Got twins? Sipping milk might be reason

Women who consume dairy products are five times more likely to have twins than those who don't, possibly because of synthetic growth hormones added to milk, says obstetrician Gary Steinman of the Long Island Jewish Medical Center, who published his findings in the May Journal of Reproductive Medicine.

This could mean that if you're contemplating pregnancy and have a family history of twins but can't fathom double duty at 3 a.m., you might consider other sources of calcium or buy organic, hormone-free dairy products. But if twins are part of the grand family plan, keep sipping those chocolate milkshakes.

Though his research is preliminary, Steinman's data and hypothesis offer an intriguing new concept: a possible connection between diet and twinning.

"The data raises some interesting questions worth investigating," said fertility specialist Jeremy Groll, author of "Fertility Foods" (Fireside Books, $16), who was not involved in the study. "Certainly in the last five to 10 years, there has been more emphasis on the role of organic foods in improving fertility and reproductive function."

Worldwide, twinning rates have been increasing since 1975, a surge that initially paralleled the introduction of assisted reproduction technology, which raises the likelihood of multiple births. The rise in older mothers, who are more likely to bear twins, also contributes to the jump.

But twinning rates continue to increase in the United States, and Steinman believes fertility treatments and "mature" mothers are only part of the explanation. His data showed insulinlike growth factor (IGF) may be another catalyst for multiple births.

IGF, which increases ovulation, is a protein that is released from the liver of animals (including humans) in response to growth hormone. It circulates in the blood and makes its way into the animal's milk.

It's thought that IGF may help embryos survive in the early stages of development. Also, in certain foods, IGF survives its journey through the digestive tract, which might explain why vegan women have a 13 percent lower concentration of IGF in the blood than in women who consume dairy, Steinman wrote.

"If anything, IGF increases the number of maturing eggs in any given cycle so that more eggs are released for possible fertilization," he said.

Past research has shown that cows with an enhanced ability to produce twin calves have elevated levels of IGF. Steinman basically found that the same thing is true in humans: The chances of twinning correlate directly with the level of IGF.

The dairy industry maintains that "Steinman's article is based on unsubstantiated observational research and, therefore, cannot determine a cause-and-effect relationship between dietary intake and multiple birth rates," according to Melissa Joy Dobbins-Buoscio, a National Dairy Council spokeswoman.

Also, milk-drinking women could be fatter (even though milk supposedly helps people lose weight) or more well-nourished than vegans, and heavier women are more likely to bear twins. Genetic makeup could also predispose a person to multiple births.

Steinman conceded that the cause-and-effect criticism is fair but said biomedical research often is hampered because of variability of the human body. He stood by his preliminary observations on the relationship between twinning and milk and hopes other investigators will be motivated to study the phenomenon.

To find out what foods might increase fertility, go to chicagotribune.com/julie online.