The provided reference indicates that smoking even 1-4 cigarettes per day carries significant health risks.
While the question asks "how many," it's important to understand that there isn't a safe number. The reference highlights the increased risks of heart disease, all-cause mortality, and lung cancer, even at very low levels of smoking.
Therefore, the answer isn't a specific recommended number, but rather an acknowledgement that even a small number of cigarettes smoked per day presents a health risk. The less you smoke, the better. Ideally, none.
