Stress, depression and underactive thyroid?

Hello, I am seeking advice concerning my husband's health. Four months ago he began a new job (he's a postdoctoral scientist) which is not going well. For this job we moved home, and he is also homesick. His working environment might be described as 'fraught' and he is incredibly stressed. Firstly, I am concerned that he is suffering from (mild?) depression and anxiety: he seems defeated, and is clearly unhappy. Sometimes he struggles to face the day and he often complains of a tight chest a nausea in the mornings before work. He is sleepy very poorly and has reduced self-esteem and confidence: for eg, he says he feels like an 'imposter' at work, as he isn't progressing with his research. He seems unable to accept that, since his colleagues are also not progressing on this project, it doesn't reflect badly on him. It is IMPOSSIBLE to persuade him to see a doctor, so I am giving him as much support as I can: I do all the work at home (I am also in research and my hours are even longer than his) and try to free up as much time as possible for him to do things which help him relax, like exercise and music. I try not to let him see how hard this is for me in case he feels bad about that as well as everything else. When he wants to, we talk about work and how he feels, and I try to help him find some perspective. I had two courses of CBT a while ago and try to pass on some of the things I learned which helped me to manage my own depression. I would, firstly, welcome any advice on the best way to support someone in his situation. My second question, however, is more practical. I recently read that stress can cause reduced thyroid activity. Is this true? It rang alarm bells for me because my husband is constantly cold (he regularly goes to work in 5 layers) and has very cold hands and feet, is always tired but often cannot sleep, frequently complains of constipation since starting the new job, and, since then also, seems to be losing his hair - but not typical male pattern baldness, rather a uniform thinning, perhaps also at the ends of his eyebrows a little. More worrying he states that he can't concentrate at work. I know these could be symptoms of lowered thyroid activity, but realise that there are other possible causes. I know thyroid supplements are available w/o prescription but we would not trust these. I am concerned that if stress is lowering his thyroid activity, loss of concentration and depression could result from that, making him feel more inadequate and more stressed, with bad results for his mental health. I imagine (please tell me if I'm wrong!) that stress would only reduce thyroid function a little, so I wonder whether he can be helped by any changes in diet? Should we consider vitamin supplements (B12?) or zinc, iodine, selenium, iron? I hope that if a small change like that could give him an energy boost and help his concentration, the depression could ease too. I realise that if his symptoms worsen I will somehow have to drag him to his GP... Finally some background: My husband is 27, male (obv!), fit & healthy - about 5'9 or 10", 9.5 stones (slightly built); runs at least one 10k per week, cycles 40 mins per day, does at least 2x 2hours of fencing per week. He eats a balanced diet, including his 5 a day, and is not vegetarian/vegan or with any restrictions except a peanut allergy. He has been in hospital only 2 times: once, when 7 years old due to a severe rotavirus infection which somehow affected his kidneys (through dehydration i guess?) and then two months ago because he had norovirus badly, could not keep down water, and had to be put on a drip for a while. He does not smoke or take any drugs (hard to persuade him even into an aspirin!) and has no history of mental health issues. He drinks a little: he used to put away 3 or 4 pints once a week but since we moved way from our friends he now only shares a pint of beer with me or a glass of wine - maybe once every 2 weeks. Thank you for any help you may be able to give! *****