A colleague sent me advance notice of an upcoming protest: a 'mass overdose' of sugar pills being organised as a protest against 'homeopathic remedies'. (Grant picked up on this & has blogged on it over at SciBlogs. This got me thinking (as these things do) about an interesting podcast by Mark Crislip, who focuses on supplements & 'complementary & alternative medicines'. This particular episode concerned claims that a particular food, supplement or treatment 'boosts the immune system'. There are a few questions you should ask when you hear such statements.
How does it boost the immune system? Your immune system has a number of inherent control mechanisms that regulate its responses. Which of these mechanisms does the food/supplement/treatment affect, and how?
Which part of the immune system does it target? After all, the mammalian immune system is a thing of many parts: non-specific & specific responses; cellular & 'humoral' components (eg antibodies); the many different types of white blood cells; signalling & regulatory chemicals such as cytokines, interleukins, & interferons... - which of these, specifically, does the food/supplement/treatment target?
What is the evidence in support of these claims? Is it based on 'in vitro' studies ie of cells that have been isolated from the system & grown & studied in the test tube? These aren't necessarily going to behave as they would in the actual organism. (I'm reminded of a study I read some years ago now, that supposedly demonstrated that drinking chicken soup really was a good thing to do when you're sick. But it didn't look at the impact on patient health of drinking chicken soup - the researchers looked at the effect of samples of soup on the activity of isolated white blood cells: specifically, whether or not it inhibited the cells' abiltiy to generate an inflammatory response. But this doesn't mean it will translate to a similar effect in the body.) In fact, it turns out that white blood cells will often generate an 'inflammatory response' in the presence of some pathogens, but this doesn't necessarily translate into an elevated body-wide immune response.
And that segues nicely into the final question: Is 'boosting the immune system' necessarily a good thing? If that response is a generalised inflammatory response, the answer is, quite possibly not. Because chronic inflammatory responses may be related to increased risk of blood clots, and those in turn can carry nasty health risks. For example, a 2006 study published in the Lancet found that people who'd had a urinary tract infection, with accompanying inflammatory response, had a heightened risk of developing a thrombosis (blood clot) in the four weeks immediately after the infection. There are similar findings from other studies. This apparent inflammation-thrombosis link hasn't yet been shown to be a causal relationship, & we do need to be careful in attributing causality (it's all too easy to get it wrong NB warning, this is humour!), but it's certainly one to consider.
In fact, in people who are in good health & do all the common-sense things needed to stay that way (ie get sufficient sleep, exercise, & food), it's neither necessary nor possible to 'boost' the activity of their immune systems. It'll work just fine all by itself :-)