Should We Fear Our Food?
Hormones in Milk
Many dairy farmers inject their cows with rbST (also called rbGH), a
genetically engineered replica of bovine growth hormone (BGH), which the
animals also produce naturally, to control milk production. Treatment typically
boosts cows' milk output by up to 15 percent, and about one third of U.S. dairy
cows are now injected with rbST. But because milk from different farms is mixed
together in tanker trucks, it's reasonable to assume that almost every carton
of milk contains some BGHtreated product, unless it's labeled organic rbST or
The Potential Danger
Ever since the FDA approved rbST in 1993, there have been allegations that
drinking the milk from treated cows increases human health risks ranging from
breast cancer to reproductive abnormalities. With these concerns in mind, the
consumer advocacy group Food & Water Watch has pressured Starbucks to
switch to hormonefree milk, with positive results. But hundreds of studies over
the years have settled most of those issues. "AntiBGH activists have lost
every round of scientific, peerreviewed research," says Phillips.
Most recently, however, a study published in The Journal of Reproductive
Medicine found that women who drank milk were three times more likely than
vegans to have twins. One theory: Insulinlike growth factor (IGF), a protein
produced by all mammals that has been linked with twinning in cows, is having
the same effect in women. "When animals receive BGH replica, their IGF
levels go up," says study author Gary Steinman, M.D., an obstetrician at
Long Island Jewish Medical Center in New Hyde Park, NY. He suspects that
elevated levels of IGF from hormonetreated cows are passed to people in milk.
No research offers slamdunk proof that rbST milk makes women have more twins.
But twinning rates in U.S. women are higher since rbST was introduced,
Steinman says, and use of assisted reproductive technologies doesn't fully
account for the increase. "The rate has gone up twice as fast here in the
U.S. as in Britain, where there's been a moratorium on synthetic BGH," he
Should You Worry?
It's unlikely that rbST or IGF in milk has anything to do with your odds of
having twins, according to Baumrucker. In fact, IGF from food can't be absorbed
directly by the body, he says. What can happen is that other proteins
in milk boost the body's production of its own IGF. But even if milk protein
indirectly raises IGF, Baumrucker adds, the elevation would be well within the
Steinman admits he hasn't connected the dots between IGF in milk from BGH
cows and twins. And if a connection does exist, you would only need to be
concerned about it if you're trying to get pregnant and don't want twins, in
which case he suggests switching to soy or organic milk as a precaution.