Alcohol and cigarettes are definitely harmful to human health. From a pack of cigarettes smoked a day clogs blood vessels, increases blood pressure. This can lead to serious heart and lung diseases. Alcohol is harmful in different doses. But if you drink a glass of wine in the evening, it will bring even a favor.
Unfortunately, the most popular answer was the wackiest. It is possible to consider edge cases, but this has nothing to do with the answer to the question, as your case is likely to be general. In general, it can be argued that by not drinking alcohol and quitting tobacco, you will significantly increase your chances of a long and healthy life.
Undoubtedly, you are not insured from a truck in Nice, but if you take 100 people, 50 of them will drink and smoke, and the other 50 lead a healthy lifestyle, then the second group, on average, will live longer and healthier.
The answer to "why" can be found in the relevant Wikipedia articles, everything is detailed there and there are links to research.
I won't say anything about cigarettes (it seems like they are harmful in any quantity, even with secondhand smoke), but alcohol in moderate doses is useful (of course, unless you drink "a harsh word for stool"), there are a whole bunch of effects positively affecting the body (google yourself, but the articles are usually in English), and according to statistics, moderate drinkers live longer than those who do not drink completely.
There are people who drink, smoke, inject, engage in promiscuous chaotic sex, take part in all sorts of underground boxing clubs, prepare a revolution, and live longer than those who lead a healthy lifestyle, but one day they find themselves on the embankment in Nice and falls under the wheels of love.