42. Milk Drinkers More Likely To Have Twins
Women who consume milk and other dairy products have twins more than twice as often as do vegan moms, according to Long Island Jewish Medical Center obstetrician Gary Steinman. The finding may help explain the strange 60 percent surge in the rate of twin births in the United States between 1977 and 2002.
The study, published in May in the Journal of Reproductive Medicine, compared the frequency of twins in the general population with that in the obstetrical histories of 1,042 vegan mothers. Steinman suspects that the disparity may be due to a protein in milk called insulin-like growth factor (IGF), which is associated with multiple ovulation. Vegans have lower blood concentrations of IGF than women who consume dairy regularly. Although IGF is present in other animal products, including meat, it seems to survive digestion only when in milk.
Of course, reproductive technologies like in vitro fertilization increase the twinning rate, as does the trend of delaying childbirth, but Steinman argues that dietary factors also play a role. In 1993 the FDA approved the use of recombinant bovine growth hormone in cows for the purpose of increasing milk production; milk from hormone-treated animals is especially rich in IGF. Between 1992 and 2001, the twinning rate in the United States increased twice as much as it did in the United Kingdom, where the hormone is banned. "We're doing something different," Steinman says, "and the only difference I can find is this growth hormone."