- By Alex Kirby BBC News Environment Correspondent
Presenter of BBC Radio Four's 'Costing the Earth' 5-4-99
- It has an eerie echo of BSE, the initials
which now mean mad cow disease. But BST is not an illness. It is a drug.
- It is an artificial hormone, a copy of
one that occurs in nature. And just as natural bovine somatotropin, to
give it its full name, promotes lactation, so artificial BST does the same.
- Cows injected with BST produce 10%, sometimes
even 15% more milk than they would do otherwise. But there is a downside.
- Painful infection
- BST causes increased health problems
in animals injected with it. They include higher infertility rates, more
mastitis - a painful infection of the teat - and a much higher incidence
- Despite that, the drug has been cleared
for use in the United States, where between a quarter and a third of all
dairy cows are thought to be injected with it.
- Milk from them and from non-BST animals
is mixed together haphazardly, and there is no way of knowing whether dairy
products in the US - or exported from it - contain BST milk.
- Five-year ban
- The European Commission imposed a five-year
ban on the sale and use of BST in 1994, on what it called socio-economic
grounds. That ban is now under review.
- Veterinary surgeons in both Britain and
Canada say that BST should remain banned to protect animal welfare. The
Canadian Government agreed that the drug presented an unacceptable threat
to the safety of dairy cows.
- But there are also concerns over possible
implications for human health. One centres on the increased use of antibiotics
to treat the increased disease that BST causes, and the risk that they
could find their way to humans.
- Cancer link
- Another worry is the fact that the milk
of cattle injected with BST contains up to five times more of a substance
called IGF-1, insulin-like growth factor one, than normal milk.
- IGF-1 has been linked with the development
of some cancers of the breast, colon and prostate.
- Professor Donald Broom, of Cambridge
university, is one of a team of senior vets advising Brussels on BST.
- He told the BBC that "the IGF-1
increase could possibly lead to a very small increase in the occurrence
of some cancers in humans - a very small risk, but a real risk".
- Dr David Challacombe, a consultant paediatrician
in Somerset, says these higher levels could over a long period help to
trigger the growth of malignant tumours.
- Clean bill of health
- BST does have its supporters. One influential
group that has given it a clean bill of health is JECFA, the Joint Expert
Committee on Food Additives.
- JECFA's members are appointed by and
answerable to two United Nations agencies, the World Health Organisation
and the Food and Agriculture Organisation.
- The drug's critics say the longest examination
of its possible toxicological effects, a 90-day study involving thirty
rats, showed significant impacts on the animals.
- The US Food and Drug Administration did
approve BST for use, but says it did not consider the rat study in reaching
- But the chairman of JECFA, Professor
Jock MacLean of Swinburne University of Technology in Melbourne, says his
committee did consider the study.
- Insignificant role
- He points out that the levels of IGF-1
present in milk from BSE cows are only a minute fraction of the amount
produced naturally by the human body, which led JECFA to conclude that
it plays no significant role.
- However, a Japanese study suggests that
IGF-1 from BST milk persists in the digestive tract long enough to pose
a far greater risk than the natural version.
- The European jury is still out on BST.
But it has heard evidence to show that there is cause for concern.