Is Recombinant Bovine Growth Hormone Safe During Pregnancy?

What is Recombinant Bovine Growth Hormone?

Recombinant bovine growth hormone (rBGH), also called recombinant bovine somatotropin (rBST), is a synthetically produced version of the naturally occurring cattle growth hormone, manufactured using genetically engineered E. coli bacteria. Injected into dairy cows, it increases milk production by 10-15%. It was FDA-approved in 1993 under the brand name Posilac (originally Monsanto, later Elanco).

Why is Recombinant Bovine Growth Hormone used in food?

Dairy producers use rBGH to increase milk yield per cow, reducing production costs. It was economically significant for large dairy operations. The FDA and the company argued it improves farm efficiency without directly harming the milk-drinking consumer.

What regulators have flagged about Recombinant Bovine Growth Hormone

The central human health concern is that rBGH treatment significantly elevates insulin-like growth factor 1 (IGF-1) levels in treated cows' milk. IGF-1 is a naturally occurring growth hormone that promotes cell growth and division. Multiple epidemiological studies have associated elevated blood IGF-1 levels with increased cancer risk in humans. A 1998 study in The Lancet (Hankinson et al.) found that women with the highest IGF-1 blood levels had approximately 7 times the breast cancer risk compared to those with the lowest levels. A 2004 meta-analysis in JNCI (the Journal of the National Cancer Institute) confirmed significant associations between high IGF-1 levels and breast, prostate, and colorectal cancer risk. The mechanistic question is whether consuming rBGH-treated milk raises blood IGF-1 levels in humans. The FDA and WHO/FAO Codex Alimentarius concluded that IGF-1 in milk is a protein largely digested in the GI tract before absorption. Canadian regulatory researchers challenged this, arguing that pasteurization reduces proteases that would otherwise break down IGF-1, potentially allowing more intact IGF-1 to survive digestion. The Codex Alimentarius Commission made history in 1999 by declining to endorse rBST safety maximum residue limits — a split vote (33 in favor of the MRL, 29 against, with abstentions) demonstrating fundamental international disagreement. This is one of very few cases where Codex failed to establish a safety standard. Animal welfare is a second major concern: Health Canada's comprehensive 1999 review found that rBGH-treated cows had 25% higher rates of clinical mastitis, 50% higher lameness risk, increased reproductive problems, and shortened productive lifespans, requiring substantially more antibiotic treatment — an antibiotic resistance concern. Canada rejected rBGH approval in 1999 after its scientific review; the EU banned it in 1999.