Rotten statistics (again)

[Hector Maletta]

Unless I am mistaken, here is another example of poor statistical method in
the medical literature: eating dairy fat prevents infertility. Skim milk
makes you infertile.
Various points of poor methodology can be (I think) spotted in the sketchy
report. The sensationalistic amplification by journalists (with the probable
help of researchers or PR people) is also easily detected.
The influence of some dairy lobby may be suspected by conspiracy freaks but
is not in clear evidence.
Hector



Low-fat dairy infertility warning
A diet rich on low-fat dairy food may make it harder for some women to
conceive, according to a study involving thousands of US women.
Harvard researchers found women who frequently ate these foods were 85% more
likely to have ovulation problems.
In contrast, the Human Reproduction study found eating full-fat dairy foods,
including ice cream, cut the risk of this type of infertility.
However, UK experts insist there is scant evidence of a link.
The research used a database of 116,000 US nurses which is regularly updated
with information about their lifestyle, diet and health.
They were asked whether they had been trying, and failing, to conceive, and
whether a diagnosis of 'ovulatory failure' - infertility due to irregularity
in the normal monthly cycle - had been made.
Over an eight year period between 1991 and 1999, 438 women reported this set
of circumstances, and their answers to questions about their diet were
analysed.
If the women ate two or more portions of low-fat dairy produce a a week, the
risk of infertility due to ovulatory failure appeared to be 85% higher.
When women eating two or more portions of full-fat dairy produce such as
whole milk or ice cream were compared with those eating one or fewer, they
had a 27% lower risk of infertility due to lack of ovulation.
Food swap
Dr Jorge Chavarro, who led the project, said that the link needed further
investigation.
He said that women trying to conceive should think about their diet: "They
should consider changing low-fat dairy foods for high-fat dairy foods; for
instance, by swapping skimmed milk for whole milk and eating ice cream, not
low fat yoghurt."
He believes the key may be that there is substance vital for healthy ovarian
function that requires the presence of fat for it to be properly absorbed
into the body.
However, other scientists say that the only compelling evidence of a link
between diet and infertility involves obesity, which is linked to a
significant reduction in the chances of conception.
Dr Richard Fleming, from the Glasgow Centre for Human Reproduction, pointed
out that women reporting a low-fat 'healthy' diet might be those already
aware of fertility issues and trying to improve their chances.
He said: "Women with ovulatory failure make up a relatively small proportion
of cases of female infertility.
"I'm not convinced that there is any reason for women who are trying to
conceive to alter their diet unless they are obese, and I would not advise
any woman to do this."
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/health/6400171.stm

Published: 2007/02/28 00:05:16 GMT