Learn Danish: En dårlig vane påvirker ens mentale helbred. - A bad habit affects one's mental health.

ens is the possessive form of the impersonal pronoun man (which translates to "one" or "you" in a general sense). It translates directly to "one's", showing that the mental health being affected belongs to people in general rather than a specific person.

Why does the adjective mentale end in -e when helbred is an et word?

In Danish, whenever an adjective comes directly after a possessive word like ens (or min, din, hans, etc.), it must take the definite -e ending. This rule overrides the noun's gender, so it becomes ens mentale helbred even though the basic form is et mentalt helbred.

Could we use sit instead of ens here, since helbred is an et word?

No, because reflexive possessives like sin or sit must refer back to the subject of the sentence. The subject here is en dårlig vane (a bad habit). A habit doesn't have mental health—a person does! Because the "owner" of the health is a general, implied person (man) and not the subject of the sentence, we must use ens.