Many people are taking insulin-like growth factor-I without even knowing it.

Abstract

To the editor, Adams does an excellent job of discussing the dangers of the exogenous augmentation of insulin-like growth factor-I (IGF-I) and properly cautions against its use, citing both lack of efficacy and potential adverse effects, such as disruption of the insulin system and carcinogenesis.1 However, many people in the United States are consuming higher levels of IGF-I than they realize and may face the same elevated risks because milk from cows treated with recombinant bovine growth hormone (rBGH) has significantly elevated IGF-I levels. Measuring these levels has even been proposed as a basis by which to test for the use of rBGH.2 In addition, the IGF-I in the milk of rBGH-treated cows is potentially more bioactive than the naturally occurring form, and this bioactivity may be increased further by pasteurization.3 Adams notes the lack of significant effects of IGF-I administration in the elderly, but this does not necessarily hold true for children, who may be at an increased risk of adverse effects. Children's rapid growth may make them more susceptible to IGF-I. In addition, children's intestines, particularly those of infants, are naturally more permeable than those in adults, which could allow greater absorption of the large IGF-I peptide. Despite the common assumption that IGF-I cannot be significantly absorbed when taken orally, several studies have shown that this is not the case. Premature babies given breast milk in addition to formula had almost twice the serum IGF-I levels of those receiving formula alone.4 This finding is not surprising because breast milk contains IGF-I and formula does not, but it does strongly suggest intestinal absorption. Furthermore, people who consumed 3 servings of milk daily had a 10% higher level of serum IGF-I and almost a 10% lower level of IGF binding protein-4 than people who drank less than 1.5 servings.5 Although healthy people may absorb only limited quantities of IGF-I, the situation is likely different for people with conditions that can cause increased intestinal permeability, such as celiac disease, Crohn's disease, autism, cirrhosis, and cow's milk allergy. The use of various medications, such as aspirin and other nonsteroidal anti-inflammatory drugs, can also increase intestinal permeability. In addition, an estimated 10% to 20% of the general “healthy” population unknowingly suffers from this condition.6 It is not enough to look at healthy adults and say that the intestinal absorption of IGF-I is negligible. Rather, the vulnerable in society need to be protected. Adams eloquently points out that the use of IGF-I for enhancing athletic performance “ignore[s] our understanding of the integrated nature of physiologic systems.”1 However, this same ignorance was used when the Food and Drug Adminstration chose to approve the use of rBGH. Let's not put corporate profits ahead of children's health. The use of growth hormones in livestock has certainly not been proven safe, and no overriding benefits would justify such risks.