BBC News reports. "People with plenty of a B-vitamin in their blood appear to be at a reduced risk of lung cancer, even if they smoke." "High levels of Vitamin B6 and the amino acid methionine cut the risk by half, a study of 400,000 people suggested."
Methionine is found in protein like meat, fish and nuts, and vitamin B6 is found in meat, nuts, vegetables and bananas. Obviously, giving up smoking (or never starting to smoke) is the best way to reduce risk of lung cancer, but these two featured nutrients are associated with lowered risk for both smokers and non-smokers.
Certain prescription drugs deplete the body of vitamin B6. I experienced this when I was a teenager, taking drugs to treat pulmonary TB. It became totally impossible for me to sleep. I could not sleep AT ALL. The drug called isoniazid had depleted my body of vitamin B6. No-one told me that my intractable insomnia was the consequence of severe lack of vitamin B6 (aka pyridoxine). The doctors probably did not know at that time, when the drugs were pretty new, that there was this side-effect. If I had been prescribed pyridoxine tablets to make up for the deficiency I would not have suffered those terrible years of insomnia, which brought in its train many other problems.