What I meant to say is that arguing whether or not ageing is a medical condition is far less important than treating its root causes, and as long as we focused on this task, we could postpone the debate to a later time. The finer points of establishing if ageing fits the definition of ‘disease’ to the letter would waste precious time we could spend saving lives instead; we should definitely not wait until the issue has been settled before we start developing rejuvenation biotechnologies. (And we are not waiting at all, luckily.) However, classifying ageing as a disease is very important and not at all pointless, as Reason of FA! explained in this post. In a nutshell, if the ageing processes that lead to age-related diseases were considered pathological, research on how to interfere with them would likely receive more funding, and drugs that target ageing itself could be approved by the FDA. (The FDA only approves drugs that target recognised diseases; if ageing isn’t recognised as one, no drugs targeting it would be approved.) I think there might be a chance that some bona-fide anti-ageing drugs would be approved even if ageing wasn’t recognised as a disease—for example, drugs that clear the amyloid plaques that build up in the brain would essentially be rejuvenation therapies preventing Alzheimer’s disease, and as such I suppose they would be approval material for the FDA, even if they did’t recognise ageing itself as a disease; nevertheless, it’s clear that things would be easier in terms of getting funding and approving drugs if the whole ageing process was classified as a disease.
That being said, if we want to decide if ageing is a disease, we really do need to have good definitions of both terms. It turns out that defining ‘disease’ is not a simple problem, and apparently WHO themselves don’t have an official definition. They do have a definition of health, though, which says among the rest that ‘ Health is […] not merely the absence of disease or infirmity’; the lack of an official WHO definition of disease makes their definition of health a bit problematic, in my opinion. I suppose they rely on the intuitive idea of ‘disease’ we all have, but as a mathematician, I find this decidedly insufficient. If you look up ‘disease’ on Wikipedia, you’ll find this:
A disease is a particular abnormal condition, a disorder of a structure or function, that affects part or all of an organism.
I don’t like this definition very much, because it might imply that a ‘normal’ condition isn’t a disease; however, the incidence of age-related disease grows higher and higher with age, to the point that I don’t see how they couldn’t be considered ‘normal’ past a certain age; that’s why I prefer a definition along the lines of ‘a definite pathological process having a characteristic set of signs and symptoms’.
As for the definition of ‘ageing’, I stick to Aubrey de Grey‘s definition, i.e. that ageing is the process of accumulation of damage the body inflicts itself as a side-effect of its normal operations. In the post we’re discussing, I said that even according to this definition, ageing wasn’t a disease, but only a cause of disease; I used a comparison I found very fit, i.e. that ageing is to age-related diseases what viruses are to infections. However, upon more careful reflection, this comparison is a bit misleading. It’s true that a virus is not a disease; however, a virus isn’t a process either, unlike ageing. A better comparison would be between age-related damage and viruses. The accumulation of damage could then be (rather loosely) compared to an infection, in the sense that both are processes that happen over time: They begin, they progress, and eventually give rise to symptoms and full-blown diseases.
Now, at least according to the second definition of ‘disease’ I provided, ageing seems to be one, because it is a pathological process (although an extraordinarily long one) that has a characteristic set of signs and symptoms. While symptoms and visible signs of ageing don’t show up until late in life, more subtle signs (accumulation of senescent cells, or cross-links, for example) are present inside your body basically at all times. The reason I call it a ‘pathological’ process is that the damage caused by ageing is, as said, a side-effect of your metabolism; it’s a bug, not a feature, left around by evolution because it was generally not serious enough to prevent you from reaching reproductive age. It’s a disease that stays silent until a certain threshold is reached—again, pretty much like an infection until there are enough viruses around to wreak havok.
Ultimately, ageing may or may not be a disease depending on the definition of ‘disease’ we want to adopt. With enough nitpicking, ageing may well not be a disease according to some definitions, but in principle we could change definitions around so much that Alzheimer’s disease stops being a disease and mountain climbing suddenly becomes one. (This is an intentionally ridiculous example.) I have no problem admitting that this is not what my previous post seemed to say, and I honestly have no idea how I managed to twist my own thoughts around so much that they ended up contradicting things I wrote before. I have a hunch I had grown a bit too fond of the metaphors I used in that post, which again seemed fitting but were confusing. I’m not a fan of revisionism, so my previous post is going to stay up right the way it is, just with a link to this one.
As a side note, some now-recognised age-related diseases were considered to be part of ‘normal’ ageing in the relatively recent past. Seems to me ‘normal’ is a safety-blanket word that we use to feel okay about not doing anything to change something that is not good and difficult to change. Or maybe, it’s just that we like feeling ‘normal’. If you’re 78 and your doctor says you’ve got high blood pressure, he’ll also probably reassure you and say that ‘at your age, it is normal’. So what? That only means that it’s common for a person of your age to have unhealthy blood pressure, and it’s in no way different from saying that it is normal for a smoker to have their lungs full of crap. It’s normal alright, but it is very bad nonetheless.