To overcome certain types of vitamin deficiencies, a few who are in the sampradayam end up partaking prohibited food such as mushrooms, garlic, etc. Are there any other ways to address vitamin deficiency without including food substances that are prohibited?

There is no compulsion to improve one’s health by including such prohibited food substances; in the days gone by, our elders lived long and healthy without partaking any forbidden food. One must have faith that it is possible to address health issues without partaking banned food substances.
No health-related issues will happen when one partakes of vegetables that are allowed by the scriptures, after offering them to Emperuman as ordained. Just by including the vegetables mentioned in the Ahara Niyamam, one can certainly live without any health-related deficiencies; the notion that certain food types help to overcome certain types of deficiencies is all modern-day prescriptions based on interested parties’ motives; no need to consider them sacrosanct.