We've all heard the breakfast cereal
commercials claiming "studies have shown" that whole
grain cereal can lower cholesterol and improve cardiac
health. The suspicion lingered, however, that while
the claims were fundamentally sound, these studies were
not of the highest quality. That can't be said of the
new Harvard study in the October 22 Archives of Internal
Medicine, which proves that whole grain cereals
reduce heart failure risk by up to 29%.
The prospective study tested the
claims made by the cereal makers using the population
of the famous Physicians' Health Study I, in which all
the guinea pigs were male doctors. Twenty years follow-up
of 21,376 doctors who kept detailed records of their
diet, medication, exercise, health and multiple other
factors, with no sponsorship from Kellogg's or Nabisco
to get in the way, should be enough to put this question
to bed.
A
COMPLETE BREAKFAST
Whole grain cereals showed a clear protective effect,
in terms of heart failure. There were 1,018 cases of
heart failure among study participants. With a baseline
risk of 1.0 for those who ate no bowls of cereal a week,
the relative risks for heart failure were 0.92 for one
bowl a week, 0.79 for two to six bowls, and 0.71 for
those eating seven or more bowls a week.
This trend was highly significant,
but only for whole grain cereals — cereals with
at least 25% whole grain or bran. For those eating processed
cereals, in which the fibrous husks are mostly removed,
the trend towards heart failure protection translated
into no protection at all.
The Physicians' Health Study began
in 1982, but this study is considered prospective even
though it involves a review of old data, says lead author
Dr Luc Djoussé of Harvard Medical School, because
"none of these guys had heart failure when they filled
out the cereal questionnaire."
OTHER
FACTORS
The study's findings control for almost every imaginable
co-variate, including age, smoking, alcohol consumption,
vegetable consumption, use of multivitamins, exercise,
plus history of atrial fibrillation, valvular heart
disease and left ventricular hypertrophy.
One advantage of a study population
composed of physicians, says Dr Djoussé, is that
"the self-reporting tends to be more accurate, because
they know what to look for." But a potential downside
is that "being highly trained and educated in these
matters, they might be doing something to reduce their
risk that we aren't measuring."
That would have to be something
pretty imaginative, given the rigorous controlling for
potential confounders in this trial. But Dr Djoussé
does regret not adding one more variable to the analysis
- left ventricular function. About half of heart failure
patients - the diastolic half - have preserved left
ventricular function which typically means a better
prognosis even though we know less about how to treat
it. The two types of heart failure may have different
risk factors. "It would have been useful to know if
whole grain cereal was more protective against one or
the other kind," he said.
MILKING
BENEFITS
Two other potential variables not measured are milk
and sugar, because few of us eat our cereal straight
out of the box. If white sugar had some unsuspected
cardio-protective properties, that might theoretically
confound the data. That seems unlikely, of course, but
what about milk? "We would have liked to collect data
about milk but didn't want to put too much burden on
the participants," says Dr Djoussé. "There is
research that suggests the calcium in milk can lower
blood pressure, but obviously high fat milk would have
a bad effect on your cholesterol."
The best evidence that milk can
be discounted as a factor is the lack of effect seen
in subjects who ate a lot of processed cereal. They
too would have benefited if milk was the real agent
of protection.
So, it looks as if whole grain
cereal is indeed significantly protective against heart
failure. But is your patient's cereal the right kind?
"You have to be careful about this," says Dr Djoussé,
"because the industry's use of the term whole grain
can be deceptive. Read the nutritional ingredients on
the box. If it says more than four grams of fibre, you
can be confident it's essentially the right kind of
cereal."
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