By comparing the twinning rate of vegan women, who consume no animal products, with that of women who do eat animal products, Gary Steinman, MD, PhD, an attending physician at Long Island Jewish (LIJ) Medical Center in New Hyde Park, NY, found that the women who consume animal products, specifically dairy, are five times more likely to have twins.

The culprit may be insulin-like growth factor (IGF), a protein that is released from the liver of animals - including humans - in response to growth hormone, circulates in the blood and makes its way into the animal's milk. IGF increases the sensitivity of the ovaries to follicle stimulating hormone, thereby increasing ovulation. Some studies also suggest that IGF may help embryos survive in the early stages of development. The concentration of IGF in the blood is about 13 percent lower in vegan women than in women who consume dairy.

The twinning rate in the United States has increased significantly since 1975, about the time assisted reproductive technologies (ART) were introduced. The intentional delay of childbearing has also contributed to the increase of multiple-birth pregnancies, since older women are more likely to have twins even without ART. "The continuing increase in the twinning rate into the 1990's, however, may also be a consequence of the introduction of growth-hormone treatment of cows to enhance their milk and beef production," said Steinman.

In the current study, when Steinman compared the twinning rates of women who ate a regular diet, vegetarian diet with dairy, and vegan diet, he found that the vegan women had twins at only one-fifth the rate of women who commonly do not exclude milk from their diets.

"This study shows for the first time that the chance of having twins is affected by both heredity and environment, or in other words, by both nature and nurture," said Steinman.

MEDICA.de; Source: North Shore-Long Island Jewish (LIJ) Health System