If I find that particular paper again I'll let you know. And depression as a consequence of subclinical hypothyroidism is very well established, but no longer generally acted upon. It used to be routinely treated as such, but when the TSH test came to prominence, most doctors started treating to make nice test results rather than treating the patients' symptoms.... despite that all the evidence is against using TSH as anything but a crude marker that something is wrong. False negatives are extremely common.
Here's a starter kit:
I have Hashimoto's thyroiditis, and I've had to take up reading the Journal of Endocrinology in sheer self-defense. It's quite shocking how much well-established endocrine research has never filtered down to GPs, never mind other specialty fields, despite that a malfunctioning endocrine system can fuck up just about anything else. I've concluded it should be the first line of inquiry (since fixing the thyroid will commonly cure a whole raft of apparently-unrelated physical and mental symptoms), but most doctors act like it's the last resort.