FACT - men get smaller in middle age

All my adult life I've been a medium size for clothes (being a 38" chest), but recently, as middle age advances, I've found that I fit into small and even extra small clothes. Am I getting smaller? Do men reduce in size as they advance through middle age?

I have been fairly lucky with my weight; it has hardly changed since my late teens, partly due to regular cycling and other vigorous and not-so-vigorous exercise. I know that I have remained the same dimensions for many decades. I'm not shrinking, so what is happening?

I've done no research into this at all, but my strong suspicion is that it is linked to the fact that the UK is following the USA into increasing average size and, yes, I'm going to say it, a greater incidence of obesity. This means that clothes retailers are feeling pressure to realign clothes sizes either to flatter the larger sizes, or simply to keep up with a shifting pattern.

Am I right or am I right?