Milk is commonly fortified with vitamin D to help prevent rickets and osteomalacia, conditions caused by vitamin D deficiency leading to poor bone mineralization. Fortification of milk is effective because it is widely consumed, ensuring better population coverage. Unlike rice, bread, or eggs, milk's nutrient composition allows for stable incorporation of vitamin D without altering taste or quality. This public health strategy has significantly reduced the incidence of vitamin D deficiency-related bone diseases worldwide.

Reference: Harrison's Principles of Internal Medicine, Jameson et al., 20th Edition.