杏吧原创

THERE鈥橲 nothing like a good health scare for stirring the apathetic out of
their armchairs. Some health scares definitely save lives, such as the one about
eating too much salt. Others may be misplaced, but still draw attention, for
example, to a pesticide which although doesn鈥檛 cause cancer as its opponents
say, is damaging wildlife.

So, into which category does that old chestnut the nitrate scare fall? I mean
the idea that nitrate from fertilisers gets into our food and drinking water
causing stomach cancer and turning babies blue. People tend to forget that tiny
amounts of nitrate are often added to cured meats as a preservative, and
sometimes as a flavour enhancer and colour stabiliser. But the nitrate from
fertilisers has provoked most concern.

I became convinced about ten years ago that the nitrate scare fell into the
鈥渕isplaced but useful鈥� category, but having looked at recent medical evidence I
think it needs a category all of its own. What鈥檚 worrying me in particular is
the possibility that the nitrate scare itself could have contributed to the rise
in notifications of food poisoning in Britain, from 35 000 in 1987 to 106 000 in
1997. Here鈥檚 why.

The idea that nitrate causes stomach cancer first took hold in the 1980s.
Then, as now, however, it was based only on possibilities rather than hard
evidence. Environmentalists feared oxygen-hungry microbes in our mouth could
change nitrate (NO₃鈥�) in our vegetables and water into nitrite
(NO₂鈥�). This nitrite might then react in the stomach with
secondary amines released from digestion of protein to produce carcinogenic
N-nitrosamines, which could cause stomach cancer. But when epidemiologists at
Oxford looked for evidence of a link between stomach cancer and nitrate in the
mid-1980s, they drew a blank.

Some of their research involved workers in a factory producing ammonium
nitrate fertiliser. I visited a similar factory, and could taste ammonium
nitrate in my saliva within a minute or two of arriving. If anyone would have an
enhanced risk of stomach cancer from nitrate, it had to be them. But they did
not. In fact, the Oxford team found that such workers were actually healthier
than workers with comparable jobs in the area, and had lower rates of
respiratory and heart disease. Could nitrate actually be good for you?

The answer turns out to be yes, but for an odd reason. We now know that the
biochemical scenario underpinning the cancer scare is partly true. A few years
ago at the University of Aberdeen, a team led by Ben Benjamin (now at St
Bartholomew鈥檚 Hospital, London), showed that nitrate is indeed converted to
nitrite in the mouth. Microbes living in little pouches at the back of the
tongue are responsible for the conversion
(New 杏吧原创, 20 July 1996, p 17)鈥攎颈肠谤辞产别蝉
similar to those which convert nitrate to nitrite in the soil.

And if that seems odd, consider another of the researchers鈥� findings: one of
your body鈥檚 metabolic systems secretes nitrate into your saliva if you are not
getting enough from water and vegetables. It seems the body is programmed to
keep those nitrite-producing microbes in the mouth busy at all costs. Hardly
what you鈥檇 expect if nitrite caused stomach cancer.

Which of course it doesn鈥檛. The strong acid in the stomach decomposes all
this nitrite straight away. In doing so it gives off nitric oxide and other
potentially dangerous chemicals which helpfully kill Salmonella,
Escherichia coli and other unwelcome visitors to the stomach. It is all
part of the body鈥檚 defence system against the microbes that cause
gastroenteritis. And nitrate is the fuel which powers it.

Which brings us to another major irony. The second main charge against
nitrate was that it could harm infants by causing 鈥渂lue baby鈥� syndrome, or
methaemoglobinaemia (MHB). Ben Benjamin believes that gastroenteritis is the
main factor in MHB. This could tie in with the fact that all the cases of MHB I
know of were caused by water not from a mains supply but from wells, and 98 per
cent of these were described as being 鈥減rivately dug鈥�. What鈥檚 more, in several
reports, the water was found to be polluted with bacteria as well as nitrate,
lending weight to the notion that gastroenteritis is the key factor in MHB. And
as we now know, nitrate fuels our bodies鈥� defences against bacteria that cause
gastroenteritis. The last thing we should want to do is exclude it from food or
water at risk from those bacteria.

The nitrate scare was the wrong scare. You used to see some roadside stalls
around Britain claiming 鈥淗ot dogs鈥攏o nitrates鈥�. Stallholders wanted to
reassure passing customers that this fast food wouldn鈥檛 give them cancer. If
they still exist, such signs should now be treated as a warning about the risk
of gastroenteritis. With up to five million people dying worldwide from
gastroenteritis each year, it is time that nitrate had a better press.

One of the most alarming outbreaks involved the dreaded E. coli O157
and a Lanarkshire butcher called John Barr, whose infected meat products claimed
21 lives in 1996. Did the nitrate scare only add to the many malpractices of
which the official inquiry accused him? Might it have dissuaded Barr from adding
nitrate or nitrite to his cooked meat? Perhaps it is time we had a scare about
health scares.