If there were a parental quiz, this would be one of the infancy extra credit questions: Why is it that babies can drink infant formula (usually made from cow's milk) at 10 months of age but they can't drink whole milk (also from cows) until after their first birthday? What's the difference?
What's the Issue?
Realistically, almost all infants drink cow's milk. If you are a breastfed baby, the cow's milk comes to you via the breast and your mom's last linguini with parmesan or decaf skinny latte. If you are a formula-fed infant, it comes from Nestlé Good Start, Enfamil Lipil, Similac Advance, or one of the other cow's milk-based infant formulas. Seeing the obvious similarity, patients sometimes ask me why they can't just switch to whole cow's milk earlier than the one year birthday. It certainly would be cheaper. Is there a downside?
Well, the answer has little to do with vitamin content, fat content, or mad cow disease—the initial guesses my patients share. Instead, low blood counts and anemia (a condition characterized by low levels of red blood cells) are truly of concern. (Read more about the causes and effects of anemia here.)
Consider the Numbers
In the 1960s, the prevalence of anemia in the American one-year-old population was 15 to 30 percent. Today, the prevalence of anemia hovers somewhere around three percent. The major change? The introduction of iron into infant formulas and the strong recommendation by pediatricians that infants drink breastmilk or iron-fortified formula until their first birthdays, both around 1971.
Some of the seminal thinking on this subject came from Dr. Howard A. Pearson, MD, in New Haven, Connecticut. In his studies, he and his colleagues found that cow's milk as the major source of nutrition in the infant diet before one year of age was associated with more significant anemia. The cause, we now know, seems to be an irritation of the intestinal lining and a resulting low-grade leakage of blood into the stool. Older children are much less likely to have this problem.