Comment by jjk166
2 years ago
There's a precipitous rise in old people, and especially otherwise healthy old people in developed countries. All those who would have died of perhaps an upper respiratory disease or an untreated infection before they had a chance to develop Alzheimer's are no longer being eliminated early. We see similar trends for most age related diseases like cancer and heart disease. It's only natural that as we get better at dealing with diseases we can cure we would see more of the ones we can't. That's not to say there couldn't be other environmental factors at play, but a rise in Alzheimer's does not necessarily mean a rise in whatever causes Alzheimer's.
> All those who would have died of perhaps an upper respiratory disease or an untreated infection before they had a chance to develop Alzheimer's are no longer being eliminated early.
OP claimed a rise in rates, not absolute numbers. Is there any plausible reason that reducing other causes of mortality might possibly cause a rise in fraction of the elderly population that develops Alzheimer's?
Depends if they meant rates or rates by age. If you mean population rates, then rising life expectancy caused by a decrease in other causes of death would absolutely increased overall pop alzheimer's rates.
If other causes of death were eliminated, you might also see an increase in alzheimer's amongst those in the same age bracket. This might be clearest with an example.
Suppose we eliminated heart disease. Life expectancy would increase. What would happen to the rates of other disease? They would go up within age groups. Because you still have to die of something. If heart disease can't take someone out, that means some other factor will be available. Much of the time people have more than one condition.
Depends on if the rise is specifically in the fraction of the elderly population, or if it's in the fraction of the general population.
If the rise is in the fraction of the general population, then an increase in the proportion of the general population that was elderly would be expected to increase the numbers of a disease of the elderly, even if nothing was happening.
If there were a rise in the proportion of e.g. 80 year-olds that were developing Alzheimer's, that'd be a different story. Although you'd still have to ask yourself if some of the conditions that were increasing the proportion of the population that are 80 year-olds were disproportionately extending the life of people with a propensity for Alzheimer's.
And this effect produces an increase in rates. Let's say that an entire population gets two dice. They roll the first one, if it's even they're out, otherwise they roll the next one. About 1 in 12 people are going to roll a 6 on that second dice. Now let's say for that first dice, you're only out if you get a 6. Now the odds of getting a 6 on the second dice is about 1 in 7, not because the second dice is any more likely to get a 6 but because a greater percentage of people who would roll 6's are rolling that second dice. The first dice in this analogy are diseases that we can now deal with, the second dice are the more intractable diseases.