The difference between 25-hydroxyvitamin D₂ and D₃ is mainly the difference in their sources. 25-Hydroxyvitamin D₂ is derived from ergosterol in plants, while 25-Hydroxyvitamin D₃ is mainly derived from 7-dehydrocholesterol, which is converted from 7-dehydrocholesterol in the epidermis and dermis of the human body. Although the sources are different, both have the same mechanism of action and need to be converted through the liver and kidneys before they can promote the absorption of calcium and phosphorus in the small intestine. When suffering from liver and gallbladder diseases or small intestinal diseases, patients will have symptoms of diarrhea or malnutrition, resulting in low calcium and phosphorus in the body, and then doctors usually recommend taking 25-hydroxyvitamin D₂ or 25-hydroxyvitamin D₃ preparations for treatment. You should also get plenty of sunlight on a daily basis, which also facilitates the conversion and absorption of vitamin D.