Vitamin D deficiency is a public health issue that not only results in skeletal disorders but is also linked to several chronic diseases. Several studies have shown that ultraviolet (UV)-treated mushrooms are a potential dietary source of vitamin D, as these mushrooms have a high rate of conversion of ergosterol to vitamin D2. However, there are gaps in knowledge about the most appropriate irradiation conditions, including the source, dose, intensity, and duration of irradiation, for maximizing vitamin D2 content in mushrooms. UVB seems to be most effective in transforming ergosterol to vitamin D2 in both fresh and dried mushrooms. Effects of drying, storage, and thermal treatments on vitamin D content in UV-treated fresh mushrooms have been reported. This knowledge is important for the mushroom industry in order to provide the market with vitamin D2-enhanced mushrooms in a safe and affordable manner. Recent studies in humans focused on the bioavailability of vitamin D2 from mushrooms. The study results showed that UV-treated mushrooms were effective in increasing serum 25-hydroxyvitamin D levels, as they contain high vitamin D2. However, other reports indicate that there are no significant changes in serum 25(OH)D levels and suggest that vitamin D2 is not as effective as vitamin D2 in increasing serum 25(OH) D levels. Vitamin D2 bioavailability is still unclear, and there is an urgent need to investigate the effectiveness, safety, and adequate amount of vitamin D2-enhanced mushrooms for reducing vitamin D deficiency and maintaining vitamin D levels.