Infants fed non-human breast milk before the age of four months have an increased chance of suffering from allergies and asthma according to a study published in the British Medical Journal (September 25, 1999;319:815-819). Researchers followed over 2,000 children from birth through age six. Children given milk before the age of four months (not human breast milk, of course) were 25% more likely to be diagnosed with allergy.
The length of time the infant obtained food exclusively by nursing was associated with only a slightly lower incidence of allergies and asthma. But the introduction of milk into the diet was associated with allergies and asthma much more strongly than the duration of breast feeding.