many fans of this national chain is the coffee. Dunkin’ is celebrating the holiday by giving guests a free medium cup of hot or iced Dark Roast coffee (no purchase necessary). However, offers at the chain can vary from franchise to franchise, so make sure to double check before you order. 
 
 Krispy Kreme 
 
 The chain known for their addictive glazed doughnuts is doubling down on this year’s freebies. Visit one of their many national locations to pick up a free cup of coffee AND a free glazed doughnut. You hear that, Dunkin’? It’s time to step up your National Coffee Day game. 
 
 Wawa 
 
 This East Coast convenience store chain with a cult following is offering a free coffee in the size of your choice at their 680+ locations — a deal that’s sure to make their devoted fan base love them even more. 
 
 Peet’s Coffee 
 
 Visit one of Peet’s 250+ stores in nine states and Washington D.C. to get a free coffee when you purchase a breakfast item. 
 
 Missouri-based Lamar’s is offering a free commemorative coffee mug along with their free 12-oz. coffee. (Photo Courtesy of Lamar’s Donuts) 
 
 Lamar’s Donuts 
 
 Take home a souvenir with this Missouri-based donut chain’s offer: free coffee and a free coffee mug at one of their 26 stores in six states. Visit the Lamar’s Facebook page to get the offer emailed to you, and make sure to get there early, as supplies are limited. 
 
 Read More ||||| Starbucks isn't giving out free coffee for National Coffee Day. It's kicking off a year-long effort to give away coffee trees. 
 
 The coffee Goliath's rivals are taking the more traditional route, seizing on the made-up holiday (carpe diem!) to promote their joe by giving it to customers. 
 
 Dunkin' Donuts (DNKN), the granddaddy of coffee, is handing out free coffee to members of its DD Perks Program. A visit to a Dunkin' Donuts in Manhattan showed a sign in the window advertising its National Coffee Day deal and a crowd spilling out onto the sidewalk. 
 
 Wawa is also giving out free coffee, of any size, to any customer who wants it. Krispy Kreme (KKD) is giving out free small coffees and glazed doughnuts, along with $1 discounts on other drinks. 
 
 A visit to a Starbucks (SBUX) in Manhattan showed business as usual, with a long line of customers but no sign of the High Holy Day for caffeine. 
 
 Starbucks will donate 70 cents -- the price of one coffee tree -- to coffee farmers for every bag of joe purchased by customers in U.S. stores. Starbucks purchases its beans from farmers in more than 30 countries. 
 
 The effort aims to alleviate a twofold problem for coffee farmers: aging trees and a fungus called "coffee rust" that slows or kills production of coffee cherries. The company said this has gutted coffee production by 50% in some areas and is particularly bad in Guatemala, El Salvador and also Mexico. 
 
 Starbucks is jump-starting the program by giving away one million trees. 
 
 This is a departure from last year, when Starbucks took a more traditional route by offering free samples of its Anniversary Blend.
– Today is National Coffee Day in America, and it's worth celebrating if for no other reason than chains all over the country are offering free cups of joe. Yahoo has a comprehensive list, which includes Dunkin' Donuts (free medium cup), Krispy Kreme (free cup, plus a free doughnut), and Peet's (free cup with breakfast item). Alas, no free cup at Starbucks, but the chain is launching a yearlong project to provide trees to coffee farmers, reports CNNMoney. The chain will donate 70 cents (the cost of a tree) for every bag of coffee bought in the US. Other reasons to partake: While at work: Fortune rounds up a series of studies finding, among other things, that coffee makes you more perceptive and that taking a coffee break with co-workers is a boon for all. Health: Take them with the appropriate grains of salt, but studies have claimed health benefits ranging from cleaner arteries to better vision to a reduced risk of ailments such as melanoma and multiple sclerosis.