mike23 Mar 5, 2022:

There may be two interpretations to this.

"One is what others have said. 'Healthy' can mean a good amount of, and so we are thinking about a considerable amount of scepticism (this is the typical spelling in BrE).

'A healthy dose' is of course a metaphor. Generally we think of doses of medication. We can consider that the dose itself is health-giving and therefore healthy. We can link the metaphor and what is being referred to with of (known as the appositive of). We say things like 'the canker of fear', where we are saying the fear is (like) a canker. In the same way, we might think that scepticism is (like) a healthy dose (of medicine). We are saying that this scepticism is health-inducing."
https://forum.wordreference.com/threads/a-healthy-dose-of-sk...