Early on, I asked both my doctor and my physical therapist if there was anything I could do nutritionally to improve my condition. It's unfortunate, but still very typical, that medical professionals appear to know next to nothing about nutrition. In any case, nobody had a suggestion.
I went snooping around the internet to see if I could find anything. Nutritional supplements are one of those things that snake oil salesmen like to latch onto, and searching the internet turns up a ton of dubious claims.
As for the science, you can find suggestive, but not definitive, research that zinc is important to production of collagen. In rats, anyway.
A few years ago, I kept tabs on my diet. At the time, I appeared to be deficient in zinc. However, I hadn't noticed any issues caused by it, and I've always been reluctant to take supplements without reason, so I didn't do anything to correct the situation.
Is it possible that my zinc deficiency led to frozen shoulder? I suppose so, although I guess there's no way to know for sure. In any case, I decided to start taking a zinc supplement soon after I started physical therapy.
I'm taking chelated zinc (50 mg of zinc amino acid chelate, 333% of the RDA) since it's supposed to be one of the more bioavailable forms of zinc. In addition, since zinc interferes with copper absorption, I'm taking a copper supplement (2 mg of copper gluconate, 100% of the RDA). I take the zinc mid-morning on an empty stomach, since that's supposed to be better for absorption. That typically gives it a couple of hours to float around without a lot of competition. I take the copper later in the day, but not on an empty stomach, since I haven't read anything that indicates that would be useful.
Recall that I had noticed an article about shoulder pain in Nigerians at PubMed. When I first thought about zinc being a possible factor in frozen shoulder, I immediately wondered whether the Nigerian diet might be deficient in zinc, leading to more cases of frozen shoulder in that area of the world. However, it doesn't appear to be the case. Some research by Onianwa, et al, says that "the estimated weighted average dietary intakes for the entire adult population [of Nigeria] were calculated to be 2.64 mg Cu/day and 15.8 mg Zn/day" which is quite near the US RDA for those minerals. So, there are no helpful clues from that research.