See if you can convince him to try high doses of Vitamin C. Attached here are two important and compelling papers:
1) "Evolution and the Need for Ascorbic Acid", Linus Pauling. Presents why we need ascorbic acid (aka Vitamin C) and why most people are chronically deficient.
2) "The Politics of Therapeutic Evaluation: The Vitamin C and Cancer Controversy", Evelleen Richards. Lays out how high-dosed Vitamin C was not given a fair chance as a cancer treatment, even when its risks are incredibly small.
The foundational book on the subject is "Vitamin C and Cancer" by Ewan Cameron and Linus Pauling. Richards also wrote an expanded book on this topic.
I recommend liposomal Vitamin C. Have him take one a day, every day. He should start to have more energy in a few days. After a few days, have him take two. He needs to take them every day. A good source of liposomal Vitamin C is here: https://optimunity.com/product/optimunity-starter/
If you can't get the liposomal variant, I recommend this pill: amazon - /Vitamin-Serving-Extract-Stearate-Capsules/dp/B086MNMWVV/