On rationality, yes, it does depend on what you consider irrational. But as far as I can see, it’s significantly more irrational to be concerned with external sources of pleasure – like money – than with whether you’re actually happy. (Homo economicus makes himself miserable.) And psychological studies tend to indicate that we lose more happiness from loss than we receive from gain; so behaving as if that’s the case is a good reflection of the truth. I guess you could take the rationality question to a meta-level and ask whether loss should lose more happiness than gain increases; but it does seem to me that the answer is yes even there, in at least some cases.

The context of this statement comes from the so-called “neuroeconomic” study of decision-making. To oversimplify, it means people behave as if losing $10 is more bad than gaining 10$ is good.

There’s definitely a long discussion to be made about whether this is “really irrational”, but that all depends on what you consider rational. It’s quite plausible that wise decision-making is not quantitatively balanced. But that just begs the question; the “irrationality” is wherever the judgments stop matching the quantitative risks and rewards.

I think the hedonic treadmill may explain health past a certain age, but not for many decades of our lives. But on reflection, that leads me to realize that we (as a culture) have fused health with other aspects of happiness, such as attractiveness. This is actually pretty reasonable, but it also seriously occludes any attempt to determine how much 16-30(or whatever)-year-olds actually value health per se.

I wonder how much the fear of losses is really irrational. If I recall the happiness studies research, when we gain some new external goods, we get a brief happiness boost then return to a set point; but when we lose them, our happiness goes down and stays down. (The hedonic treadmill.) Since health is something that we’re very likely to progressively lose, that might actually be a sensible reason to put a high priority on it.

Health has to play some role in the good life- after all, if your health is bad enough (or nonexistent), there’s not a whole lot else you can do. This very danger, the steep consequences of its absence, make it easy to focus on: it’s easier to fear sickness/death than boredom.

Is that a wise way to weigh things? To some extent, it’s not really an answerable question: it’s a matter of value, a judgment question, and different people can honestly give different answers. Adam will gain more out of being in healthy shape, while Bob will gain more out of enjoying those cheeseburgers. Of course, that’s a cheap answer: part of the mission of philosophy is to work past the judgment errors that arise in such unconsidered decisions. But I’m hesitant to offer such a philosophical answer, because in this case the details are everything. How certain are we that diet/medicine X will appreciably improve health? How much else must be sacrificed to follow through with X? These are answerable questions, but only for each individual X.

I would imagine that people frequently make mistakes about the value of health to their good life, but I imagine that those mistakes don’t differ systematically from the mistakes we make about other potential sources of ‘goodness.’ IIRC, people do tend to have disproportionate/irrational preferences to avoid losses- which could translate to a magnification of factors motivated by fear, as I described above. In that way, it’s possible that people do put too much weight on health. But I suspect that in most of our decision-making processes, small and large, we’re just as afraid of other losses as we are of health losses.

It may be that we don’t have a health-driven society: instead, we have the patina of one. This raises questions about the historic origins of this trend. When did health start being such a major focus of our culture? (Though “when” is just a means to get at “why”.) Is this a 20th-century, baby-boomer, marketing-driven phenomenon? Have we just focused so much on health because it’s one part of the good life (or, perhaps, “another part”, after toy acquisition) that can be commoditized and paid for?

But while this discussion is interesting, it only tangentially addresses your main point, which is whether we *should* value health so much. I’ll put my thoughts on that in a second comment later.