Do they really recover? I thought that the damage was pretty much irrevocable.
Destroyed lung doesn't come back, so once you've got COPD and are toting around an oxygen tank, yes, most of the damage is permanent. But in general you have to smoke a LOT to reach that milestone ... we're talking 80+ pack years (ie, 1 pack/day for 80 years, 2 packs/day for 40 years, etc). However, damaged lungs can recover to a significant degree. Here's a rough timeline for objectively measurable benefits to quitting smoking (with an emphasis on health before/during/after surgery) -
Reduced carboxyhemoglobin (carbon monoxide poisoning) and nicotine concentrations in less than a day - important for wound healing.
Improved ciliary function in 2-3 days.
Reduced sputum production in 1-2 weeks.
Improved lung function (by standard pulmonary function testing) in 4-6 weeks.
Immune function essentially returned to normal in 6-8 weeks.
A measurable reduction in overall postoperative morbidity and mortality after 8-12 weeks.
When you quit, it's actually common to experience worsened coughing/sputum production for the first week or so.
Most people who smoke don't die of cancer. The major health problems from smoking are related to progressive damage to the lungs and increased risk of cardiovascular disease. Both of these can be mitigated and partially reversed, even if you quit smoking late in life. Chronic bronchitis, for example, will just go away when you quit.
The only time I'd say it's too late to quit is if you just left the hospital with a new diagnosis of metastatic lung cancer. Might as well light 'em up two at a time then.