If you can't live without a strong cup of coffee — or three — every morning, it might not be due to bad sleep habits or a lack of willpower. New research by the Harvard School of Public Health and the National Cancer Institute, and published in the journal PLoS Genetics, suggests that your genes might play a role in determing the amount of coffee you drink. Here, a brief guide:

What did the researchers find?
They scanned genetic variations in 40,000 people who had participated in past dietary surveys, and found that two stretches of DNA known to be involved in breaking down caffeine in the liver were more likely to be present in people who actually consumed more caffeine. That suggests that one reason behind the habits of heavy coffee drinkers is that their bodies are better able to process caffeine quickly.

How much more coffee do people with these genes drink?
People with the coffee-junkie DNA consumed about 40 extra milligrams of caffeine each day. That amounts to an extra cup of coffee or can of soda every day.

By why does this gene make people drink more coffee?
The heavy drinkers metabolize caffeine faster, so the authors of the study figure that their bodies cry out for that next hit of coffee sooner than those who metabolize caffeine more slowly.

So is coffee addiction all in these genes?
No. The DNA variations the researchers found only accounted for about 1 percent of the total differences in caffeine consumption. That suggests that there may be other genes that also play a role in determining how much caffeine our bodies can handle. "There are hundreds of genes known for specific medical conditions — for dietary consumption we know very little," study author Dr. Neil Caporaso says, as quoted by BBC News. "Now, for the first time, we know specific genes that influence the amount of caffeine that individuals consume."

Sources: MSNBC, BBC News, TIME, Boston Globe