How do nicotine and tobacco cause cancer? A. by decreasing blood-sugar levels
B. by damaging or changing a cell's DNA
C. by increasing heart rate
D. by increasing phlegm and mucous production

 B. by damaging or changing a cell's DNA

Studies have shown that nicotine speeds up cell growth which leads to tumors forming in the lungs. Nicotine was found to inhibit the tumor suppressor gene known as CHEK2 (short for Checkpoint kinase 2). This gene is effectively like the brakes on cell growth. Without these brakes in place, the cells divide well beyond their intended rate and amount.

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