Although an early participant in the world of Usenet newsgroups, I'm a latecomer to the world of blogging. I don't read or participate in blogs often, and as a newbie will undoubtedly make mistakes of etiquette and function much as I did in the very early days of Usenet before I got a feel for the music of the newsgroups. I hope anyone reading this will take this into account and cut me some slack!
I'd been considering for a while now blogging about evidence and medicine, something I spend a fair amount of my time thinking about in any case, but a couple of events pushed me to take the plunge.
The first was when a relative, a woman in her mid-40's, called to tell me that she'd seen her new primary care doctor. The doctor had run tests on her including checking a lipid profile. The lipid profile showed a total cholesterol of 160, an HDL of 44, and an LDL of 105. Based on these results, the doctor informed her that she should be very concerned about her "low" HDL number and told her to start taking fish oil.
This was an interesting interpretation of the results and an unusual suggestion for management, and it gives some sense of my concerns about how evidence is used, ignored, or misused in medicine. This relative had a low normal blood pressure, no smoking history, did not have diabetes, and had no family history of coronary heart disease. As such, there is even some controversy as to whether she should have had a lipid profile checked at all.
Assuming a lipid profile was worth doing, she should certainly have been told that this was an excellent profile putting her at low risk for a cardiovascular event, and that there was little modern medicine could do to substantially affect her risk. Her 10-year risk of an event (using the 2008 calculator that overestimates vascular risk by including things that probably shouldn't be included -- a blog for another day) works out to about 2.2%. If we pretend that somehow fish oil could increase her HDL to 80 and that she would get all the same benefit as if her HDL were naturally 80, we could drop her calculated risk to about 1.4%. So, if she took medication daily for 10 years, she would reduce her risk of an event (under these outlandishly favorable assumptions) by 0.8%. Not something this relative was interested in doing.
But, do we even know that fish oil raises HDL? The main effect of fish oil on lipids is to lower triglycerides. Most studies suggest that fish oil only raises HDL levels by about 3%, so we might expect an increase from an HDL of 44 to an HDL of 45. It's hard to see how the doctor felt this would fix the woman's "low" HDL.
But, beyond that, we have no solid evidence that raising HDL with medication improves outcomes. Changing HDL with medication is a surrogate outcome for that medication -- that is, it is of no direct interest to the patient unless it also predicts better cardiovascular outcomes, and HDL appears to be a poor surrogate. Some medications that raise HDL appear to cause harm and worse vascular outcomes.
As for whether fish oil supplements are beneficial through some non-HDL mechanism, I think we can safely say that the jury remains out as to whether a woman in her 40s at low cardiac risk could expect any important benefit from fish oil supplementation.
Interestingly, my relative's doctor also checked her vitamin D level and told her that a level of 34 (in the normal range) was concerningly low and that she should start taking 1000 IU of vitamin D per day (she was already taking 400 IU). Vitamin D supplementation is controversial, with lots of people claiming big benefits, but we can safely say for now (again, perhaps a longer blog for another day) that there is no solid evidence that having a woman with a normal vitamin D level start taking additional vitamin D is likely to be of any benefit to her.
My relative asked what I thought these events said about her doctor, but I'm not really sure. I see decisions like this made all the time, where evidence is misunderstood, misapplied, or ignored. I have the sense that this particular doctor may believe she is getting out ahead of the evidence -- suggesting therapies that she believes will be proven down the road to be of benefit. She could, of course, turn out to be right, but we should be very hesitant to give preventive medications without a decent evidentiary basis. Other drugs that raise HDL have increased mortality. Supplementation with other vitamins that were thought beneficial has turned out to cause cancer or increase mortality.
I said there were a couple of events that prompted me to start this blog, but this post seems long enough. I'll talk about other events in future postings.