May 21, 2006
Dairy Diet Increases Incidence Of Twin Births

Dairy products greatly up the odds of having twins and the use of growth hormone to increase milk production may have increased the frequency of twins.

NEW HYDE PARK, NY An obstetrician well known for his care of and research into multiple-birth pregnancies has found that dietary changes can affect a woman's chances of having twins, and that her overall chance is determined by a combination of diet and heredity. 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 study is published in the May 2006 issue of the Journal of Reproductive Medicine, available May 20.

The Lancet recently published an invited comment by Dr. Steinman on dietary influences on twinning in the journal's May 6 issue.

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 Dr. Steinman.

So there are multiple factors increasing the incidence of twins: older age at time of reproduction, use of in vitro fertilization (IVF), consumption of dairy products, and possibly the use of growth hormone treatment of cows.

The increased incidence of twins has one big drawback. If you want to have smart children then avoid twins.

OBJECTIVES: To determine whether twins have lower IQ scores in childhood than singletons in the same family and, if so, whether differences in fetal growth explain this deficit. DESIGN: Cohort study. SETTING: Scotland. PARTICIPANTS: 9832 singletons and 236 twins born in Aberdeen between 1950 and 1956. RESULTS: At age 7, the mean IQ score of twins was 5.3 points lower (95% confidence interval 1.5 to 9.1) and at age 9, 6.0 points lower (1.7 to 10.2) than that of singletons in the same family. Adjustment for sex, mother's age, and number of older siblings had little effect on these differences. Further adjustment for birth weight and gestational age attenuated the IQ difference between twins and singletons: the difference in mean IQ was 2.6 points (-1.5 to 6.7) at age 7 and 4.1 points (-0.5 to 8.8) at age 9. CONCLUSIONS: Twins have substantially lower IQ in childhood than singletons in the same family. This effect cannot be explained by confounding due to socioeconomic, maternal, or other family characteristics, or by recruitment bias. The reduced prenatal growth and shorter gestations of twins may explain an important part of their lower IQ in childhood.

I wonder if better nutrition for mothers pregnant with twins could at least partially compensate for the effects of carrying twins on brain growth. Maybe a diet higher in omega 3 fatty acids, choline, and/or other nutrients could compensate?

Update: Since twinning rates fall during periods of food shortage (as happened during World War II) another interpretation of these results is that vegan women have fewer twins because they are nutrient deficient.

Other scientists say vegan women may bear fewer twins because they are less well nourished. Dr Paul Haggarty of the Rowett Research Institute in Aberdeen says there may be other nutrients that vegan women lack.

So maybe dairy consumption isn't causing an unnatural outcome? Then again, maybe it is.

Share |      Randall Parker, 2006 May 21 03:14 PM  Biotech Reproduction

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