Doctors say cow's milk can lead to iron deficiency anemia, allergies, diarrhea, heart disease, colic, cramps, gastrointestinal bleeding, sinusitis, skin rashes, acne, increased frequency of colds and flus, arthritis, diabetes, ear infections, osteoporosis, asthma, autoimmune diseases, and more, possibly even lung cancer, multiple sclerosis and non-Hodgkin's lymphoma.