Bovine hormones: Unpalatable prospects

Sally Best investigates whether a post-Brexit relaxation on the use of bovine hormones could affect public health in the UK

 Following the UK’s withdrawal from the EU Customs Union, the UK will be able to negotiate trade deals with countries that currently have limited trade agreements with the EU, such as the US. This may allow access to goods at lower tariffs than the EU imposes, as well as goods that it bans. 

There may, however, be health consequences to these post-Brexit food standards, along with threats to animal welfare. At present, the UK complies with EU law, which is informed by the European Food Safety Authority (EFSA). New negotiations may result in the import of produce that does not comply with EFSA laws – including milk from cattle treated with recombinant bovine somatotropin (rBST). Food safety standards may become a bargaining chip in trade negotiations, for example with the US. 

In 1993, the Food and Drug Administration (FDA) approved rBST in the US for use in increasing milk production in cows. The FDA’s reports concluded that milk and meat from rBST-injected cows was ‘safe and wholesome’, and appropriate for use in the commercial food supply chain. Conversely, a report commissioned by the EU in 1999 suggested that consumption of milk from cows treated with rBST had possible detrimental effects on human health ( This led to the ban on rBST use within the EU – begging the question: is this hormone safe for use in the UK’s commercial food chain?

rBST: the facts

rBST is developed using recombinant DNA technology, which produces synthetic versions of the hormone bovine somatotropin (BST). It is injected into cattle in order to enhance milk production by promoting growth and cell replication. BST stimulates milk production by increasing levels of insulin-like growth factor (IGF-1). Its aim is to increase profit margins. 

BST is synthesised in the US by Monsanto, under the name Posilac. Administered at the ‘optimal quantity’, rBST is said to stimulate an increase in milk production by 10-15% per cow. By 2007, rBST injections were administered to 17% of US cows. 

Although rBST is sufficiently chemically dissimilar from human growth hormone somatotropin that it does not have any direct effects in humans, Bovine IGF-1 – which is increased upon administration of rBST – is chemically similar to human IGF-1, so is biologically active in humans. Consequently, consumption of milk from rBST cattle could conceivably increase the levels of biologically active IGF-1 within the consumer’s bloodstream. Epidemiological studies reveal that high levels of circulating IGF-1 in humans is associated with an increased risk of numerous common cancers, including breast, lung, colon-rectum and prostate ( 

In 1998, Michelle Limoli, who worked for the FDA as the associate director for the EU at the time, stated: “The FDA firmly maintains that [rBST] is a safe and beneficial product for humans and animals alike.” She insisted that there was “no significant risk to human safety through ingestion of products from rbST-injected animals” and that this had been proven through “countless studies [that] found insignificant risks of cancer, antibiotic resistance, and allergic reactions”. This stance is still held by the FDA. Furthermore, the World Health Organization and the  Food and Agriculture Organization of the UN found that rBST can be used without any detrimental health effects for consumers. It has been noted by commentators that the FDA conducted one of the most rigorous “post-approval monitoring programmes” on rBST; furthermore, the FDA suggests that any apparent increase in IGF-1 in milk from rBST-treated cows that could be linked to a significant risk of cancer was only ‘slightly’ higher than that in untreated milk. They suggested this increase was less than that found in the normal variation of IGF-1 in untreated milk due to natural factors (

Statistically significant effects 
However, any food with a possible health risk should be subject to extensive scrutiny. As recognised by TB Mepham in two co-authored papers, “the possibility of deleterious effects [caused by rBST injected milk] was dismissed by the FDA”, despite the statistically significant effects produced in rats following orally administered IGF-1. These were deemed “sporadic results”. Further, Mepham highlighted that IGF-1 is not destroyed during the pasteurisation process and indicated that, due to the similarity between bovine and human IGF-1, the bovine IGF-1 increase caused by rBST injection would have a negative biological effect on the human gut. Moreover, FDA tests on effects of the hormone were deemed “inadequate”. This potential lack of oversight and scientific integrity raises concerns. 

“High levels of circulating IGF-1 in humans is associated with an increased risk of numerous common cancers”

Additionally, The American Cancer Society has stated that “more research is needed” to determine the levels of IGF-1 increase in rBST-treated milk, adding: “The extent to which intact, active IGF-1 is absorbed through the human digestive tract remains uncertain.” Studies at Harvard Medical School 
( found that women and men with higher levels of IGF-1 were at greater risk of developing colorectal and prostate cancer respectively. The studies suggested the most common sources of IGF-1 were milk, fish and poultry.  

The products on our shelves should have undergone comprehensive scientific scrutiny to prove that they are safe for human consumption – and rBST is arguably not. How will the UK avoid pressure to adversely modify current food standards 
in order to secure future trade deals?

There is also the animal welfare issue. Recent meta-analyses show a 25% increase in mastitis, a 55% increase in risk of lameness and a 40% reduction in fertility in rBST-injected cattle. Manufacturers claim these side-effects are all treatable with “careful management”. The current rBST packet label indicates that there are 21 side effects for cows administered with this hormone, including “injection site lesions which may remain permanent”. The European Commission recognises the stress induced in the cow upon administration of rBST. These side-effects compromise the animal’s autonomy, using them as a machine to generate maximal yield. Furthermore, illness in cows caused by rBST administration is typically treated using antibiotics; there is fear that these could form residues in milk, leading to antibiotic resistance in consumers. 

It is imperative that post-Brexit animal welfare is maintained to the highest possible standard. Complying with US farming methods could see unnecessary harm caused to animals through the use of such synthetic hormones. These threats should be considered when making future trade deals, to ensure that food safety does not become a bargaining chip during trade negotiations and fall below our current EFSA standards. 

Sally Best is an environmental biologist and scientific journalist

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