Answers
03/16/1994

<TITLE>Dietary IGF-I and rbST</TITLE>
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T94-17                                      Susan M. Cruzan
Mar. 16, 1994                               (301) 443-3285

                     Dietary IGF-I and rbST

     FDA has been receiving inquiries about whether insulin-like
growth factor (IGF-I) associated with the use of recombinant bovine
somatotropin (rbST) in dairy cows could have adverse effects on
people who consume the milk from treated cows.  Specifically,
allegations have been made that dietary IGF-I will cause breast
cancer.
     FDA and other scientific and regulatory bodies have thoroughly
examined the safety of milk produced by rbST-treated cows and have
concluded that it is safe.  The consumption of dietary IGF-I plays
no role in either inducing or promoting any human disease, nor does
it cause malignant transformations of normal human breast cells. 
     The following may be used to respond to inquiries.
     IGF-I is a natural protein required for normal growth and
health maintenance.  IGF-I is structurally and chemically similar
to insulin and is normally present in almost all body tissues and
fluids including human breast milk and saliva.
       Abnormally low levels of IGF-I are associated with several
disease conditions including dwarfism, malnutrition, osteoporosis
and infertility.  It has been suggested that a decline in 
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                                        Page 2, T94-17, IGF-I  
IGF-I levels in human tissue causes many of the degenerative
changes associated with aging.
     FDA has reviewed several comprehensive studies to determine if
administering rbST to cows affects the IGF-I content of their milk.
These studies have demonstrated that rbST does not increase the 
IGF-I content. 
        The IGF-I that occurs naturally in human breast milk occurs
at about the same concentration as that found in cow's milk. 
Levels of IGF-I in cows' milk and meat are very much lower than the
levels found naturally in human blood and other body tissues.  
     IGF-I is not absorbed intact. Dietary IGF-I in milk and meat
is broken down in the gastrointestinal tract by digestion.
Undigested IGF is excreted.    
     In conclusion, the suggestion that IGF-I in milk can induce or
promote breast cancer in humans is scientifically unfounded and
misguided.  FDA has determined that milk from rbST-treated cows is
safe for human consumption and has not been found to be different
from milk from non-treated cows.   
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