At this point, we all know that smoking is bad for us — really, really bad.

A newly released CDC Vital Signs report helps clarify just how bad we are talking about. Tobacco use is linked to a full 40% of cancer cases in the US, according to the report.

That means that even though smoking rates have gone down in the country overall, there were about 660,000 people diagnosed with cancer related to tobacco every year from 2009 to 2013. Each of those years about 343,000 died from one of those cancers.

It's not just lung cancer, either, though more than half of these cancers are either lung or colorectal cancers. But we also know tobacco can cause cancers of the mouth and throat, voice box, esophagus, stomach, kidney, pancreas, liver, bladder, cervix, colon and rectum, along with a type of leukemia.

"There are more than 36 million smokers in the U.S.," CDC Director Dr. Tom Frieden said in a press release emailed to Business Insider. "Sadly, nearly half could die prematurely from tobacco-related illnesses, including 6 million from cancer, unless we implement the programs that will help smokers quit."

Quitting at any point in time does help reduce cancer risk, according to the CDC. But at the same time, it's important to know that because the ways that smoking changes a person's DNA, some of the changes caused by smoking are permanent.

"If you smoke four to five packs of cigarettes in your lifetime, it doesn't sound [like] that much, but you still get several mutations in every cell in your lungs and these are permanent, they do not go away," theoretical biologist Ludmil Alexandrov, first author on a recent study examining how smoking affects DNA, recently told The Guardian. "There are a lot of things that do revert back when you stop smoking, and this shouldn't discourage people from giving up, but the specific mutations in the lung cells are like scars."

There's no such thing as a "safe" level of smoking, unfortunately. But that doesn't mean that changing behavior isn't worth it. The new report says that declining smoking rates since 1990 mean that we've avoided a 1.3 million deaths from tobacco-related cancer.

"When states invest in comprehensive cancer control programs — including tobacco control — we see greater benefits for everyone," Dr. Lisa Richardson, director of the CDC's Division of Cancer Prevention and Control, said in a statement. "We have made progress, but our work is not done."