It’s well-established at this point that news outlets rarely
report positive medical findings with the same enthusiasm as negative medical
findings, much in the same way that a young man helping an elderly woman across
the street doesn’t garner as much attention as a burglary or fire.
Unfortunately, when people get their medical information from local or national
news, it often means that doctors end up having to do a lot of explaining.
An example of this phenomenon happened this past week when the New York Times reported that for some people, exercise worsens cardiac risk
factors like blood pressure and triglycerides. Of course, this flies in the
face of our current understanding of lifestyle and its effects on improving
health, and it has some docs worried that their patients may let up on
exercise. There are two points that this article has brought up for me, and I
hope you find them of help in interpreting this result, a result the lead
author termed, ‘bizarre’. (If you're interested, here's the original article)
The first is that, in research, we are constantly bombarded by
conflicting information, and that this information needs to be analyzed and
understood by clinicians in order to make sense. There’s a somewhat dated
expression from the world of computer science that I like to use in this
situation: ‘Garbage in, garbage out’. In computing, this means that erroneous
entries produce erroneous results, but I mean it to mean that disorganized data
results in disorganized opinions. Like the blind men describing the elephant,
scientists using separate samples of data will reach differing conclusions, and
the data doesn’t organize itself – it’s up to us to gather all of this
information and synthesize it into a coherent whole.
When we have data that conflicts with prior information,
it’s usually telling us something that we ought to know, and were previously
unaware of, but rarely does it supersede the other information or somehow overturn
it. Thus, the elephant is in some circumstances is like a rope, in others like
a wall, and in others like a tree trunk, but it’s always a large grey mammal.
Similarly, this information about exercise is telling us something that we
didn’t previously know – what exactly it is hasn’t yet been determined, but in
no case does it invalidate the information we already have that in most cases,
exercise is linked to decreased risk of hypertension, heart disease, diabetes,
depression, cancer, and overall mortality.
The second point to bring up in this discussion is that of
outcomes versus surrogate markers. In practicing medicine, our goal is always
the preservation of the patient’s health and the alleviation of suffering,
because these are the things that happen in real life and that matter to
patients. In research terms, they’re outcomes – they are the measurable real
life effects we aim to achieve. However, research based strictly on outcomes is
expensive, time-consuming, and in certain cases, frought with ethical concerns
(think about who would willingly take placebo compared to a potentially
life-saving substance). To overcome these obstacles, we instead shoot for
shorter goals – these are surrogate markers. Surrogate markers include things
like cholesterol, blood sugar, blood pressure, and other similar lab markers or
physical exam findings. We use these markers to measure someone’s likelihood of
reaching one of the real-life outcomes we’re trying to prevent.
Unfortunately, though these are very useful tools, the link
isn’t always perfect. A classic example is that fish oil has a somewhat
paradoxical effect of slightly raising LDL cholesterol, but significantly
lowers one’s likelihood of having a coronary event. Similarly, many people have
escaped having a stroke despite ragingly high blood pressure. In analyzing this
data on exercise, then, we have to ask ourselves about markers versus outcomes
– this study shows that cardiovascular risk markers are adversely affected in a
minority of people who start exercising, but on the other hand, many other
studies show that exercise is associated with significantly lower risk of
having a cardiovascular event. In my book, outcomes trump markers.
In the end, this information is probably going to tell us
something useful. Perhaps a minority of people have a transient elevation of
certain markers when they start exercise, that is followed by a long-term
lowering of risk factors. Perhaps there is a small subset of people who need
specially-tailored exercise programs that won’t cause this elevation. As the
authors point out in the paper, we really don’t know what this information
means. In the interim, I’m going to continue plugging for the benefits of
exercise, because while I believe that important information will come from
this surprising finding, I don’t think it’s going to overturn the consensus
that exercise is beneficial for the vast majority of people.
