7.2—rBST has nothing at all to do with twinning

rBST treatment of cows doesn’t cause a higher rate of twin births

See Genetic Roulette’s False Claims at Bottom of Page

Analysis of Peer-Reviewed Research:

Genetic Roulette correctly cites the literature that claims that higher levels of IGF-1 are correlated with a high frequency of twinning.  Several different lines of evidence support this conclusion.  Smith argues that since milk from rBST treated diary cows contains more IGF-1, women who consume it will give birth to a higher incidence of twins.  He cites the 32 percent increase in twins in the last 30 years in the US where rBST is used, as compared to the 16% increase in the UK where rBST is not used, to support this assertion.  There is only one thing wrong with Smith’s argument.  The scientific evidence shows clearly that rBST-treated milk has levels of IGF-1 that are the same as those found in conventional milk.   Smith is simply repeating long discredited falsehoods when he claims that milk from rBST-treated cows contains more IGF-1.   Smith does mention that the increased rate of twins has been attributed to in vitro fertilization and birthing later in life but cannot stop himself from making yet another baseless charge against genetic engineering.

1.  Milk from rBST treated cows has the same level of IGF-1 as milk from untreated cows.  Genetic Roulette provides interesting information about the association of high blood levels of IGF-1 with increased frequency of twining (Steinman 2006).  Smith then incorrectly asserts that milk from rBST-treated cows has higher levels of IGF-1—it does not (Vicini and others 2008)—so Smith’s whole argument is based on a false statement of the facts.  There are other more subtle problems with Smith’s argument.  For example, the opponents of rBST erroneously claim that rBST treatment increases IGF-1 concentration of milk 10%.  We now know this is incorrect, however, even if it were true, this amount of IGF-1 would contribute a minute amount to dietary IGF-1 intake.  More importantly, the level of IGF-1 in milk is far below that which has been used in oral feeding studies in animals in which IGF-1 produced changes in the animals (see response to Sect. 7.1; Goldstein and others 2006).  IGF-1 is largely digested in the GI system and only small amounts of it are absorbed.  In the final analysis, Genetic Roulette has the facts wrong, but even if it were right, the small IGF-1 increase would be of no consequence to the twining rate.

2.  The difference in frequency of twins in the US and UK is not evidence that rBST treatment of cattle is responsible. The population studies that show a 32 percent increase in the frequency of twins in the US over the last 30 years while during the same period the rate only increased 16 percent in the UK may be accurate observations.  These kinds of populations studies cannot, however, reveal the cause of such differences because there are many variables that could have contributed.  Smith notes that childbearing later in life and in vitro fertilization are both known to contribute to a higher frequency of twins.  There may be other factors that are not mentioned as well.  In order to determine the most likely cause, investigators would need to compare the differences between the two populations for factors such as average maternal age, frequency of in vitro fertilization, blood concentrations of IGF-1 and a host of other possible contributors.  The results of this kind of analysis would, however, only point to the best candidate causes but they would not prove the cause.  Proof that a change in one of the factors such as maternal age caused the increased number of twins to be born would require carefully controlled research with matched groups of subjects.  Genetic Roulette ignores the scientific methods used to establish cause and affect relationships, indeed, it ignores the most likely known causes of the higher rate. Smith instead seizes another opportunity to make assertions about genetically engineered products in the total absence of evidence.  Smith also commits his favorites logical fallacy, our old friend the post hoc fallacy.


Gary Steinman.  2006.  Mechanisms of Twinning. VII. Effect of Diet and Heredity on Human Twinning Rate.  Journal of Reproductive Medicine. 51: 405-410.

Vicini J, Etherton T, Kris-Etherton P, Ballam J, Denham S, Staub R, Goldstein D, Cady R, McGrath M  and Lucy M. Survey of retail milk composition as affected by label claims regarding farm-management practices. J Am Diet Assoc. 2008;108:1198-1203.

Goldstein DA, Kowalczyk DF, Vicini JL, Buonomo FC, Farmer DR. J. 2006. Twinning and higher intake of dairy products.  Journal Reproductive Medicine. 52:140-141.

Genetic Roulette Falsely Claims:

Milk from rbGH -treated cows likely increases the rate of twin births

1. Higher IGF – 1 levels increase the rate of twin births

2. Since milk drinkers increase their IGF-1, correspondingly they have higher twinning rates

3. Milk from cows injected with bovine growth hormone has higher IGF-1 levels

4. Drinking milk from injected cows should increase the twinning rate even more

5. The number of twins grew at twice the rate in the United States compared to the United Kingdom, where rbGH is banned

Genetic Roulette contends that because milk from rbGH-treated cows contains more IGF-1, women who drink it will have a higher number of twin births.

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