A book club sounds like a pleasant way to spend an evening. It also happens to combine several of the things most reliably linked to better health: regular social contact, mental stimulation, and something to look forward to.
The social benefit
Meeting regularly with people who share an interest is genuinely protective. Loneliness carries real health costs, and a standing monthly gathering with real conversation is one of the simplest ways to counter it.
The mental benefit
Discussing a book asks more of you than reading it alone. You have to form a view, defend it, and consider someone else's. That exercise sharpens critical thinking and keeps the mind flexible.
The mood benefit
Book clubs give structure and anticipation to the calendar. Having something to prepare for, and people expecting you, lifts mood in a way that is easy to underestimate.
Starting one
Keep it simple. A handful of people, a regular date, one book at a time, and an agreement that nobody has to finish it to show up. The reading matters. The gathering matters more.